Quantitative microbial risk assessment of drinking water treated with advanced water treatment process

Campylobacter jejuni is one of the major causes of waterborne disease in Japan. A quantitative microbial risk assessment (QMRA) was conducted to evaluate the health risk caused by this pathogen in drinking water treated with a supposed advanced treatment process including ozonation and granular activated carbon adsorption. Coagulation-sedimentation, rapid sand filtration, ozonation, and chlorine disinfection are considered as the main microbial barriers of the process. The overall removal efficacy by four treatment steps was estimated to be the median and mean values of 11.1 log₁₀ and 10.4 log₁₀, respectively. The mean value of the yearly risk of infection was estimated to be 1.09 × 10⁻⁷ infection/person/yr. The sensitivity analysis shows that the complete removal of suspended solids and particulates in the source water is extremely important to stably produce safe drinking water. The uncertainty analysis demonstrated that the factor with large impact on yearly risk of infection was the hydraulic condition of ozone contactor. It can be pointed out that an accurate estimation for the dispersion number for full-scale ozone contactor is needed. Furthermore, data collection to determine the C. jejuni/Escherichia coli (C/E) ratio in the source water is highly required to improve the accuracy of the quantitative microbial risk assessment (QMRA).