Effect of flow rate on the performance of Biosand Filter

Lack of access to safe drinking water is an issue in some areas where centralized water treatment is not possible, the biosand filter (BSF) one of several such point-of-use technologies is available. This study was conducted in Côte d’Ivoire to evaluate the effect of flow rate on the performance of the BSF. Three biosand filter (BSF) built in Poly vinyl chloride was used to investigate the effect of three flow rates (1.95 L/d in BSF1; 3.9 L/d in BSF2 and 7.8 L/d in BSF3) for 91 days. Each BSF was filled with 15 cm of gravel, 90 cm of sand and 40 cm of supernatant water. Physical and chemical parameters were analyzed in raw water and filtered water with standards methods. The results showed that the percentage removal of TSS approximately the same for all filters. Ammonium concentrations ranged from 37 to 170 μg.L-1, 110 to 190 μg.L-1 and 150 to 278 μg.L-1 for filtered waters of BSF1, BSF2 and BSF3, respectively. Nitrite concentrations in filtered waters of BSF1 (2 - 33 μg.L-1) were less than those of BSF2 (5 - 45 μg.L-1) and BSF3 (7 - 49.5 μg.L-1). Nitrate concentrations in filtered waters of BSF2 (1.9 to 4 mg.L-1) and BSF3 (1.6 to 4.2 mg.L-1) were higher than those of BSF1 (0.6 to 2.3 mg.L-1). Chemical Oxygen Demand removal efficiency for BSF3 (68.2 ± 9.5%) was lower compared to BSF2 (82.6 ± 3.8%) and BSF1 (93.7 ± 2.8%). The flow rate has an influence only on the removal of ammonium, nitrite, nitrate and Chemical Oxygen Demand. The best treatment results were obtained with the minimum flow rate (1.95 L/d)