The 11th International Conference on Water Resource and Environment (WRE 2025)

Abstract: Disinfection by-products (DBPs), formed from biofilm extracellular polymeric substances (EPS) and organic matter during regular disinfection practices in drinking water distribution systems, poses a potential threat to drinking water safety. However, the diverse DBP formations induced by the intertwined organic matter and bacterial EPS remains elusive.
In this study, we investigate both disinfectant methods and divalent ions on DBP formation in simulated drinking water distribution system (DWDS). Biofilm analysis results revealed that at 0.5 mg/L of disinfectant residual, both Cl2 and NH2Cl were not effective to remove biofilms. As the disinfectant residual increased, biofilms could be eradicated by Cl2, while remaining biofilms were still present even under the highest allowable NH2Cl dose (4 mg/L). However, when Cl2 residuals reached 2 mg/L, DBP concentrations in bulk water increased sharply, with trihalomethanes and haloacetic acids being the most prevalent DBP species. In addition, divalent ions in bulk water can significantly inhibit DBPs formation. Mechanistically, divalent ions promote the complexation of negative charged groups and thus inhibit carbonaceous DBP formation, while the hindering chlorine substitution of hydrogen atoms on α-carbon and amine groups reduces nitrogenous DBP formation. Conversely, Ca2+ and Mg2+ could facilitate biosorption processes that increased the yields of DBPs. Both EPS and adsorbed algal organic matter can provide halogenated reactive sites for DBP formation, exhibiting diverse aromatic substances and unsaturated (lignin and tannins) compounds. Overall, this study provides insights into optimizing disinfection protocols for water utilities by balancing the benefits of disinfection application for biofilm control with minimized toxic DBP formation in DWDS.