Numerous pathogens exist in treated wastewater, leading to possible population health and ecological security risks when treated waste water is reused or discharged. To investigate the influence of different patterns of discharge on microbial diffusion in the municipal treated waste water, high-throughput sequencing technology was used to analyze the bacterial community structure, dominant flora, and typical pathogens. It was found that those bacteria were distributed in 58 classes. There were 32 species with a relative abundance of more than 1%. While there were only 41 classes in the water sample taken as a direct discharge to the sea, and there were 28 species with relative abundances of more than 1%. The water sample collected as a discharge to the sea through a river displayed higher bacterial diversity than the sample collected as a direct discharge to the sea, indicating that the microorganisms in the treated waste water was more likely to diffuse in when directly discharged to the sea. The relative abundance of dominant bacteria decreased with an increase in the diffusion distance, while the relative abundance of Cyanobacteria increased as the diffusion distance increased. The relative abundance in the water sample collected as a discharge to the sea through a river was higher. The dominant bacteria in the two systems are to Proteobacteria, Bacteroidetes, and Firmicutes. However, the dominant bacteria at the class and species levels quite dissimilar in the two systems. The bacterial diversities near the outfall were much higher than that in the seawater (blank sample), and the abundance was higher, which related to sewage treatment. In addition, there was a certain amount of pathogens and potential pathogens, including Pseudoalteromonas haloplanktis and Pseudomonas anguilliseptica, which were highly pathogenic. Their relative abundances were still higher after dilution. Arcobacter spp. was related to human and animal diarrhea and bacterial and other diseases. Therefore, the detection of these types of bacteria when the treated waste water is discharged is very important.
Keywords: bacteria in water; community structure; diffusion; high-throughput sequencing; sewage treatment.