Performance evaluation of biosand filter modified with iron oxide-coated sand for household treatment of drinking water

The biosand filter (BSF), intermittently operated household slow-sand filter, was modified by introducing a 10-cm thick layer of iron oxide-coated sand. Long-duration (about four months) tests were conducted to compare the performance of the modified BSF (MBSF) with the conventional BSF in terms of their efficiency in removing bacteria and turbidity under different operating conditions. Filters were charged daily with 20 L or 40 L natural canal water (turbidity 10.0 ± 1.2 NTU; faecal coliforms 365 ± 251 MPN/100 mL; pH 8.4 ± 0.4) or seeded tap water (turbidity 14.7 ± 4.3 NTU; Escherichia coli 3850 ± 736 CFU/mL; pH 7.9 ± 0.3). Results showed that the performance of MBSF in terms of faecal coliform and E. coli removals was better by at least one-log10 unit throughout the filter operation. The mean bacterial removal was low for BSF for the first month (90.0%), while it was 99.3% for MBSF during the same period. Bacteria and turbidity removals increased with time as filter ripening (maturation) occurred in both the filters. No significant difference was observed in turbidity removal between BSF and MBSF, and mean effluent turbidity was around 1 NTU for BSF and MBSF representing > 90% removal. When daily charge was increased from 20 L to 40 L, a reduction in bacterial removal was noted in both the filters indicating the influence of operating conditions. Effluent physico-chemical quality remained within the guideline values for drinking water.

Research highlights
► Addition of a layer of iron oxide-coated sand improves efficiency of biosand filter.
► This is especially beneficial during maturation period and after cleaning operation.
► Bacterial removal improved by at least one-log unit.