Comparative treatment performance and hydraulic characteristics of pumice and sand biofilters for point-of-use water treatment

Abstract

This study has investigated the comparative treatment and hydraulic performance of biosand filters (BSFs) of pumice and sand filter media, with Escherichia coli and turbidity as the principal indicators of water quality. The study has also assessed the effect of resting time on E. coli and turbidity removal. The performances of three filter columns consisting of sand, pumice, and sand/pumice dual media with a bed depth of 80 cm were evaluated over 4 months continuously. The columns were charged twice daily with local canal water. The pumice and the dual media filters achieved 24 and 14%, respectively, greater volume production per cycle compared to that of the sand filter. The pumice filter had consistently lower filtrate turbidity than the other filters with about 98.5% turbidity removal. Average E. coli removals were similar for all filters and corresponded to 0.9–1.8 log units for unripened media, and 1.4–3.3 log units for ripened media. It was observed that resting time of more than 4 h was necessary to achieve significant E. coli removal. Hydraulic and water quality profiles indicated that schmutzdecke development in the pumice layer was not effective as in the sand bed.