ABSTRACT
Objective To carry out the risk assessment on health effects of viruses in reused wastewater in city.Methods During May-November in2002,the concentration of total coliform and fecal coliform in water sample s collected from waste water after secondary treatment of wastewater treatment plant and reused waste water treated by conventional wastewater-reuse technical process in Xian Baishiqiao Wastewater Treatmen t Center were determined,and the hypothesis testing on the normal distribution of monitoring data was carried out.Meanwhile the removal efficacy of coliform in wastewater with chlorine disinfection was ob-served.The beta-Possion model,the model for evaluating the infection probability of pathogenic microorganism in drinking water,and Monte Carlo simulated method were used for the risk assessment on health effects of viruses in reused wastewater in city.Re sults The monitoring data on concentrations of fecal coliform in water samples collected from secondarily treated wastewater and reused wastewater showed log-normal distribution.The removal efficacies of coliform from wastewater were4log at condi-tions of7mg /L chlorine and20-minute contact time,and5log at conditions of15mg /L chlorine and20-minutes-contact time.The means of annual risk value of health effects of viruses in reused wastewater were1.21?10 -6 for the reuse of wastewater in greening and4.31?10 -8 for the reuse in irrigation of farmland respectively,the highest risk values for these two reuse methods were all below10 -4 ,the acceptable annual risk value for drinking water ruled by Surface Water Treatment Rules published by USEPA.The probability of annual risk value