Risk assessment of infection by giardia in effluent discharging river

Many wastewater treatment plants (WTPs) in China still discharge effluent into rivers and lakes. A quantitative microbial risk assessment (QMRA) of infection by Giardia was performed to determine the human health risks associated with the use of an effluent discharging river for recreational purposes, irrigation and source of drinking water in north China. The average public exposure to cysts was estimated, based on the concentrations, recovery efficiency, removal efficacy and disinfection efficiency. The exponential dose-response model was chosen to determine the probability of infection from ingestion of various numbers of cysts. The calculated risk of infection of swimming and irrigation was calculated as 1.62×10^-2 per person per year (pppy) and 1.48×10^-2 pppy, respectively, both of which were much higher than the acceptable risk of 10^-4 pppy. As for source of drinking water, the risk at the treatment using UV or ozone disinfection would meet the 10^-4 pppy, whereas those at the others using only chlorination were calculated as 1.56×10^-3, consequently can not meet the 10^-4 pppy. The result indicated that risk of Giardia infection by discharge of WTPs effluent should be considered.