Chlorine and chlorine dioxide oxidation of natural organic matter in water treatment plants
Kadir Özdemir
Abstract
The formation of trihalomethanes (THMs) during chlorine (Cl2) and chlorine dioxide (ClO2) treatment was investigated.Water samples were collected from three drinking water sources, namely, Büyükçekmece Lake water (BLW) in Istanbul City, Kızılcapınar Lake water (KLW), and Ulutan Lake water (ULW) in Zonguldak City, Turkey.The results of the study show that Cl2 treatment forms more THMs in all three water sources compared to ClO2 treatment.Further, due to the Cl2 treatment, the maximum THMs concentrations were observed in BLW (121.15 μg/dm 3 ) samples, followed by KLW (97.26 μg/dm 3 ) and ULW(88.52 μg/dm 3 ) samples within the reaction time of 24 h for 5 mg/dm 3 of Cl2 dose.However, it was found that the concentrations of THMs formed at three water sources with applied ClO2 treatment under the same conditions were significantly reduced.As a result of the ClO2 treatment at the end of the reaction time of 24h, THMs concentrations formed in BLW, KLW, and ULW were recorded as 30.26,16.53, and 17.71 μg/dm 3 , respectively.On chlorination, chloroform (CFM) was found the dominant THM species in all water sources.All THM species contents ranged from 1.98 µg/dm 3 to 11.23 µg/dm 3 and the highest level of dibromochloromethane (BDCFM) was observed as the major THM species among all species in BLW due to the ClO2 treatment.Also, the formation of inorganic DBPs such as chlorate (ClO3 -) and chlorite (ClO2 -) was evaluated during ClO2 oxidation.The levels of ClO2 -formed due to the ClO2 oxidation were higher than those of ClO3 -levels for BLW, KLW, and ULW samples and varied from 19 to 55%, and from 37 to 60% of the applied ClO2 doses (2-10 mg/dm 3 ), respectively.On the other hand, ClO3-levels varied between 5 and 9% and 2 and 6% of the applied ClO2 concentration for the KLW and ULW samples, respectively.