Professional Assessment of Water Treatment Plant Performance Using Chemical Analysis in Ogun State

Water treatment plants serving urban and peri-urban populations in Ogun State, South West Nigeria, are expected to produce drinking water that consistently meets national and international quality standards, yet comprehensive chemical quality assessment of their performance is rarely conducted and publicly reported. This study assessed the treatment performance of three water treatment plants in Abeokuta, Sagamu, and Ilaro using chemical analysis of raw, intermediate, and treated water samples. Samples were collected at monthly intervals over one year from intake points, post-sedimentation, post-filtration, and distribution network tap points. Physical parameters, inorganic chemical constituents including chlorine residual, fluoride, nitrate, iron, turbidity, and trihalomethane formation potential were determined. Trihalomethane formation potential was measured using a simulated distribution system test with 48-hour chlorination at 25 degrees Celsius. All three plants achieved adequate removal of turbidity, reaching treated water values below 1 NTU. Residual chlorine was maintained within the 0.2 to 0.5 mg/L range at treatment plant outlets but fell below 0.1 mg/L at distant distribution points in two systems. Iron breakthrough occurred in the Ilaro plant during elevated raw water iron episodes. Trihalomethane formation potential exceeded the US EPA guideline of 80 micrograms per litre during months of high organic loading in raw water. These results identify specific operational weaknesses and recommend optimisation of coagulation dosing, distribution system booster chlorination, and enhanced monitoring of trihalomethane precursors in source waters.

Keywords: water treatment performance, trihalomethanes, chlorination, water quality, Ogun State