Biosand water filter: Effects of sand size and sand column height on filtered water quality

Abstract

The study investigated the performance of locally assembled Biosand Water Filters (BSFs) with varied sand sizes and sand column heights. The main objective of the study was to contribute to water quality improvement through the assessment of the filtration capacity of selected sand sizes and sand column heights for use in the Biosand filter. The raw water source was an open well in Nabweru, a peri-urban slum located in Kawempe Division, Kampala. A total of 18 BSFs were constructed and experimentation carried out for a period of 5 weeks. Sand sizes; (<0.6, 0.6- 1, 1-2) mm and sand column heights; (300, 500, 700) mm each replicated 3 times were used. Daily water collection, filtration and water quality analysis of both the raw and filtered water was done. A flow rate of 320 ml/min was maintained throughout the experimental period. The results indicate that; sand sizes up to dmax = 1 mm reduced selected parameters nearly to the level of the widely recommended sand size dmax <0.7 mm, and World Health Organization (WHO) and Uganda National Bureau of Standards (UNBS) drinking water standards. Sand size dmax =2 mm however did not achieve drinking water standards. Also sand column heights of 500 & 700 mm achieved drinking water standards while 300 mm did not. All selected sand sizes and sand column heights improved the quality of raw water. The study recommends that more research be done on filtration capacity of larger grained sizes of 0.6-1 mm & 1-2 mm amended with activated carbon for further improving water quality and; a longer duration study with larger sand sizes to see if performance remains constant over time.