The Risk Assessment Of Pathogenic Microorganism For Wastewater Reuse And Reclamation

Wastewater reuse is one of the efficient ways to lessen water pollution and solve the lack of water in the city. Recent years, the wastewater reuse has become the studying key and tactic countermeasure of solving water shortage in the world. So it is important to study the influence of the reclaimed water on human health and the environment using the method of risk assessment.This paper first monitored the density of the coliform in secondary treatment effluent from a typical wastewater treatment plant, and then the removal efficiency of coliform and virus by conventional wastewater treatment techniques and chlorine and ozone disinfection was experimented. Many times test indicates that the density of total coliform and fecal coliform in wastewater fits log-normal distribution. Referring difference wastewater reuse standard, the probability of the reclamation water by wastewater reuse technical process and chlorine and ozone disinfection meets the quality standards was calculated, The coliform in secondary effluent presented high risk to human health and ecological environment; the probability of coliform in reclamation water by coagulation sediment and filtration process meets the reuse standards is 75.03% for corn irrigation and industry. But the safety of the coliform in the wastewater after chlorine disinfection and ozone disinfection for reusing is 100% which presented less risk to human health and ecological environment.Taking Coxsackie B3 virus as virological tracer, the characteristics of pathogen removal by chlorine disinfection, ozone disinfection, coagulation-sedimentation-filtration and ultrafiltration were studied. In order to compare the difference between the removal efficiency of bacteria and that of virus, total coliform and fecal coliform densities were also analyzed using membrane filtration method. The coagulation-filtration process and UF can remove approximately 21ogs CoxB3 virus; the chlorination almost has no effect of CoxB3 virus inactivation at the residual chlorine dose range l~6mg/L at pH 6 and pH 7.5; ozone disinfection remove approximately 41ogs of seeded CoxB3 virus when the ozone dose was 2.1mg/L with a contact time of 15min. However, the UF, chlorination and ozonation can almost achieve a complete removal of the total coliform and fecal coliform, while the coliform removal by coagulation-filtration process is about 31ogs. Experiments results indicated that the virus has a greater resistance to disinfection than bacteria.The experiments results show that the coliform of reclamation wastewater meet the standards does not indicate that the viruses also get a high removal, the effective disinfection process must be employed to achieve a high safety of reclaimed wastewater to assure the human health and environment.