Influence of operating parameters on the performance of a household slow sand filter

The biosand filter (BSF), an intermittently operated household slow sand filter, is one of the commonly used household water purification methods in the rural areas of developing countries. In this study, long-duration tests were conducted in the laboratory to investigate the influence of two important operating parameters, namely the pause period (idle time) and the charge volume on the performance of BSF by using full-scale BSFs. The filters were charged daily with 20 or 40 L of tap water spiked with Escherichia coli or sewage with different pause periods. Results indicated that during the ripening (maturation) of the filter, which took about one month, E. coli removal was low, with an average value <90.0%. Maximum E. coli reduction observed in the test was around 3 log₁₀ units. Doubling the daily charge volume from 20 L to 40 L significantly reduced E. coli removal by at least one log₁₀ unit. Reducing residence time within the filter also impaired the filtrate quality. Cleaning of the filter considerably reduced the bacterial removal efficiency. The aesthetic quality of treated water was good, with a mean effluent turbidity of <1.5 NTU, and was not affected by the variations in charge volume and pause period.