Speciation and formation of iodinated trihalomethane from microbially derived organic matter during the biological treatment of micro-polluted source water

Water sources are micro-polluted by the increasing range of anthropogenic activities around them. Disinfection byproduct (DBP) precursors in water have gradually expanded from humic acid (HA) and fulvic acid to other important sources of potential organic matter. This study aimed to provide further insights into the effects of microbially derived organic matter as precursors on iodinated trihalomethane (I-THM) speciation and formation during the biological treatment of micro-polluted source water. The occurrence of I-THMs in drinking water treated by biological processes was investigated. The results showed for the first time that CHCl2I and CHBrClI are emerging DBPs in China. Biological pre-treatment and biological activated carbon can increase levels of microbes, which could serve as DBP precursors. Chlorination experiments with bovine serum albumin (BSA), starch, HA, deoxyribonucleic acid (DNA), and fish oil, confirmed the close correlation between the I-THM species identified during the treatment processes and those predicted from the model compounds. The effects of iodide and bromide on the I-THM speciation and formation were related to the biochemical composition of microbially derived organic precursors. Lipids produced up to 16.98 μg L−1 of CHCl2I at an initial iodide concentration of 2 mg L−1. HA and starch produced less CHCl2I at 3.88 and 3.54 μg L−1, respectively, followed by BSA (1.50 μg L−1) and DNA (1.35 μg L−1). Only fish oil produced I-THMs when iodide and bromide were both present in solution; the four other model compounds formed brominated species.