Analysis of Natural Organic Matter as Precursors of Trihalomethanes and Its Removal in Water Treatment Plant

Disinfection is an important step in water treatment, but unpredictable compounds are produced as disinfection by-products (DBPs). DBPs are harmful products to human health so their formation must be prevented during treatment, especially for drinking water treatment. An organic compound such as natural organic matter (NOM) is the main precursor of DBPs due to its presence in river water. The Water Treatment Plant (WTP) in Indonesia, mostly uses river water as raw water. Analysis of the organic matter is very important as this research aims to determine the ability of the WTP units to reduce precursors and the formation of DBPs. The sample was filtered by a 0.45µm microfilter. The presence of NOM was evaluated by the dissolved organic carbon (DOC) parameters, ultraviolet at 254 nm absorbance (UV₂₅₄), and specific UV absorbance (SUVA). Then measure the Trihalomethanes (THMs) as DBPs after the disinfection. The results of analysis from five WTPs, the DOC concentration is between 3.30 – 8.20 mg/L; UV₂₅₄ is 0.70 – 0.10 cm^-1; SUVA is 0.90 – 3.13 L/mg.m. The ability of conventional WTP units such as coagulation-sedimentation-filtration in removing DOC is around 7% – 42%; UV₂₅₄ is 17% – 35%; SUVA is 6% – 69%. For the THMs, the concentration after the disinfection is 4.50 – 127 µg/L. It can be concluded that conventional WTP units are not effective in reducing NOM and the potential of DBPs formation is still high.