Because of their simplicity, efficiency, and economy, slow sand filters are appropriate means of water treatment for community water supply in developing countries and for small water systems in other areas of the world, including the United States. The basic elements of a slow sand filter are described, as are planning, design, and construction aspects, with special emphasis on maintenance. Some cost figures for systems in India and Colombia are included. Operational procedures for maintenance and resanding are set out.

This paper explores through case studies the quality of water service delivery in four different water utilities in Kenya and Ghana. The research confirms that the utilities' current performance indicators by themselves are insufficient to assess the access of users to good-quality water service delivery. The case studies show that low-income populations receive a poor quality of water service delivery. The paper concludes that benchmarking needs to be complemented with a more in-depth analysis of the water service delivery by water providers.

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This paper assesses the operational and design aspects of coagulation and flocculation in upflow gravel filters (CF-UGF) in a multi-stage filtration (MSF) plant. This study shows that CF-UGF units improve the performance of MSF considerably, when the system operates with turbidity above 30 NTU. It strongly reduces the load of particulate material before the water enters in the slow sand filters (SSF) and therewith avoids short filter runs and prevents early interruption in SSF operations. The removal efficiency of turbidity in the CF-UGF with coagulant was between 85 and 96%, whereas the average efficiency without coagulant dosing was 46% (range: 21–76%). Operating with coagulant also improves the removal efficiency for total coliforms, <i>E-coli</i> and HPC. No reduction was observed in the microbial activity of the SSF, no obstruction of the SSF bed was demonstrated and SSF runs were maintained between 50 and 70 days for a maximum head loss of 0.70 m. The most important advantage is the flexibility of the system to operate with and without coagulant according to the influent turbidity. It was only necessary for 20% of the time to operate with the coagulant. The CF-UGF unit represented 7% of total construction costs and the O&M cost for the use of coagulant represented only 0.3%

Abstract. This paper assesses the operational and design aspects of coagulation and flocculation in upflow gravel filters (CF-UGF) in a multi-stage filtration (MSF) plant. This study shows that CF-UGF units improve the performance of MSF considerably, when the system operates with turbidity above 30 NTU. It strongly reduces the load of particulate material before the water enters in the slow sand filters (SSF) and therewith avoids short filter runs and prevents early interruption in SSF operations. The removal efficiency of turbidity in the CF-UGF with coagulant was between 85 and 96 %, whereas the average efficiency without coagulant dosing was 46 % (range: 21-76 %). Operating with coagulant also improves the removal efficiency for total coliforms, E-coli and HPC. No reduction was observed in the microbial activity of the SSF, no obstruction of the SSF bed was demonstrated and SSF runs were maintained between 50 and 70 days for a maximum head loss of 0.70 m. The most important advantage is the flexibility of the system to operate with and without coagulant according to the influent turbidity. It was only necessary for 20 % of the time to operate with the coagulant. The CF-UGF unit represented 7 % of total construction costs and the O&M cost for the use of coagulant represented only 0.3 %.