Effects of typical water components on the UV254 photodegradation kinetics of haloacetic acids in water

This study investigated a range of typical water components and parameters, including pH, carbonate, bicarbonate, halides , nitrate, dissolved organic matter (DOM), free chlorine, and initial concentration, on the photodegradation kinetics of seven different haloacetic acids (HAAs) with different halogen substitutions. The results show that the photolysis rates can generally be enhanced by additions of free chlorine and iodide yet decelerated by increases of DOM and bromide. In contrast, pH and feeding HAA concentration did not affect the photodegradation of HAAs significantly over pH ranges from 6 to 11 or doses from 0.05 to 50 mg/L. One exception existed that hydroxide, bicarbonate, and carbonate apparently inhibited the photolysis kinetics of monochloroacetic acid, suggesting that indirect photolysis via hydroxyl radical was partially responsible for this compound. As for the combined influences of water matrix, the photolysis rates of HAAs dosed into tap, lake, and ocean waters were lower than those dosed into ultrapure water by on average 21–38%, indicating that most components in these real waters tended to suppress the photolysis. The study therefore demonstrates the complexity of DBP removal using a UV system, and such results may help assessment of the real potential of UV photolysis for HAA control in water.