Effect of alkaline pH on the stability of halogenated DBPs

The objective of this study was to investigate the effect of alkaline pH on the stability of halogenated disinfection by-products in the absence of chlorine residuals. The results showed that the concentrations of trihalomethanes (THMs) and dihaloacetic acids (DHAAs) increased substantially under alkaline pH conditions without chlorine residuals. The hydrolysis of unstable THM and DHAA intermediates could be important pathways leading to the increases of THMs and DHAAs. The hydrolyzable THM and DHAA intermediates accounted for approximately 20% of the unknown total organic halogen (UTOX) formed by chlorine. The formation of trihaloacetic acids (THAAs) stopped in the absence of chlorine residuals. The UTOX-to-TOX ratio decreased with increasing pH value and time in the absence of chlorine residuals. Total organic chlorine (TOCl), total organic bromine (TOBr), and total organic iodine (TOI) were dehalogenated through basecatalyzed reactions. The stability of TOCl, TOBr, and TOI was in the order of TOCl > TOBr > TOI.