iSSF (Intermittently Operated Slow Sand Filtration System)
The iSSF is a gravity-fed slow sand filtration system.
The iSSF is a large slow sand filtration system that is designed to be intermittently operated as water becomes available. Without requiring electricity, water is gravity fed through sand where bacteria and turbidity are removed.
Cambodia, Philippines, Nicaragua, Kenya, and the Democratic Republic of the Congo (DRC)Correspondence with CAWST
Community-sized sand filters such as SSWM sand filter design.
SDG 6: Clean water and sanitation
Rural schools and communities
The iSSF is built from locally-available materials such as water supply tanks, PVC pipe, and sand. The iSSF Manual is available free to download.
Aid organizations work with communities and/or schools to build the system.
~200 unitsCorrespondence with CAWST
The iSSF is operated by filling the reservoir tank with dirty water. Water flows from the reservoir tank into the filter tank via PVC pipe. The water is gravity fed though the biolayer, sand, and underdrain layers in the filter tank. The water then flows through a PCV pipe to the storage tank.
A schematic is available on pages 7-11 in the iSSF Manual
CAWST provides technical support for individuals and organizations.
During a field evaluation in Cambodia, 75% of the sampled iSSF filtered water had zero E. coli and 95% had <10 E. coli. Described on page 52 of the iSSF manual.
The filter should be monitored and maintained regularly to ensure safety. Instructions for maintenance are provided in the iSSF manual.
Adding chlorine to the outlet tank can increase the safety of the water.
“Performance of Intermittently Operated Slow Sand Filters in Rural Schools in Cambodia” presented by Ray Cantwell of Samaritan’s Purse at the UNC Water and Health Conference in 2015
There has been significant academic research on the Household Biosand Filter.
Field evaluations such as testing in Cambodia (page 52 of the iSSF manual).
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