The Removal Efficiency of Typical Opportunistic Pathogens by Advanced Treatment Process of Reclaimed Water and Health Risk Assessment

In this study, two combined processes of coagulation sedimentation-NaClO disinfection and coagulation sedimentation-ultrafiltration (UF)-NaClO disinfection are used as advanced treatment processes to explore the removal effect and mechanism of the combined processes on Legionella, Pseudomonas aeruginosa, Mycobacterium avium, and Escherichia coli in the secondary effluent. In addition, reclaimed water was reused in the landscape as an evaluation scenario, Monte Carlo simulation of the health risk of opportunistic pathogens in process effluent was carried out, and the microbiological safety of the two processes was evaluated. The results showed that the combined process of coagulation sedimentation-UF-NaClO has a good removal effect on Legionella, Pseudomonas aeruginosa, Mycobacterium avium, and Escherichia coli, and the removal rates are 99.8%, 98.6%, 99.4%, and 99.1%, respectively. There is a significant positive correlation between the concentration of Escherichia coli in the secondary effluent and the three opportunistic pathogens, but the correlation between the concentration of Escherichia coli in the effluent and the three opportunistic pathogens is no longer significant after the two combination processes. The three opportunistic pathogens has the lowest single-exposure infection probability after secondary effluent coagulation sedimentation-UF-NaClO disinfection and reuse for urban landscape leisure activities. The safety rate for human health may range from 70.9% to 100%.Practical ApplicationsReclaimed water reuse is an important way to alleviate the current water crisis. Common deep-treatment technologies include coagulation and sedimentation, filtration, activated carbon adsorption, disinfection, and so on. Using secondary effluent from municipal wastewater treatment plants as the treatment target, the researchers studied the reclaimed water treatment process through simulation tests. The researchers examined the correlation between opportunistic pathogens and E. coli. Comparing the traditional filtration process and ultrafiltration in terms of engineering and construction benefits, although ultrafiltration has a higher cost per unit of water volume, it has a smaller footprint, the advantage in land cost can completely offset the disadvantage in construction cost, and the effluent water quality situation is also improved compared with the traditional filtration process. In addition, in order to ensure the microbiological safety of reclaimed water reuse and landscape water, it is necessary to evaluate the risk to human health caused by opportunistic pathogens in secondary effluent and effluent from different deep-treatment processes using risk assessment techniques, and to propose corresponding safety assurance techniques and processes. Therefore, ultrafiltration is feasible as a treatment unit for deep treatment and can be used as a reference basis for practical applications.