Optimization of ozone dosage in an ozone contact tank using a numerical model

Ozone has been widely applied in drinking water and wastewater treatment plants, and it is essential to determine the ozone dosage and its ratio in ozone contact tank to increase the ozone absorption and utilization rates. Batch experiments were performed to determine the first-order reaction rate coefficient of ozone (k1) in different raw water qualities. Results showed that k1 had an exponential decaying relationship with the ozone consumption amount (ΔO3). Based on the ozone mass transfer and decomposition kinetics, a numerical model was developed to optimize the total ozone dosage and its ratio in three aeration parts by calculating the ozone absorption and utilization rates in an ozone contact tank. The ozone absorption rate was little affected by the water quality, and an even distribution of ozone could greatly increase the ozone absorption rate. However, the ozone utilization rate was tightly related with the water quality. For waters that consumed ozone quickly, ozone should be dosed equally in three aeration parts to increase the ozone utilization rate up to 94.3%. Otherwise, more ozone should be dosed in the first aeration part. An increase in ozone utilization rate would induce an increase in the degree of water purification. This model could give theoretical support for the determination of ozone dosage and its ratio in water treatment plants rather than experience.