Evaluation on disinfection by-products control by the conventional and O3-biological activated carbon process: Based on long term operation results.

The advanced treatment of ozone-biological activated carbon (O3-BAC) has been widely applied in drinking water treatment plants (DWTPs) globally. However, its performance varies greatly with source water quality and operation time. This study took three long-term operated DWTPs in East China with conventional and O3-BAC process as the research objects. The bulk water quality indices and disinfection by-products (DBPs) precursors in lake or river source waters and unit process effluent were detected monthly for one year. The lake source water has higher organic matter and less nitrogenous matter than river source water. The average removal of DOC, UV254, DON, trihalomethane formation potential (THMFP), N-nitrosodimethylamine (NDMA) and NDMAFP by each DWTP was in range of 30.2 %-39.1 %, 57.1 %-75.0 %, 36.4 %-61.6 %, 35.6 %-39.6 %, 87.6 %-94.0 % and 49.7 %-74.4 %, respectively. The O3-BAC process contributed less removal on these indices than the conventional part. Notably, the removal of BAC processes varied substantially among DWTPs, potentially linked to activated carbon media life (from months to 10 years), i.e. media replacing interval. As BAC media life increases, its adsorption performance gradually deteriorates, while biofilm development, biomass, and microbial activity increase greatly and the microbial communities show higher diversity. However, the enhancement of biological activity fails to compensate for the decline in adsorption of bulk organic matter, THMFP, and NDMAFP. This study highlights the critical impacts of source water and BAC media life on controlling DBPs and their precursors, providing key insights for optimizing drinking water treatment.