Numerous microorganisms, especially pathogens, exist in treated wastewater, which leads to possible risk to population health and marine ecological security when treated wastewater is discharged into the sea. This study selects Maidao municipal sewage treatment plant as the location. The microbial community and the dynamic distribution and seasonal variation of pathogens are analyzed by high-throughput sequencing technology. The results showed that the microbes in the discharge were distributed into 20 to 27 phyla, and the dominant phyla were Proteobacteria, Firmicutes, and Bacteroidetes, which were mainly distributed in 44 to 65 classes. The predominant pathogens are mainly composed of Gammaproteobacteria, Betaproteobacteria, and Epsilonproteobacteria in the Proteobacteria category. The proportion of most dominant phyla and classes in the sample decreased with an increase in diffusion distance. There were mainly 55 species pathogenic bacteria in the water discharging into the sea. The pathogenic genes in the discharge were mainly related to cancer, cardiovascular disease, immune system diseases, infectious diseases, metabolic diseases, and neurodegenerative diseases. When compared with the blank samples, it was found that the biomass of pathogenic bacteria decreased sharply with the diffusion by the seawater, and most of the pathogens were not detected 1000 m away from the seashore. Arcobacter spp. caused human and animal diarrhea and bacteremia, Acinetobacter spp. caused nosocomial infections, and Shewanella hafniensis posed a threat to seafood farming and fishing. The three species of pathogenic bacteria mentioned above occupied a fairly large proportion of the discharge into the sea.
Keywords: diffusion; discharge into the sea; microbial community structure; municipal treated wastewater; pathogens.