To study the effect of combined ultraviolet (UV) chloramine disinfection on viruses in a drinking water supply system, a full-scale experiment was conducted to analyze the distribution, variability, community structure, and hosts of viruses using metagenomics. The results showed that the combined UV chloramine process reduced the number of virus species (6.13%) and gene abundance (51.97%) but did not completely remove the viruses from the water. The United States Environmental Protection Agency (USEPA) report that virus removal efficiencies from water can reach 99%-99.99% based on culturing methods. However, in this study, metagenomic analysis indicated a total virus removal rate of only 93.46%. Therefore, the detection of viruses in water using culturing method cannot reliably detect viruses in drinking water. Caudovirales are the most abundant type of virus in water supply systems and are sensitive to chloramine disinfection. Lentivirus, as a virus that can infect humans and vertebrates, has strong resistance to UV and chloramine disinfection. The main virus hosts in the studied water supply system were bacteria (61.50%). The viruses in the raw water were mainly parasitic in Synechococcus. The dominant virus host was Pseudomonas in both the effluent water and pipe network water. The gene abundance of the Pseudomonas aeruginosa host in the pipe network increased by 342.62%, which requires further attention as a virus risk in pipe network systems. Overall, combined UV chloramine disinfection was more effective at the removal of virus hosts than single UV disinfection (51.97% compared to 0.79%).
Keywords: combined ultraviolet chloramine disinfection; drinking water; metagenomics; virus community; water supply systems.