Effectiveness of chlorine as a pre-oxidation mechanism in water treatment for turbidity removal in groundwater as a water efficiency strategy

Abstract

Groundwater supply has been one of the pillars of socio and economic development, especially in the dry regions of Sri Lanka, where reliable water sources are very scarce. With the rising water demand, water conservation through recycling and reusing has become an important strategy in a sustainable built environment. The Murunkan aquifer is one of the most utilized aquifer systems in Northern Province. The average extraction from the Murunkan aquifer is approximately 10,000 m3 /d. The yield is nearing saturated, thus leading to a few water quality variations. Variations in turbidity level in Murunkan groundwater sources could be a consequence of precipitation of insoluble reduced iron (Fe2+), manganese (Mn2+) and other oxides. The study is focused on investigating the effectiveness of chlorine as a pre-oxidation mechanism in rapid sand filtration for turbidity removal in groundwater. The pilot filter consists of particle sizes of 25mm, 16mm, 10mm, 2-5mm with a layer thickness of 75 mm, 50mm, 30mm, and 50mm, respectively, and sieved ordinary silica sand as filter media with 700 mm layer thickness. The chlorine solution is added at the inlet point of the filter. A retention time is maintained between 20-25 minutes to allow oxidation above the sand bed within the rapid sand filter model. The effluent from the filter was tested for turbidity based on APHA standards for 15 trials. Raw water turbidity ranges between 0.27-3 NTU, while treated water turbidity ranges between 0.21-0.68 NTU. The maximum turbidity removal percentage was 77% while turbidity removal was observed in 60% of samples. It is also found that there is a trend in increasing removal percentage with the increase of raw water turbidity and the number of trials conducted, however, removal efficiency does not have any definite trend with chlorine concentration.