Department Sanitation, Water and Solid Waste for Development

Gravity Driven Membrane Filtration (GDM)

Gravity-driven membrane (GDM) filtration is a water treatment method that uses the gravity pressure of water and ultrafiltration membranes with a pore size of 20-40nm. When biofilm is allowed to form on the membrane over time, water flux stabilizes at 4-10 litres per hour per square meter of membrane and filters do not clog. Very little maintenance is required to operate GDM systems. Project evaluations revealed that systems are very durable and can be operated over years only requiring a monthly backflush. Filters remove all classes of pathogenic microorganisms including viruses, bacteria and protozoa.

Due to their ease of operation and independence of external inputs such as replacement parts, chemicals or electricity, community scale systems of GDM can be installed in remote areas and can be managed by local communities. Alternatively, GDM household filters provide water treatment to individual users.

More information about research on gravity driven membrane filtration at Eawag

In March 2017, Eawag and FHNW received the Swiss Prize for Sustainable Development, the prix eco.ch for the GDM activities with the project Gravit'eau.

» Click here for the Gravity Driven Membrane (GDM) User Guide and Videos

Gravity Driven Membrane Filtration in Water Kiosks in Uganda

Since June 2014, five water kiosks were established in Busime, Bulwande, Lugala, Bumeru and Bulundira in Busia and Namayingo Districts of Uganda to evaluate the feasibility of Gravity Driven Membrane filtration for drinking water treatment at community scale. Each system treats up to 6000L of water per day from Lake Victoria, providing treated water to local schools and the surrounding community.

Water from Lake Victoria is pumped up to the treatments systems at the school using a solar pump. Membrane modules are placed in a first tank where water is filtered and flows driven by gravity to the safe water storage tank. The treated water is available for the community at the taps of a water kiosk. Project evaluation revealed that the GDM systems are very robust, can be operated with little maintenance over years also in very remote rural contexts and that they provide reliable water quality.

Water quality assessments at the household level however revealed that water is being recontaminated during transport and storage due to critical hygienic conditions. We are therefore experimenting with different approaches to reduce recontamination risks such as providing residual disinfection via installing passive in-line chlorination at the water treatment system und using improved, cleaned water containers for transport and storage.

Elements that contribute to sustainable operation of the water kiosks include: An enabling environment, adequate management and business planning, accountability in financial handling, low cost for operation and maintenance, ownership and demand from the community, sufficient capacity for maintaining and repairing the systems, support from the Government’s extension services and supply chains for spare parts. In a case study, we described and analysed the business and management model of the GDM kiosks and how it evolved over time.

Publications

Assessment of low-cost, non-electrically powered chlorination devices for gravity-driven membrane water kiosks in eastern Uganda

Recontamination during transport and storage is a common challenge of water supply in low-income settings, especially if water is collected manually. Chlorination is a strategy to reduce recontamination. We assessed seven low-cost, non-electrically powered chlorination devices in gravity-driven membrane filtration (GDM) kiosks in eastern Uganda: one floater, two in-line dosers, three end-line dosers (tap-attached), and one manual dispenser. The evaluation criteria were dosing consistency, user-friendliness, ease of maintenance, local supply chain, and cost. Achieving an adequate chlorine dosage (∼2 mg/L at the tap and ≥ 0.2 mg/L after 24 h of storage in a container) was challenging. The T-chlorinator was the most promising option for GDM kiosks: it achieved correct dosage (CD, 1.5-2.5 mg/L) with a probability of 90 per cent, was easy to use and maintain, economical, and can be made from locally available materials. The other in-line option, the chlorine-dosing bucket (40 per cent CD) still needs design improvements. The end-line options AkvoTur (67 per cent CD) and AquatabsFlo® (57 per cent CD) are easy to install and operate at the tap, but can be easily damaged in the GDM set-up. The Venturi doser (52 per cent CD) did not perform satisfactorily with flow rates > 6 L/min. The chlorine dispenser (52 per cent CD) was robust and user-friendly, but can only be recommended if users comply with chlorinating the water themselves. Establishing a sustainable supply chain for chlorine products was challenging. Where solid chlorine tablets were locally rarely available, the costs of liquid chlorine options were high (27-162 per cent of the water price).
Dössegger, L.; Tournefier, A.; Germann, L.; Gärtner, N.; Huonder, T.; Etenu, C.; Wanyama, K.; Ouma, H.; Meierhofer, R. (2021) Assessment of low-cost, non-electrically powered chlorination devices for gravity-driven membrane water kiosks in eastern Uganda, Waterlines, 40(2), 92-106, doi:10.3362/1756-3488.20-00014, Institutional Repository

Keeping water from kiosks clean: strategies for reducing recontamination during transport and storage in Eastern Uganda

Drinking water is frequently recontaminated during transport and storage when water is poured into jerrycans. To address this issue, three strategies aiming at reducing these recontamination risks were implemented at water kiosks in Eastern Uganda. In all three strategies, water at the kiosks was chlorinated to a free residual chlorine (FRC) concentration of 2 mg/L at the tap of the kiosk. In addition, water was collected in different containers for drinking water transport: a) uncleaned jerrycans, b) cleaned jerrycans, and c) cleaned improved containers with a wide mouth and a spigot. Water quality in the containers was compared to that of a control group collecting unchlorinated water in uncleaned jerrycans. Water samples were collected at the tap of the kiosk, from the containers of 135 households after they were filled at the tap, and from the same containers in the households after 24 h of water storage. The samples were analysed for counts of E. coli, total coliforms, and FRC. Household interviews and structured observations were conducted to identify confounding variables and to assess the influence of water, sanitation, and hygiene infrastructure and practices on recontamination.
All three intervention strategies contributed to significantly lower E. coli recontamination levels after 24 h than in the control group (Median (Mdn) = 9 CFU/100 mL, Interquartile Range (IQR) = 25). Median E. coli counts and mean FRC consumption were higher in uncleaned jerrycans (Median = 1 CFU/100 mL, IQR = 6, ΔFRC = 1.8 mg/L) than in cleaned jerrycans (Median = 0 CFU/100 mL IQR = 2, ΔFRC = 1.6 mg/L) and the lowest in cleaned improved containers (Median = 0 CFU/100 mL, IQR = 0, ΔFRC = 1.2 mg/L). The FRC concentration at the tap of 2 mg/L was too low to protect water from E. coli recontamination in uncleaned jerrycans over 24 h. Cleaning the jerrycans was inconvenient due to their small openings, therefore, sand was used. The cleaning with sand reduced recontamination with E. coli but did not reduce the count of total coliforms. Improved containers with a larger opening allowed for cleaning with a brush and showed the lowest levels of recontamination for both E. coli and total coliforms. In addition to the intervention strategies, households receiving a higher number of WASH education visits within the previous year had lower recontamination levels of E. coli in stored water (OR = 0.54, p = .003).
Gärtner, N.; Germann, L.; Wanyama, K.; Ouma, H.; Meierhofer, R. (2021) Keeping water from kiosks clean: strategies for reducing recontamination during transport and storage in Eastern Uganda, Water Research X, 10, 100079 (8 pp.), doi:10.1016/j.wroa.2020.100079, Institutional Repository

Influence of container cleanliness, container disinfection with chlorine, and container handling on recontamination of water collected from a water kiosk in a Kenyan slum

The study assessed whether using clean containers that had been disinfected with chlorine at a water kiosk in the Kangemi slum in Nairobi reduced recontamination of treated water during drinking transport and storage. At the same time, the impacts of container handling and hygiene conditions at the household level on water quality changes during storage were evaluated. Data were collected during interviews with 135 households using either new, clean Maji Safi containers (MSCs) that had been disinfected with chlorine or normal uncleaned jerrycans (NJCs). Bacteriological water quality and free chlorine levels in both types of containers were measured after container filling at the kiosk and in the same containers after 24 h storage in households. The use of MSCs significantly reduced the risk of recontaminating the treated water. After water filling at the kiosk, none of the MSCs contained Escherichia coli bacteria, and 2.8% were contaminated after 24 h storage. In contrast, 6.2% of NJCs were contaminated after filling, and 15.2% after 24 h storage. Multivariate logistic regression indicated that the use of a clean water container and sufficient chlorine and the frequency of cleaning the container in the household mitigated recontamination. We suggest further investigation of water container designs that facilitate cleaning.
Meierhofer, R.; Wietlisbach, B.; Matiko, C. (2019) Influence of container cleanliness, container disinfection with chlorine, and container handling on recontamination of water collected from a water kiosk in a Kenyan slum, Journal of Water and Health, 17(2), 308-317, doi:10.2166/wh.2019.282, Institutional Repository

GDM-Wasserkioske. Sauberes Trinkwasser für die ländliche Bevölkerung Ugandas

In ländlichen Gegenden Ugandas werden die an der Eawag entwickelten Ultrafiltrationsanlagen eingesetzt, um die Versorgung mit sauberem Trinkwasser sicherzustellen. Die Anlagen an den Ufern des Lake Victoria können mit sehr geringem Aufwand und ohne externe Ressourcen betrieben werden. Wasserqualitätsuntersuchungen haben gezeigt, dass die Anlagen zuverlässig sauberes Wasser liefern. Mit dem Verkauf des Wassers wird ein Einkommen generiert, das den täglichen Betrieb und Unterhalt der Anlagen sichert.
Peter, M.; Meierhofer, R. (2018) GDM-Wasserkioske. Sauberes Trinkwasser für die ländliche Bevölkerung Ugandas, Aqua & Gas, 98(5), 36-39, Institutional Repository

Membrane filtration reduces recontamination risk in chlorinated household water containers

The study was conducted in the catchment area of two Gravity Driven Membrane Filtration (GDM) water kiosks in Uganda. It assessed if the cleaning and disinfection of jerrycans with chlorine can reduce risks for regrowth and recontamination of treated water during storage in undisturbed containers, as well as at the household level. In addition, the impact of water handling, household hygiene and safe storage determinants on water quality was evaluated. Results indicate that the cleanliness of the water storage container has a critical impact on water quality changes during storage. Safe drinking water at the point of consumption after 24 hours of storage at the household level can be achieved with a combination of ultrafiltration and subsequent chlorination.
Meierhofer, R.; Rubli, P.; Dreyer, K.; Ouma, H.; Wanyama, K.; Peter-Varbanets, M. (2017) Membrane filtration reduces recontamination risk in chlorinated household water containers, In: WEDC conference 40, 2595 (7 pp.), Institutional Repository

Evaluating novel gravity-driven membrane (GDM) water kiosks in schools

This paper presents results of the field evaluation of three gravity driven membrane (GDM) water kiosks purifying Victoria lake water in schools in Uganda. The study evaluated the technical performance of the systems and the feasibility of the operation and maintenance concepts over two years of operation, as well as the financial viability of the business model and management concept and overall system sustainability. The results show that GDM water kiosks are a simple technology capable of treating turbid surface water and can autonomously supply good quality water to schools and communities. They require little maintenance, are simple to operate and maintain, and with trained local O&M team support, they offer sustainability of operation in remote low-income areas. The business and management model evaluation has not yet been completed and is ongoing.
Peter-Varbanets, M.; Dreyer, K.; McFadden, N.; Ouma, H.; Wanyama, K.; Etenu, C.; Meierhofer, R. (2017) Evaluating novel gravity-driven membrane (GDM) water kiosks in schools, In: WEDC conference 40, 2735 (7 pp.), Institutional Repository

Gravity-driven membrane disinfection for household drinking water treatment

Ultrafiltration (UF) has been proven to be very effective in the treatment of water for the removal of particles, colloids and microorganisms. However, household application of UF is limited due to membrane fouling which results in complex and maintenance-intensive UF systems. In gravity-driven membrane disinfection (GDMD) technology, a stable membrane flux of 4-10 L.h-1m-2 is observed during ultrafiltration without any backflushing, chemical cleaning or an external energy supply for over 24 months, while operated at relatively low pressures (40-65 cm of water column). This novel approach to operate UF systems at stable flux conditions can be considered an important breakthrough in membrane technology, as it allows development of a robust, maintenance-free, low-cost and user-friendly household water treatment system, which has a great potential for implementation.
Peter-Varbanets, M.; Johnston, R.; Meierhofer, R.; Kage, F.; Pronk, W. (2011) Gravity-driven membrane disinfection for household drinking water treatment, In: Shaw, R. (Eds.), The future of water, sanitation and hygiene in low-income countries - innovation, adaptation and engagement in a changing world. Proceedings of the 35th WEDC international conference, Loughborough University, Loughborough, UK, 6-, 1086 (8 pp.), Institutional Repository

Project Reports and Documents

Gravity Driven Membrane Filtration for Household Systems

A first design of a GDM system for drinking water treatment at household level was developed 2011 after an extensive evaluation of the technology in the laboratory. 24 α-protoypes were evaluated in households in Kenya to assess the performance, functionality of the filter in the context of a low-income country and evaluate acceptance and user-friendliness.

In collaboration with ZHdK, Zurich University of Arts a β-prototype was developed in 2013 taking into consideration insights from the field evaluation of the α-protoype. These β-prototype were produced and evaluated in Bolivia to assess performance, handling and acceptance of users and willingness to pay for such products.

Project results of gravity driven membrane filtration for household water treatment