Study On The Model And Optimization Of Ozone Contact Tank

Ozone-biological activated carbon process has been applied in 75 drinking water treatment plants in China until 2013. However, in the process of designing and operating the ozone contact tank, the total ozone dosage and the mass ratio of ozone in three stages is always determined without theoretical proof. Therefore, research on model for the simulation of ozone mass transfer and reaction kinetics in ozone contact tank has important practical significance.In this study, an ozone mass transfer and reaction model based on a bubble column was established. The model was validated by investigating the ozone mass transfer and oxidation efficiency of groundwater and synthetic water containing humic acid. On this basis, another ozone mass transfer and reaction model based on ozone contact tank was also established to put forward ways to optimize the total ozone dosage and the mass ratio of ozone in three stages.Based on this study, the following conclusions were drawn:(1) Based on the two-film theory and ozone reaction kinetics, ozone mass transfer and reaction model was established. Analytical solution of the model for the ozone reaction satisfied with first-order reaction kinetics was achieved. Numerical solutions of the model for the ozone reaction unsatisfied with first-order reaction kinetics were achieved based on organic matter consumption and ozone consumption, respectively.(2) Groundwater and synthetic water containing humic acid were used as the source water to validate the model. The results showed that when groundwater was used as the source water, the model could predict the outlet aqueous ozone concentration and off-gas ozone concentration precisely with the error within 20%. The outlet aqueous ozone concentrations increased with increasing inlet ozone concentration, gas flow rate and water depth, while it decreased with increasing water flow rate. The mass transfer efficiency of counter flow was higher than that of co-current flow under the same condition. When synthetic water containing humic acid was used as the source water, the ozone reaction process didn’t fit the first-order kinetics. When the model based on ozone consumption was used to verify the result, in which the relationship between ozone reaction rate and ozone consumption was exponential, the results were acceptable with the error within 18%.(3) A model of ozone mass transfer and reaction kinetics based on ozone contact tank was established, and analytical sensitivity was made. Ozone contact tank could be optimized based on this model. Firstly, the mass ratio of ozone in three stages could be optimized according to the maximum ozone utilization rate. Then the total ozone dosage could be optimized based on the outlet ozone concentration. The results showed that for three different kinds of water in the order of ozone-depleting rates from slow to fast, the mass ratios of ozone in three stage were 7:3:0, 4:4:2 and 4:3:3, and the total ozone dosages were 0.9~1.1 mg/L, 1.1~1.3 mg/L and 1.5~1.7 mg/L, respectively.In this paper, the total ozone dosage and the mass ratio of ozone in three stages could be optimized through determining the ozone consumption curve. The results had certain guiding significance on operating ozone contact tank in water treatment plants.