Multistage Filtration: An Innovative Water Treatment Technology

The technology of multiple stage filtration (MSF) presented here is a combination of coarse gravel prefiltration and slow sand filtration (SSF). This combination allows treating of surface water that has considerable levels of contamination, well above the levels that can be treated by SSF alone. To improve the performance of MSF, other treatment processes such as simple sedimentation, sand traps, and screens can precede MSF technology. Wherever possible, terminal disinfection needs to be included as a safety barrier after MSF. MSF retains the advantages of SSF in that it is a robust and reliable treatment method that can be maintained by operators who have low levels of formal education. It is much better suited than conventional chemical water treatment to conditions in rural communities and small and medium size municipalities in the South as well as in more remote areas in the North. The article provides a summary description of the components of MSF systems and the findings of recent research. It gives an overview of cost implications and ends with a selection guide. Keywords: slow sand filtration; roughing filtration; water treatment plants; guidelines; design; construction costs; maintenance; planning; dynamic roughing filtration; upflow roughing filtration; until-stage filtration