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Chlorine is used as a disinfectant and an oxidant in drinking water treatment to protect the public health from pathogenic microorganisms. However, if applied to raw water with humic materials, it leads to the formation of halogenated organic compounds that are a potentially serious environmental and health problem. This renders pre-chlorination of raw waters to oxidise iron inappropriate. Coagulation, the principal treatment process for removal of THM precursors, is therefore essential for chlorination by-product control. In this study, the impact of pre-chlorination and the performance of Moringa oleifera as a coagulant aid at Masaka waterworks were assessed. An average increase of trihalomethanes of over 4,000% at aeration and pre-chlorination stage was observed at the plant. From the jar tests, alum with Moringa oleifera reduced dissolved organic concentration by 47.1%. The treated water after sedimentation tasted salty but after filtration and chlorination, the salty taste disappeared. Residual iron values of 1.38 mg/L and 3.05 mg/L were achieved with MOC-SC as coagulant aid and alum alone respectively. The jar test results indicated that use of alum with Moringa oleifera as coagulant aid is promising as a first stage in the treatment train for waters with humic materials and high content of iron.

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