Trihalomethane (THM) formation from synergic disinfection of biologically treated municipal wastewater: Effect of ultraviolet (UV) irradiation and titanium dioxide photocatalysis on dissolve organic matter fractions

The trihalomethane (THM) formation of two synergic disinfection methods, UV/chlorination and TiO2 photocatalysis/chlorination, was evaluated to assess the health and ecological risks of biologically treated municipal wastewater. The effect of molecular characteristics of dissolved organic matter (DOM) from membrane bioreactor (MBR) and A2/O process treated municipal wastewaters was investigated. Results showed that THM formation was elevated in both UV/chlorination and TiO2/chlorination synergic disinfection processes compared to chlorination alone. The UV/chlorination process formed the most THMs. Both UV irradiation and UV/TiO2 photocatalysis were found to (i) degrade high molecular weight (MW) THM precursors to small fractions, and (ii) increase the amount of humic acid-like and fulvic acid-like components. Compared with UV irradiation, UV/TiO2 photocatalysis preferably degraded aromatic protein I, aromatic protein II and soluble microbial byproduct-like. Content of CO band and CO band in DOM after UV/TiO2 photocatalysis was lower than that after UV irradiation. In addition, specific THM formation potential of the precursors in the MBR-treated municipal water was higher than that in the A2/O-treated municipal water.