Raw Water Treatment with Cl2 and ClO2:Comparison of Two Major Class of Disinfection By-Products Formation

Epidemiological studies have demonstrated the cellu-lar toxicity of trihalomethanes (THMs) and haloacetic acids (HAAs) that usually form during water treat-ment with chemical chlorine disinfectants such as chlorine and chlorine dioxide. THMs and HAAs formation potential of organic precursor in a surface water source for water treatment with Cl₂ and ClO₂ was studied with reference to key determinants. It was observed that the concentration of THMs and HAAs formed during ClO₂ treatment was significantly lower than that formed during Cl₂ treatment concentration that formed during chlorination. HAAs, dominated with bromo-HAAs were predominantly formed with a negligible amount of THMs during ClO₂ treatment. The combined total of HAAs and THMs formed dur-ing chlorine dioxide treatment was only 10–21% of that formed for chlorination. Among the HAAs spe-cies, dibromoacetic acid accounted for 86% of total HAAs during chlorine dioxide treatment whereas di-chloroacetic acid (36.7%) followed by dibromoacetic acid (20.4%) and bromochloroacetic acid (16.9%) were major constituent formed during chlorination. Species shift towards more toxic bromo-HAAs may pose a concern on shifting water treatment from chlo-rine to chlorine dioxide, particularly for bromide-containing water.