Indexed on: 17 Dec '09Published on: 17 Dec '09Published in: Environmental Science & Technology
A bench-scale study was performed to investigate formation and speciation of halonitromethanes (HNMs) in raw and treated waters obtained from a drinking water treatment plant. HNM species were measured after chlorination, ozonation-chlorination, chloramination, and ozonation-chloramination, and compared with trihalomethanes (THMs). Pre-ozonation before chlorination resulted in enhanced HNM formation, producing trihalogenated HNMs as major species. Formation of THMs showed very a different formation pattern from HNM formation such that it was much higher in the raw than the treated water, and decreased after pre-ozonation. These findings indicated that precursors and formation pathways for HNMs and THMs are not the same. Increases in pH and bromide concentrations increased HNM and THM formation during ozonation-chlorination and THM formation during chlorination. The bromide effect shifted the formation of HNMs and THMs toward brominated species, with its impact being greater in the treated than raw water. On the other hand, there was no pH or bromide effect on HNM formation during chlorination. The presence of nitrite increased HNM formation under both chlorination and ozonation-chlorination conditions, but it had no influence on THM formation. HNM formation during ozonation-chloramination remained about 1 microg/L level even at the highest bromide and nitrite concentrations. Monochloramination alone did not form any measurable HNMs. The results indicated that the use of chloramine can be an effective way to minimize HNM formation at typical drinking water treatment conditions.