Control of disinfection byproducts (DBPs) by ozonation and peroxone process: Role of chloride on removal of DBP precursors

The objective of this study was to remove regulated DBP precursors by using ozonation and peroxone process (H₂O₂/O₃). Regarding formation potentials of trihalomethanes (THMs) and haloacetic acids (HAAs), the role of chloride in chlorination and ozonation/peroxone processes was revealed. The organic compounds in water samples from rapid sand filtration preferably yielded the THM formation potentials, rather than HAAs. Ozonation with the typical applied doses (1-5 mg L^-1) was ineffective for removals of THM and HAA precursors. The peroxone process only decreased the formation potentials of THMs. The reduction of THMs by the peroxone process resulted from decreases in either chloroform or dibromochloromethane. However, the limitation was found in the H₂O₂/O₃ ratios of 2.0-3.0. The removals of HAA precursors were much more difficult than that of THM precursors by ozonation and peroxone processes. The oxidation of organic compounds was able to promote the HAA formations. Ozonation with the typical ozone doses increased the chloroform formations, while decreases in bromide-containing THMs occurred. Effect of ozonation on changes in HAAs speciation was unclear. The peroxone process likely promoted the dichloroacetic acids and trichloroacetic acids. The presence of chloride (1-5 g L^-1) highly enhanced the THM and HAA formation potentials. NaCl addition greatly increased the bromide-containing THMs, while the chloroform decreased. For HAAs, the presence of chloride promoted the bromide-containing HAAs and monochloroacetic acids. The presence of chloride played a role as a promotor for strong chlorinating agents in chlorination, rather than as a scavenger in ozonation and peroxone processes.