Performance assessment of modified biosand filter with an extra disinfection layer

Biosand filters (BSFs) have been used widely as an efficient, inexpensive, and appropriate point-of-use technology. Several organizations are promoting filters without adequate testing, which may not lead to sufficiently safe devices. The objective of this study was to evaluate the performance of a modified biosand filter (MBSF) with an extra disinfection layer (brass or zero valent iron (ZVI)) and three layers of underdrain in a range of parameters including Escherichia coli, total coliform, turbidity, pH, and dissolved oxygen. On average, a 91.29% reduction (log 1.43) in total coliform, 98.7% reduction (log 2.6) in E. coli and 88.71% reduction in turbidity were observed for the control. There was a 90.11% reduction (log 1.41) in total coliform, 98.2% reduction (log 2.25) in E. coli, and 88.5% reduction in turbidity for MBSF brass. A 96.93% reduction (log 1.81) in total coliform, 97.33% reduction (log 2.36) in E. coli and 91.5% reduction in turbidity for MBSF ZVI were observed. Adding brass as a disinfection layer in MBSF did not improve bacteria and turbidity removal rates. Adding ZVI as a disinfection layer gave better turbidity and total coliform removal relative to control and MBSF brass. Water quality remained within drinking water standards for all filters.