RISK EVALUATION OF PATHOGENS IN WASTEWATER RECLAMATION AS A DRINKING WATER SOURCE

Urbanized areas in Japan have suffered from the water shortage in recent years. The water shortage will become more serious due to the increase of the water demand and the irregular rainfall. The wastewater reclamation is recognized as one of the most effective countermeasures for the water shortage. However, the wastewater reclamation has a high infectious risk because a number of pathogens may exist in the wastewater. It is essential to develop in advance the wastewater reclamation system able to make up for the water shortage and in parallel to minimize the infectious risk. In this study, infectious risks by poliovirus 1 in the wastewater reclamation of the Abukuma watershed, Japan, were evaluated in three scenarios A-1, A-2 and B. In scenarios A-1 and A-2, the wastewater was reclaimed as a part of the drinking water source. A half of the shortage in the water resource was replaced by the reclaimed wastewater in the scenario A-1. All of the shortage was replaced in the scenario A-2. The wastewater was reclaimed only for toilet flush in the scenario B. The effect of the wastewater reclamation on reducing the damage from the water shortage was also evaluated. The damage was quantified by the product [%•day] of the percentage of the water shortage [%] and the period of the water shortage [day].The infectious risk did not increase in reclaiming the disinfected secondary effluent in all scenarios. When the secondary effluent without disinfection was reclaimed in the scenarios A-1 and A-2, annual infectious risks increased with the reduction of the damage from the water shortage. If more than 400%•day of the damage from the water shortage was reduced in the scenario A-2, the following relationship was obtained (R2=0.97):Y=0.00058•exp(0.0047•X), if X>400%•daywhere, X was the reduced damage from the water shortage [%•day] and Y was the annual infectious risk. According to this equation, reducing the damage of 850%•day brought ten times higher infectious risk than that in case of no reclamation (3.1 × 10−3).In the scenario B, the infectious risk in reclaiming the secondary effluent without disinfection was about six times as high as that in reclaiming the disinfected effluent.