Chlorinated disinfection by-product formation during DOM removal by discharge plasma: Insights into DOC structure alterations

Dissolved organic matters (DOM) are important precursors for chlorinated disinfection by-products (DBPs). Little information is available regarding correlations among DOM removal, DBPs formation, and DBPs-associated toxicity in the plasma process. In this study, four sources of humic substances (HAI, HAII, HAIII, and HAIV) were chosen as the targeted DOM, and their removal performances and DBPs formation were investigated. The removal efficiencies of UV254 for HAI, HAII, HAIII, and HAIV were 81.6%, 75.6%, 64.2%, and 79.5% after 60 min plasma treatment, respectively. Plasma oxidation resulted in conversion of high aromatic DOM to low molecular weight components. As a result, total DBP contents decreased by 68.1%, 59.4%, 41.6%, and 50.9% for HAI, HAII, HAIII, and HAIV after 60 min plasma oxidation, respectively. High aromatic components were the main pre -cursors of trichloroacetic acid (TCAA) and trichloromethane; lower molecular weight components contributed to chloralhydrate formation. Reactivity and contents of N played major roles in dichloroacetonitrile formation. Total calculated toxicities of DBPs derived from HAI and HAII decreased by 57.5% and 59.4% after 60 min treatment, respectively, while fewer changes were observed from HAIII and HAIV. Plasma oxidation significantly reduced C-DBPs toxicity, but more attention should be paid to N-DBPs toxicity with low C/N ratio.