Today, Engineers Without Borders-Howard University installed the first of six biosand filters in Choimim, Kenya. Biosand filters purify dirty water and make it safe to drink. They are very useful both in rural and urban areas and often are adopted in areas that lack safe piped water.

The team began work early after a hearty Kenyan breakfast complete with chai (black tea with milk) and mandazi (comparable to a French beignes).First, the team prepared the materials including the sieving of gravel and sand to remove grass and other contaminants.The team rinsed the gravel about six or seven times to ensure it was clean. With the materials ready, the tough task was getting the 200-pound concrete biosand filter in place at the orphanage.  The trip was 1000 ft. across rain-saturated grass, a muddy ditch and up two sets of shaky wooden steps. The filter made it safely. Faculty advisor John Tharakan and Running Water International co-founder Isaac Soita took turns helping EWB-HU member Ade carrying the filter.

Photography by Kerry-Ann Hamilton

Each filter contains six items:

1. The concrete outer shell, built using approximately half a sack of cement mixed with two sacks of gravel and a sack and a half of sand

2.  A length of PVC pipe, ~ 2.25’ in length and 0.5” in diameter

3.  A diffuser plate full of small holes, made from metal or pottery

4.  A 21” layer of clean, washed, medium-grade sand

5.  A 2” layer of small gravel

6.  A 2” layer of small stones or large gravel

How does it work?

Contaminated water is poured into the reservoir on an intermittent basis. The water slowly passes through the plastic diffuser and percolates down through the biolayer, sand and gravel. Treated water naturally flows from the outlet tube.

Team Lead Aleah Holt, explains the process this way:

When you pour the dirty water in the top of the filter, the biolayer (The first 2-4” of the sand surface) consumes the bacteria…simply put, the good bacteria eats the bad bacteria. After the dirty water passes through the biolayer, the sand (the deepest layer) captures all the particles. After the water filters through the sand, any remaining particles or bacteria can be captured in gravel because it is dark and no oxygen is present. After leaving the gravel layer, the clean water exits through the outlet pipe and is safe for consumption. 

The most time consuming part of the process is the preparation of the materials. However, the installation takes less than 1 hour.

The experiment with the plastic filters will begin on Monday morning. On Sunday night, the team stayed up late calculating, measuring and re-sketching. The community will arrive at 10 a.m. to observe the installation of the second biosand filter. The goal is to produce an even cheaper version of the concrete biosand filters. The local cost is $4500 Kenyan Shillings (USD 45). Because most people in Choimim make less than one US dollar a day, a biosand filter is too costly for a single family. Build the Village Director James Esendi is currently exploring how families can pool their resources to purchase additional filters, maybe 4 or 5 families sharing a filter. The team will install a filter at the Siwo clinic and in three homes over the next two days.

Dr. Kerry-Ann Hamilton, director of strategic communications and marketing, is traveling with EWB-HU on their service mission to Kenya. The blog “Water is Life” chronicles the travels and work of the 9-member delegation from Howard University.