Effects of Humic Acid and Bromide on Trihalomethane Formation during Water Disinfection with Chlorine

Abstract

Chlorination is one of the most important methods used in water disinfection. Chlorine reacts with natural organic substances in water and causes the formation of disinfection byproducts that might cause health problems. The predominant by-product of chlorination is trihalomethanes. Humic substances, which make up the majority of natural organic substances, are the primary precursors of trihalomethanes. In this study, the effect of different doses of chlorine on the formation of chloroform, bromodichloromethane, dibromochloromethane and bromoform in the presence of natural organic matter and bromide in drinking water was evaluated. Artificial raw water samples prepared with the addition of 2, 3 and 5 mg/L humic acid representing natural organic matter were subjected to chlorination at doses of 1, 2 and 3 mg/L and analysed on the 0th, 3rd and 7th day. The only trihalomethane formed was chloroform with a concentration of 20.52-131.13 μg/L. Increased humic acid and chlorine levels resulted in increased chloroform content. Free chlorine in the water caused chloroform formation to continue even on the 7th day. Accordingly, the amount of chloroform formed increased with the contact time. While the chlorine dose was constant, increased humic acid resulted in decreased free chlorine. To evaluate the effect of bromide on trihalomethane formation, 200 μg/L bromide was added to 2 mg/L humic acid containing water, and 1 mg/L and 2 mg/L chlorination was applied. At the end of the chlorination process in bromide-free waters, only 23.46-41.90 μg/L of chloroform was formed. In the presence of bromide, chloroform, bromodichloromethane, dibromochloromethane and bromoform were formed and the total trihalomethane level increased to 50.03-85.59 μg/L. While the ratio of brominated trihalomethane increased, the amount of chlorinated species decreased.