Comparison of chlorine decay models under varying temperature and UV254 for water supply

Bulk chlorine decay in water distribution systems is strongly influenced by temperature and organic matter. Higher temperatures accelerate chlorine decay reactions, while organic matter acts as a primary reactive substance. Accurate chlorine decay modeling depends on precise coefficient estimation. This study used nonlinear coefficient relationships incorporating temperature, initial chlorine concentration, and UV (Ultraviolet absorbance at 254 nm, as an organic matter indicator) in three models: first-order (FO), variable parabolic reaction coefficient (VPRC), and second-order (SO). The SO models consisted of SO1 (based on chlorine concentration) and SO2 (incorporating both chlorine and UV). In situ experiments at a water treatment plant during dry and wet periods simulated real-world conditions. Both the VPRC and SO2 models showed comparable performance in predicting chlorine decay. While the SO2 model is more suitable when additional UV254 decay needs to be considered, particularly for byproduct formation prediction. These relationships offer a robust framework for modeling chlorine decay under varying conditions.