Role of precursors in the formation of trihalomethanes during chlorination of drinking water and wastewater effluents from a metropolitan region in western India

Dissolved organic matter (DOM) is the primary precursor that reacts with chlorine to form potentially carcinogenic/mutagenic disinfection byproducts (DBPs). The prime objective of this study was to compare the nature of DOM in samples collected from drinking water and wastewater treatment plants in western India and to relate their nature and concentration to trihalomethane (THM) formation. The effects of chlorine dose, bromide ion, contact time, and pH on THM formation were also studied. The surrogate parameters, such as UV absorbance at 254 nm and dissolved organic carbon (DOC) were monitored for each experiment to understand their correlation with THM formation in the selected water and wastewater systems. Fluorescence spectroscopy revealed that DOM in wastewater was dominated by protein-like components, while DOM in water samples consisted mostly of humic-like components, which exhibited greater THM formation potential. Fractionation of DOM into various fractions followed by reaction with chlorine revealed that the hydrophobic acid and neutral fractions of DOM were primarily responsible for THM formation. Thus, methods that target removing these fractions before chlorination would have maximum impact on reducing THM formation.