Characteristics of natural organic matter and formation of chlorination by-products at Masaka waterworks

To minimise the formation of chlorination by-products (CBPs) it is imperative that attention is directed towards the structure and occurrence of natural organic matter (NOM) in raw water sources, and its flow and fate during water treatment processes. In this study, an assessment of the characteristics and flow of NOM along the treatment train at the full scale treatment plant at Masaka, Uganda, was made. Results indicated that 79% of the NOM, determined as total organic carbon, was in the dissolved form (DOC) with 83% of the DOC being hydrophilic in character. The insignificant amount of hydrophobic fraction in the raw water implies that the contributing fraction to THMs formation was mainly the hydrophilic component which subsequently was poorly removed along all units except clarification. The treated water from all unit processes provided specific ultraviolet absorbance values greater than 2 L/mg-m at 254 nm wavelength, indicating that it still had a high potential of reacting with chlorine to form CBPs. This renders water from Nabajjuzi River as unsuitable for chlorination in early stages of treatment and necessitating modification of the processes to reduce or avoid formation of unwanted by-products.