The Influence of Cu(II) on the Formation and Distribution of Disinfection By-Products during the Chlorination of Drinking Water

Abstract

The catalytic effect of Cu(II) on the formation of disinfection by-products (DBPs) and chlorine degradation during chlorination of humic acid (HA) solutions was comparatively investigated under different experimental conditions. The experimental results showed that the total organic halogen (TOX) and trihalomethane (THM) formation increased with increasing Cu(II) concentration during chlorination, while haloacetic acids (HAAs) increased insignificantly. Accelerated chlorine decay and increased TOX and HAA formation were observed at high pH in the presence of 1.0 mg/L Cu(II) compared with that observed at low pH but THM formation decrease. Furthermore, the Cu(II) effect catalyzed the formation of brominated DBPs as it did for chlorine analogues in the presence of bromide ion. The microcalorimetry analysis demonstrated that more DBPs were formed in the Cu(II)-catalyzed chlorination, in which second-order rate constants obtained from reaction of HA with chlorine under given experimental conditions were 0.00256 M−1 s−1 (without Cu(II)) and 0.00865 M−1 s−1 (with Cu(II)), respectively. To discriminately examine the role of Cu(II) in greater detail, nine model compounds, which approximately represent the chemical structural units of HA, were individually oxidized by chlorine. It was demonstrated that carboxylic acids significantly enhanced the formation of TOX, THMs, and HAAs in the presence of Cu(II). Based on the previously published information and our experimental results, the possible pathway for Cu(II)-catalyzed TOX, THM, and HAA formation from chlorination of carboxylic acids were tentatively proposed.