This study was carried out in the ozone (O3) and biological activated carbon (BAC) section of a drinking water plant to investigate the effects of O3 on microbial and effluent disinfection by-products (DBPs) in BAC during drinking water treatment. The water quality, dissolved organic matter (DOM) characteristics, microbial activity, and DBPs formation at different O3 concentrations were analyzed. Results showed that the effect of O3 on microorganisms is mainly that it increased the utilization efficiency of DOM. However, excessive O3 increased the amount of organic matter such as protein and microbial metabolites (SMPs) in the effluent. When the O3 concentration increased from 0 mg·L-1 to 2.0 mg·L-1, the survival rate of microorganisms in the BAC decreased from 95.10% to 62.60%. However, since O3 transforms organic matter into a biodegradable substance, we found that microbial activity increased by 62.52% and that the biofiltration of the BAC was enhanced. When the O3 concentration was further increased to 4.0 mg·L-1, the microbial survival rate decreased to 49.9% and the protein and SMPs produced by the microorganisms increased. This resulted in an increased formation of carbon-containing DBPs (C-DBPs) and nitrogen-containing DBPs (N-DBPs) by 41.93% and 7.18%, respectively. In summary, an appropriate dosage of O3 was beneficial for removing DOM by O3-BAC, but we found that an excessive O3 concentration caused the formation of new DBPs precursors.
Keywords: biological activated carbon (BAC); disinfection by-products; dissolved organic matter; microorganism; ozone.