Slow Sand Filters (Purdue University) Chad Jafvert, Professor, Civil Engineering/Environmental & Ecological Engineering [email protected] https://engineering.purdue.edu/~jafvert/ John Howarter, Assistant Professor Materials Sciences & Engineering, Environmental and Ecological Engineering Sciences [email protected] What they do: The slow sand filters (SSFs) significantly improve water quality by removing particles and dissolved organic chemicals from the water, reducing turbidity below the U.S. drinking water standard of 1.0 NTU, and allow the water to be disinfected by means other than boiling (microfiltration, chlorination, UV). About our filters: Our approach has been “to design” using small, easily shipped components, for easy final construction at the point‐
of‐use, using locally obtained 5 gallon pails or 55 gallon drums, and sand. We expect this approach to lead to an overall greater impact by reducing overall costs and construction time. Design and Operation: Our point‐of‐use SSFs are made from readily available 5 gallon plastic pails or 55 gallon drums. For the pail SSFs, one “unit” consists of a stack of two 5‐gallon pails. Because the volume of water within the sand is approximately 10 Liters, typically 10 Liters water can be poured in 1 unit (a 2‐pail unit) every 8 hours, so that 30 Liters of water can be produced each day. Four pails in one home, therefore can treat 60 L each day. For the 55 gallon drum units, one drum filter can treat 200 liters of water each day. Improvement over other SSF: Every other slow sand filter uses gravel layers at the bottom of the filter as the “water collection zone”. Our filters do not use gravel. Instead, we use a porous plastic plate enclosed within a mesh bag. Reasons for this include:  There is only 1 media (sand) to prepare (sieve and rinse).  If the filter becomes clogged, all the sand can be removed and rinsed, making for easy maintenance.  The pails, fittings, and sand (bagged) can be transported, and anyone can do the final assembly. Sieving the Sand: We have designed a portable trommel for sieving the sand. The trommel has an external drum for sieving out the coarse material, and a removable internal drum for sieving out the “fines”.  The trommel can be quickly disassembled and transported in airline checked baggage (with no extra fees).  The trommel shown in the photo was transported to Colombia, and put together by students at a rural elementary school. Filters in a rural elementary school in Colombia and testing chlorine demand (right), and water before and after treatment, 15 months after installation of the filters at this school (left). A filter made from a used 210 Liter (55 gallon) drum in, Kenya (above), and filters at a community center in Arusha, Tanzania (right). In January, 2015, parts for 100 pail filters were sent to Nelson Mandela African Institute of Science and Technology. SSFs in a home in Qinghai Provence, China (installed in cooperation with Purdue’s U.S.‐
China Ecopartnership and Qinghai Normal University in Xining, China). Faculty at Qinghai Normal University discussing filter performance with the homeowner in a rural village. Water before SSF treatment (left) Water after SSF treatment (Right)