Trihalomethanes formation potential in potable water from small waterworks in Chingmai and its reduction using optimal dosage of polyaluminum chloride

Abstract

The main objective of this study was to investigate trihalomethane concentration (THMs) and trihalomethane formation potential (THMFP) in raw water and in water supply from two small waterworks in Aung-Keaw and Mae-Hia case study. THMs in raw water was not detected while THMFP of average 253.32 and 251.52 ug/L were detected in Aung-Keaw and Mae-Hia waterworks, respectively. The characteristics of raw water (pH, alkalinity, turbidity, TOC, DOC and UV-254) were also determined. The average value of TOC were 2.61 and 2.05 mg/L, whereas DOC were 0.48 and 0.41 mg/L and UV-254 were 0.1277 and 0.1447 for Aung-Keaw and Mae-Hia reservoirs, respectively. THMs in water supply of average at 60.0 and 62.5 ug/L while THMFP of 40.2 and 46.4 ug/L from Aung-Keaw and Mae-Hia waterworks, respectively, were obtained. The results showed that average THMs were lower than such THMs standard (80 ug/L) proposed by US.EPA. TOC, DOC and UV-254 were also determined in the water supply, the relatively low value of these parameters were obtained comparing to those obtained in raw water. The second objective was to determine THMFP reduction using PACI as coagulant in Jar-Test experiments. The experiments were carried out under the condition of pH ranged from 6 to 10 and at PACI dosages between 0.5 to 5 mg/L. The results were indicated that the best condition of PACI coagulation for THMFP reduction was at the pH values of 7 for both Aung-Keaw and Mae-Hia water sources. THMFP can be sharply removed within the short range of PACI adding from 0 to 0.5 mg/L. It was found that THMFP can be reduced of about 70% at PACI dosage of 0.5 mg/L and THMFP reduction can be increased to maximum of about 95% at PACI dosage of 5 mg/L for the both water sources. Furthermore, the main THMFP species in raw water were Chloroform (CHC13) and Bromodichloromethane (CHCl2Br) of about 69.8% and 3.2%., respectively. In addition, the matrix correlations among surrogates for NOM (THMFP, DOC, TOC, and UV-254) were investigated. The results presented that THMFP and TOC was the good correlation (R2 = 0.9331). The correlation between THMFP and DOC as well as DOC and TOC was good level with R2 0.9257 and 0.9865, respectively. By contrast, UV-254 was not a proper parameter used to represent the quantity of NOM because very low of R2 were obtained.