Swiss Federal Institute of Aquatic Science & Technology (EAWAG)
A gravity fed household water purification system.
EAWAG is an ultrafiltration low-pressure system for household water treatment. Ultrafiltration is an effective technology to treat water and can be applied on a decentralized scale. Most ultrafiltration membranes have pores, which are smaller than the size of bacteria and viruses. Thus, water filtered through these membranes is micro-biologically safe.
EAWAG – Swiss-based and internationally active research institute within the ETH domain (Swiss Federal Institute of Science and Technology)
Projected Cost: ~20 CHF ($20 USD) per household
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Goal 6: Clean water and sanitation
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In gravity-driven membrane (GDM) technology, no backflushing or cleaning is used. Pressure necessary to press water through the membranes is generated by gravity, which is generated by difference of water levels between two storage tanks. As a feed, natural water (river, spring, well or rainwater) can be used without pre- or post-treatment. BIO-CEL® membrane sheets with a pore size of 40 nm are placed vertically inside the membrane tank. The sheets are manufactured by Microdyn-Nadir and are usually employed in membrane bioreactors for wastewater treatment. Although turbid waters can also be used, a pretreatment is required if the water becomes extremely turbid (> 500 NTU). The clean water tank has dimensions for a total volume of 10 liters, the membrane tank has dimensions for 20 liters.
Please see images showing the preliminary design and schematic for the filter mechanism
Expected life span 5-8 years (This has not yet been tested)
48 L of safe drinking water per day only with 0.5 m^(2) of membrane, which is sufficient to cover drinking water needs of a family. The Kenya trials were conducted with household filter prototypes with a target capacity of 2-5 L per hour. GDM systems can be operated with turbid water (up to 100 NTU) or high organic matter content (including diluted wastewater with a TOC of about 12 mg/L). Membranes used in GDM systems entirely remove protozoa and bacteria, and preliminary data shows 99.99 % retention of viruses
EAWAG, Kenya Water for Health Organization (KWAHO)
Field observations are strongly indicating high recontamination factors linked with maintenance and unsanitary conditions.
Redesigning of the tap might help prevent recontamination risks
How often/when should maintenance be performed?
Akhondi, E., Wu, B., Sun, S., Marxer, B., Lim, W., Gu, J., Liu, L., Burkhardt, M., McDougald, D., Pronk, W., Fane, A. G. 2015. Gravity-driven membrane filtration as pretreatment for seawater reverse osmosis: Linking biofouling layer morphology with flux stabilization, Water Research, 70, 158-173, dx.doi.org/10.1016/j.watres.2014.12.001.
Several published papers dating back to 2009 are listed here under the “download” button.
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