Investigating feasibility of use of bio-sand filters for household water treatment in Epworth, Zimbabwe

Abstract

This study investigated the feasibility of using bio-sand filters for household water treatment as an option to improve drinking water quality at household level. Drinking water from hand-dug shallow wells (depth <10m) was analyzed for pH, turbidity, chloride, nitrates, Electrical Conductivity (EC), Dissolved Oxygen (DO) and faecal coliforms. Three laboratory pilot water plants each comprising of a 90 mm diameter and 800 mm deep plastic cylinder with three different combinations of filter media (BSF1, BSF2 and BSF3) were set up. BSF1 comprised of sand only, BSF2 contained sand and a 50 mm thick layer of iron and sand mixture and BSF3 comprised of sand and a 100 mm thick layer of iron and sand mixture. The filters were fed with 1.5 litres of well water daily and composite samples of influent and effluent were collected for analysis daily for four weeks. The average values of the parameters for the raw well water used for the pilot plants were 6.75 (pH), 32.5 NTU (turbidity), 126 mg/L (chloride), 15 mg/L (nitrates), 303 μS/cm (EC), 2.2 mg/L(DO) and 1521 cfu/100 mL (faecal coliforms). There were significant differences (p > 0.05) between influent and effluent parameters for all three filters. The concentration of iron in the effluent was less than 0.03 mg/L for all filters. After four weeks, the bacterial removal efficiencies were 94.8%, 99.2% and 99.5% for BSF1, BSF2 and BSF3, respectively. The bio-sand filters modified with iron and sand mixture (BSF2 and BSF3) had a higher efficiency in reducing bacteria compared to the sand only filter (BSF1). Chemical dosage will be required to further improve the water quality.