A dose optimization method of disinfection units and synergistic effects of combined disinfection in pilot tests

The increasing requirement for reclaimed water has made it necessary to utilize multiple disinfection processes for efficient removal of organoleptic indicators, while guaranteeing microbial safety. However, there is not a proper way to appropriately distribute the operation load between different disinfection units. This study provides a new method to optimize doses of sequential ozonation, ultraviolet (UV) irradiation and chlorine disinfection units, and investigates the synergistic effects of combined disinfection on the basis of pilot tests. In this method, the minimal ozone dose is determined first for the removal of colority. The chlorine dose is then adjusted according to the required residual chlorine. At last, since it has few side effects and relatively low operating costs, UV dose is determined by the remaining requirement of microbial indicator reduction. By this method, the effluent of disinfection could meet the discharge standards of colority, residual chlorine, and microbial indicators. The operating cost was reduced by 48.7%, mainly by lowering the ozone dosage. The production of disinfection by-products (DBPs) was effectively controlled by decreasing the chlorine dosage compared with the original working conditions in the plant. Moreover, ozone pretreatment effectively improved the coliform inactivation efficiency of chlorine, and the combined disinfection method alleviated the tailing phenomenon and achieved a higher maximum log reduction of coliforms. The proposed method can help water reclamation plants reasonably determine operational loads between disinfection units with low cost and guaranteed performance.