Department Process Engineering

Urine nitrification is pH-sensitive due to limited alkalinity and high residual ammonium concentrations. This study aimed to investigate how the pH affects nitrogen conversion and the microbial community of urine nitrification with a pH-based feeding strategy. First, kinetic parameters for NH₃, HNO₂, and NO₂^- limitation and inhibition were determined for nitrifiers from a urine nitrification reactor. The turning point for ammonia-oxidizing bacteria (AOB), i.e., the substrate concentration at which a further increase would lead to a decrease in activity due to inhibitory effects, was at an NH₃ concentration of 12 mg-N L^-1, which was reached only at pH values above 7. The total nitrite turning point for nitrite-oxidizing bacteria (NOB) was pH-dependent, e.g., 18 mg-N L^-1 at pH 6.3. Second, four years of data from two 120 L reactors were analyzed, showing that stable nitrification with low nitrite was most likely between pH 5.8 and 6.7. And third, six 12 L urine nitrification reactors were operated at total nitrogen concentrations of 1300 and 3600 mg-N L^-1 and pH values between 2.5 and 8.5. At pH 6, the AOB Nitrosomonas europaea was found, and the NOB belonged to the genus Nitrobacter. At pH 7, nitrite accumulated, and Nitrosomonas halophila was the dominant AOB. NOB were inhibited by HNO₂ accumulation. At pH 8.5, the AOB Nitrosomonas stercoris became dominant, and NH₃ inhibited NOB. Without influent, the pH dropped to 2.5 due to the growth of the acid-tolerant AOB “Candidatus Nitrosacidococcus urinae”. In conclusion, pH is a decisive process control parameter for urine nitrification by influencing the selection and kinetics of nitrifiers.

Space agencies are developing Bioregenerative Life Support Systems (BLSS) in view of upcoming long-term crewed space missions. Most of these BLSS plan to include various crops to produce different types of foods, clean water, and O₂ while capturing CO₂ from the atmosphere. However, growing these plants will require the appropriate addition of nutrients in forms that are available. As shipping fertilizers from Earth would be too costly, it will be necessary to use waste-derived nutrients. Using the example of the MELiSSA (Micro-Ecological Life Support System Alternative) loop of the European Space Agency, this paper reviews what should be considered so that nutrients recycled from waste streams could be used by plants grown in a hydroponic system. Whereas substantial research has been conducted on nitrogen and phosphorus recovery from human urine, much work remains to be done on recovering nutrients from other liquid and solid organic waste. It is essential to continue to study ways to efficiently remove sodium and chloride from urine and other organic waste to prevent the spread of these elements to the rest of the MELiSSA loop. A full nitrogen balance at habitat level will have to be achieved; on one hand, sufficient N₂ will be needed to maintain atmospheric pressure at a proper level and on the other, enough mineral nitrogen will have to be provided to the plants to ensure biomass production. From a plant nutrition point of view, we will need to evaluate whether the flux of nutrients reaching the hydroponic system will enable the production of nutrient solutions able to sustain a wide variety of crops. We will also have to assess the nutrient use efficiency of these crops and how that efficiency might be increased. Techniques and sensors will have to be developed to grow the plants, considering low levels or the total absence of gravity, the limited volume available to plant growth systems, variations in plant needs, the recycling of nutrient solutions, and eventually the ultimate disposal of waste that can no longer be used.

Separation of urine at the source allows for the efficient recovery of nitrogen, phosphorus and other nutrients and reduces the load of these nutrients on wastewater treatment plants. Before urine can be used as a fertilizer, a treatment for nitrogen stabilization is required. Nitrification is a well-suited process for urine stabilization and is also the targeted approach in bioregenerative life support systems for Space such as in the MELiSSA project. However, due to the limited alkalinity and the high residual ammonium concentration, urine nitrification without alkalinity addition is very pH sensitive, which can compromise stable urine nitrification. Usually, the pH is controlled with the influent. Nevertheless, process failures can occur, namely nitrite accumulation, complete cessation of nitrification, and the growth of acid-tolerant ammonia-oxidizing bacteria (AOB), which can further lower the pH during periods of limited urine and lead to the emission of harmful nitrogen oxide gases. [...]

Die Urinseparierung ermöglicht eine effiziente Rückgewinnung von Stickstoff, Phosphor und anderen Nährstoffen und führt zur Entlastung der Kläranlagen. Bevor Urin als Düngemittel verwendet werden kann, ist jedoch eine Stickstoffbehandlung erforderlich. Dafür bietet sich die Nitrifikation an, welche auch im Rahmen der bioregenerative Lebenserhaltungssysteme für Weltraumanwendungen wie das MELiSSA Projekt untersucht werden. Aufgrund der begrenzten Alkalinität und der hohen Ammoniumkonzentration ist die Nitrifikation von Urin ohne Erhöhung der Alkalinität jedoch sehr pH-empfindlich, was die Stabilität der Urinnitrifikation gefährdet. Normalerweise wird der pH-Wert mit dem Zufluss geregelt. Dennoch kann es zu Prozessstörungen kommen, wie zur Akkumulation von Nitrit, zum vollständigen Erlegen der Nitrifikation und zum Wachstum säuretoleranter Ammoniakoxidierenden Bakterien (AOB), die den pH-Wert bei geringem Urinzuflus weiter senken und zur Emission schädlicher Stickoxidgase führen können. [...]

Nitrification is well-suited for urine stabilization. No base dosage is required if the pH is controlled within an appropriate operating range by urine feeding, producing an ammonium-nitrate fertilizer. However, the process is highly dependent on the selected pH set-points and is susceptible to process failures such as nitrite accumulation or the growth of acid-tolerant ammonia-oxidizing bacteria. To address the need for a robust and reliable process in decentralized applications, two different strategies were tested: operating a two-position pH controller (inflow on/off) with a narrow pH control band at 6.20/6.25 (∆pH = 0.05, narrow-pH) vs. a wider pH control band at 6.00/6.50 (∆pH = 0.50, wide-pH). These variations in pH also cause variations in the chemical speciation of ammonia and nitrite and, as shown, the microbial production of nitrite. It was hypothesized that the higher fluctuations would result in greater microbial diversity and, thus, a more robust process. The diversity of nitrifiers was higher in the wide-pH reactor, while the diversity of the entire microbiome was similar in both systems. However, the wide-pH reactor was more susceptible to tested process disturbances caused by increasing pH or temperature, decreasing dissolved oxygen, or an influent stop. In addition, with an emission factor of 0.47%, the nitrous oxide (N₂O) emissions from the wide-pH reactor were twice as high as the N₂O emissions from the narrow-pH reactor, most likely due to the nitrite fluctuations. Based on these results, a narrow control band is recommended for pH control in urine nitrification.

Adsorption on activated carbon is a common process to remove pharmaceuticals in wastewater treatment. Activated carbon adsorption is usually applied to wastewater with a low content of biological degradable organics, i.e. after biological treatment. Especially low molecular weight (LMW) compounds are known to compete with pharmaceuticals for adsorption sites. The goal of this study was to test the hypothesis that biological treatment is necessary for efficient pharmaceutical removal. Source-separated urine after anaerobic storage (anaerobically stored urine) and after aerobic biological removal of organics without nitrification (organics-depleted urine) were used in this study. In anaerobically stored urine 60% of the organic compounds were LMW organics, of which about 40% were acetate and propionate. 74% of the DOC and 100% of acetate and propionate were removed during aerobic biological treatment. To investigate the effect of the organic compounds on pharmaceutical removal, sorption experiments with 19 spiked pharmaceuticals and one artificial sweetener were conducted with powdered activated carbon. Ethanol, another LMW organic, was included in the study, as it is regularly used for pharmaceutical spiking thereby strongly increasing the DOC content. The experiments showed that the adsorption of the pharmaceuticals and the sweetener were hardly affected by the easily biodegradable LMW organics or ethanol. Therefore, it was concluded that biological pre-treatment is not necessary for efficient pharmaceutical adsorption. Since acetate, propionate and ethanol contribute substantially to the DOC content but do not absorb UV light, the latter is recommended as indicator for pharmaceutical removal in solutions with high contents of biodegradable LMW organics.

Die Wasserwirtschaft mit Kanalisation und zentralen Kläranlagen ist nicht mehr zukunftsfähig und global keine Lösung. Umweltingenieur:innen der ETH Zürich und der Eawag bereiten den Weg zu einer kreislauffähigen und dezentraleren Wasserinfrastruktur.

Acid-tolerant ammonia-oxidizing bacteria (AOB) can open the door to new applications, such as partial nitritation at low pH. However, they can also be problematic because chemical nitrite oxidation occurs at low pH, leading to the release of harmful nitrogen oxide gases. In this publication, the role of acid-tolerant AOB in urine treatment was explored. On the one hand, the technical feasibility of ammonia oxidation under acidic conditions for source-separated urine with total nitrogen concentrations up to 3.5 g-N L^-1 was investigated. On the other hand, the abundance and growth of acid-tolerant AOB at more neutral pH was explored. Under acidic conditions (pH of 5), ammonia oxidation rates of 500 mg-N L^-1 d^-1 and 10 g-N g-VSS^-1 d^-1 were observed, despite high concentrations of 15 mg-N L^-1 of the AOB-inhibiting compound nitrous acid and low concentration of 0.04 mg-N L^-1 of the substrate ammonia. However, ammonia oxidation under acidic conditions was very sensitive to process disturbances. Even short periods of less than 12 h without oxygen or without influent resulted in a complete cessation of ammonia oxidation with a recovery time of up to two months, which is a problem for low maintenance applications such as decentralized treatment. Furthermore, undesirable nitrogen losses of about 10% were observed. Under acidic conditions, a novel AOB strain was enriched with a relative abundance of up to 80%, for which the name “Candidatus (Ca.) Nitrosacidococcus urinae” is proposed. While Nitrosacidococcus members were present only to a small extent (0.004%) in urine nitrification reactors operated at pH values between 5.8 and 7, acid-tolerant AOB were always enriched during long periods without influent, resulting in an uncontrolled drop in pH to as low as 2.5. Long-term experiments at different pH values showed that the activity of “Ca. Nitrosacidococcus urinae” decreased strongly at a pH of 7, where they were also outcompeted by the acid-sensitive AOB Nitrosomonas halophila. The experiment results showed that the decreased activity of “Ca. Nitrosacidococcus urinae” correlated with the limited availability of dissolved iron at neutral pH.

Combining partial nitrification, granular activated carbon (GAC) filtration, and distillation is a well-studied approach to convert urine into a fertilizer. To evaluate the environmental sustainability of a technology, the operational carbon footprint and therefore nitrous oxide (N₂O) emissions should be known, but N₂O emissions from urine nitrification have not been assessed yet. Therefore, N₂O emissions of a decentralized urine nitrification reactor were monitored for 1 month. During nitrification, 0.4-1.2% of the total nitrogen load was emitted as N₂O-N with an average N₂O emission factor (EF_N2O) of 0.7%. Additional N₂O was produced during anoxic storage between nitrification and GAC filtration with an estimated EF_N2O of 0.8%, resulting in an EF_N2O of 1.5% for the treatment chain. N₂O emissions during nitrification can be mitigated by 60% by avoiding low dissolved oxygen or anoxic conditions and nitrite concentrations above 5 mg-N L^-1. Minimizing the hydraulic retention time between nitrification and GAC filtration can reduce N₂O formation during intermediate storage by 100%. Overall, the N₂O emissions accounted for 45% of the operational carbon footprint of 14 kg-CO_2,equiv kg-N^-1 for urine fertilizer production. Using electricity from renewable sources and applying the proposed N₂O mitigation strategies could potentially lower the carbon footprint by 85%.

Human urine is rich in valuable nitrogen which can easily be lost due to biological urea hydrolysis and subsequent ammonia volatilization. While this enzymatic reaction can be prevented by alkalizing the urine, recent studies suggest that chemical urea hydrolysis can result in substantial nitrogen losses when drying alkalinized urine at high temperatures. Furthermore, it was previously suggested that CO₂ dissolution from the air used to evaporate water from alkalinized urine could result in a pH decrease to values which allows for biological urea hydrolysis and subsequent ammonia losses. This study aimed to determine the kinetics of chemical urea hydrolysis in alkalinized human urine and confirm the effect of CO₂ dissolution with controlled laboratory experiments. We measured the change in urea concentration at different temperatures and pH values for real human urine and determined the corresponding rate constants for chemical urea hydrolysis. We showed that the rate constant increases as a function of temperature and that pH has a negligible effect on the rate of chemical urea hydrolysis in the high pH range of alkalized urine (>11). The rate constants for chemical urea hydrolysis in a saturated calcium hydroxide solution were found to be 0.00147 d^-1, 0.00595 d^-1, 0.0204 d^-1 and 0.0848 d^-1 for temperatures of 25°C, 40°C, 55°C and 70°C, respectively. The effect of CO₂ dissolution on urea hydrolysis was determined by aerating human urine alkalinized with calcium hydroxide (Ca(OH)₂). In order to represent biological urea hydrolysis, urease was added to the solution. The computer simulations of the experimental results showed that CO₂ dissolution and the subsequent dissociation of carbonic acid to carbonate ions, bicarbonate ions and protons is the main cause of the pH decrease, but CaCO₃ precipitation, and NH₃ volatilization foster the pH decrease. However, biological urea hydrolysis prevents the pH from decreasing below 9. Residual undissolved Ca(OH)₂ was shown to substantially delay the pH decrease. Overall, this work provides valuable insights into the mechanisms of urea hydrolysis in alkalinized urine during dehydration, which can be used to design more efficient decentralized sanitation systems and minimize nitrogen losses.

Phosphorus (P) is an essential element to all living beings but also a finite resource. P-related problems center around broken P cycles from local to global scales. This paper presents outcomes from the 9th International Phosphorus Workshop (IPW9) held 2019 on how to move towards a sustainable P management. It is based on two sequential discussion rounds with all participants. Important progress was reported regarding the awareness of P as finite mineable resource, technologies to recycle P, and legislation towards a circular P economy. Yet, critical deficits were identified such as how to handle legacy P, how climate change may affect ecosystem P cycling, or working business models to up-scale existing recycling models. Workshop participants argued for more transdisciplinary networks to narrow a perceived science-practice/policy gap. While this gap may be smaller in reality as illustrated with a Swiss example, we formulate recommendations how to bridge this gap more effectively.

Human excreta are a sustainable, economical source of nutrients, and can be used to produce recycling fertilizer for horticulture by collecting and processing the contents of dry toilets. Herein, we discuss the key categories of risk associated with the main groups of materials commonly found in dry toilets. The study was part of the development of a German product standard for marketable and quality-assured recycling fertilizers from human excreta for use in horticulture. Particular attention is paid to ensuring that the fertilizer is epidemiologically and environmentally harmless and that the quality of the recycling fertilizer is adequate in terms of low pollution and nutrient availability. In sum, the risk of transmissible human pathogens lies within the human excreta, particularly feces; plant materials added during composting are of particular phytosanitary relevance; pharmaceutical residues in excrements and chemical additives are potential sources of pollutants; non-biodegradable contaminants can cause pollution and injury; and the horticultural risks involve mainly the ammonia emission potential and in some cases the salinity effects of urine. These risks can be reduced significantly (i) with education of users around proper operation of dry toilets and the consequences of adding inappropriate waste, (ii) with facilitation of proper use with general waste bins and clear instructions, and importantly (iii) by using modern sanitization and cleaning processes and testing for harmful substances under the guidance of local laws and regulations, ensuring safe and high-quality fertilizers. In conclusion, the benefits of using dry toilet contents to produce fertilizers for use in horticulture are unquestionable. Our analysis highlights the need to support recycling optimization and awareness for the purpose of a sustainable circular economy and to minimize the risk of harm to humans and the environment overall.

Over the last 15 years, urine treatment technologies have developed from lab studies of a few pioneers to an interesting innovation, attracting attention from a growing number of process engineers. In this broad review, we present literature from more than a decade on biological, physical-chemical and electrochemical urine treatment processes. Like in the first review on urine treatment from 2006, we categorize the technologies according to the following objectives: stabilization, volume reduction, targeted N-recovery, targeted P-recovery, nutrient removal, sanitization, and handling of organic micropollutants. We add energy recovery as a new objective, because extensive work has been done on electrochemical energy harvesting, especially with bio-electrochemical systems. Our review reveals that biological processes are a good choice for urine stabilization. They have the advantage of little demand for chemicals and energy. Due to instabilities, however, they are not suited for bathroom applications and they cannot provide the desired volume reduction on their own. A number of physical-chemical treatment technologies are applicable at bathroom scale and can provide the necessary volume reduction, but only with a steady supply of chemicals and often with high demand for energy and maintenance. Electrochemical processes is a recent, but rapidly growing field, which could give rise to exciting technologies at bathroom scale, although energy production might only be interesting for niche applications. The review includes a qualitative assessment of all unit processes. A quantitative comparison of treatment performance was not the goal of the study and could anyway only be done for complete treatment trains. An important next step in urine technology research and development will be the combination of unit processes to set up and test robust treatment trains. We hope that the present review will help guide these efforts to accelerate the development towards a mature technology with pilot scale and eventually full-scale implementations.

We present the results of three field tests and three laboratory tests of a new physical-chemical urine treatment system, which can recover all nutrients, while pathogens are inactivated. The system consists of two steps. In the first reactor, biological processes including urea hydrolysis are prevented by mixing fresh urine with calcium hydroxide (Ca(OH)₂). Due to the high pH value and the high availability of calcium, phosphate can be recovered by precipitation. The high pH value also fosters the inactivation of microorganisms, including pathogens. In the second reactor, water is evaporated at low energy consumption by blowing unheated ambient air over the stabilized urine. Stabilization in the first reactor was successful in all field and laboratory tests. The pH value remained between 12 and 13, except for short dips due to shortages of Ca(OH)₂. Nearly all phosphorus (92-96%) precipitated and could be recovered as calcium phosphate in the first reactor, while nitrogen and potassium overflowed with the urine into the evaporation reactor. The efficiency of the second treatment step was very different for field and laboratory experiments and depended on the duration of the experiment. During a four-day laboratory test, nitrogen recovery was 98%. In contrast, nitrogen recovery was only around 20% in the long-term field experiments. The high nitrogen losses occurred, because biological urea hydrolysis was not inhibited anymore, when the pH value in the second reactor decreased due to the dissolution of high amounts of carbon dioxide from the ambient air. Potassium was not subject to any significant loss, and the measured recovery in the solid evaporation product was 98%. Evaporation rates ranged between 50 g m^-2 h^-1 (RH = 82±13%, T = 12±6°C) and 130 g m^-2 h^-1 (RH = 60±19%, T = 24±5°C) in the three field tests. Apart from some disturbances due to low supply of Ca(OH)₂, the urine module functioned without any substantial failures and was simple to maintain. The minimum consumption of Ca(OH)₂ at full capacity was 6 g·L^-1 urine and the electricity demand was 150 Wh kg^-1 water evaporated from urine, resulting in operational costs of 0.05 EUR pers^-1 d^-1.

Safe and accessible water services for hand hygiene are critical to human health and well-being. However, access to handwashing facilities is limited in cities in the Global South, where rapid urbanisation, service backlogs, lack of infrastructure and capacity, and water scarcity impact on the ability of local governments to provide them. Community participation and the co-production of knowledge in the development of innovative technologies, which are aligned with Water, Sanitation and Hygiene (WASH) principles, can lead to more sustainable and socially-acceptable hand hygiene systems. This paper presents the outcomes of the testing of the Autarky handwashing station, a technology that provides onsite treatment and recycling of handwashing water, in an informal settlement in Durban, South Africa. The transdisciplinary research approach adopted enabled the participation of multiple stakeholders with different knowledge systems in the framing, testing and evaluation of the system. The process of co-producing knowledge, as well as the outcomes of the testing, namely high levels of functionality and social acceptability of the technology, supported the WASH principles. The evaluation revealed that the Autarky handwashing station is a niche intervention that improved access to safe and appealing handwashing facilities in an informal settlement. Its novel design, socially desirable features, reliability and ability to save water increased its acceptance in the community. The testing of the system in a real-world context revealed the value of including communities in knowledge production processes for technology innovation. Further work is required to ensure that real-time monitoring of system function is feasible before such systems can be implemented at larger scale.

The provision of water and sanitation for all that is safe, dignified, reliable, affordable and sustainable is a major global challenge. While centralized sewer-based sanitation systems remain the dominant approach to providing sanitation, the benefits of non-sewered onsite sanitation systems are increasingly being recognised. This paper presents the outcomes of the testing of the Blue Diversion Autarky Toilet (BDAT), a sanitation system providing hygiene and dignity without relying on water and wastewater infrastructure, in a peri-urban household in Durban, South Africa. The BDAT was used by a single household as their only form of sanitation during three months of technical and social testing. An analysis based on technical data in combination with interpretive, qualitative research methods revealed that the BDAT functioned well and achieved high levels of social acceptance in the test household. The flushing, cleanliness and odour-free nature of the sanitation technology, its functionality, the household's previous sanitation experience, and their experience with and understanding of water scarcity, were the main factors underpinning their positive response to this innovation in sanitation. The testing process resulted in broader developmental benefits for the household, including improved basic services due to the upgrading of the electrical and existing sanitation system, social learning, and improved relationships between household members and the local state. A transdisciplinary research process, which emerged through the assessment, enabled the integration of different forms of knowledge from multiple actors to address the complexity of problems related to the development of socially just sanitation. The benefit of engaging with societal actors in sanitation innovation and assessing its outcomes using both the technical and social sciences is evident in this paper.

Urine has great potential to be an effective fertilizer due to its high nutrient content, however, it can contain potentially worrying pharmaceuticals. Our objective was to study whether urine storage and aerobic biological treatment, i.e. nitrification, was sufficient to remove pharmaceuticals or an additional treatment with activated carbon was necessary to produce a fertilizer from urine. We investigated the abatement of twelve pharmaceuticals, including antibiotics and antivirals, in laboratory experiments representing the treatment steps of anaerobic storage of source-separated human urine, stabilization using partial and full nitrification under acclimatized and non-acclimatized conditions, and treatment of nitrified urine using powdered activated carbon (PAC). Two-month-long-term storage of urine was insufficient to substantially degrade the pharmaceuticals, except for hydrochlorothiazide (>90%). In the partial and full nitrification fed-batch reactors, atazanavir, ritonavir, and clarithromycin were rapidly removed, with biotransformation rate constants greater than 10 L g_SS⁻¹d⁻¹. Darunavir, emtricitabine, trimethoprim, N4-acetylsulfamethoxazole, sulfamethoxazole, atenolol, diclofenac, and hydrochlorothiazide were degraded slowly, with biotransformation rate constants of < 1 L g_SS⁻¹d⁻¹. With 200 mg PAC L⁻¹, at least 90% of each investigated pharmaceutical was removed. Yeast estrogen screen tests and bioluminescence inhibition tests revealed efficient removal of estrogenicity (99%) and toxicity (56%) using nitrification, and a reduction of 89% and 64%, respectively, using 200 mg PAC L⁻¹. With our study, we provide biotransformation rate constants of compounds never previously investigated. We also show that a combination of nitrification and PAC adsorption enables the production of a safe fertilizer with sufficiently low pharmaceutical concentrations and no removal of beneficial nutrients.

The simulation of wastewater treatment plants allows obtaining predictive results when one needs to understand, evaluate, optimize, or design a plant. However, one of the bottlenecks of simulation feasibility is to obtain reliable and dynamic influent data. This difficulty is even more important when alternative scenarios are considered, such as source-separated streams. The present paper offers an influent generator to simulate scenarios where urine is separated at the source and at a user-specified level of retention. The proposed tool contains several blocks to include different contributions (household and industrial wastewater) and, due to its flexibility, allows the user to easily modify the parameters to fit other case studies. The tool allowed generating dynamic, long-term, and predictive data for both urine and wastewater streams. Also, the extensive set of state variables ensured the generation of influents for different modeling platforms.

Sensing nitrite in-situ in wastewater treatment processes could greatly simplify process control, especially during treatment of high-strength nitrogen wastewaters such as digester supernatant or, as in our case, urine. The two technologies available today, i.e. an on-line nitrite analyzer and a spectrophotometric sensor, have strong limitations such as sample preparation, cost of ownership and strong interferences. A promising alternative is the amperometric measurement of nitrite, which we assessed in this study. We investigated the sensor in a urine nitrification reactor and in ex-situ experiments. Based on theoretical calculations as well as a practical approach, we determined that the critical nitrite concentrations for nitrite oxidizing bacteria lie between 12 and 30 mg_N/L at pH 6 to 6.8. Consequently, we decided that the sensor should be able to reliably measure concentrations up to 50 mg_N/L, which is about double the value of the critical nitrite concentration. We found that the influences of various ambient conditions, such as temperature, pH, electric conductivity and aeration rate, in the ranges expected in urine nitrification systems, are negligible. For low nitrite concentrations, as expected in municipal wastewater treatment, the tested amperometric nitrite sensor was not sufficiently sensitive. Nevertheless, the sensor delivered reliable measurements for nitrite concentrations of 5-50 mg_N/L or higher. This means that the amperometric nitrite sensor allows detection of critical nitrite concentrations without difficulty in high-strength nitrogen conversion processes, such as the nitrification of human urine.

Mit innovativen Technologien werden im Water Hub unter realen Bedingungen Ressourcen aus dem Abwasser gewonnen und Kreisläufe geschlossen. Die Forschung in diesem Living Lab erlaubt es, praxisnahe Erfahrungen zu machen, Schwachstellen schnell zu identifizieren und das System zu optimieren. Bei der Implementierung dieser dezentralen Technologien spielen die lokalen Herausforderungen und Begebenheiten stets eine wichtige Rolle.

Recent developments in high- and middle-income countries have exhibited a shift from conventional urban water systems to alternative solutions that are more diverse in source separation, decentralization, and modularization. These solutions include non-grid, small-grid, and hybrid systems to address such pressing global challenges as climate change, eutrophication, and rapid urbanization. They close loops, recover valuable resources, and adapt quickly to changing boundary conditions such as population size. Moving to such alternative solutions requires both technical and social innovations to co-evolve over time into integrated socio-technical urban water systems. Current implementations of alternative systems in high- and middle-income countries are promising, but they also underline the need for research questions to be addressed from technical, social, and transformative perspectives. Future research should apply a transdisciplinary research approach through socio-technical "lighthouse" projects that apply alternative urban water systems at scale. Such research should leverage experience from lighthouse projects in a range of socio-economic contexts, identify their potentials and limitations from an integrated perspective, and share their successes and failures across the urban water sector.

Nitrification and distillation of urine allow for the recovery of all nutrients in a highly concentrated fertilizer solution. However, pharmaceuticals excreted with urine are only partially removed during these two process steps. For a sustainable and safe application, more extensive removal of pharmaceuticals is necessary. To enhance the pharmaceutical removal, which is already occurring during urine storage, nitrification and distillation, an adsorption column with granular activated carbon (GAC) can be included in the treatment train. We executed a pilot-scale study to investigate the adsorption of eleven indicator pharmaceuticals on GAC. During 74 days, we treated roughly 1000 L of pre-filtered and nitrified urine spiked with pharmaceuticals in two flow-through GAC columns filled with different grain sizes. We compared the performance of these columns by calculating the number of treated bed volumes until breakthrough and carbon usage rates. The eleven spiked pharmaceuticals were candesartan, carbamazepine, clarithromycin, diclofenac, emtricitabine, hydrochlorothiazide, irbesartan, metoprolol, N₄-acetylsulfamethoxazole, sulfamethoxazole and trimethoprim. At the shortest empty bed contact time (EBCT) of 25 min, immediate breakthrough was observed in both columns shortly after the start of the experiments. Strong competition by natural organic material (NOM) could have caused the low pharmaceutical removal at the EBCT of 25 min. At EBCTs of 70, 92 and 115 min, more than 660 bed volumes could be treated until breakthrough in the column with fine GAC. The earliest breakthrough was observed for candesartan and clarithromycin. On coarse GAC, only half the number of bed volumes could be treated until breakthrough compared to fine GAC. The probable reason for the later breakthrough with fine GAC is the smaller intraparticle diffusive path length. DOC and UV absorbance measurements at 265 nm indicated that both parameters can be used as indicators for the breakthrough of pharmaceuticals. In contrast to pharmaceuticals and DOC, the nutrient compounds ammonium, nitrate, phosphate, potassium and sulfate were not removed significantly. A comparison with literature values suggests that the amount of GAC needed to remove pharmaceuticals from human excreta could be reduced by nearly two orders of magnitude, if urine were treated on site instead of being discharged and treated in a centralized wastewater treatment plant.

On-site wastewater reuse can improve global access to clean water, sanitation and hygiene. We developed a treatment system (aerated bioreactor, ultrafiltration membrane, granular activated carbon and electrolysis for chlorine disinfection) that recycles hand washing and toilet flush water.
Three prototypes were field-tested in non-sewered areas, one in Switzerland (hand washing) and two in South Africa (hand washing, toilet flushing), over periods of 63, 74 and 94 days, respectively.
We demonstrated that the system is able to recycle sufficient quantities of safe and appealing hand washing and toilet flush water for domestic or public use in real-life applications. Chemical contaminants were effectively removed from the used water in all prototypes. Removal efficiencies were 99.7% for the chemical oxygen demand (COD), 98.5% for total nitrogen (TN) and 99.9% for phosphate in a prototype treating hand washing water, and 99.8% for COD, 95.7% for TN and 89.6% for phosphate in a prototype treating toilet flush water. While this system allowed for true recycling for the same application, most on-site wastewater reuse systems downcycle the treated water, i.e., reuse it for an application requiring lower water quality. An analysis of 18 selected wastewater reuse specifications revealed that at best these guidelines are only partially applicable to innovative recycling systems as they are focused on the downcycling of water to the environment (e.g., use for irrigation). We believe that a paradigm shift is necessary and advocate for the implementation of risk-based (and thus end-use dependent) system performance targets to evaluate water treatment systems, which recycle and not only downcycle water.

Ammonia recovery from urine avoids the need for nitrogen removal through nitrification/denitrification and re-synthesis of ammonia (NH₃) via the Haber-Bosch process. Previously, we coupled an alkalifying electrochemical cell to a stripping column, and achieved competitive nitrogen removal and energy efficiencies using only electricity as input, compared to other technologies such as conventional column stripping with air. Direct liquid-liquid extraction with a hydrophobic gas membrane could be an alternative to increase nitrogen recovery from urine into the absorbent while minimizing energy requirements, as well as ensuring microbial and micropollutant retention. Here we compared a column with a membrane stripping reactor, each coupled to an electrochemical cell, fed with source-separated urine and operated at 20 A m⁻². Both systems achieved similar nitrogen removal rates, 0.34 ± 0.21 and 0.35 ± 0.08 mol N L⁻¹ d⁻¹, and removal efficiencies, 45.1 ± 18.4 and 49.0 ± 9.3%, for the column and membrane reactor, respectively. The membrane reactor improved nitrogen recovery to 0.27 ± 0.09 mol N L⁻¹ d⁻¹ (38.7 ± 13.5%) while lowering the operational (electrochemical and pumping) energy to 6.5 kWhe kg N⁻¹ recovered, compared to the column reactor, which reached 0.15 ± 0.06 mol N L⁻¹ d⁻¹ (17.2 ± 8.1%) at 13.8 kWh_e kg N⁻¹.
Increased cell concentrations of an autofluorescent E. coli MG1655 + prpsM spiked in the urine influent were observed in the absorbent of the column stripping reactor after 24 h, but not for the membrane stripping reactor. None of six selected micropollutants spiked in the urine were found in the absorbent of both technologies.
Overall, the membrane stripping reactor is preferred as it improved nitrogen recovery with less energy input and generated an E. coli- and micropollutant-free product for potential safe reuse. Nitrogen removal rate and efficiency can be further optimized by increasing the NH₃ vapor pressure gradient and/or membrane surface area.

Nitrification of wastewater requires control for the purposes of efficiency and of stability. However, first, the highly complex microbial community in wastewater treatment plants and very different compositions of wastewaters impede a complete understanding of nitrification. Second, the determination of the states of the process is seldom exact because sensors are subject to a high level of wear and tear. Consequently, instrumentation, control, and automation (ICA) of nitrification processes are a challenge. I hypothesize that soft-sensors - based on the signals of robust, physical sensors - and specially designed control loops, which do not need redundant information to correct for drift, can reduce the maintenance needs for the control of nitrification. Consequently, the econonomical application range for ICA of nitrification processes can be extended.
A large part of this thesis is dedicated to the stabilisation of urine nitrification as a pretreatment for nutrient recovery. To this end, an online nitrite detection and an according control of the process are required. Furthermore, the thesis comprises an ammonia aeration controller, which is based on pH signals, to be used in municipal wastewater. The four chapters of the thesis focus on the following topics.
The first chapter investigates calibration experiments for in-line UV-Vis sensors. Such sensors can serve as soft-sensors for numerous substances. With differently designed experiments, data for the calibration of UV-Vis based nitrite models in high strength wastewater was recorded. Online experiments executed in-situ allow calibrating similarly exact models like experiments which are conducted by spiking additional nitrite. The good performance of the models being based on online experiments is explained by the correlation of other light-absorbing substances in the process with nitrite.
The second chapter evaluates the potential of a stoichiometry-based soft-sensor for nitrite. The stoichiometry of nitrification theoretically allows distinguishing the ammonia and the nitrite oxidation rates by means of the derivatives of the dissolved oxygen and of the pH signal and in turn detecting nitrite accumulations. We show that under relatively ideal conditions the dynamics in the ratio of the two derivatives show similarities with the dynamics in the nitrite concentration. Factors that deteriorate this information quality are identified.
The third part of this thesis investigates how drifting sensor signals can be used as an input for a feedback controller without relying on redundant information to correct this drift. The controller shall prevent uncontrolled nitrite accumulation in a urine nitrification system. To this end, the controller does not use the absolute value of the nitrite signal, but its 1^st and 2^nd derivative as inputs. By controlled accumulation and degradation of nitrite, the controller can keep the derivatives continuously informative. The switch from substrate inhibition to substrate limitation of the nitrite oxidising bacteria can be identified by means of the inflection point in the signal. The developed controller is tested successfully on a lab-scale reactor.
The fourth chapter of this thesis describes an ammonia based aeration controller. These controllers usually require maintenance intensive instrumentation. Therefore a new ammonia soft sensor for continuously operated municipal wastewater treatment plants is developed. It relies on the 1^st derivative of a pH difference measured over the aerated zone. This soft sensor is successfully tested in a controller deployed on various municipal wastewater treatment plants. The controller was designed to increase its robustness towards drift in the pH signals.

Sensor drift is commonly observed across engineering disciplines, particularly in harsh media such as wastewater. In this study, a novel stabilizing controller for nitrification of high strength ammonia solutions is designed based on online signal derivatives. The controller uses the derivative of a drifting nitrite signal to determine if nitrite-oxidizing bacteria (NOB) are substrate limited or substrate inhibited. To ensure a meaningful interpretation of the derivative signal, the process is excited in a cyclic manner by repeatedly exposing the NOB to substrate-limited and substrate-inhibited conditions. The resulting control system successfully prevented nitrite accumulations for a period of 72 days in a laboratory-scale reactor. Slow disturbances in the form of feed composition changes and temperature changes were successfully handled by the controller while short-term temperature disturbances are shown to pose a challenge to the current version of this controller. Most importantly, we demonstrate that drift-tolerant control for the purpose of process stabilization can be achieved without sensor redundancy by combining deliberate input excitation, qualitative trend analysis, and coarse process knowledge.

Long-term human Space missions depend on regenerative life support systems (RLSS) to produce food, water and oxygen from waste and metabolic products. Microbial biotechnology is efficient for nitrogen conversion, with nitrate or nitrogen gas as desirable products. A prerequisite to bioreactor operation in Space is the feasibility to reactivate cells exposed to microgravity and radiation. In this study, microorganisms capable of essential nitrogen cycle conversions were sent on a 44-days FOTON-M4 flight to Low Earth Orbit (LEO) and exposed to 10⁻³–10⁻⁴ g (gravitational constant) and 687 ± 170 µGy (Gray) d⁻¹ (20 ± 4 °C), about the double of the radiation prevailing in the International Space Station (ISS). After return to Earth, axenic cultures, defined and reactor communities of ureolytic bacteria, ammonia oxidizing archaea and bacteria, nitrite oxidizing bacteria, denitrifiers and anammox bacteria could all be reactivated. Space exposure generally yielded similar or even higher nitrogen conversion rates as terrestrial preservation at a similar temperature, while terrestrial storage at 4 °C mostly resulted in the highest rates. Refrigerated Space exposure is proposed as a strategy to maximize the reactivation potential. For the first time, the combined potential of ureolysis, nitritation, nitratation, denitrification (nitrate reducing activity) and anammox is demonstrated as key enabler for resource recovery in human Space exploration.

Background and aims The current paradigm for phosphorus (P) fertilizers applied to calcareous soil is that almost entirely water soluble P fertilizers are efficient and sparingly soluble P fertilizers are not efficient P sources for crops. We hypothesize that this paradigm does not apply to recycled P fertilizers and that other P pools can explain the plant use of recycled P fertilizers on calcareous soil.
Methods We applied ³³P isotopic dilution method to evaluate recycled P fertilizers based on plant P uptake from fertilizer relative to plant uptake from a water soluble P reference fertilizer. The predictability of fertilizer effectiveness based on sequentially extracted P forms and X-ray diffraction pattern of recycled fertilizers derived from sewage sludge, human urine and organic waste was evaluated.
Results The plant experiments showed that tested recycled P fertilizers including compost were more effective than rock phosphate. The water insoluble P contained in urine based products was almost as effective as a fully water soluble P fertilizer. The tested recycled P fertilizers are characterized by complex P compounds differing in solubility which were so far not considered in the water and citric acid extraction methods. The fraction of resin- and NaHCO₃ extractable fertilizer P explained effectiveness of P fertilizer applied to the calcareous and to an acidic soil.
Conclusion We concluded that water solubility is not required when P forms in recycled products are comparable to reactions products of rock phosphate based fertilizers in soil. Alternatives to fully water soluble P fertilizers are available to supply P to crops grown on calcareous soil efficiently.

Der Gewässerschutz in der Schweiz und damit die Qualität der ober- und unterirdischen Gewässer haben allgemein einen beachtlichen Stand erreicht. Diese erfreuliche Tatsache darf nicht darüber hinwegtäuschen, dass lokal im ländlichen Raum und ausserhalb erschlossener Baugebiete weiterhin Handlungsbedarf besteht. Einerseits gibt es bei bestehenden dezentralen Abwasserinfrastrukturen nach wie vor Anlagen, welche die Einleitungsbedingungen nicht erfüllen.

Der vorliegende Leitfaden soll helfen, diese bestehenden Lücken im Gewässerschutz zu schliessen und eine einheitliche Abwasserentsorgung im ländlichen Raum zu gewährleisten. Er wurde von einer breit abgestützten Projektgruppe des VSA erarbeitet, in welcher Vertreter aus Bund, Kantonen und der Eawag mitwirkten.

Das Dokument ersetzt den VSA-Leitfaden "Abwasser im ländlichen Raum" vom Oktober 2005 und die 1995 publizierte "Richtlinie für den Einsatz, die Auswahl und die Bemessung von Kleinkläranlagen" des VSA. Der Leitfaden 2017 ist neu strukturiert und enthält aktuelle Komponenten der ländlichen Abwasserentsorgung insbesondere für: - Das Vorgehen der Lösungsfindung
- Die Spezielle Abwasserarten
- Die Speicher- und Anschlusssysteme
- Die Reinigungssysteme
- Den Betrieb und Unterhalt von Kleinkläranlagen (KLARA)

Im Weiteren berücksichtigt die vorliegende Version zwischenzeitlich veröffentlichte Vollzugshilfen von BAFU und BLW ("Baulicher Umweltschutz in der Landwirtschaft", 2011 und "Nährstoffe und Verwendung von Düngern in der Landwirtschaft", 2012) sowie etablierte Hilfsmittel der Kantone. Auch Ausführungsmöglichkeiten zu den jeweiligen Themen sind im Dokument enthalten. Das Massnahmenspektrum ist bewusst weit gehalten: Obwohl mit dem Anschluss der Liegenschaften an die öffentliche Kanalisation mit zentraler Abwasserreinigung das Abwasserproblem weitgehend gelöst sein kann, drängen sich auch im ländlichen Raum häufig Massnahmen an der Quelle auf.

Der Leitfaden richtet sich an Vollzugsbehörden, Planungsbüros, Gemeinden und weitere interessierte Stellen. Bei der Suche nach einer spezifischen Abwasserlösung wird empfohlen, sich im Vorfeld bei der kantonalen Fachstelle zu erkundigen. Dasselbe gilt analog auf Gemeindeebene.

Ammonia oxidation decreases the pH in wastewaters where alkalinity is limited relative to total ammonia. The activity of ammonia oxidizing bacteria (AOB), however, typically decreases with pH and often ceases completely in slightly acidic wastewaters. Nevertheless, nitrification at low pH has been reported in reactors treating human urine, but it has been unclear which organisms are involved. In this study, we followed the population dynamics of ammonia oxidizing organisms and reactor performance in synthetic fully hydrolyzed urine as the pH decreased over time in response to a decrease in the loading rate. Populations of the β-proteobacterial Nitrosomonas europaea lineage were abundant at the initial pH close to 6, but the growth of a possibly novel Nitrosococcus-related AOB genus decreased the pH to the new level of 2.2, challenging the perception that nitrification is inhibited entirely at low pH values, or governed exclusively by β-proteobacterial AOB or archaea. With the pH shift, nitrite oxidizing bacteria were not further detected, but nitrous acid (HNO₂) was still removed through chemical decomposition to nitric oxide (NO) and nitrate. The growth of acid-tolerant γ-proteobacterial AOB should be prevented, by keeping the pH above 5.4, which is a typical pH limit for the N. europaea lineage. Otherwise, the microbial community responsible for high-rate nitrification can be lost, and strong emissions of hazardous volatile nitrogen compounds such as NO are likely.

This study was part of the VUNA project aimed to develop an affordable sanitation system that produces a valuable fertiliser, reduces pollution of water resources and promotes health. Urine diversion dry toilets (UDDTs) simplify the on-site hygienisation of faeces and allow for nutrient recovery from urine. Social acceptance is vital for the implementation of the UDDT, because sanitation is only effective if the system not only provides a well-designed toilet and effective waste management, but also offers users a facility that caters to their needs and is sensitive to their cultural lifestyle. This study used qualitative and quantitative methods to investigate acceptance, use and maintenance of UDDTs. Key findings indicate lower levels of acceptance of UDDTs among the elderly, who are accustomed to traditional pit toilets. The users aspire to own a flush toilet, perceived to be indicative of household wealth. A dominant concern was emptying the pit and the quality of the building material. Community interventions are required that will promote acceptance, understanding and encourage proper use and maintenance of the UDDT, and may need some technology modification. There is an urgent need for increased community participation to address users' perceptions, attitudes and behaviour concerning the UDDT.

Separate collection of urine, which is only 1% of wastewater volume but contains the majority of nitrogen humans excrete, can potentially reduce the costs and energy input of wastewater treatment and facilitate recovery of nitrogen for beneficial use. Ion exchange was investigated for recovery of nitrogen as ammonium from urine for use as a fertilizer or disinfectant. Cation adsorption curves for four adsorbents (clinoptilolite, biochar, Dowex 50, and Dowex Mac 3) were compared in pure salt solutions, synthetic urine, and real stored urine. Competition from sodium and potassium present in synthetic and real urine did not significantly decrease ammonium adsorption for any of the adsorbents. Dowex 50 and Dowex Mac 3 showed nearly 100% regeneration efficiencies. Estimated ion exchange reactor volumes to capture the nitrogen for 1 week from a four-person household were lowest for Dowex Mac 3 (5 L) and highest for biochar (19 L). Although Dowex Mac 3 had the highest adsorption capacity, material costs ($/g N removed) were lower for clinoptilolite and biochar because of their substantially lower unit cost.

The separate collection and treatment of urine allows for an environmentally friendly and cost-efficient management of the nutrients contained in urine. The primary goal should be to recover all these nutrients. However, in some cases it will be economically or ecologically more sensitive to recover only the phosphorus, while nitrogen is removed together with organic substances (measured as chemical oxygen demand, COD) and pathogens. In this study, we investigated the use of galvanostatic electrolysis for the removal of nitrogen and COD from real stored urine. Non-active type boron-doped diamond (BDD) and active type thermally decomposed iridium oxide film (TDIROF) anodes were evaluated using batch experiments. On both anodes, ammonia was exclusively removed by indirect oxidation with active chlorine (AC: Cl₂, HClO, and ClO⁻). As a consequence, ammonia was not completely removed, if chlorine was consumed by competing processes. While COD was present, ammonia removal was faster on TDIROF (227 ± 16 gN m⁻² d⁻¹ at 20 mA cm⁻²) than on BDD (43 ± 20 gN m⁻² d⁻¹ at 20 mA cm⁻²). The reason for the slower ammonia removal on BDD was the enhanced reaction of AC with organic molecules. In fact, hydroxyl radicals broke organic molecules down to shorter chain molecules which reacted with most of the AC leaving only little AC for the oxidation of ammonia. This preferential oxidation of organics resulted in very high COD removal rates on BDD (above 420 gCOD m⁻² d⁻¹ at 20 mA cm⁻² for COD concentrations above 1000 mgCOD L⁻¹). A main drawback of electrolysis with both anodes was the high energy demand (BDD: 55 W h gCOD⁻¹ and 766 W h gN⁻¹ for 90% and 6% removal, respectively. TDIROF: 67 W h gCOD⁻¹ and 77 W h gN⁻¹ for 30% and 40% removal. All at 20 mA cm⁻²). It can be concluded that BDD and TDIROF anodes could be combined in series for a fast, complete, and more energy efficient electrochemical urine treatment: COD could be removed on BDD before the residual ammonia would be removed on TDIROF.

Human urine can be processed into market-attractive fertilizers like struvite; however, concerns regarding the microbial safety of such products remain. The present study evaluated the inactivation of in situ heterotrophs, total bacteria as observed by flow cytometry, and inoculated Enterococcus spp. and Salmonella typhimurium during the drying of struvite under controlled temperature (from 5 to 35 °C) and relative humidity (approximately 40 and 80%) as well as dynamic field conditions. Bacteria accumulated in the struvite cake during struvite filtration. Despite the use of sublethal temperatures, all bacteria types were subsequently inactivated to some degree during struvite drying, and the inactivation typically increased with increasing drying temperature for a given relative humidity. Heterotrophic bacteria inactivation mirrored the trend in total bacteria during struvite drying. A linear relationship was observed between inactivation and sample moisture content. However, bacteria survivor curves were typically nonlinear when struvite was dried at low relative humidity, indicating bacterial persistence. Weibull model survivor curve fits indicated that a shift in the mechanism of inactivation may occur with changing humidity. For increased efficiency of bacterial inactivation during the production of struvite, initial heating under moist conditions is recommended followed by desiccation.

Source-separated urine contains most of the excreted nutrients, which can be recovered by using nitrification to stabilize the urine before concentrating the nutrient solution with distillation. The aim of this study was to test this process combination at pilot scale. The nitrification process was efficient in a moving bed biofilm reactor with maximal rates of 930 mg N L⁻¹ d⁻¹. Rates decreased to 120 mg N L⁻¹ d⁻¹ after switching to more concentrated urine. At high nitrification rates (640 mg N L⁻¹ d⁻¹) and low total ammonia concentrations (1,790 mg NH₄-N L⁻¹ in influent) distillation caused the main primary energy demand of 71 W cap⁻¹ (nitrification: 13 W cap⁻¹) assuming a nitrogen production of 8.8 g N cap⁻¹ d⁻¹. Possible process failures include the accumulation of the nitrification intermediate nitrite and the selection of acid-tolerant ammonia-oxidizing bacteria. Especially during reactor start-up, the process must therefore be carefully supervised. The concentrate produced by the nitrification/distillation process is low in heavy metals, but high in nutrients, suggesting a good suitability as an integral fertilizer.

Struvite is a solid phosphorus fertilizer that can be recovered easily from source-separated urine by dosing it with a soluble form of magnesium. The process is simple and low-cost, however, previous studies have shown that the cost of magnesium in low-income countries is crucial to the viability and implementation of struvite precipitation. Literature has proposed producing inexpensive magnesium locally by making magnesium oxide from magnesite. This paper aimed to investigate whether process requirements, costs, and environmental impacts would make this process viable for magnesium production in decentralized settings. Magnesite samples were calcined at temperatures between 400 °C and 800 °C and for durations between 0.5 h and 6 h. The release of magnesium was tested by dissolution in phosphate-depleted urine. The optimal processing conditions were at 700 °C for 1 h: magnesite conversion was incomplete at lower temperatures, and the formation of large crystallites caused a decrease in solubility at higher temperatures. The narrow optimal range for magnesium production from magnesite requires reliable process control. Cost estimations for Nepal showed that using local magnesite would provide the cheapest source of magnesium and that CO2 emissions from transport and production would be negligible compared to Nepal's overall CO₂ emissions.

Environmental process modeling is challenged by the lack of high quality data, stochastic variations, and nonlinear behavior. Conventionally, parameter optimization is based on stochastic sampling techniques to deal with the nonlinear behavior of the proposed models. Despite widespread use, such tools cannot guarantee globally optimal parameter estimates. It can be especially difficult in practice to differentiate between lack of algorithm convergence, convergence to a non-global local optimum, and model structure deficits. For this reason, we use a deterministic global optimization algorithm for kinetic model identification and demonstrate it with a model describing a typical batch experiment. A combination of interval arithmetic, reformulations, and relaxations allows globally optimal identification of all (six) model parameters. In addition, the results suggest that further improvements may be obtained by modification of the optimization problem or by proof of the hypothesized pseudo-convex nature of the problem suggested by our results.

In this study, we investigated the prevention of enzymatic urea hydrolysis in fresh urine by increasing the pH with calcium hydroxide (Ca(OH)₂) powder. The amount of Ca(OH)₂ dissolving in fresh urine depends significantly on the composition of the urine. The different urine compositions used in our simulations showed that between 4.3 and 5.8 g Ca(OH)₂ dissolved in 1 liter of urine at 25 °C. At this temperature, the pH at saturation is 12.5 and is far above the pH of 11, which we identified as the upper limit for enzymatic urea hydrolysis. However, temperature has a strong effect on the saturation pH, with higher values being achieved at lower temperatures. Based on our results, we recommend a dosage of 10 g Ca(OH)₂·L⁻¹ of fresh urine to ensure solid Ca(OH)₂ always remains in the urine reactor which ensures sufficiently high pH values. Besides providing sufficient Ca(OH)₂, the temperature has to be kept in a certain range to prevent chemical urea hydrolysis. At temperatures below 14 °C, the saturation pH is higher than 13, which favors chemical urea hydrolysis. We chose a precautionary upper temperature of 40 °C because the rate of chemical urea hydrolysis increases at higher temperatures but this should be confirmed with kinetic studies. By considering the boundaries for pH and temperature developed in this study, urine can be stabilized effectively with Ca(OH)₂ thereby simplifying later treatment processes or making direct use easier.

The water utility of Durban, eThekwini Water and Sanitation (EWS), installed urine-diverting dry toilets to provide sanitation to under-served communities in rural and peri-urban areas. While faeces was treated by dehydration, urine was discharged into a soak away in the ground. EWS teamed up with the Swiss Federal Institute of Aquatic Science and Technology (Eawag) and other partners in Switzerland and South Africa to valorise this resource. The VUNA project developed a sanitation system which produces a valuable fertiliser from urine, reduces pollution of water resources and promotes the acceptance of dry toilets.

In Durban/Südafrika werden urinseparierende Toiletten zur Grundversorgung der Bevölkerung in den Vorstadtgebieten eingesetzt. Die Eawag, das Wasserforschungsinstitut des ETH-Bereichs, hat mit dem VUNA-Projekt (www.vuna.ch) die Stadtwerke von Durban dabei unterstützt, die im Urin enthaltenen Wertstoffe zu nutzen. Ziel des Projektes war es, die Akzeptanz der Trockentoiletten zu erhöhen, die Nährstoffe in Form eines wertvollen Düngers wiederzugewinnen und Umweltverschmutzung zu verhindern.

This paper assesses the inactivation performance and mechanisms in urine nitrification reactors using bacteria and bacteriophages as surrogates for human pathogens. Two parallel continuous-flow moving bed biofilm reactors (MBBRs) were operated over a two-month period. One MBBR was used to conduct a continuous spike experiment with bacteriophage MS2. The second reactor provided the matrix for a series of batch experiments conducted to investigate the inactivation of Salmonella typhimurium, Enterococcus spp., MS2, Qβ, and ΦX174 during urine nitrification. The roles of aeration, biological activity, and solution composition in inactivation were evaluated. Whereas bacteriophages ΦX174 and MS2 remained infective following urine nitrification, partial inactivation of bacteriophage Qβ was observed. Qβ inactivation was attributed primarily to aeration with a potential additive effect of biological processes, i.e., processes that are attributable to the presence of other microorganisms such as sorption to biomass, predation or enzymatic activity. Tailing of Qβ inactivation to a plateau indicated a protective effect of the solution components in aerated nitrification reactors. In contrast to the bacteriophages, S. typhimurium and Enterococcus spp. were mainly affected by biological processes: they were inactivated in biologically active nitrification reactors while remaining stable in chemically equivalent filtered controls. The tested bacteria could, for example, be out-competed by other microbial communities or sorbed to biomass in the reactor. Microbial communities did not adapt to inactivate bacteriophage MS2 (e.g., via increased prevalence of virus predators) in the experimental time-scale evaluated, with no observed inactivation of MS2 during continuous input for 51 days in the flow-through MBBR. The compilation of these results suggests that biological nitrification as a fertilizer production process remains insufficient as a stand-alone technology for the sanitization of source-separated urine.

In eThekwini, South Africa, the production of agricultural fertilizers from human urine collected from urine-diverting dry toilets is being evaluated at a municipality scale as a way to help finance a decentralized, dry sanitation system. The present study aimed to assess a range of human and environmental health hazards in source-separated urine, which was presumed to be contaminated with feces, by evaluating the presence of human pathogens, pharmaceuticals, and an antibiotic resistance gene. Composite urine samples from households enrolled in a urine collection trial were obtained from urine storage tanks installed in three regions of eThekwini. Polymerase chain reaction (PCR) assays targeted 9 viral and 10 bacterial human pathogens transmitted by the fecal–oral route. The most frequently detected viral pathogens were JC polyomavirus, rotavirus, and human adenovirus in 100%, 34% and 31% of samples, respectively. Aeromonas spp. and Shigella spp. were frequently detected gram negative bacteria, in 94% and 61% of samples, respectively. The gram positive bacterium, Clostridium perfringens, which is known to survive for extended times in urine, was found in 72% of samples. A screening of 41 trace organic compounds in the urine facilitated selection of 12 priority pharmaceuticals for further evaluation. The antibiotics sulfamethoxazole and trimethoprim, which are frequently prescribed as prophylaxis for HIV-positive patients, were detected in 95% and 85% of samples, reaching maximum concentrations of 6800 μg/L and 1280 μg/L, respectively. The antiretroviral drug emtricitabine was also detected in 40% of urine samples. A sulfonamide antibiotic resistance gene (sul1) was detected in 100% of urine samples. By coupling analysis of pathogens and pharmaceuticals in geographically dispersed samples in eThekwini, this study reveals a range of human and environmental health hazards in urine intended for fertilizer production. Collection of urine offers the benefit of sequestering contaminants from environmental release and allows for targeted treatment of potential health hazards prior to agricultural application. The efficacy of pathogen and pharmaceutical inactivation, transformation or removal during urine nutrient recovery processes is thus briefly reviewed.

Urine contains about 50 % of the phosphorus (P) and about 90 % of the nitrogen (N) excreted by humans and is therefore an interesting substrate for nutrient recovery. Source-separated urine can be used to precipitate struvite or, through a newly developed technology, nitrified urine fertilizer (NUF). In this study, we prepared ³³P radioisotope- and stable ¹⁵N isotope-labeled synthetic NUF (SNUF) and struvite using synthetic urine and determined P and N uptake by greenhouse-grown ryegrass (Lolium multiflorum var. Gemini) fertilized with these products. The P and N in the urine-based fertilizers were as readily plant-available in a slightly acidic soil as the P and N in reference mineral fertilizers. The ryegrass crop recovered 26 % of P applied with both urine-based fertilizers and 72 and 75 % of N applied as struvite and SNUF, respectively. Thus, NUF and urine-derived struvite are valuable N and P recycling fertilizers.

Sanitizing human and animal waste (e.g., urine, fecal sludge, or grey water) is a critical step in reducing the spread of disease and ensuring microbially safe reuse of waste materials. Viruses are particularly persistent pathogens and can be transmitted through inadequately sanitized waste. However, adequate storage or digestion of waste can strongly reduce the number of viruses due to increases in pH and uncharged aqueous ammonia (NH₃), a known biocide. In this study we investigated the kinetics and mechanisms of inactivation of the single-stranded RNA virus MS2 under temperature, pH and NH₃ conditions representative of waste storage. MS2 inactivation was mainly controlled by the activity of NH₃ over a pH range of 7.0–9.5 and temperatures lower than 40 °C. Other bases (e.g., hydroxide, carbonate) additionally contributed to the observed reduction of infective MS2. The loss in MS2 infectivity could be rationalized by a loss in genome integrity, which was attributed to genome cleavage via alkaline transesterification. The contribution of each base to genome transesterification, and hence inactivation, could be related to the base pK_a by means of a Bronsted relationship. The Bronsted relationship in conjunction with the activity of bases in solution enabled an accurate prediction of MS2 inactivation rates.

Ein neuartiges Recyclingverfahren gewinnt aus Urin wertvolle Nährstoffe zurück, die sich als Dünger verkaufen lassen. Das schont natürliche Ressourcen, entlastet Kläranlagen und macht Sanitärsysteme in Entwicklungsländern wirtschaftlich attraktiver. Drei Anlagen sind schon in Betrieb: eine an der Eawag in Dübendorf und zwei in der südafrikanischen Stadt Durban.

With an innovative recycling method, valuable nutrients recovered from urine can be sold as fertilizers. As well as conserving natural resources, this reduces water pollution and makes sanitation systems in developing countries economically more attractive. Three pilot plants are already in operation – one at Eawag in Dübendorf and two in the South African city of Durban.

Une nouvelle technique de valorisation permet d'extraire les éléments nutritifs de l'urine et de fabriquer un fertilisant commercialisable. Cette approche préserve les ressources naturelles, limite les charges à traiter dans les stations d'épuration et augmente la rentabilité des systèmes d'assainissement dans les pays en développement. Trois stations pilotes sont déjà en fonction: une à Dübendorf et deux dans la ville sud-africaine de Durban

In wastewater treatment, the rate of ammonia oxidation decreases with pH and stops very often slightly below a pH of 6. Free ammonia (NH₃) limitation, inhibition by nitrous acid (HNO₂), limitation by inorganic carbon or direct effect of high proton concentrations have been proposed to cause the rate decrease with pH as well as the cessation of ammonia oxidation. In this study, we compare an exponential pH term common for food microbiology with conventionally applied rate laws based on Monod-type kinetics for NH₃ limitation and non-competitive HNO₂ inhibition as well as sigmoidal pH functions to model the low pH limit of ammonia oxidizing bacteria (AOB). For this purpose we conducted well controlled batch experiments which were then simulated with a computer model. The results showed that kinetics based on NH₃ limitation and HNO₂ inhibition can explain the rate decrease of ammonia oxidation between pH 7 and 6, but fail in predicting the pH limit of Nitrosomonas eutropha at pH 5.4 and rates close to that limit. This is where the exponential pH term becomes important: this term decreases the rate of ammonia oxidation to zero, as the pH limit approaches. Previously proposed sigmoidal pH functions that affect large pH regions, however, led to an overestimation of the pH effect and could therefore not be applied successfully. We show that the proposed exponential pH term can be explained quantitatively with thermodynamic principles: at low pH values, the energy available from the proton motive force is too small for the NADH production in Nitrosomonas eutropha and related AOB causing an energy limited state of the bacterial cell. Hence, energy limitation and not inhibition or limitation of enzymes is responsible for the cessation of the AOB activity at low pH values.

Monitoring of nitrite is essential for an immediate response and prevention of irreversible failure of decentralized biological urine nitrification reactors. Although a few sensors are available for nitrite measurement, none of them are suitable for applications in which both nitrite and nitrate are present in very high concentrations. Such is the case in collected source-separated urine, stabilized by nitrification for long-term storage. Ultraviolet (UV) spectrophotometry in combination with chemometrics is a promising option for monitoring of nitrite. In this study, an immersible in situ UV sensor is investigated for the first time so to establish a relationship between UV absorbance spectra and nitrite concentrations in nitrified urine. The study focuses on the effects of suspended particles and saturation on the absorbance spectra and the chemometric model performance. Detailed analysis indicates that suspended particles in nitrified urine have a negligible effect on nitrite estimation, concluding that sample filtration is not necessary as pretreatment. In contrast, saturation due to very high concentrations affects the model performance severely, suggesting dilution as an essential sample preparation step. However, this can also be mitigated by simple removal of the saturated, lower end of the UV absorbance spectra, and extraction of information from the secondary, weaker nitrite absorbance peak. This approach allows for estimation of nitrite with a simple chemometric model and without sample dilution. These results are promising for a practical application of the UV sensor as an in situ nitrite measurement in a urine nitrification reactor given the exceptional quality of the nitrite estimates in comparison to previous studies.

Urine contains over 80% of the total nitrogen but accounts for less than 1% of the total wastewater volume. Due to higher concentrations, nitrogen removal from source-separated urine is potentially much cheaper and less energy intensive than from wastewater. For many cities, removing nitrogen in small decentralized reactors could be more efficient and affordable than in large treatment plants situated at the end of extensive sewer networks. However, due to a lack of personnel and expensive instruments, process control of small on-site reactors is potentially critical. In addition, process stability and resilience tend to be low due to a lower microbial diversity. Therefore, the main goal of this thesis is to contribute to the development of a reliable and simple process configuration for decentralised nitrogen removal from urine. [...]

Urin beinhaltet über 80% des gesamten Stickstoffs und macht aber nur etwas weniger als 1% des gesamten Abwasservolumens aus. Aufgrund der höheren Konzentrationen ist Stickstoffentfernung aus separat gesammeltem Urin potentiell günstiger und verbraucht weniger Energie als Stickstoffentfernung aus dem gesamten Abwasser. Stickstoffentfernung in kleinen dezentralen Reaktoren könnte deshalb für viele Städte effizienter und erschwinglicher sein als in grossen Reinigungsanlagen am Ende von weitläufigen Kanalisationsnetzen. Da aber kein Personal und keine teuren Instrumente zur Verfügung stehen, kann die Prozesskontrolle von kleinen, dezentralen Reaktoren kritisch sein. Aufgrund der niedrigeren mikrobiellen Diversität, ist in kleinen Systemen tendenziell auch mit einer geringeren Stabilität und Belastbarkeit der Prozesse zu rechnen. Das Hauptziel dieser Arbeit war deshalb, einen Beitrag zur Entwicklung eines einfachen und robusten Prozesses zur dezentralen Stickstoffentfernung aus Urin zu leisten. [...]

In nitritationammox reactors, several bacterial groups contribute to the overall nitrogen conversion. Knowing the activity of the main bacterial groups, especially of anaerobic ammonium-oxidising bacteria (AMX), is extremely helpful to understand the process and optimise its operation. Mass balances of dissolved compounds such as ammonium, nitrite and nitrate commonly allow the determination of bacterial activities in a nitritationammox process, but the activity of heterotrophic bacteria (HET) is usually neglected. However, even in wastewater with a low organic substrate content, heterotrophic denitrification can contribute substantially to nitrogen removal. The goal of this study was to critically evaluate the applicability of mass balances for the determination of the relevant bacterial activities in a nitritationammox process with high HET activity. We set up and solved mass balances of different degrees of complexity. Both linear equation systems, with catabolic reactions alone and with balances according to the activated sludge model stoichiometry, do not allow estimation of any of the considered bacterial activities. When kinetic rate expressions are included, it is possible to compute the concentrations of all considered bacterial groups, but the estimation uncertainty is far too high for practical purposes: the relative standard deviation for AMX is 5280%. In a completely autotrophic system, the relative standard deviation for AMX is only 5%, which proves that the high standard deviations are due to the complexity of the nitration–anammox process with HET activity. The high standard deviations of the calculated bacterial concentrations can be significantly reduced by adding an additional mass balance for the total biomass (standard deviation for AMX activity 1210%). The required number of measurements to achieve an acceptable precision, in our example about 600 conversion rate measurements to reach a 50% standard deviation for the AMX concentration, is still far too high though for practical purposes. To conclude, mass balances including kinetics theoretically allow the observation of the bacterial activities in nitritationammox reactors with high HET activity. However, the required precision of the calculated conversion rates, the uncertainty of stoichiometric and kinetic parameters and the reactor dynamics (unsteady conditions) make mass balances unsuitable for practical estimation of AMX activity. Due to high frequency and new online instruments, mass balances might become a suitable tool in the future.

In recent years, a large number of urine-diverting dehydration toilets (UDDTs) have been installed in eThekwini to ensure access to adequate sanitation. The initial purpose of these toilets was to facilitate faeces drying, while the urine was diverted into a soak pit. This practice can lead to environmental pollution, since urine contains high amounts of nutrients. Instead of polluting the environment, these nutrients should be recovered and used as fertiliser. In 2010 the international and transdisciplinary research project VUNA was initiated in order to explore technologies and management methods for better urine management in eThekwini. Three treatment technologies have been chosen for the VUNA project. The first is struvite precipitation, a technology which has already been tested in multiple projects on urine treatment. Struvite precipitation is a simple and fast process for phosphorus recovery. Other nutrients, such as nitrogen and potassium, remain in the effluent and pathogens are not completely inactivated. Therefore, struvite precipitation has to be combined with other treatment processes to prevent environmental pollution and hygiene risks. The second process is a combination of nitrification and distillation. This process combination is more complex than struvite precipitation, but it recovers all nutrients in one concentrated solution, ensures safe sanitisation and produces only distilled water and a small amount of sludge as by-products. The third process is electrolysis. This process could be used for very small on-site reactors, because conversion rates are high and the operation is simple, as long as appropriate electrodes and voltages are used. However, nitrogen is removed and not recovered and chlorinated by-products are formed, which can be hazardous for human health. While urine electrolysis requires further research in the laboratory, struvite precipitation and nitrification/distillation have already been operated at pilot scale.

Electrolysis can be a viable technology for ammonia removal from source-separated urine. Compared to biological nitrogen removal, electrolysis is more robust and is highly amenable to automation, which makes it especially attractive for on-site reactors. In electrolytic wastewater treatment, ammonia is usually removed by indirect oxidation through active chlorine which is produced in-situ at elevated anode potentials. However, the evolution of chlorine can lead to the formation of chlorate, perchlorate, chlorinated organic by-products and chloramines that are toxic. This study focuses on using direct ammonia oxidation on graphite at low anode potentials in order to overcome the formation of toxic by-products. With the aid of cyclic voltammetry, we demonstrated that graphite is active for direct ammonia oxidation without concomitant chlorine formation if the anode potential is between 1.1 and 1.6 V vs. SHE (standard hydrogen electrode). A comparison of potentiostatic bulk electrolysis experiments in synthetic stored urine with and without chloride confirmed that ammonia was removed exclusively by continuous direct oxidation. Direct oxidation required high pH values (pH > 9) because free ammonia was the actual reactant. In real stored urine (pH = 9.0), an ammonia removal rate of 2.9 ± 0.3 gN·m⁻²·d⁻¹ was achieved and the specific energy demand was 42 Wh·gN⁻¹ at an anode potential of 1.31 V vs. SHE. The measurements of chlorate and perchlorate as well as selected chlorinated organic by-products confirmed that no chlorinated by-products were formed in real urine. Electrode corrosion through graphite exfoliation was prevented and the surface was not poisoned by intermediate oxidation products. We conclude that direct ammonia oxidation on graphite electrodes is a treatment option for source-separated urine with three major advantages: The formation of chlorinated by-products is prevented, less energy is consumed than in indirect ammonia oxidation and readily available and cheap graphite can be used as the electrode material.

Electrolysis is a promising technology for the on-site treatment of source-separated urine. It is the many degrees of freedom (electrode material, electrode potential, current density, cell design), the electrical conductivity of urine and the high amenability to automation which make electrolysis attractive. It was the objective of this thesis to understand the electro-oxidation of organic substances and ammonia to apply electrolysis successfully for the removal of these compounds from stored source-separated urine. To achieve this goal, a variety of electrochemical experiments were conducted with anodes consisting of boron-doped diamond (BDD), thermally decomposed iridium oxide film (TDIROF) or graphite and a new experimental procedure was developed to assess the time dependent production of volatile organic chlorination by-products (OCBPs). [...]

Die Elektrolyse ist eine vielversprechende Technologie für die Behandlung von Urin. Es sind die vielen Freiheitsgrade (Elektrodenmaterialien, Elektrodenpotential, Stromdichte, Zellendesign), die elektrische Leitfähigkeit des Urins sowie das hohe Automatisierungspotential, welche die Elektrolyse attraktiv machen. Es war das Ziel dieser Arbeit, die elektrochemische Oxidation von organischen Substanzen und Ammoniak zu verstehen, um diese für die dezentrale Behandlung von gelagertem Urin anzuwenden. Es wurden elektrochemische Experimente mit Bor-versetzten Diamant-(BDD), thermisch hergestellten Iridiumoxidfilm- (TDIROF) und Graphitanoden durchgeführt. Um dabei die Entstehung von leichtflüchtigen, chlorierten Nebenprodukten (CNPs) zu verfolgen, wurde eine neue experimentelle Methode entwickelt. [...]

Chlorination byproducts (CBPs) are harmful to human health and the environment. Their formation in chlorine mediated electro-oxidation is a concern for electrochemical urine treatment. We investigated the formation of chlorate, perchlorate, and organic chlorination byproducts (OCBPs) during galvanostatic (10, 15, 20 mA·cm^–2) electro-oxidation of urine on boron-doped diamond (BDD) and thermally decomposed iridium oxide film (TDIROF) anodes. In the beginning of the batch experiments, the production of perchlorate was prevented by competing active chlorine and chlorate formation as well as by direct oxidation of organic substances. Perchlorate was only formed at higher specific charges (>17 Ah·L^–1 on BDD and >29 Ah·L^–1 on TDIROF) resulting in chlorate and perchlorate being the dominant CBPs (>90% of initial chloride). BDD produced mainly short chained OCBPs (dichloromethane, trichloromethane, and tetrachloromethane), whereas longer chained OCBPs (1,2-dichloropropane and 1,2-dichloroethane) were more frequently found on TDIROF. The OCBPs were primarily eliminated by electrochemical stripping: On BDD, this pathway accounted for 40% (dichloromethane) to 100% (tetrachloromethane) and on TDIROF for 90% (1,2-dichloroethane) to 100% (trichloromethane) of what was produced. A post-treatment of the liquid as well as the gas phase should be foreseen if CBP formation cannot be prevented by eliminating chloride or organic substances in a pretreatment.

Electrochemical ammonia oxidation has gained a lot of attention recently as an efficient method for ammonia removal from wastewater, for the use in ammonia-based fuel cells and the production of high purity hydrogen. Thermally decomposed iridium oxide films (TDIROF) have been shown to be catalytically active for direct ammonia oxidation in aqueous solutions if NH₃ is present. However, the process was reported to be rapidly inhibited on TDIROF. Herein, we show that this fast inhibition of direct ammonia oxidation does not result from surface poisoning by adsorbed elemental nitrogen (N_ads). Instead, we propose that direct ammonia oxidation and oxygen evolution can lead to a drop of the local pH at the electrode resulting in a low availability of the actual reactant, NH₃. The hypothesis was tested with cyclic voltammetry (CV) experiments on stagnant and rotating disk electrodes (RDE). The CV experiments on the stagnant electrode revealed that the decrease of the ammonia oxidation peaks was considerably reduced by introducing an idle phase at open circuit potential between subsequent scans. Furthermore, the polarization of the TDIROF electrode into the hydrogen evolution region (HER) resulted in increased ammonia oxidation peaks in the following anodic scans which can be explained with an increased local pH after the consumption of protons in the HER. On the RDE, the ammonia oxidation peaks did not decrease in immediately consecutive scans. These findings would not be expected if surface poisoning was responsible for the fast inhibition but they are in good agreement with the proposed mechanism of pH induced limitation by the reactant, NH₃. The plausibility of the mechanism was also supported by our numerical simulations of the processes in the Nernstian diffusion layer. The knowledge about this inhibition mechanism of direct ammonia oxidation is especially important for the design of electrochemical cells for wastewater treatment. The mechanism is not only valid for TDIROF but also for other electrodes because it is independent of the electrode material.

VUNA is a trans-disciplinary project that is developing a system to collect source-separated urine and process it into fertiliser. Collection logistics, treatment technologies, and social and economic assessments of nutrient recovery are some of the activities worked on by the VUNA team.

The nitritation/anammox process has been mainly applied to high-strength nitrogenous wastewaters with very low biodegradable organic carbon content (<0.5g COD·g N^–1). However, several wastewaters have biodegradable organic carbon to nitrogen (COD/N) ratios between 0.5 and 1.7g COD·g N^–1 and thus, contain elevated amounts of organic carbon but not enough for heterotrophic denitrification. In this study, the influence of elevated COD/N ratios was studied on a nitritation/anammox process with suspended sludge. In a step-wise manner, the influent COD/N ratio was increased to 1.4g COD·g N^–1 by supplementing digester supernatant with acetate. The increasing availability of COD led to an increase of the nitrogen removal efficiency from around 85% with pure digester supernatant to >95% with added acetate while the nitrogen elimination rate stayed constant (275 ± 40mg N·L^–1·d^–1). Anammox activity and abundance of anammox bacteria (AMX) were strongly correlated, and with increasing influent COD/N ratio both decreased steadily. At the same time, heterotrophic denitrification with nitrite and the activity of ammonia oxidising bacteria (AOB) gradually increased. Simultaneously, the sludge retention time (SRT) decreased significantly with increasing COD loading to about 15 d and reached critical values for the slowly growing AMX. When the SRT was increased by reducing biomass loss with the effluent, AMX activity and abundance started to rise again, while the AOB activity remained unaltered. Fluorescent in-situ hybridisation (FISH) showed that the initial AMX community shifted within only 40 d from a mixed AMX community to "Candidatus Brocadia fulgida" as the dominant AMX type with an influent COD/N ratio of 0.8 g COD·g N^–1 and higher. "Ca. Brocadia fulgida" is known to oxidise acetate, and its ability to outcompete other types of AMX indicates that AMX participated in acetate oxidation. In a later phase, glucose was added to the influent instead of acetate. The new substrate composition did not significantly influence the nitrogen removal nor the AMX activity, and "Ca. Brocadia fulgida" remained the dominant type of AMX. Overall, this study showed that AMX can coexist with heterotrophic bacteria at elevated influent COD/N ratios if a sufficiently high SRT is maintained.

Ist eine ressourcenschonende Abwasserreinigung durch Abwassertrennung und Dezentralisierung realistisch? Rund 40 international bekannte Wissenschafter und Wissenschafterinnen behandeln auf 520 Seiten in einem 2013 erschienenen Buch nuanciert diese Fragestellung. Die Editoren der Eawag diskutieren das Thema des Buches im Schweizer Kontext.

This paper offers a methodology for structuring the design space for innovative process engineering technology development. The methodology is exemplified in the evaluation of a wide variety of treatment technologies for source-separated domestic wastewater within the scope of the Reinvent the Toilet Challenge. It offers a methodology for narrowing down the decision-making field based on a strict interpretation of treatment objectives for undiluted urine and dry feces and macroenvironmental factors (STEEPLED analysis) which influence decision criteria. Such an evaluation identifies promising paths for technology development such as focusing on space-saving processes or the need for more innovation in low-cost, energy-efficient urine treatment methods. Critical macroenvironmental factors, such as housing density, transportation infrastructure, and climate conditions were found to affect technology decisions regarding reactor volume, weight of outputs, energy consumption, atmospheric emissions, investment cost, and net revenue. The analysis also identified a number of qualitative factors that should be carefully weighed when pursuing technology development; such as availability of O&M resources, health and safety goals, and other ethical issues. Use of this methodology allows for coevolution of innovative technology within context constraints; however, for full-scale technology choices in the field, only very mature technologies can be evaluated.

Separation at the source and decentralized treatment of urine, feces, and greywater is a novel concept for wastewater management. This approach is particularly suitable for regions where the availability of water resources is low or the infrastructure for centralized wastewater treatment is missing. Urine is the main contributor of nutrients to municipal wastewater (80 % of nitrogen and 50 % of phosphorus). Since the urine volume is small (1.3 L · s^-1 · d^-1), nutrient removal (or recovery) could be achieved in small decentralized reactors.
Some properties of electrochemical processes make them particularly suitable for urine treatment in a small decentralized reactor: no chemicals have to be added, the reaction can be easily started and terminated, a wide range of compounds can be oxidized or reduced, and the electric parameters current and voltage can be used for process automation and remote process control. However, electrochemical processes also have some drawbacks: the energy consumption is higher than for comparable biological processes, side reactions can produce unwanted by-products, and efficient electrodes are often expensive.
The main focus of this article is on the electrochemical removal of nitrogen and phosphorus from source-separated urine. Bioelectrochemical systems for urine treatment will not be discussed, because the research is still at an early stage. Some possible applications of bioelectrochemical systems for urine treatment have been presented in Udert et al..

In this thesis the resilience of complete and partial nitrification of source-separated urine under dynamic conditions were investigated and compared. The process stability of nitrification reactors is important for their commercial application. In partial nitrification the alkalinity contained in urine allows nitrifying 50% of the ammonia whereas in complete nitrification the dosage of a base allows the nitrification of almost 100% of the ammonia. Due to considerations about Monod kinetic substrate limitation of Ammonia Oxidizing Bacteria (AOB) it was hypothesized that complete nitrification is more prone to nitrite accumulation and therefore less stable than partial nitrification. A computer model based on Monod kinetics should help to understand the processes and the resilience of urine nitrification reactors. Laboratory experiments were conducted in 7 L moving bed biofilm reactors (MBBR) to analyze the behavior of the two processes in respect to changes in temperature and inflow. The total ammonia concentration in the inflow was on average 1750±150 mg N L^-1. Complete nitrification has at same conditions a lower nitrification rate than partial nitrification due to the lower ammonia concentration in the reactor. In order to reach comparable nitrification rates complete and partial nitrification reactors were therefore operated at two different pH values of 7 and 6 respectively. The average nitrification rate in complete nitrification was 1.08±0.17 g N m-2 d-1 and in parital nitrification 0.90±0.25 g N m-2 d-1 with regard to biofilm carrier surface (Kaldnes^®). During all experiments no essential difference of process stability between complete and partial nitrification were observed. Both processes remained stable during temperature fluctuations between 20 °C and 32 °C when urine inflow was constant. pH-diven inflow control led to substantial nitrite accumulation and to a break down of nitrification due to an increase of the inflow caused by increasing AOB activity at higher temperatures. It could be shown that the dynamics of bacterial growth due to temperature changes are damped when pH is not controlled. Instantaneous increase of the inflow caused severe nitrite accumulations in both processes. A reliable process control should therefore consider the effects of temperature and restrict load fluctuations to a minimum. The developed model was able to describe the dynamics of nitrogen conversion due to temperature changes but failed in the prediction of process instabilities caused by increasing inflow.

Im Forum Chriesbach der Eawag ist ein NoMix-System installiert, das den Urin sammelt und getrennt vom restlichen Abwasser abführt. Da der Urin einen Grossteil an Nährstoffen wie Stickstoff enthält, kann er separat aufbereitet und anschliessend als landwirtschaftlicher Dünger genutzt werden. Im Leitungssystem wird der Harnstoff, welcher die grösste Stickstoffkomponente im Urin bildet, durch Bakterien abgebaut. Für ein besseres Verständnis der Harnstoffhydrolyse muss bekannt sein, wie lange der Urin im Leitungssystem verweilt. Um die Aufenthaltszeit von Urin zu quantifizieren wurden in dieser Arbeit Tracerversuche mit Bromid durchgeführt. Dabei wurden neben einer mittleren Aufenthaltszeit auch der Einfluss der Benutzerfrequenz und der Distanz, also dem Stockwerk aus dem der Urin kommt, untersucht. Zusätzlich wurde die Aufenthaltszeit mit Hilfe einer Urinbilanz berechnet, bei der die summierten Input und Output Kurven des Urins aufgezeichnet wurden. Die zeitliche Verschiebung der beiden Kurven beschreibt eine mittlere Verweilzeit.
Die Tracerversuche zeigten, dass sich die Aufenthaltszeit des Bromids und des eigentlichen Urins deutlich unterscheiden. Der Tracer repräsentiert somit nicht wie ursprünglich angenommen den Grundstrom. Wie aus der Urinbilanz hervorging hat der Urin eine mittlere Verweilzeit von 31 Minuten mit einer Standartabweichung von 12 Minuten. Die mittlere Aufenthaltszeit des Bromids ist gemäss den Tracerversuchen etwa viermal grösser. Das unterschiedliche Verhalten ist dadurch zu erklären, dass das Bromid im Leitungsrohr in den Biofilm diffundiert und deshalb mehr Zeit als der Urin benötigt. Mit zunehmender Benutzerfrequenz gleichen sich die beiden Aufenthaltszeiten an, da mehr Urin vorhanden ist, in welches das Bromid zurückdiffundieren kann. Das Stockwerk beeinflusst die Aufenthaltszeit des Urins und des Bromids. Der Einfluss auf das Bromid ist jedoch grösser, da die Diffusion in den Biofilm in den vertikalen Leitungen grösser ist als in den horizontalen.
Auf die Verweilzeit des Harnstoffs konnte aus den Ergebnissen auf Grund der Diffusion nicht geschlossen werden, da weder der Urin noch das Bromid repräsentativ sind. Es kann aber mit grosser Wahrscheinlichkeit gesagt werden, dass auch der Harnstoff und weitere gelöste Stoffe in den Biofilm diffundieren und damit eine grössere Aufenthaltszeit als der Urin besitzen.

With the goal of nutrient recovery, full nitrification of human urine is investigated for its stabilization in simple, decentralized reactors. In a first part of this work, undiluted urine was completely nitrified in a laboratory-scale moving-bed biofilm reactor (MBBR), with automated dosage of a KHCO₃ solution keeping the pH at 7.0-7.1. The effluent contained up to 2706 mg-N/L of nitrate; on average > 99% of the total nitrogen. Maintaining low concentrations of ammonium and nitrite (generally below 1 ‰ and 4.7‰ respectively of the influent total ammonia) proved to reduce the risks of dramatic process instabilities due to inhibition with nitrous acid and free ammonia. Although full nitrification by adding a base presents several advantages, for decentralized applications, it is recommended to add alkalinity in a way requiring less expensive and complex material than by dosing a basic solution.
Hoping that calcite (CaCO₃) could be a simple alternative to buffer nitrification, in a second part we studied the dissolution of chalk powder in synthetic urine solutions, both in the presence and absence of phosphate. Experiments and simulations with PHREEQC verified the hypothesis that phosphate may precipitate on the surface of calcite, and thus slow down dissolution. In the absence of phosphate, calcite dissolved rapidly until saturation of the solution. By contrast, with the high phosphate concentrations in stored urine (around 200-250 mg_P/L), calcite dissolution was inhibited by the rapid formation of  amorphous calcium-phosphate (ACP; eventually converting into hydroxyapatite, HAP) directly on the particle’s surface, as was revealed by XRD and REM analysis. To prevent calcite passivation, precipitation of struvite (MgNH₄PO₄•6H₂O) is suggested before the full nitrification reactor.  In real urine, the effect of biofilm growth directly on calcite may be of advantage to compensate possibly too slow calcite dissolution, and should inform further work.

When magnesium is added to source-separated urine, struvite (MgNH₄PO₄·6H₂O) precipitates and phosphorus can be recovered. Up to now, magnesium salts have been used as the main source of magnesium. Struvite precipitation with these salts works well but is challenging in decentralized reactors, where high automation of the dosage and small reactor sizes are required. In this study, we investigated a novel approach for magnesium dosage: magnesium was electrochemically dissolved from a sacrificial magnesium electrode. We demonstrated that this process is technically simple and economically feasible and thus interesting for decentralized reactors. Linear voltammetry and batch experiments at different anode potentials revealed that the anode potential must be higher than −0.9 V vs. NHE (normal hydrogen electrode) to overcome the strong passivation of the anode. An anode potential of −0.6 V vs. NHE seemed to be suitable for active magnesium dissolution. For 13 subsequent cycles at this potential, we achieved an average phosphate removal rate of 3.7 mg P cm⁻² h⁻¹, a current density of 5.5 mA cm⁻² and a current efficiency of 118%. Some magnesium carbonate (nesquehonite) accumulated on the anode surface; as a consequence, the current density decreased slightly, but the current efficiency was not affected. The energy consumption for these experiments was 1.7 W h g P⁻¹. A cost comparison showed that sacrificial magnesium electrodes are competitive with easily soluble magnesium salts such as MgCl₂ and MgSO₄, but are more expensive than dosing with MgO. Energy costs for the electrochemical process were insignificant. Dosing magnesium electrochemically could thus be a worthwhile alternative to dosing magnesium salts. Due to the simple reactor and handling of magnesium, this may well be a particularly interesting approach for decentralized urine treatment.

Several treatment methods can be used to transfer dissolved compounds from source-separated wastewater streams onto or into a solid phase. A critical review of these methods will be given here. The emphasis will be placed on the recovery of nutrients, especially from human urine; the treatment of other waste streams will be described in brief.

Why are we editing a book about source separation and decentralization? We live in Switzerland, an industrialized country with a highly advanced and well-functioning wastewater management system. But even in Switzerland, the central system is reaching its limits, shortcomings, which become very obvious from a global perspective. We are proud to have been able to assemble contributions from renowned authors worldwide from both research and practice. They share with us their experience and thoughts about the current wastewater system. They analyze its advantages, but also deficiencies and they have the courage to breach the paradigm that central wastewater treatment is the only possible approach in urban areas. Many of the authors of this book are pioneers in the field and have been paving the way to a more sustainable and equitable handling of wastewater. We are greatly indebted to all the authors for their contributions to this book, but even more so for their continuous research on source separation and decentralization. We hope that this book will help develop this new area into a mature field in science as well as in practice. [...]

Electrolysis of source separated urine is an efficient technology for COD and ammonia removal. Despite a huge of research about electrochemical treatment of wastewater the formation and emission of toxic and carcinogenic disinfection by-products (DBPs), is still not understoood in detail. The aim of this masterthesis is to contribute to the optimisation of the electrolysis of stored urine by a better understanding of the DBP formation.
For this purpose two control variables, anode material and current density, are investigated. DBP formation was analysed in nine galvanostatic experiments with the anode materials boron-doped diamond (BDD), iridium dioxide (Ti/IrO₂) and graphite. Current densities of 5, 10, 15 and 20 mA cm^-2 were applied to a discontinuous electrolysis cell filled with 350 mL of stored urine. The gas above the electrolyte was extracted and drawn through two traps in series filled with dodecane by a gas pump. Periodically taken samples from the reactor were analysed with GCMS, IC and Hach Dr. Lange tests for concentrations of six selected DBPs, COD, ammonia, Chloride and Chlorate. Samples from the raps were analysed for DBP concentrations. [...]

Stripping is the most common process for the selective recovery of ammonia from wastewater. Two stripping technologies have been used for source-separated urine: first, air stripping of ammonia with subsequent ammonia adsorption in acid, and second, steam stripping with ammonia recovery in the condensate. In this chapter, we discuss the basic concepts of air stripping, because it is probably more suitable for decentralized reactors than steam stripping. We will also present results of air stripping/acid adsorption and steam stripping experiments with urine. Furthermore, we will discuss the conditions that can lead to passive ammonia stripping in urine-collecting systems. In the future, passive stripping could be a low-energy option for ammonia recovery in on-site systems.
The focus of this chapter is on the treatment of source-separated urine. However, we will also refer to the treatment of digester supernatant during the discussion of the basic concepts of air stripping. Since our literature review did not reveal any report about ammonia stripping from blackwater, we will not discuss this application.
Throughout the text, we will use the term ammonia for the sum of free ammonia (NH₃) and ammonium (NH₄⁺). To specifically address the two forms of ammonia, we will use the chemical formula NH₃ and NH₄⁺. The terms for carbonate and phosphate will be used accordingly.

Biological processes are the gold standard for nitrogen removal in municipal wastewater treatment, because they are more energy-efficient and require fewer resources than physico-chemical processes. Several studies have shown that biological processes can also be used for nitrogen removal from urine and blackwater, the two source-separated waste streams with the highest nitrogen loads. However, biological processes are not only used for nitrogen removal but also for nitrogen recovery: with nitrification the volatile ammonia in urine can be stabilized as nitrate or ammonium nitrate. This is a suitable pretreatment step for the evaporative recovery of all nutrients in one solid product.
In this chapter, we present the basic processes for biological nitrogen conversion in wastewater treatment and we discuss laboratory and pilot-scale experiments of nitrogen conversion in urine and blackwater.

Electrochemical processes offer many possibilities for decentralized wastewater treatment. Besides the direct oxidation and reduction of major pollutants they can also be used for coagulation and precipitation processes, disinfection or targeted micropollutant removal. While those processes require energy, wastewater can also be used as a direct source for electricity, either in purely chemical fuel cells or in bioelectrochemical systems. Several processes have been tested for source-separated waste streams, especially for urine. However, no pilot plants or long-term experiences have been reported so far. In this chapter, we present basic concepts of electrochemical treatment, possible applications for source-separated waste streams and we summarize and discuss existing data especially with respect to energy.

Is sewer-based wastewater treatment really the optimal technical solution in urban water management? This paradigm is increasingly being questioned. Growing water scarcity and the insight that water will be an important limiting factor for the quality of urban life are main drivers for new approaches in wastewater management. Source Separation and Decentralization for Wastewater Management sets up a comprehensive view of the resources involved in urban water management. It explores the potential of source separation and decentralization to provide viable alternatives to sewerbased urban water management.
During the 1990s, several research groups started working on sourceseparating technologies for wastewater treatment. Source separation was not new, but had only been propagated as a cheap and environmentally friendly technology for the poor. The novelty was the discussion whether source separation could be a sustainable alternative to existing end-of-pipe systems, even in urban areas and industrialized countries.
Since then, sustainable resource management and many different sourceseparating technologies have been investigated. The theoretical framework and also possible technologies have now developed to a more mature state. At the same time, many interesting technologies to process combined or concentrated wastewaters have evolved, which are equally suited for the treatment of source-separated domestic wastewater.
The book presents a comprehensive view of the state of the art of source separation and decentralization. It discusses the technical possibilities and practical experience with source separation in different countries around the world. The area is in rapid development, but many of the fundamental insights presented in this book will stay valid.
Source Separation and Decentralization for Wastewater Management is intended for all professionals and researchers interested in wastewater mamagement, wheter or not they are familiar with source separation.

Recent studies have shown that electrolysis can be an efficient process for nitrogen removal from urine. These studies have been conducted with urea solutions or fresh urine, but urine collected in NoMix toilets and urinals has a substantially different composition, because bacteria hydrolyse urea quickly to ammonia and carbonate. In this study, we compared electrochemical removal of nitrogen from synthetic solutions of fresh and stored urine using IrO₂ anodes. We could show that in fresh urine both ammonia and urea are efficiently eliminated, mainly through chlorine-mediated oxidation. However, in stored urine the presence of carbonate, arising from urea hydrolysis, leads to an inhibition of ammonia oxidation. We suggest two parallel mechanisms to explain this effect: the competition between chloride and carbonate oxidation at the anode and the competition between chlorate formation, enhanced by the buffering effect of carbonate, and ammonia oxidation for the consumption of active chlorine in the bulk. However, further experiments are needed to support the latter mechanism. In conclusion, this study highlights the negative consequences of the presence of carbonate in urine solutions, but also in other wastewaters, when subjected to an electrolytic treatment on IrO₂ in alkaline media.

This master thesis is part of the VUNA project which aims for nutrient recovery and treatment of urine in decentralized treatment facilities. Electrolysis is used to remove nitrogen through electrolytic ammonia oxidation. It is a promising treatment option because it is not susceptible to inflow variations. However, a disadvantage of electrolysis is that chlorinated organics, which are dangerous for environmental and human health, might be formed.
The overall goal of this master thesis is to analyze the processes of chlorinated organics formation during electrolytic treatment of stored urine. The subgoals are to choose four chlorinated, organic substances of interest, to develop a measurement method for these substances, to quantify the current efficiency in experiments with urine and to either accept or reject the following hypotheses: 1) Chlorinated organics are formed during the electrolytic treatment of stored urine. 2) If the electrode potential applied in electrolytic urine treatment is lower than the potential needed for chloride oxidation, no chlorinated organics are formed. [...]

Electrodes for nitric and nitrous oxide have been on the market for some time, but have not yet been tested for an application in wastewater treatment processes. Both sensors were therefore assessed with respect to their (non)linear response, temperature dependence and potential cross sensitivity to dissolved compounds, which are present and highly dynamic in nitrogen conversion processes (nitric oxide, nitrous oxide, nitrogen dioxide, ammonia, hydrazine, hydroxylamine, nitrous acid, oxygen, and carbon dioxide). Off-gas measurements were employed to differentiate between cross sensitivity to interfering components and chemical nitric oxide or nitrous oxide production. Significant cross sensitivities were detected for both sensors: by the nitrous oxide sensor to nitric oxide and by the nitric oxide sensor to ammonia, hydrazine, hydroxylamine and nitrous acid. These interferences could, however, be removed by correction functions. Temperature fluctuations in the range of ±1 °C lead to artifacts of ±3.5% for the nitric oxide and ±3.9% for the nitrous oxide sensor and can be corrected with exponential equations. The results from this study help to significantly shorten and optimize the determination of the correction functions and are therefore relevant for all users of nitric and nitrous oxide electrodes.

Struvite precipitation is a simple technology for phosphorus recovery from source-separated urine. However, production costs can be high if expensive magnesium salts are used as precipitants. Therefore, waste products can be interesting alternatives to industrially-produced magnesium salts. We investigated the technical and financial feasibility of wood ash as a magnesium source in India. In batch experiments with source-separated urine, we could precipitate 99% of the phosphate with a magnesium dosage of 2.7 mol Mg mol P^{− 1}. The availability of the magnesium from the wood ash used in our experiment was only about 50% but this could be increased by burning the wood at temperatures well above 600 °C. Depending on the wood ash used, the precipitate can contain high concentrations of heavy metals. This could be problematic if the precipitate were used as fertilizer depending on the applicable fertilizer regulations. The financial study revealed that wood ash is considerably cheaper than industrially-produced magnesium sources and even cheaper than bittern. However, the solid precipitated with wood ash is not pure struvite. Due to the high calcite and the low phosphorus content (3%), the precipitate would be better used as a phosphorus-enhanced conditioner for acidic soils. The estimated fertilizer value of the precipitate was actually slightly lower than wood ash, because 60% of the potassium dissolved into solution during precipitation and was not present in the final product. From a financial point of view and due to the high heavy metal content, wood ash is not a very suitable precipitant for struvite production. Phosphate precipitation from urine with wood ash can be useful if (1) a strong need for a soil conditioner that also contains phosphate exists, (2) potassium is abundant in the soil and (3) no other cheap precipitant, such as bittern or magnesium oxide, is available.

Nitrous oxide (N₂O) is an environmentally important atmospheric trace gas because it is an effective greenhouse gas and it leads to ozone depletion through photo-chemical nitric oxide (NO) production in the stratosphere. Mitigating its steady increase in atmospheric concentration requires an understanding of the mechanisms that lead to its formation in natural and engineered microbial communities. N₂O is formed biologically from the oxidation of hydroxylamine (NH₂OH) or the reduction of nitrite (NO⁻₂) to NO and further to N₂O. Our review of the biological pathways for N₂O production shows that apparently all organisms and pathways known to be involved in the catabolic branch of microbial N-cycle have the potential to catalyze the reduction of NO⁻₂ to NO and the further reduction of NO to N₂O, while N₂O formation from NH₂OH is only performed by ammonia oxidizing bacteria (AOB). In addition to biological pathways, we review important chemical reactions that can lead to NO and N₂O formation due to the reactivity of NO⁻₂, NH₂OH, and nitroxyl (HNO). Moreover, biological N₂O formation is highly dynamic in response to N-imbalance imposed on a system. Thus, understanding NO formation and capturing the dynamics of NO and N₂O build-up are key to understand mechanisms of N₂O release. Here, we discuss novel technologies that allow experiments on NO and N₂O formation at high temporal resolution, namely NO and N₂O microelectrodes and the dynamic analysis of the isotopic signature of N₂O with quantum cascade laser absorption spectroscopy (QCLAS). In addition, we introduce other techniques that use the isotopic composition of N₂O to distinguish production pathways and findings that were made with emerging molecular techniques in complex environments. Finally, we discuss how a combination of the presented tools might help to address important open questions on pathways and controls of nitrogen flow through complex microbial communities that eventually lead to N₂O build-up.

In this study we present a method to recover all nutrients from source-separated urine in a dry solid by combining biological nitrification with distillation. In a first process step, a membrane-aerated biofilm reactor was operated stably for more than 12 months, producing a nutrient solution with a pH between 6.2 and 7.0 (depending on the pH set-point), and an ammonium to nitrate ratio between 0.87 and 1.15 gN gN⁻¹. The maximum nitrification rate was 1.8 ± 0.3 gN m⁻² d⁻¹. Process stability was achieved by controlling the pH via the influent. In the second process step, real nitrified urine and synthetic solutions were concentrated in lab-scale distillation reactors. All nutrients were recovered in a dry powder except for some ammonia (less than 3% of total nitrogen). We estimate that the primary energy demand for a simple nitrification/distillation process is four to five times higher than removing nitrogen and phosphorus in a conventional wastewater treatment plant and producing the equivalent amount of phosphorus and nitrogen fertilizers. However, the primary energy demand can be reduced to values very close to conventional treatment, if 80% of the water is removed with reverse osmosis and distillation is operated with vapor compression. The ammonium nitrate content of the solid residue is below the limit at which stringent EU safety regulations for fertilizers come into effect; nevertheless, we propose some additional process steps that will increase the thermal stability of the solid product.

The microbial population and physicochemical process parameters of a sequencing batch reactor for nitrogen removal from urine were monitored over a 1.5-year period. Microbial community fingerprinting (automated ribosomal intergenic spacer analysis), 16S rRNA gene sequencing, and quantitative PCR on nitrogen cycle functional groups were used to characterize the microbial population. The reactor combined nitrification (ammonium oxidation)/anammox with organoheterotrophic denitrification. The nitrogen elimination rate initially increased by 400%, followed by an extended period of performance degradation. This phase was characterized by accumulation of nitrite and nitrous oxide, reduced anammox activity, and a different but stable microbial community. Outwashing of anammox bacteria or their inhibition by oxygen or nitrite was insufficient to explain reactor behavior. Multiple lines of evidence, e.g., regime-shift analysis of chemical and physical parameters and cluster and ordination analysis of the microbial community, indicated that the system had experienced a rapid transition to a new stable state that led to the observed inferior process rates. The events in the reactor can thus be interpreted to be an ecological regime shift. Constrained ordination indicated that the pH set point controlling cycle duration, temperature, airflow rate, and the release of nitric and nitrous oxides controlled the primarily heterotrophic microbial community. We show that by combining chemical and physical measurements, microbial community analysis and ecological theory allowed extraction of useful information about the causes and dynamics of the observed process instability.

Human urine has the potential to be a sustainable, locally and continuously available source of nutrients for agriculture. Phosphate can be efficiently recovered from human urine in the form of the mineral struvite (MgNH₄PO₄·6H₂O). However, struvite formation may be coupled with the precipitation of other constituents present in urine including pathogens, pharmaceuticals, and heavy metals. To determine if struvite fertilizer presents a microbiological health risk to producers and end users, we characterized the fate of a human virus surrogate (phage ΦX174) and the eggs of the helminth Ascaris suum during a low-cost struvite recovery process. While the concentration of phages was similar in both the struvite and the urine, Ascaris eggs accumulated within the solid during the precipitation and filtration process. Subsequent air-drying of the struvite filter cake partially inactivated both microorganisms; however, viable Ascaris eggs and infective phages were still detected after several days of drying. The infectivity of both viruses and eggs was affected by the specific struvite drying conditions: higher inactivation generally occurred with increased air temperature and decreased relative humidity. On a log–log scale, phage inactivation increased linearly with decreasing moisture content of the struvite, while Ascaris inactivation occurred only after achieving a minimum moisture threshold. Sunlight exposure did not directly affect the infectivity of phages or Ascaris eggs in struvite cakes, though the resultant rise in temperature accelerated the drying of the struvite cake, which contributed to inactivation.

This research investigated the possibility of transferring phosphorus from human urine into a concentrated form that can be used as fertilizer in agriculture. The community of Siddhipur in Nepal was chosen as a research site, because there is a strong presence and acceptance of the urine-diverting dry toilets needed to collect urine separately at the source. Furthermore, because the mainly agricultural country is landlocked and depends on expensive, imported fertilizers, the need for nutrient security is high. We found that struvite (MgNH₄PO₄·6H₂O) precipitation from urine is an efficient and simple approach to produce a granulated phosphorus fertilizer. Bittern, a waste stream from salt production, is a practical magnesium source for struvite production, but it has to be imported from India. Calculations show that magnesium oxide produced from locally available magnesite would be a cheaper magnesium source. A reactor with an external filtration system was capable of removing over 90% of phosphorus with a low magnesium dosage (1.1 mol Mg mol P), with coarse nylon filters (pore width up to 160 ± 50 μm) and with only one hour total treatment time. A second reactor setup based on sedimentation only achieved 50% phosphate removal, even when flocculants were added. Given the current fertilizer prices, high volumes of urine must be processed, if struvite recovery should be financially sustainable. Therefore, it is important to optimize the process. Our calculations showed that collecting the struvite and calcium phosphate precipitated spontaneously due to urea hydrolysis could increase the overall phosphate recovery by at least 40%. The magnesium dosage can be optimized by estimating the phosphate concentration by measuring electrical conductivity. An important source of additional revenue could be the effluent of the struvite reactor. Further research should be aimed at finding methods and technologies to recover the nutrients from the effluent.

Depleting fertiliser supplies call for alternative nutrient sources. Promising low-cost technologies to recover nutrients from urine were therefore field-tested in Nepal.

Urine is the source of the major part of plant nutrients in municipal wastewater. Therefore, full nutrient recovery from source-separated urine is an attractive option for both treating wastewater and gaining a valuable fertilizer product. Full nutrient recovery can be achieved by first stabilizing collected urine by nitrification and then concentrating the urine by distillation. Since concentrations of all salts in urine increase with increasing removal of water also the sodium chloride (NaCl) content is high in the end. There are two problems related to NaCl, the first being the synergistic decomposition of ammonium nitrate by chloride and the second being soil salinity and sodicity related problems when applying the product as fertilizer. [...]

The electrochemical oxidation of ammonia (NH₄⁺/NH₃) in sodium perchlorate was investigated on IrO₂ electrodes prepared by two techniques: the thermal decomposition of H₂IrCl₆ precursor and the anodic oxidation of metallic iridium. The electrochemical behaviour of Ir(IV)/Ir(III) surface redox couple differs between the electrodes indicating that on the anodic iridium oxide film (AIROF) both, the surface and the interior of the electrode are electrochemically active whereas on the thermally decomposed iridium oxide films (TDIROF), mainly the electrode surface participates in the electrochemical processes.
On both electrodes, ammonia is oxidized in the potential region of Ir(V)/Ir(IV) surface redox couple activity, thus, may involve Ir(V). During ammonia oxidation, TDIROF is deactivated, probably by adsorbed products of ammonia oxidation. To regenerate TDIROF, it is necessary to polarize the electrode in the hydrogen evolution region. On the contrary, AIROF seems not to be blocked during ammonia oxidation indicating its fast regeneration during the potential scan. The difference between both electrodes results from the difference in the activity of the iridium oxide surface redox couples.

Problem: The most wastewater produced in modern countries is treated by centralised wastewater treatment plants which have a low technological flexibility and high financial costs. The phosphate in the wastewater, a nutrient, is burned and diverted into the rivers. Since the reserves of phosphate rock are limited this thesis tries to define a way to recover it by electro-coagulation.
Solution: Novaquatis (EAWAG) propose to separate the urine from wastewater and to treat it separately in a small scale reactor to recover the phosphate.
A method for the phosphate recovery from urine is the struvite precipitation. Struvite is usually obtained by the addition of magnesium mineral. The dosage control and storage of the powder aren’t well adapted to small reactors. The electro-coagulation of phosphate has potential to be a better solution at the household scale.
Process: The electro-coagulation of phosphate from urine is based on the electro-dissolution of a magnesium electrode. The dissolved magnesium reacts with phosphate and ammonium, present in urine, to struvite. The struvite is recovered and sold as fertilizer.
Thesis: The electro-coagulation isn’t yet a well known process. The thesis tried to define and to optimize the whole process. The design of a small scale reactor, a simple controlling and monitoring possibilities are studied. Finally the economical and technical suitability of the process is evaluated.
Method: Two metal plates, used as electrodes, are put into a one litre reactor filled with a synthetic solution simulating urine. The working electrode is made of magnesium and the counter-electrode of stainless steel. A constant voltage was applied, inducing the dissolution of magnesium. Many variables were measured during the phosphate elimination, like pH, current, conductivity, etc. A series of experiments was set up to optimize the process.
Experiment: To understand the process some basic experiments were done. Afterwards the electro-coagulation was performed with different voltages to find out an optimal one. It appeared that in some conditions the magnesium plate was covered with a white layer, a struvite layer, which inhibits the electro-coagulation process. How to prevent the formation of this layer is described.
Results: The first results were promising, the struvite was actually produced and the phosphate almost completely removed. The optimal voltage was defined in the range of +1.0V to +1.25V avoiding the struvite layer formation on the working electrode by lower voltage and the electrolysis of the solution at higher voltage.
A nice way to monitor the process is to follow the changes of the conductivity of the solution and the change of the working electrode potential. The rate of electro-dissolution of magnesium is dependent on the current, so by setting the current, we can control the process well, even stop it.
Suitability: The different experiments showed the process of electro-coagulation is undoubtedly a technologically suitable way to recover phosphate from urine. The process can only be profitable considering the saving costs by the wastewater treatment plant. The cost of the production of the magnesium electrode is difficult to be compensated by the selling of the struvite fertilizer.
Conclusion: The result of this thesis will certainly promote the process of electro-coagulation, since the process is working well and easy to control. The different open points are mentioned in order to confirm the promising results described in this project.

Phosphorus is an essential compound for plants. But the major phosphorus source for fertilizers - phosphate rock - is a limited resource. To close the nutrient cycle, phosphorus should be recovered from waste streams. Urine has a high phosphate content, which can be recovered as struvite.
Struvite is a magnesium-ammonium-phosphate (NH₄MgPO₄ · 6 H₂O) and can be used as a slow release fertilizer in agriculture. As magnesium is the limited compound in urine, a magnesium source has to be added for struvite precipitation. Conventional methods consist in the dosage of a magnesium salt. Electrocoagulation on the other hand dissolves magnesium electrochemically from a magnesium electrode.
For electrocoagulation magnesium is oxidized to magnesium ions at the magnesium anode, water is reduced to hydrogen gas at the steel cathode. To enhance the reaction speed a voltage source can be added. The voltage source can either be applied between the magnesium and a reference electrode (magnesium potential, three electrode configuration) or between the magnesium and the steel electrode (cell voltage, two electrode configuration). The advantage of the three electrode configuration being that the magnesium potential determines directly the reactions that can take place at the magnesium electrode.
Two sets of experiments have been conducted: voltammetry and batch experiments. For voltammetry the applied magnesium potential was changed with time to detect electrode characteristics. For the batch experiments the voltage source (magnesium potential or cell voltage) was kept constant over time.
Voltammetry and batch experiments showed that the magnesium electrode is sensitive to layer formation at magnesium potentials below -800 mV. An electrode potential of -600 mV seemed to be a very appropriate potential concerning reaction speed and energy consumption. An electrocoagulation reactor can either be operated by applying an electrode potential or a cell voltage. Applying a cell voltage will be the easier configuration, as no potentiostat is needed. A cell voltage of at least 1000 mV should be applied to prevent layer formation.
The monitored cell voltage/electrode potential (depending on electrode configuration) showed a maximum/minimum as phosphate was removed from urine. It can therefore be used as a parameter to control the magnesium dissolution in order to not waste magnesium. A continuous reactor could then be operated in sequencing batch mode, using three tanks:
storage tank, electrocoagulation reactor and settling tank.
It has been shown that electrocoagulation is a very functional method to recover struvite from natural urine. The advantage of electrocoagulation against chemical dosing will be found in a high magnesium efficiency and in a high automation possibility.

The electrochemical oxidation of ammonia (NH₃ and/or NH₄⁺) in the presence of chloride was investigated on a Ti/PtO_x–IrO₂ electrode. It was shown that ammonia is effectively removed from solution via electrogenerated active chlorine. Based on mass balances, nitrogen is postulated to be the main product of ammonia electrolysis. In the bulk, the concentration of chloramines was low. This could be explained by the fact that the oxidation of ammonia takes place close to the electrode surface where an excess of chlorine relative to ammonia is ensured during the process. This results in the oxidation of ammonia to N₂ and in a local pH decrease. As a result, chloramines were decomposed in the proximity of the electrode prior to diffusing into the bulk.

Direct (non-mediated) electrochemical oxidation of ammonia on boron-doped diamond (BDD) electrode proceeds mainly at high pH (>8) via free ammonia (NH₃) oxidation. To enhance ammonia oxidation on BDD at low pH (<8), where mainly ammonium (NH₄⁺) is present, oxidation of ammonia was mediated by active free chlorine. In this process, electro-generated in situ active chlorine rapidly reacts with ammonia instead of being further electro-oxidized to chlorate at the electrode surface. Thus, active chlorine effectively removes ammonia from an acidic solution, while the formation of by-products such as chlorate and possibly perchlorate is minimized.

The electrochemical oxidation of ammonia was investigated on a Ni/Ni(OH)₂ electrode prepared by potential cycling of a Ni electrode in 1 M NaClO₄. It was found that oxidation of ammonia is strongly pH dependent and proceeds mainly at pH values above 7. This indicates that NH₃ rather than NH₄⁺ is oxidized on nickel electrodes. Oxidation of ammonia occurs in the potential region of Ni(II)/Ni(III) redox activity resulting in formation of a clear peak. Ni/Ni(OH)₂ is not deactivated during ammonia oxidation even at high ammonia concentrations. A considerable fraction of the ammonia was oxidized to nitrate (11%), while the rest were gaseous nitrogen compounds. It is postulated that nitrogen was formed via a mechanism involving direct electron transfer from ammonia to the anode whereas the formation of nitrate involved oxygen transfer from water to an ammonia molecule.

All of the sulfur in human excreta ends up as dissolved sulfate in the urine. If released to the environment, sulfate is not problematic because it is stable. However, if it comes in contact with water containing a large amount of organics, sulfate transformation to sulfide starts as soon as the water is depleted of oxygen and nitrate, producing a bad smell and intoxicating the microbiology. The largest problem in wastewater treatment is probably the corrosion in anaerobic sewer systems due to sulfide oxidation. Another problem is the H2S production during biogas generation, which necessitates gas washing. Since it is an essential plant nutrient [18] and a widely applied element in industry [23], recovering sulfur from urine can be of interest. Within the scope of a master thesis of 16 weeks the bioelectrochemical sulfate removal from stored, source-separated urine was analyzed. The iodometric method was applied to urine in order to measure dissolved sulfide, thiosulfate, and sulfite. In a microbial electrolysis cell a sulfate load of 4.10 ± 0.17 g SO²⁻₄ -S m⁻² biofilm surface d⁻¹ was microbially transformed to sulfide which was subsequently oxidized to elemental sulfur at an anode potential of 0.06 V. Comparison between dissimilatory sulfate reduction with and without electrochemical sulfide oxidation showed an increase of the sulfate degradation rate of 30 % to 1.48 g SO²⁻₄ -S m⁻² biofilm surface d⁻¹ when sulfide was electrochemically oxidized. A mass balance of sulfur over the reactor showed that dissolved sulfur disappeared in the reactor. Based on the sulfur balance, a sulfide oxidation rate was estimated yielding 0.35 g SH⁻-S m⁻²d⁻¹. The process combination of biological sulfate reduction and subsequent partial sulfide oxidation to elemental sulfur was applied successfully to stored, source-separated urine. In a future work, the process parameters need to be improved, first of all the tradeoff between biofilm surface on the anode and free anode surface for sulfide oxidation. A separation of the biological and electrochemical processes would be suitable for further experiments on the bioelectrochemical sulfate reduction. Additionally a more throughout analysis of the conversion of the sulfur species in the reactor should be done. The limitations of the sulfate degradation need to be analyzed.

Variations in influent loads pose major challenges for biological wastewater treatment. Could increased biodiversity allow for more stable operation, and does this mean that biodiversity should also be protected in wastewater treatment plants? Using molecular biological methods, we can now quantify biodiversity and specific groups of microorganisms in complex systems.

Schwankende Zulauffrachten stellen die biologische Abwasserreinigung vor grosse Herausforderungen. Kann hier eine erhöhte Biodiversität helfen und ist Biodiversität also auch in der Kläranlage erstrebenswert? Molekularbiologische Methoden erlauben es uns heute, die Artenvielfalt und spezifische Organismengruppen in komplexen Systemen zu quantifizieren.

Der Anammox-Prozess (anaerobe Ammoniumoxidierung) ist eine Möglichkeit Stickstoff biologisch abzubauen. Anammox hat im Gegensatz zu Nitrifikation/Denitrifikation den Vorteil, dass kein leicht abbaubarer Kohlenstoff verbraucht wird. Die Anwendung dieses Prozesses in dezentralen Urinbehandlungsanlagen wird an der Eawag in Dübendorf seit 2008 in einer Pilotanlage getestet. Die Messungen mit einer Sauerstoff-, einer Leitfähigkeits- und einer pHSonde haben gezeigt, dass die Signale während eines Zyklus einen charakteristischen Verlauf aufweisen.
Das führte zur Vermutung, dass sich der Prozess anhand dieser drei Sondensignale überwachen lässt. Das Ziel war die Untersuchung folgender Frage: Können anhand einer Kombination der drei Parameter Sauerstoff, pH-Wert und Leitfähigkeit biologische Prozesse identifiziert und quantifiziert werden?
In der vorliegenden Arbeit werden folgende vier Hauptaufgaben vorgestellt:
• Tabelle zur quantitativen Bewertung der Sondensignale
• Quantifizierung des Stickstoffabbaus mittels der Leitfähigkeit
• Modellierung der Leitfähigkeit
• Unterscheidung von Anammox und heterotropher Denitrifikation anhand des pH-Werts und der Leitfähigkeit.
Die Tabelle zur qualitativen Bewertung der Sondensignale ist ein nützliches Mittel um rasch eine Aussage zum Zustand des Systems machen zu können. In der zur Verfügung stehenden Zeit, konnten nicht alle Störfälle beurteilt werden. Sie müssen noch modelliert werden, damit man die Tabelle vervollständigen kann.
Die Quantifizierung des Stickstoffabbaus durch die Leitfähigkeitsabnahme ist ein interessanter Ansatz. Bedingt durch einige Parameter - das Strippen von CO2 und der Abbau von organischen Stoffen zu Beginn des Zyklus - ist die Unsicherheit der Bestimmung des Stickstoffabbaus derzeit noch zu gross, um eine zuverlässige Aussage machen zu können. Es sind weitere Untersuchungen nötig um festlegen zu können, wie diese Parameter miteinzubeziehen sind.
Die Leitfähigkeit lässt sich mit der allgemeinen Formel gut berechnen. Werden bei der Berechnung alle gemessenen Ionen miteinbezogen, wird die Leitfähigkeit durch das Ergebnis der Modelle deutlich überschätzt. Ein besseres Resultat wird erzielt, wenn man die Leitfähigkeit mit der Aktivität modelliert.
Eine Unterscheidung von heterotropher Denitrifikation und Anammox ist zurzeit (noch) nicht möglich. Bei beiden Prozessen nimmt der pH-Wert zu und die Leitfähigkeit nimmt ab. Die modellierten Veränderungen sind so gering, dass die Sondensignale unter Einbezug der Messunsicherheit schwierig zu interpretieren sind. Zudem ist die Frage des Einflusses von Puffern noch nicht geklärt.
Zusammenfassend ist zu sagen, dass die Onlineüberwachung mit Sonden, die die beschriebenen drei Schlüsselsignale ermitteln, ein guter Ansatz ist. Dieses Vorgehen ermöglicht eine Prozessüberwachung ohne grossen Messaufwand. Der pH-Wert wird bereits heute für die Steuerung der Zykluslänge verwendet. Die Sauerstoffkonzentration gibt Auskunft über die Funktion der Belüftung und die Messdaten der Leitfähigkeit können evtl. in Zukunft für die Quantifizierung des Stickstoffabbaus verwendet werden.

Membrane aerated bioreactors (MABR) provide attachment for biofilm and supply air for biological processes.
An MABR operated in coninously stirred tank reactor (CSTR) treats undiluted urine (high ammonium, pH value around 9) to produce NH₄-NO₃ with a pH value around 6. The main influence factors investigated in the system were mainly the free ammonia (FA), free nitrous acid (FNA) and carbonate concentration.
The experiment was designed into 3 phases. Phase 1 was operated in batch-mode using tapwater as start-up medium. Phases 2 and 3 were started with a conditioning saline solution and then switched to the CSTR mode. Activated sludge was used as inoculum for biofilm in phase 1. Sludge used to build conditioned biofilm in phase 2 was a mixture of equal volumes of activated sludge and sludge from a partial nitratation and anammox (PNAA) system. In phase 3, the biofilm was grown from activated sludge and the NOB of the biofilm were selectively cultured using 10ml batch doses of 0.5M NaNO2 .
Influent paramenters analysed were NH₄, NO₂, NO₃, dissolved COD, total inorganic carbon (TIC) whilst in the effluent, the parameters determined were NH₄, NO₂, NO₃ and TIC. Dissolved oxygen (DO) concentration and pH in the reactor were taken daily.
During phase 1, COD degradation and ammonium loss were observed. Nitrification was inhibited by FA concentration of above 300mg/l though the value later decreased to 40mg/l. Average oxygen concentration was 9mg/l and pH of the medium averaged above 8.0. Effect of FNA was not observed. During phase 2, a constant load of 0.12gN/d was supplied. FA concentration gradually increased to 40mg/l and eventually inhibited NOB activity but the AOB continuously produced nitrite. There was no FNA effect. Average oxygen concentration was 8mg/l and pH ranged between 7 and 8. In phase 3, varying loads of 0.05 to 0.22gN/d was delivered. Maximum concentration of FA was 0.07mg/l and the highest value of FNA was 0. 09mg/l. Average oxygen concentration was 7.0mg/l and pH averaged 6.5. There was hardly measurable carbonate in the system though NOB and AOB continuously functioned that a solution of ammonium nitrate (1:3) was produced at non-steady state.

Struvite (MgNH₄PO₄·6H₂O) recovery from wastewater streams has been known as an efficient nutrient recycling method. However, current research has predominantly addressed high-end solutions to overcome fertilizer shortages in agriculture and prevent eutrophication in receiving waters.
The present study focused on low-cost struvite recovery from stored human urine, by optimizing a process developed at pilot scale in the peri-urban settlement of Siddhipur in the Kathmandu Valley (Nepal). A combination of laboratory and field experiments were conducted to develop a design for an improved cost-effective struvite production reactor – completely constructed with locally available materials. [...]

La récupération de struvite (MgNH₄PO₄·6H₂O) à partir d'eaux usées est connue en tant que méthode de recyclage de nutriments efficace. Néanmoins, la recherche actuelle se concentre principalement sur des solutions de haute gamme, afin de surmonter les pénuries d'engrais en agriculture ou de réduire l'eutrophisation de cours d'eaux récepteurs.
À travers l'optimisation d'un procédé développé à échelle pilote dans le village périurbain de Siddhipur dans la Vallée de Kathmandou (Népal), la présente étude vise à une récupération de struvite à bas coûts à partir d'urine humaine. La combinaison d'expérience de terrain et en laboratoire a conduit à la conception d'un réacteur – construit entièrement avec des matériaux locaux – de production de struvite amélioré. [...]

The NoMix toilet system of Eawag’s main building «Forum Chriesbach» has been in operation for three years. So far, NoMix toilets, waterless urinals and urine pipes do not show any clogging problems. Clogging was only observed in the siphons of some of the urinals. Due to the simple handling of exchanging the siphons, the problems could be solved easily. Toilets and urinals did not cause odour problems inside the building. However, outside the building (on the roof), odour problems occurred. The cause is ammonia gas emissions from the urine pipes. At the moment, the most important remaining problem for an efficient separation of urine and feces is the correct use of the NoMix toilets by non-acquainted users. New users have to be informed accordingly. A close collaboration with the maintenance service provider proved to be a critical factor for an optimal operation of the NoMix toilet system.

The electrochemical behaviour of ammonia (NH₄⁺/NH₃) in sodium perchlorate at pH 9 has been investigated on electrochemically grown anodic iridium oxide film (AIROF) electrode. In base electrolyte at pH 9, the Ir(IV)/Ir(III) surface redox couple exhibits unusually large separation of the oxidation/reduction peaks (ΔE_p~ 750 mV) due to the local pH changes within the oxide film. These local pH changes are induced by protons released/consumed during the Ir(IV)/Ir(III) redox activity. As a consequence, the local pH within AIROF changed up to 10 units during potential cycling. The presence of ammonia at pH 9 prevents these local pH changes because NH₄⁺/NH₃ buffer the solution inside the electrode. As a consequence, ΔE_p of Ir(IV)/Ir(III) was reduced to 100 mV. It has been shown further that ammonia oxidation is mediated by Ir(V), resulting in the appearance of anodic peaks in forward and backward scans.

Important amounts of nutrients excreted by humans are found in human urine. This provides the motivation for separating urine and recycling it, as fertilizer, back to agricultural land for food production. Urine diverting toilets have been increasingly being promoted in Nepal and more than 500 units have been installed since 2002 (Das and Kumar, 2008). However, potential drawbacks to urine handling systems are the risk of ammonia evaporation and the relatively large volumes to be handled. In that situation struvite technology has been established to trap the phosphates in a solid fertilizer. Using the technology could reduce the huge volume of urine and transporting cost. However, struvite production also generates effluent. Struvite effluent reuse has significant potential benefits on both a local and global scale, such as re-circulating plant nutrients like nitrogen and potassium back to agriculture.
This thesis explores the potential reuse of struvite effluent in Siddhipur Nepal. The hypotheses being investigated are that 1) preliminary struvite precipitation prevents clogging during drip fertigation with urine and 2) that drip-fertigation with urine is superior to bucket spreading, because the ammonia volatilization is strongly reduced.
When the nutrients in effluent are beneficially utilized through irrigation some amount of pollutants discharged into our waterways can be reduced.
In this study the small plots for drip irrigation and ammonia volatilization were established. The amount of clogging was based on measurements of head loss in the tank and time of application. The ammonia volatilization measurements were collected in each hour after application.
Boric acid was used to trap the ammonia volatilized in the plots. The method was successfully used to determine that more ammonia volatilized in the plot of the bucket application for up to 2.3 times as compared with drip effluent plot. The largest loss (11% of the applied N) was measured after application of 45 L of urine per plot. Virtually no volatilizations were detected (on the first 6hrs) when the urine was applied to the freshly tilled soil. The results also suggest that reuse of struvite effluent through drip irrigation is possible without full clogging (only 30% decrease of flow rate).
The reuse of effluent from a struvite reactor is beneficial in terms of the nutrients that are made available and when applied through drip irrigation the loss of ammonia is reduced. In addition, the reuse of effluent can contribute towards the reduction of importing the commercial fertilizers.

Decentralized systems which treat separated wastewater streams according to their specific properties are quite promising according to the newest research results. The use of a microbial electrolysis cell (MEC) to treat urine and produce hydrogen gas is such a novel technology. The MEC consists of two chambers which are connected via a cation exchange membrane. By applying voltage, the oxidation of organic substrate (assisted by exoelectrogens) at the anode can be coupled with a proton reduction at the cathode. EAWAG takes part in the investigations and set a MEC into operation in February 2009. The goal of this Master project is to understand and quantify the influence of some of the most important process parameters such as applied voltage, temperature and pH.
The chronoamperometry measures the current at stepwise higher applied voltages. The influence of the applied voltage on the system performance was linear before reaching slowly a limit. The needed minimum voltage was determined to 238 mV. Those chronoamperometric curves gave indications that the system got diffusion limited with time. The coulombic efficiency represents the ratio between produced hydrogen according to the measured current and the theoretical possible hydrogen production calculated with a COD balance. The low coulombic efficiency of 57.7% leads as well to the assumption, that other bacteria degrade the organic substrate. Once the MEC was opened and a biofilm consisting of two layers could be observed: the wanted exoelectrogens and undesired other bacteria. By analyzing samples from the anode and the cathode chamber the sulphate degrading bacteria could be quantified to contribute 3% to the COD-consumption. Additional measures such as installing an oxygen-sensor to judge the possibility of aerobic growth or off-gas measurements to quantify the methanogenic growth should be considered. After classifying the bacteria, parameters to damage them uniquely should be investigated.
The temperature experiment presented a linear increase in performance of 2.3% per degree. As the system is probably diffusion limited, the effect was caused by a bigger diffusive flux due to a temperature-dependent diffusion coefficient. The reaction at the cathode was not limiting at a pH between 6 and 9. When the pH was changed and the anode potential was fixed, the measured current increased 25% per pH unit. The growth curve of the exoelectrogens depends therefore linearly on the pH. If the applied voltage was constant, the current increase reached a limit, as due to the higher pH, the anode potential decreased. Sample analysis from the anode and cathode chamber proved, that the proton transport via the membrane is insignificant. The pH is therefore controlled in both chambers by adding sodium hydroxide solution or hydrochloric acid. If some day a perfect proton-exchange membrane is developed, proton-gradients might play a role and the before mentioned results from the pH-experiments might change. Nowadays, instead of adding chemicals, the effluent of the anode could be connected to the influent of the cathode. At the same time, this would unfortunately decrease the hydrogen purity. Some improvements are still needed, before the first full-scale reactor can be built. Another problem will be that resistances get bigger in a full-scale reactor. The measured resistances during the experiment decreased linearly with temperature and plotted against the applied voltage, a minimum resistance at 650 mV was found. For a full-scale reactor it would pay off to choose the operation parameters such that resistances get minimized.
So there is still a long way to go before the first full-scale reactor will be set into operation. The biggest problems for the analyzed reactor at the moment are the growing competition and the insignificant proton-diffusion.

In the face of increasing phosphorus prices, Nepal, like all agrarian societies is in imminent need of a low-cost, sustainable source of phosphorus and nitrogen.
The town of Siddhipur in the Kathmandu valley was selected as a study site to determine the feasibility of establishing a community-scale struvite processing centre using source-separated urine as a feedstock. Focus groups, workshops and household questionnaires were used to determine cultural acceptability and willingness to pay. Urine quality and quantity measurements, along with fertilizer cost analysis were used to determine the economic feasibility. A regression analysis using the current, local value of the nutrients was used to calculate the theoretical value of struvite; the estimated nutrient value of struvite was found to be 24–41 NRp per kilogram, which is in the same range as locally available Diammonium Phosphate (DAP). The production of struvite would currently cost about 25 NRp/kg due to high prices of available magnesium sources. Nevertheless, struvite precipitation can be economically feasible for at least three reasons. First, Nepal possesses own magnesite deposits, which might allow to produce cheaper magnesium sources. Second, customers are likely to pay more for locally produced struvite than for imported synthetic fertilizers Third, the effluent from struvite precipitation can also be used as a valuable and efficient nitrogen and potassium fertilizer. Despite shadow-pricing based on the constituent nutrients, the true value of struvite can not be known until it is produced and sold.

A new project in Nepal examines whether the production of fertiliser from urine can inspire residents to take up improved sanitation, while reducing their dependency on imported chemicals. By harvesting urine and converting it to “struvite”, the farmers of Siddhipur may better resist the coming years of fertiliser shortages.

Deposits and blockages from inorganic precipitation can adversely affect the operation of sewage treatment plants and domestic water supplies and result in substantial costs. Whilst the problem is generally well-known for hard drinking water, there is an increasing number of reports on precipitation in sludge water treatment in sewage plants, particularly plants with biological elimination of phosphates. This article discusses the chemical conditions for precipitation. Using the examples of drinking water and digester supernatant, it examines the most important chemical parameters and the key environmental influences – solubility of the solid phases, the composition of the water, pH value, release of carbon dioxide, biological decomposition processes, temperature and ionic strength. This article shows how the supersaturation of mineral solutions can be calculated.

Microbial fuel cells (MFC's) have been operated with manifold substances. Experiments with municipal wastewater, swine wastewater and even brewery wastewater had been successfully conducted. In previous studies the application of separated urine, with its comparable high energy content, showed breakdown of electricity generation. Studies with MFCs showed inhibition e ects due to salinity, ammonium concentration or pH. Which of these factors in urine is limiting, was to determine in this study.
For these experiments a two chamber MFC with graphite electrodes was used. At the cathode a ferricyanide solution was used as nal electron acceptor. In the startup ammonium concentration was low in the anode solution and pH was set to 7 with the help of a phosphate bu er. Ionic strength was from the beginning as high as in urine. Acetate was used as substrate and electron donor. After a certain power output was reached ammonium was continuously increased until the maximal concentration of 6.35 gN/l. In the next experiment pH was stepwise increased from pH 7 to pH 9.
Current generation showed a strong temperature dependence. It could be modeled well by the arrhenius approach. Power output was therefore doubled by an increase of temperature from 15 °C to 25 °C. Maximal power density of the cell was 180 mW/m². An increase of ammonium concentration to 6.35 gN/l did not lead to a breakdown in power output as in earlier studies. Though a slight decrease in power output was observed, it is not clear if that was caused by the ammonium concentration. The increase of pH from 7 to 9 lead to an increase of power output from 1.3 to 8.2 mW/m². An ammonia concentration up to 3.4 gN/l did apparently not have an e ect on exoelectrogenic bacteria.
All the tested parameters did not inhibit power output substantially. Therefore urine treatment with microbial fuel cells still seems to be a practicable solution even tough other possible inhibitory factors must be checked and stored urine has to be applied as well.

Biocatalyzed electrolysis is a microbial fuel cell based technology for the generation of hydrogen gas and other reduced products out of electron donors. Examples of electron donors are acetate and wastewater. An external power supply can support the process and therefore circumvent thermodynamical constraints that normally render the generation of compounds such as hydrogen unlikely. We have investigated the possibility of biocatalyzed electrolysis for the generation of methane. The cathodically produced hydrogen could be converted into methane at a ratio of 0.41 mole methane mole^-1 acetate, at temperatures of 22 ± 2°C. The anodic oxidation of acetate was not hampered by ammonium concentrations up to 5gNL^-1. An overview is given of potential applications for biocatalyzed electrolysis.

In Nordeuropa wurde ein energieintensives System aufgebaut, das einerseits Ammonium und Nitrat für die Landwirtschaft herstellt, anderseits die gleichen Moleküle in der Kläranlage eliminiert. Da in häuslichem Abwasser nahezu 80% des gesamten Stickstoffs aus menschlichem Urin stammen, zielen neuartige Sanitärkonzepte auf Urintrennung und -verwertung ab, um den N-Kreislauf zu schliessen. Jedoch sind mehrere Pilotprojekte zu dem Ergebnis gekommen, dass die Stickstoffkonzentrationen in gelagertem Urin im Vergleich zu frischem Urin stark abnehmen. Dies haben Beobachtungen an der Eawag in Dübendorf bestätigt, wo im Jahre 2005 15 Trenntoiletten und 2 Lagertanks installiert wurden (NoMix-Anlage).
Die Untersuchungen dieser Diplomarbeit haben ergeben, dass die Ausgasung von NH3 während des Transports und der Lagerung für 30-60% Stickstoffverlust verantwortlichist. Der Kamineffekt treibt Ammoniak aus der natürlichen Belüftungsleitung heraus. Dieses Gas wurde mit Hilfe von „Impinger“ erfasst und sein Massenstrom in Beziehung zur Aussentemperatur gesetzt, um die Ausgasung über Zeit modellieren zu können. Als Beitrag zur Konzentrationsabnahme spielt auch die Verdünnung mit Spülwasser eine Rolle. Diese beruht auf einer Designschwäche der eingesetzten Trenntoilette, die bei Anwenderfehlbenutzung Spülwasser durch ein Ventil zum Urintank fließen lässt. Die Bilanz der Stickstofffracht zeigt die Schwäche der bestehenden NoMix-Anlage hinsichtlich der Urinwiederverwertung auf. Im Kapitel "Systembeurteilung" werden leichte  Umbaumöglichkeiten aufgezeigt, die die Effizienz dieses Abwassertrennkonzeptes steigern und den Eintrag von Ammoniak in der Umwelt mindern können.

In Northern Europe industrial food production relies on synthetic nitrogen fertilizer, the massive application of which has adverse effects on the environment. On the other hand the same compounds naturally present in urban wastewater are removed in expensive treatment plants. Urine source separation technology seems to be a promising concept that could recover 80% of nitrogen from the urban wastewater and close the nutriment cycle. However, a significant number of pilot projects showed that the nitrogen concentration of the stored urine is much lower than expected. The EAWAG confirmed the same finding through investigation of the installed urine collecting system, composed of 15 NoMix toilets and 2 collecting tanks.
The analysis of this diploma thesis shows that the ammonia volatilisation during the transport and storage of the urine is largely responsible for the low concentration in the tank. Between 30 and 60 % of total nitrogen input gas out of the ventilation pipe,depending on the outdoor temperature (stack effect). The ammonia flow could be measured with “Impinger” and modelled over the time. The weak design of that toilet prototype combined with wrong use let flush water reach the tank and enhance the decrease of concentration. The nitrogen balance reveals the low N-recovery of urine in that NoMix plant. The concluding remarks of this thesis point at improvements regarding the efficiency of the system and the ammonia diffusion in the environment.

The combination of nitritation and autotrophic denitrification (anammox) in a single sequencing batch reactor (SBR) is an energy efficient process for nitrogen removal from high-strength ammonia wastewaters. So far, the process has been successfully applied to digester supernatant. However, the process could also be suitable to treat source-separated urine, which has very high ammonium and organic substrate concentrations (up to 8,200 gN/m³ and 10,000 gCOD/m³). In this study, reactor performance was tested for digester supernatant and diluted source-separated urine. Ammonium concentrations in both solutions were similar (between 611 and 642 gN/m³), thus reactor performance could be directly compared. Differences were mainly due to higher activity of heterotrophic bacteria in urine. Nitrogen removal was slightly higher for source-separated urine, because heterotrophic bacteria denitrified the nitrate that was produced by anammox bacteria. In spite of higher heterotrophic growth with source-separated urine, calculated sludge concentrations at steady state were higher with digester supernatant due to accumulation of inert particulate organic matter from the influent. Although the sludge concentrations are less problematic for source-separated urine, process instabilities are more likely, because lower pH values are reached and heterotrophic denitrification can cause sudden increases of nitrite concentrations and/or nitric oxide. Both compounds inhibit aerobic ammonium oxidizing bacteria, heterotrophic bacteria and, most importantly, anammox bacteria. Nitrite and nitric oxide production by heterotrophic denitrification must be better understood to optimize nitritation/anammox for source-separated urine.

Urine separation is a very interesting process to recover phosphate from wastewater because it contains 550 mg PO₄-P l^-1. The preferred technology at the moment is struvite precipitation by the addition of MgCl₂ or MgO. This is not ideal at the household level, as the particularly dosage of the correct amount of magnesium salts is not very easy. Thus the technical feasibility of two alternative technologies was estimated in batch experiments at the lab-scale: adsorption of phosphate on GFH and calcite, or phosphate precipitation by electrochemical dissolution of magnesium.
The adsorption of phosphate out of untreated synthetic urine (pH=8.9) on a typical GFH/calcite mix (7:3) obtained maximally a load of 9 mg PO₄-P g^-1 adsorbent which was considered to be insufficient.
Further tests were conducted on synthetic urine after nitrogen removal (pH=6.3). GFH showed very good adsorption capacity of 47.5 mg PO4-P g^-1 GFH according to a Langmuir isotherm and high affinity to phosphate (32 mg PO₄-P g^-1 can be reached at 25 mg PO₄-P l^-1 in solution). However, the adsorption kinetics was rather slow, as 7 days were needed with grain size 0.8-1.25 mm to get in equilibrium. The application of a surface diffusion model could not well approximate the equilibrium time due to the high solute concentrations. 75% of the adsorbed phosphate could be recovered by 7 days desorption in 0.1 M Na(OH).
The addition of calcite was shown not to decrease the adsorption/desorption properties of GFH at pH=6.3 while its maximal phosphate load at that pH was maximally 7.4 mg PO₄-P g^-1, thus too small.
The process of electrochemical magnesium dissolution is shown to be a technically feasible process. Very good magnesium (99%) and current (over 100 %) efficiencies were obtained by applying a constant current (1.95/3.9 mA cm^-2] on two magnesium electrodes plunged in untreated synthetic urine when the polarity was changing every 30 minutes until phosphate was depleted. Current efficiencies above 100% are thought to be due to Local Cell Action which leads to magnesium electrode self-dissolution. A reduction of current efficiency was observed with time, as a precipitation layer formed on the electrodes. This layer had an impact on the energy needed to resolve the magnesium (up to 4 Wh g^-1 P) but also on the current efficiency which decreased with time in otherwise equal experiments.
The same passivation behaviour of the sacrificial magnesium was observed when stainless steel was used as cathode. By their intrinsic potential difference (measured as 1.2 V) , elimination rates of 0.29 mg PO₄-P l^-1 h^-1cm^-2 were observed. The current efficiencies were lower than in the experiments with two magnesium electrodes, ranging around 50%, depending negatively on the period the magnesium electrode was used and on the applied current intensity. This is thought to be due to the passivation of the electrode and to the fact that more self-dissolution could occur if the electrodes are longer in contact with urine. One series of measurements furthermore suggests that the oxidation of chloride to chlorine gas could account for a substantial part of the inefficiencies.
No of pH, conductivity and voltage measurement could be identified as process control master variable, as it a difference in absolute value cannot be estimated,
Unfortunately, neither of pH, conductivity and voltage measurement could be identified as potential process control because their behaviour was not observed to change when phosphate in solution was depleted.

The identification of decentralized urine treatment processes is a crucial issue considering source separating sanitary systems (NoMix technology). In this work the suitability of urine treatment with microbial fuel cells (MFCs) has been tested in the laboratory. MFCs hold great promises for urine treatment, since organic substances and nitrogen can be eliminated at the anode and cathode respectively.
First, a MFC was started based on synthetic wastewater containing acetate in the anodic and nitrate in the cathodic influent to eliminate COD using a denitrifing cathode. Unfortunately, the denitrification process at the cathode never started. Instead of nitrate oxygen was the electron acceptor, although oxygen was only present in small amounts of approximately 0.3 mgO₂/L .
In a second experiment the anode was fed with 30-,10- and 3-times diluted synthetic urine solutions, corresponding to urine after storage, again containing acetate as COD. At the cathode oxygen was supplied as electron acceptor by aeration of the catholyte. The cell was characterized in each operation state by means of electrode measurements, current interruption tests, cell polarization and power curves.
For a reference measurement taken when the anode was fed with synthetic wastewater prior to the changeover to 30-times diluted synthetic urine, the maximum power point (MPP) was 11.6 W/m³_NAC. In the transition state from synthetic wastewater to 30-times diluted synthetic urine, a MPP of 16.0 W/m³_NAC was reached. At close to steady state conditions with 30-times diluted synthetic urine as anolyte, the MPP was 14.3 W/m³_NACC. With a MPP of 11.8 W/m³_NAC, the maximum attainable power in the case of a 10-times diluted synthetic urine, went back to a level similar to the reference case. The reduction in maximum attainable power with decreasing dilution can be explained with a higher internal resistance of the cell, compensating the positive effect of increasing pH on the anodic reaction reduction potential. Furthermore, an increased overpotential at the anode was calculated for a 10-times diluted synthetic urine anolyte. When a 3-times diluted solution was fed to the anode, the power density collapsed and could not be recovered by going back to a 10-times diluted solution.
These findings suggest that anodic bacteria grown in synthetic wastewater are not able to sustain COD elimination even in diluted synthetic urine.

Urin macht weniger als 1% des Abwasservolumens aus, ist aber für rund 80% der Stickstoffbelastung verantwortlich. Würde Urin nicht ins Abwasser gelangen, sondern bereits in der Toilette getrennt gesammelt und anschliessend dezentral behandelt, so wären die Stickstofffrachten in die Kläranlagen bedeutend geringer. Die in der Kläranlage eingesetzte Technik könnte dadurch vereinfacht und verbilligt werden und die gesetzlichen Grenzwerte zur Belastung der Gewässer mit Nährstoffen könnten mit geringerem Aufwand eingehalten werden. Um ein solches System dezentral zu betreiben, bedarf es einerseits kleiner, selbständig funktionierender Anlagen und andererseits braucht es ein geeignetes Verfahren. In der vorliegenden Arbeit wurde im Blick auf diese zwei Anforderungen einer solchen Anlage in einem einstufigen Reaktor im SBR-Betrieb die simultane Ammoniumoxidation von aeroben und anoxischen Ammonium Oxidierern (AOB und Anammoxbakterien) zur Stickstoff-entfernung aus Faulwasser und Urin untersucht. Dazu wurden Versuche zur Bestimmung der Vorgänge im Reaktor unter verschiedenen Belüftungsraten und Substraten durchgeführt und ein mathematisches Modell erstellt um die Abläufe im Reaktor zu simulieren. Im Modell wurden neben den biologischen Prozessen die chemischen Gleichgewichte berücksichtigt und zusätzlich der pH und die Leitfähigkeit simuliert. Implementiert wurde das Modell in Berkeley Madonna. In der Arbeit konnte gezeigt werden, dass Anammoxbakterien durchaus mit Sauerstoffkonzentrationen im tieferen Bereich (<0.2 g_O2m^-3) umgehen können. Die Modellierung hat gezeigt, dass die Anammoxbakterien nicht nur eine aerobe Phase ungeschädigt überstehen, sondern in dieser sogar aktiven Stoffumsatz zeigen. Simultane aerobe und anoxische Ammoniumoxidation ist somit möglich. Dies bedeutet für die Praxis, dass beide Bakteriengruppen in einer einstufigen Anlage vorhanden sein können. Für die Simulation der Leitfähigkeit und des pHs wurde ersichtlich, dass bei der Leitfähigkeit die Ionenstärke im Reaktor berücksichtigt werden muss und dass der pH stark durch chemische und physikalische Prozesse beeinflusst wird. Im Bezug zum längerfristigen Betrieb mit Urin konnte keine abschliessende Aussage gemacht werden. Es scheint aber, dass das Anammoxverfahren ideal zur Entstickung geeignet ist, da mit dem Substrat aus dem Urin eine vollkommene Eliminierung des Stickstoffes möglich wird.

We look at the most important issues of the global nitrogen and phosphorus cycle and conclude that the nutrients from human metabolism are of no importance for the global nitrogen cycle and of minor importance for the global phosphorus cycle. However, for water pollution control, N and P from the human metabolism are of extreme importance. Nitrogen is mainly an issue for coastal waters, whereas P is an issue for freshwater and coastal areas alike. It is by now generally recognised that coastal ecosystems are exceedingly important for human well-being and at the same time highly endangered. The recycling issue is of high importance in areas where nutrient application is low due to economic constraints. NoMix technology (urine source separation) holds a large promise to become an efficient mainstream technology. The largest short-term potential is found in densely populated areas in coastal areas without existing infrastructure and in areas with nutrient deficiency, especially in urban areas with a large nutrient potential. We believe, however, that these technologies will, with time, also become competitive in Europe.

Up to 80 percent of the nitrogen and 50 percent of the phosphorus in the wastewater streams that enter the wastewater treatment plant (WWTP) comes from urine but urine accounts for only one percent of the wastewater stream. If urine is collected and treated separately, water pollution can be controlled better, it might be possible to close nutrient cycles and WWTP’s can be dimensioned smaller and the risk of ammonium discharges from combined sewer overflows can be reduced.
In this work the possibilities are investigated to remove nitrogen from urine in a sequencing batch reactor (SBR) with the help of ammonium oxidizing bacteria, Anammox bacteria and heterotrophic bacteria.
The SBR was first operated with digester supernatant to replace the bulk volume. Hereafter it was operated with five time diluted urine. The urine was diluted five times to have about the same concentrations as in the digester supernatant. In the beginning of the operation of the reactor each batch started with an anoxic phase to facilitate the use of nitrate for the degradation of dissolved organic substrate. The goal was to reduce nitrite and COD concentrations concomitantly.
With experiments it could be shown that in increase of the air flow from 40 mL/min to 50 mL/min
did not increase the oxygen concentration in the reactor. It could also be shown that during the aerobic phases nitrite build up takes place; the Anammox bacteria are too slow to reduce all the nitrite that is produced by the ammonium oxidizing bacteria. In anoxic phases nitrite reduction takes place.
The efficiency of the reactor can be enhanced by operating the system with continuous aeration. In this way nitrifying bacteria and Anammox bacteria can work continuously what makes the batches shorter. However, when the system was changed to continuous aeration the nitrite concentration in the reactor increased a lot. This was caused by reduction of nitrate to nitrite by heterotrophic bacteria and nitrite production in the sedimentation phase. The initial anoxic phase was deleted and the batches ended with an anoxic phase for the Anammox to reduce the nitrite concentrations. It was not possible to operate the reactor with continuous aeration.
Higher pH values in the reactor have positive effects on the nitrogen removal rate but not at the reduction of the total nitrogen concentration. The pH in the reactor can be increased by exchanging more of the volume with urine, by adding basic chemicals or by stripping of CO₂. It could also be shown that long batches (about 30 hours) are not better for the nitrogen degradation compared to shorter batches (about 15 hours) because in the second half of the batch only seven percent more degradation is reached.

The basic idea of the NoMix toilet is simple: urine is drained - separately from other wastewater - into a collection tank. However, urine pipes can easily be blocked by mineral precipitates, and nutrient concentrations in the urine collected may be lower than expected. The results of our laboratory experiments and computer simulations should facilitate the development of improved appliances in collaboration with the sanitary technology sector.

Urine separation is a promising alternative to present-day’s waste water management. It can help to manage our nutrient flows in a sustainable way. Currently, techniques are being developed to recycle and treat source-separated urine. These techniques, however, must consider the spontaneous processes that change the separated urine. The initial cause of changes is the contamination with microorganisms, which can hardly be avoided in urine-collecting systems. The most important transformation processes are microbial urea hydrolysis, mineral precipitation and ammonia volatilisation. Additionally, a variety of microorganisms, including pathogens, may grow in source-separated urine. In this paper we give an overview of the effects that the spontaneous transformation processes may have. We focus on nitrogen, phosphorus, magnesium, calcium, potassium, sulphur, organic substances, pathogens and the buffering capacity. The discussion is based on own research results and literature reviews. This overview will help to develop appropriate technologies for urine recycling.

In long-term experiments with membrane aerated biofilm reactors we observed complete nitrite oxidation in highly concentrated ammonium nitrite solutions with a contaminant pH decrease to values below 3. The maximum initial concentration for ammonium was 42 mM and for nitrite was 41 mM. We hypothesized that (1) acid-tolerant ammonium oxidizing bacteria were responsible for the pH decrease, and (2) chemical processes caused complete nitrite oxidation at low pH values. To test this hypothesis we set up a mechanistic computer model based on kinetic data from literature and we validated the model with additional experiments. The simulations fitted the measurements very well. Additionally, an experiment with the inhibitor allylthiourea showed that ammonium-oxidizing bacteria were active at pH values far below 5.5. Experiments in a sterile reactor confirmed the chemical nitrite oxidation to nitrate. Nitrogen balances revealed that 8 ± 4% of the initial nitrogen (ammonium, nitrite, and nitrate) were lost during the cycles. On the basis of measurements and simulations we concluded that volatilization was responsible for the significant nitrogen loss. We estimated that about half of the lost nitrogen volatilized as nitrous acid HNO₂. The rest mainly volatilized as dinitrogen N₂ and nitrous oxide N₂O.

Precipitates from urine cause severe blockages in urinals of public restrooms, waterless urinals and NoMix toilets.
This paper presents a study in which the precipitation phenomena were investigated in detail.
The results show:
- the precipitates mainly consist of the phosphate minerals struvite and hydroxylapatite
- the bacterial degradation of urea triggers precipitation
- the use of flushing water reduces the formation of precipitates and is not the promoter
The study helps to develop processes that prevent blockages caused by urine precipitation. Possible approaches are presented in this paper.

Die Siphons und Leitungen von öffentlichen, hochfrequentierten Urinalen können sehr rasch verstopfen. Ein gutes Beispiel dafür sind die Urinale im Ankunftsterminal A des Flughafens Zürich. Die Siphons und Leitungen dieser Urinale müssen rund alle drei Monate ausgewechselt bzw. gereinigt werden.

Precipitation in urine-separating toilets (NoMix toilets), waterless urinals, and conventional urinals causes severe maintenance problems. Additionally, the partial fixation of nutrients in precipitates may affect the later use and treatment of source-separated urine. The goal of this study was to characterise the mineral composition of the precipitates and to identify the main causes for precipitation. X-ray diffraction analysis showed that the main crystalline compounds are struvite, hydroxyapatite, and calcite. We measured concentrations in the solutions of the traps and of the urine collection tank for estimating saturation indices, extent of urea degradation, urine dilution, and elimination of solutes. Our results indicate that bacterial urea degradation triggers precipitation. The composition of the precipitates depends on the urine dilution with flushing water: in low diluted urine, struvite is the main compound, while calcite dominates in systems with high urine dilution. HAP occurs over a wide range of dilution factors. A high fraction of phosphate is incorporated into the precipitates. Dilution with tap water increases this fraction by providing the limiting calcium and magnesium ions. Currently, constructing exchangeable traps seems to be the best solution to deal with problematic precipitation.

Precipitation in urine-separating toilets (NoMix toilets) and waterless urinals causes severe maintenance problems and can strongly reduce the content of soluble phosphate. In this study, we present a computer model for estimating the precipitation potential (PP) in urine-collecting systems. Calculating the PP enables to predict the composition and mass concentration of precipitates. We used our computer model for investigating how urea hydrolysis and dilution with flushing water affect precipitation. In a previous study, we found that microbial urea hydrolysis (ureolysis) triggers precipitation and that the amount of precipitates is limited by calcium and magnesium. With the present simulations, we could confirm these findings. We determined that only a small fraction of urea has to be hydrolysed for reaching 95% of the maximum PP. Since urease-positive bacteria are abundant in urine-collecting systems, strong precipitation is very likely. In further simulations, we determined that struvite (MgNH₄PO₄·6H₂O) and hydroxyapatite (HAP, Ca₁₀(PO₄)₆(OH)₂) are the main precipitate compounds. If urine is highly diluted with tapwater, calcite (CaCO₃) occurs as well. HAP is the only calcium phosphate mineral, although several others were supersaturated. Additionally, the simulations indicated that urine dilution diminishes the risk of blockages, since the mass concentration of precipitates decreases with the volume of flushing water. Rainwater flushing is more effective than flushing with tapwater. Moreover, flushing with tapwater leads to high phosphate fixation, because the total amount of calcium and magnesium ions increases, while the total amount of phosphate keeps constant. Finally, we compared simulation results with field measurements and found good agreement at low and very high urine dilution.

In laboratory experiments, source-separated urine was stabilised with nitrification and denitrified via nitritation and anaerobic ammonium oxidation. The highest total ammonia concentration in the influent was 7,300 gN/m³, the maximum pH 9.2. In a moving bed biofilm reactor (MBBR) with Kaldnes^® biofilm carriers, we stabilised urine as a 1:1 ammonium nitrate solution. The maximum nitrification rate was 380 gN/m³/d corresponding to 1.7 gN/m² _biofilm/d. Nitrite ammonium solutions were produced in a continuous flow stirred tank reactor (CSTR) with 4.8 days sludge retention time (SRT) at 30°C and in a sequencing batch reactor (SBR) with more than 30 days SRT. Nitrate build-up was negligible in both reactors. Nitritation rates were 780 gN/m³/d in the CSTR and 280 gN/m³/d in the SBR, respectively. However, shortening the cycles would increase nitritation in the SBR. High concentrations of nitrous acid, salts, and presumably hydroxylamine suppressed nitrite oxidation in the nitritation reactors. In all three nitrification reactors, maximally 50% of the influent total ammonia was oxidised without pH control. None of the common inhibition or limitation approaches could explain why ammonia oxidation always stopped at pH values around 6. In a batch experiment, we showed that source-separated urine can be denitrified autotrophically by anammox bacteria.

Blockages caused by inorganic precipitates are a major problem of urine-collecting systems. The trigger of precipitation is the hydrolysis of urea by bacterial urease. While the maximum amount of precipitates, i.e. the precipitation potential, can be estimated with equilibrium calculations, little is known about the dynamics of ureolysis and precipitation. To gain insight in these processes, we performed batch experiments with precipitated solids and stored urine from a urine-collecting system and later simulated the results with a computer model. We found that urease-active bacteria mainly grow in the pipes and are flushed into the collection tank. Both, bacteria and free urease, hydrolyse urea. Only few days are necessary for complete urea depletion in the collection tank. Two experiments with precipitated solids from the pipes showed that precipitation sets in soon after ureolysis has started. At the end of the experiments, 11% and 24% of urea was hydrolysed while the mass concentration of newly formed precipitates already corresponded to 87% and 97% of the precipitation potential, respectively. We could simulate ureolysis and precipitation with a computer model based on the surface dislocation approach. The simulations showed that struvite and octacalcium phosphate (OCP) are the precipitating minerals. While struvite precipitates already at low supersaturation, OCP precipitation starts not until a high level of supersaturation is reached. Since measurements and computer simulations show that hydroxyapatite (HAP) is the final calcium phosphate mineral in urine solutions, OCP is only a precursor phase which slowly transforms into HAP.

Introduction
Intensive agriculture and urban sewage burden the environment with high nutrient loads. An improved nutrient management is necessary to remove present damages and to prevent future impacts. Nutrient losses to the environment can be strongly reduced, if nutrients from waste water are recycled to agriculture.
Human urine is the most important nutrient source of household waste water. It contributes about 80% of nitrogen and 60% of phosphorus, but accounts for less than one percent of the waste water volume. Separate collection of human urine would strongly reduce the demands on waste water treatment, because no enhanced nutrient elimination would be necessary to prevent eutrophication. Furthermore the separate collection and application of urine would be an efficient method to recycle nutrients from urban sewerage to agriculture.
Waterless urinals and NoMix toilets are available for urine separation. In urine-collecting systems the separated urine is directed to a collection tank where it is stored for later transport to a treatment facility.
In existing systems biological and chemical processes hamper the technical realisation of urine separation. By hydrolysing urea, bacteria cause a strong increase of ammonia and pH. Under these conditions large amounts of phosphate minerals precipitate, which can lead to pipe blockages. The produced ammonia is volatile. Degassing of ammonia can cause odour problems and significant nitrogen losses. [...]

Einleitung
Intensive Landwirtschaft und Siedlungsabwässer belasten die Umwelt mit hohen Nährstoffeinträgen. Ein besseres Nährstoffmanagement ist notwendig, um entstandene Schäden zu beheben und künftige zu verhindern. Nährstoffverluste in die Umwelt können stark verringert werden, wenn die Nährstoffe aus dem Abwasser in die Landwirtschaft rezykliert werden.
Menschlicher Urin ist die wichtigste Nährstoffquelle des kommunalen Abwassers. Er liefert ca. 80% des Stickstoffs und 60% des Phosphors, macht aber weniger als ein Prozent des Abwasservolumens aus. Die getrennte Sammlung von Urin würde die Abwasserreinigung stark entlasten, weil in Kläranlagen keine erweiterte Nährstoffelimination mehr notwendig wäre, um die Gewässereutrophierung zu bekämpfen. Die separate Sammlung und Ausbringung von Urin wäre zudem eine sehr effiziente Massnahme, um Nährstoffe von der Siedlungswasserwirtschaft in die Landwirtschaft zu rezyklieren.
Für die separate Sammlung von Urin stehen wasserlose Urinale und NoMix-Toiletten zur Verfügung. In Urinsammelanlagen wird der Urin nach der Abtrennung in einen Sammeltank geleitet und dort zwischengelagert, bevor er zur Weiterverarbeitung abtransportiert wird.
In bestehenden Systemen erschweren allerdings biologische und chemische Prozesse die Urinseparierung. Bakterien hydrolisieren den im Urin enthaltenen Harnstoff und erhöhen dadurch die Ammoniakkonzentration und den pH. Unter diesen Bedingungen fallen grosse Mengen an Phosphatmineralien aus, was zu Verstopfungen der Leitungen führen kann. Das produzierte Ammoniak ist flüchtig. Ausgasungen können Geruchsbelästigungen und erheblichen Stickstoffverluste verursachen. [...]

Urinausfällungen treten in Urinalen und No-Mix-Toiletten auf und führen häufig zu Verstopfungen. Trotz der grossen Bedeutung der Urinausfällungen für die Funktionsfähigkeit von Urinalen, gibt es bisher kaum wissenschaftliche Untersuchungen zu diesem Thema. Ziel des gemeinsamen Projektes der GEBERIT Technik AG und der EAWAG war es, erste qualitative Aussagen zur Zusammensetzung und zu den Ursachen der Urinausfällungen zu erhalten. Drei verschiedene Toilettentypen wurden untersucht: herkömmliche wassergespülte Urinale, wasserlose Urinale der Firma URIMAT und eine No-Mix-Toilette, die an der EAWAG installiert ist. [...]

Als Fortsetzung des Projektes "Charakterisierung von Urinausfällungen in wassergespülten und wasserlosen Urinalen sowie in No-Mix-Toiletten" (Geberit und EAWAG 2000) wurden mehrere Urinale einer Toilettenanlage des Flughafens Kloten untersucht. Ziel der Messungen war es, die Erkenntnisse des ersten Projektes durch weitere Daten zu überprüfen und zu erganzen. [...]

Nutrient control is generally acknowledged to be an important part of domestic wastewater treatment. However, it is not as widely recognised that nutrient control is only necessary due to the presence of urine in wastewater. With urine separation and a subsequent treatment or recycling, only solids and organic matter need to be removed for the treatment of domestic wastewater. Urine separation combined with recycling of primary and secondary sludge would make it possible to close nutrient cycles. Problems with pharmaceutics and hormones in the receiving waters would be alleviated. From a technical point of view, the separate collection of urine is possible with a so-called 'No-Mix'-Toilet: after separation the urine is stored in the household and in the night, when the sewers are more or less empty, it is led through the sewers are more or less empty, it is led through the sewers to the treatment plant. Just before it reaches the treatment plant, the urine must be collected and separately treated or recycled.

Both denitrification and biological phosphorus removal depend on the presence of readily biodegradable carbon. Primary sludge fermentation is one way of producing such substrates. Soluble products of sludge fermentation are mainly short-chain fatty acids with two to five carbon atoms (84% of dissolved COD). In considering molar degradation rates by denitrifying organisms in batch experiments, the acids can be divided into two groups: the preferentially degraded linear forms of C₂ to C₅ acids and the branched C₄ and C₅ acids. The non-identified fraction (16% COD) which might contain acids with more than five carbon atoms is also removed by the activated sludge either by degradation or adsorption. In batch experiments with anaerobic and aerobic cycles, the uptake rate for short-chain fatty acids by phosphorus accumulating organisms and the ratio of phosphorus release to substrate uptake are determined. Acetate and propionate are taken up much faster than the C₄ and C₅ acids, which show very similar rates. For the ratio of phosphorus release to substrate uptake the situation is more complicated. The acids with four carbon atoms show by far the highest values.