Formation of halonitromethanes, dichloroacetonitrile, and trichloromethane in the presence of E. coli and nitrophenols during UV/post-chlorination.

Nitrophenols and E. coli widely coexist in surface water and can form chlorinated disinfection byproducts (Cl-DBPs) in chlorine-based disinfection processes. However, the coexistence of nitrophenols and E. coli affecting Cl-DBPs formation has not been reported. Herein, the formation of chlorinated halonitromethanes (Cl-HNMs), dichloroacetonitrile (DCAN), and trichloromethane (TCM) in the simultaneous presence of nitrophenols and E. coli was investigated in the UV/post-chlorination process. Results indicated the coexistence of nitrophenols and E. coli ((1-2) × 10 CFU mL) enhanced Cl-DBPs formation, but excessive E. coli ((1-2) × 10 CFU mL) dramatically inhibited that. Moreover, appropriate UV fluences promoted Cl-DBPs formation, and increasing chlorine dose and nitrophenol concentration enhanced that. Besides, alkaline pH decreased Cl-HNMs and DCAN formation but facilitated TCM formation. Subsequently, the Cl-DBPs formation mechanisms and pathways were explored in the simultaneous presence of E. coli and nitrophenols. When nitrophenols and E. coli were present in real waters, more complicated formation phenomena of Cl-DBPs were observed compared to those in simulated waters (SWs). Finally, Cl-DBPs generated in real waters exhibited lower toxicities than those generated in SWs. This study provides new insights into Cl-DBPs formation in the presence of organic substances and bacteria, simultaneously contributing to a better UV/post-chlorination process application.