Water reclamation can help meet agricultural irrigation and nutrient demands. Due to high nutrient loads, vermifiltration is often considered a suitable treatment solution for reclamation in agriculture. However, the ability of vermifiltration to meet irrigation standards is understudied. This study explores the feasibility of reclamation through irrigation and fertigation from two full-scale vermifilters treating black- and sedimented greywater in parallel and evaluates the removal efficiencies of metallic trace elements (MTEs), E. coli, and 15 organic micropollutants (OMPs). Microplastics in the effluent were also quantified. The results show that, for reclamation in agriculture, post-treatment of the vermifilter effluent is necessary to ensure reliable and sufficient effluent quality. Despite an overall log removal of 3.67, E. coli is the most restrictive parameter, conforming to irrigation standards only after the second post-treatment step. Various constraints, due to high nitrate concentrations and salinity, would also be necessary to avoid negative environmental and agronomic impacts. For fertigation, careful planning is needed to overcome excessive and variable nitrogen loads. Despite low and variable MTE removal, the effluent quality meets irrigation standards. Average removal of OMPs is 91 ± 15 %, and the coefficient of variation is <10 % for two-thirds of the OMPs. Suggested optimizations to improve the usability in agriculture include adding a disinfection step and urine separation. Future studies should focus on the impacts of vermifilter reclamation in agriculture on soil and crops, as well as the potential for designations such as toilet flushing and street cleaning, which are likely more advantageous in urban settings.

Due to low investment and operational costs, chemical and energy independence, and a high potential to contribute to circular wastewater management practices, vermifiltration is a globally relevant wastewater treatment solution. Despite its potential, insufficient knowledge of the full-scale performance and the absence of guidelines for optimal design and operation impede vermifiltration from being widely implemented. This study analyzed the performance of two full-scale vermifilters treating domestic blackwater and greywater sediments in winter and summer in Switzerland. For the first time, the operating conditions of both vermifilters were determined empirically, where the blackwater vermifilter observed 4 times lower hydraulic loading rates, though 10 times larger nitrogen loading rates than the greywater sediments vermifilter. Both vermifilters demonstrated the ability to maintain high removal efficiencies for organics and solids (>75 % for BOD₅, COD, and TSS), though nutrient removal was lacking (<30 % for TN and TP). The design and operation used in the full-scale vermifilters are, in general, recommendable, as no clogging was observed, and the performance of the vermifilters did not vary with season. In addition, with post-treatment, the effluent complied with discharge standards 100 % of the time. Insights into optimal design and operation include separate urine treatment, increased vermifilter depth, and alternative and intermittent feeding regimes. Such modifications would likely decrease the post-treatment requirements, spatial footprint, and investment costs. Overall, the results of this study conclude that when employing favorable design and operation conditions, vermifiltration is a relevant, reliable, and resilient wastewater treatment solution for both urban and rural areas worldwide.

Nearly half (46%) the world’s population is now served by non-sewered sanitation. In urban areas of low- and middle-income countries, this translates to onsite storage of wastewater in tanks and pits until it can be collected and transported by road to treatment, which is commonly referred to as fecal sludge management. The microbial communities that develop during storage of this wastewater remain understudied, leaving practitioners and scientists to speculate on best management practices such as downstream treatment and climate mitigation measures. In this study, we collected samples from 135 randomly selected containments across the city of Lusaka, Zambia, and evaluated statistical relations of 16S rRNA gene sequence data to types and volume of wastewater going into containments, disturbances (i.e., emptying events), characteristics of accumulated wastewater during storage, and metrics of downstream treatment processes. At the phyla level, 80% of the identified microorganisms belonged to Firmicutes, Proteobacteria and Bacteroidota. Focusing in at the genera level, microbial diversity and composition were statistically related to volumes of water usage, properties of wastewater in containments (total organic carbon, total kjeldahl nitrogen, ammonium nitrogen, pH), and metrics of stabilization and dewatering performance. In Lusaka, a core community was identified with 104 of the 1,247 identified genera being present in >90% of the containments. In contrast, 936 genera were present in <60% of the containments, indicating that niche or transient organisms may also be important in unravelling metabolic processes such as sulfur reduction, methanogenesis, and ammonia tolerance. Community similarity was independent of time since last emptied, indicating stability of microbial communities over time. Identified metabolic differences between pit latrines (i.e., less water usage) and septic tanks (i.e., more water usage) indicate that methanogens more actively convert organic matter to methane in the more dilute wastewater in septic tanks, which could be globally relevant for greenhouse gas mitigation from non-sewered sanitation.

Almost half of the global population relies on non-sewered sanitation, wherein wastewater is treated directly at source or stored onsite and transported by road to treatment facilities (i.e., fecal sludge management). For the protection of public health and environmental ecosystems, efficient non-sewered sanitation systems are needed, in particular in urban areas where infrastructure lags behind rapid urbanization. Wastewater delivered to treatment plants in non-sewered areas has highly variable characteristics, as it arrives in batches from variable infrastructure. Established systems to handle this variability are often land- or energy-intensive, while operation of low-footprint alternatives strongly depends on the wastewater characteristics, making them difficult to implement for highly variable wastewater. The use of sensors could improve process control and increase the robustness of treatment technologies, while reducing the required footprint. However, there are no studies comparing the effectiveness of different sensor methods to measure solids in non-sewered wastewater. We therefore chose six sensors for predicting solids in wastewater and evaluated their performance in variable wastewater with a range of solids content, inorganic particles, salts, and fats. This work demonstrated that the sensors were affected differently by the variable wastewater. Micro-wave and Coriolis-flow technologies were strongly impacted by the addition of fat, oil, and grease as well as salts and inorganics, whereas optical sensors were mostly affected by inorganics, with optical light-attenuation having the lowest overall error, making it the best option for variable wastewater. A low-cost optical light-attenuation sensor had similar accuracy as a more expensive one when the solids content was low, indicating its value for inexpensive monitoring of effluent solids in decentralized settings. Additionally, three sensors were applied for process control of chemically enhanced dewatering with conditioners and geotextiles. Controlling conditioner dosing with sensors in the flocculation tank improved performance with 77% solids reduction, which is in the range of the alternative, time-intensive jar-test method (83% reduction). This study reveals that sensors can be useful in non-sewered wastewater management when the type of input wastewater is accounted for and that even low-cost sensors (<100 USD) can be suitable for many applications.

Stabilization and dewatering are essential treatment mechanisms for the management of fecal sludge (FS) that accumulates in onsite containment, but reliable predictors of treatment performance are lacking. FS in Lusaka, Zambia is typically 80–98% water, which when delivered to treatment first requires dewatering, followed by stabilization of varying levels of organic matter. In addition, varying levels of stabilization are themselves observed to influence dewatering performance. Therefore, this study evaluated rapid and low-cost metrics of stabilization and their relation to dewaterability. Fourteen metrics of stabilization were evaluated based on 11 criteria in a decision matrix. Four metrics were selected to then evaluate method performance and suitability with FS samples (n = 27). The relation between stabilization and dewatering performance of collected samples were analyzed, and also following anaerobic stabilization in the laboratory. The study found that metrics based on physical–chemical characteristics such as volatile/total solids (VS/TS) and biological oxygen demand/chemical oxygen demand (BOD/COD) were not reliable for measuring FS stabilization and its relation to dewaterability. Metrics that rely on microbial activity such as SOUR (specific oxygen uptake rate) are more promising based on the consistent results obtained throughout this study.

There is limited understanding of the potential for anaerobic digestion and biogas production from fecal sludge. In this study, biomethane potential (BMP) tests from fresh, stored, and dewatered fecal sludge, together with co-digestion with fresh foodwaste, revealed that fresh fecal sludge produced similar cumulative biogas (CBG) to fresh foodwaste (615–627 mL/gVS), while stored fecal sludge showed a wide range of gas production (13–449 mL/gVS). Co-digestion significantly enhanced the CBG production of fresh (1.2×), dewatered (1.5×), and stored (29–36×) fecal sludge. In BMP tests with the higher range of gas production, a biphasic CBG production was observed, with degradation of readily biodegradable organics occurring during the first week. The first-order rate coefficients indicated hydrolysis limitation, which was also confirmed by the presence of slow-growing methanogens (Halobacterota). Priming with co-digestion significantly enhanced CBG from stored fecal sludge. The physical–chemical metrics VS/TS and TOC/TN were not predictors of biogas production, while BOD/COD and sCOD were better indicators, suggesting that metrics of stabilization representing biologically available fractions are more representative than metrics of entire pools of organic matter. This study suggests that biogas production from anaerobic digestion is viable for fresh fecal sludge, whereas for stored fecal sludge it requires co-treatment or pretreatment.

Half of the world’s population is now served by non-sewered sanitation, yet the field remains fragmented, with a focus on individual research agendas, and prevalence of imprecise terminology that hinders scientific learnings and leads to misconceptions. The field is at a decisive juncture, with scientific knowledge taking off that holds the potential to fulfil the urgent need for inclusive sanitation in a rapidly urbanizing world. In this critical Review, relevant and diverse research results are assembled with findings translated to one consistent terminology, to provide scientific evidence to draw out interlinkages and learnings, debunk common misconceptions and identify key research needs. Properties of non-sewered wastewater are highly variable, and degradation during storage has a direct impact on greenhouse gas emissions and downstream treatment processes, which facilitate different resource recovery. New technologies and wastewater-based epidemiology can help to address the lack of monitoring. The findings are presented by wastewater properties, biological processes during storage, treatment processes and monitoring.

Reasonable estimates for quantities and qualities (Q&Q) of fecal sludge that accumulate in onsite sanitation containments are fundamental for the design of appropriate management and treatment solutions, from community to city-scale. There are increasing attempts to improve Q&Q estimates, but current approaches are still at a conceptual level, and are not yet standardized with confirmed statistical relationships. To reach this level, we will need consistent approaches for planning, measuring, and global collaborations. Hence, the objectives of this study were: (1) to assess and compare Q&Q of fecal sludge from seven cities and communities, and explore statistical relationships that could be used to increase accuracy of Q&Q estimations; (2) to test and launch the Volaser device for measuring in situ volumes of fecal sludge; and (3) to capture lessons learned from field implementation with collaborators in seven countries during a global pandemic when no international travel was possible. The study took place in Ghana, India, Lebanon, Kenya, Sierra Leone, Uganda, and Zambia during the COVID-19 pandemic. Q&Qs were measured in 204 containments with a Volaser, laboratory analysis, and questionnaire. Results indicate that there are differences in Total Solids (TS) and Chemical Oxygen Demand (COD) in fecal sludge based on containment type, toilet type, source, and whether there is a water connection on the premises. Based on the results of this study, together with previously published open-source data, an empirical relationship for Volatile Solids (VS) and TS of 0.49 (R² = 0.88) was established using 1,206 data points. For COD/TS, no significant relationship was observed. Developing such empirical relationships will be useful for planning and modeling approaches. An external evaluation was conducted to evaluate overall project management, Volaser technology transfer, and effects of collaborating during the COVID-19 pandemic. Success factors for collaborating with new and existing partners without face-to-face meetings included laboratory capacity and experience with analytical methods, study objectives that were relevant for the partner and locality, and a strong quality assurance plan to ensure comparability of results. The lessons learned can be taken forward as ways to reduce carbon footprint, and contribute to resilient, inclusive development research projects.

Reliable dewatering performance remains a key challenge in fecal sludge management, and the controlling factors or mechanisms are not well understood. There remain limited studies on constituents in feces and fecal sludge and how they affect the dewaterability of fecal sludge. This study aimed at evaluating a range of constituents in feces, and to gain empirical knowledge toward a mechanistic understanding of how they influence dewaterability. In this study, cellulose reduced capillary suction time, decreased supernatant turbidity, and increased cake solids. While hemicellulose decreased supernatant turbidity, lignin increased supernatant turbidity, capillary suction time, and cake solids. Extracellular polymeric substances (EPS) increased both capillary suction time and supernatant turbidity and decreased cake solids, whereas lipids increased turbidity. Cations had no significant effect on dewatering properties. Overall, fecal sludge stored in containments had better dewatering performance than ‘fresh’ fecal sludge, which was attributed to stabilization. Field fecal sludge had a higher relative abundance of Pseudomonas, which is associated with better aggregation, and fewer small particles (<10 μm) that clog filters to reduce dewatering performance. Further understanding of stabilization and developing an agreed-upon metrics of stabilization are essential for predicting fecal sludge dewatering performance, and developing smaller footprint dewatering treatment technologies.

Progress toward Sustainable Development Goals for global access to safe sanitation is lagging significantly. In this Feature, we propose that misleading terminology leads to errors of categorization and hinders progress toward sanitation service provision in urban areas. Binary classifications such as "offsite/onsite" and "sewered/nonsewered" do not capture the need for "transport to treatment" or the complexity of urban sanitation and should be discarded. "Fecal sludge management" is used only in the development context of low- or middle-income countries, implying separate solutions for "poor" or "southern" contexts, which is unhelpful. Terminology alone does not solve problems, but rather than using outdated or "special" terminology, we argue that a robust terminology that is globally relevant across low-, middle-, and upper-income contexts is required to overcome increasingly unhelpful assumptions and stereotypes. The use of accurate, technically robust vocabulary and definitions can improve decisions about management and selection of treatment, promote a circular economy, provide a basis for evidence-based science and technology research, and lead to critical shifts and transformations to set policy goals around truly safely managed sanitation. In this Feature, the three current modes of sanitation are defined, examples of misconceptions based on existing terminology are presented, and a new terminology for collection and conveyance is proposed: (I) fully road transported, (II) source-separated mixed transport, (III) mixed transport, and (IV) fully pipe transported.

Poor and unpredictable dewatering performance of fecal sludge is a major barrier to sanitation provision in urban areas not served by sewers. Fecal sludge comprises everything that accumulates in onsite containments, and its characteristics are distinct from wastewater sludges and from feces. There is little fundamental understanding of what causes poor dewatering in fecal sludge. For the first time, we demonstrate that particle size distribution is a driver of dewatering performance in fecal sludge, and is associated with level of stabilization. Higher concentrations of small particles (<10 μm) and smaller median aggregate size (D50) corresponded to poor dewatering performance (measured by capillary suction time (CST) and supernatant turbidity) in field samples from Kenya and Uganda and in controlled laboratory anaerobic storage experiments. More stabilized fecal sludge (higher C/N, lower VSS/TSS) had better dewatering performance, corresponding to lower concentrations of small particles. Samples with the largest aggregates (D50 > 90 μm) had higher abundance of Gammaproteobacteria Pseudomonas, and samples with the smallest aggregates (D50 ≤ 50 μm) were characterized by higher abundance of Bacteroidetes Vadin HA17 and Rikenellaceae. Contrary to common perceptions, stabilization, particle size distribution, and dewatering performance were not dependent on time intervals between emptying of onsite containments or on time in controlled anaerobic storage experiments. Our results suggest that the stabilization process in onsite containments, and hence the dewaterability of sludge arriving at treatment facilities, is not dependent on time in containment but is more likely associated with specific microbial populations and the in-situ environmental conditions which promote or discourage their growth.