The influence of three important parameters, namely, pause time, charge volume and influent turbidity on the performance of a biosand filter (BSF) was assessed by employing response surface methodology with a Box-Behnken design. Fifteen runs were conducted in triplicate using a full-scale BSF with a pore volume of 19.6 L, and the performance of the filter was assessed by monitoring total coliforms, Escherichia coli and turbidity of the effluent. Results showed that there was a significant improvement in the microbiological quality of filtered water when the pause time was increased from 12 to 36 h, while it deteriorated as charge volume was increased from 10 to 30 L. The effluent microbiological quality was unaffected by changes in the influent turbidity in the range of 10–50 NTU. Further, effluent turbidity was not significantly affected by the changes in any of the operating parameters, and it remained below 1.5 NTU in all the runs. At optimum conditions of pause time 23 h, charge volume 19.4 L and influent turbidity 32 NTU, bacterial removal exceeded 99.4%. The results show that charging of the filter with about one pore volume of water once a day would be the ideal operating strategy for a BSF.

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