Study of filtration process for the treatment of surface water

Abstract

Although ground water is available in almost all of the rural areas of Bangladesh, due to traditional habit, vast majority of rural people still use surface water sources for various domestic purposes. Water from these sources is physically and bacteriologically contaminated due to unhygienic practices and need proper treatment to make it potable. Treatment methods $uch as slow sand and rapid sand filtration are not directly applicable in many cases due to high concentration of turbidity and also economically not feasible under rural economic condition in Bangladesh. This research investigates the effectiveness of horizontal flow coarse media roughing filter for a simple pretreatment of the highly turbid and bacteriologically contaminated surface water. A model horizontal flow roughing filter consists of three chambers was filled with aggregates of different sizes. Artificially contaminated turbid water of 130 NTU turbidity was allowed to pass through the filter medias with constant rate of filtration. The model plant effectively reduced the raw water turbidity to the level of average 3.27 NTU. Provision of an intermediate buffer zone in first chamber increased the effective length of filter run by about 80 percent. A sedimentation basin, designed on the basis of settling column test has been observed advantageous over second chamber of roughing filter. The third chamber of the model plant which consists of only gravel and coarse sand significantly reduced the bacterial concentration, but traditional method of filtration/ disinfaction is further necessary to reduce the coliform counts to the level of acceptance.