Health Risk Assessment And Sensitivity Analysis Of Opportunistic Pathogens In Reclaimed Water Landscape Reuse

With the accelerating pace of reclaimed water reuse,the microbial safety problem in the process of reclaimed water reuse has become increasingly prominent.The presence of a large number of opportunistic pathogens in the secondary effluent of WWTPs poses potential risks to human health.In this study,two combined processes of coagulation sedimentation-NaClO disinfection and coagulation sedimentation-Ultrafiltration(UF)-NaClO disinfection were used as deep treatment processes.To explore the removal effect and mechanism of the combined process on Legionella,Pseudomonas aeruginosa,Mycobacterium avium and Escherichia coli in the secondary effluent.Taking Beijing Olympic Forest Park as the evaluation scene of reclaimed water landscape reuse,the health risk assessment and the sensitivity analysis of uncertainty factors were carried out on the opportunistic pathogens.The results showed that the combined process of coagulation sedimentation-UF-NaClO had a good removal effect on Legionella,Pseudomonas aeruginosa,Mycobacterium avium and Escherichia coli,the removal rates were 99.8%,98.6%,99.4% and 99.1%,respectively.There was 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 was no longer significant after the two combination processes.After secondary effluent coagulation precipitation-UF-NaClO disinfection and reuse for urban landscape leisure activities,the single exposure infection probability of the three opportunistic pathogens is the lowest,and the safety rate of human health can reach from 70.9% to 100.0%.In the landscape water body of Beijing Olympic Forest Park,the concentration of Legionella is the highest in summer,about 1 to 2 orders of magnitude higher than in winter.The concentration of Pseudomonas aeruginosa was higher in spring and summer,about 1order of magnitude higher than in winter.Mycobacterium avium has the highest concentration in winter and the lowest in summer,about 1 order of magnitude lower than in winter.The concentration of Escherichia coli is the lowest in summer and the highest in winter.The single exposure infection probability of Legionella is below 0.0560 to 0.1850,and the health and safety guarantee rate of human health is ranging from 37.7% to 66.5%.The single exposure infection probability of Pseudomonas aeruginosa is below 0.0450 to 0.0480,and the safety guarantee rate of human health is above 90.00%.The single exposure infection probability of Mycobacterium avium is below 0.0570 to 0.1300,and the safety guarantee rate of human health is ranging from 62.6% to 83.7%.The annual health risk of opportunistic pathogens exposed when boating on the lake and children play with water is the highest with Mycobacterium avium,followed by Legionella,and the lowest with Pseudomonas aeruginosa.When stacked water platform viewing,the infection risk of Pseudomonas aeruginosa is not considered,and the annual health risk of opportunistic pathogen exposure is that Mycobacterium avium is higher than Legionella.The results of sensitivity analysis showed that the annual risk value of Legionella infection in the three exposure routes were most affected by the uncertainty of annual exposure frequency,and in the stacked water platform viewing,attention should be paid to the exposed volume.The annual health risk value of Pseudomonas aeruginosa infection in both exposure routes of boating on the lake and children play with water were more affected by the uncertainty of the exposure volume and Pseudomonas aeruginosa concentration values.The annual risk value of Mycobacterium avium infection in the three exposure routes were greatly affected by the uncertainty of annual exposure frequency,and the influence of Mycobacterium avium concentration values should also be paid attention to in boating lake and children playing water.In addition,seasonal change and opportunistic pathogen removal rate were also affected the health risk assessment results of opportunistic pathogens.In summary,the coagulation sedimentation-UF-NaClO combination process can effectively control the concentration of opportunistic pathogens in the secondary effluent,and has low microbial health risk in landscape leisure activities.