Natural fabrics in slow sand filtration

Previous research at Imperial College, London, UK has shown that slow sand filters protected by layers of non-woven synthetic fabrics, namely polypropylene have increased run times in between periods of shut down and regular maintenance, compared to un-protected slow sand filters by up to a factor of 8. This is achieved by the application of fabric layers on the surface of the sand bed. Through careful selection of fabrics, the filtration processes can be concentrated in the fabric layers, hence preventing solids penetration through to the sand, resulting in a reduction in the rate of head loss development. So, as well as extended run times, fabric protected sand filtration can also eliminate the need for sand removal and cleaning. This paper is concerned with replicating these earlier findings through the use of natural fabrics, to a) open up new markets for natural tropical fibres and, b) make available the advantages of protected slow sand filtration to developing countries, utilising local materials and/or minimising the use of foreign exchange. The research has been solely a feasibility study to determine whether natural fibres are suitable materials for the protection of slow sand filters. Other factors, although important, are not considered at this stage.