| Ozone is widely used in industrial wastewater treatment because of its excellent oxidation effect and no secondary pollution.The bubble tower is a common ozone contact reactor,and its treatment effect is related to factors such as gas source(flow rate,ozone concentration),liquid source(flow rate,properties of liquid phase),aerator(area,pore size,pore rate)and reactor structure,etc.When other conditions are certain,the structural form of the reactor has a greater impact on ozone transfer efficiency and treatment effect,mainly reflected in water turbulence,gas content distribution,bubble diameter,etc.There is no unified design specification for bubble-type ozone contact reactor.It is generally believed that increasing the working water depth of the reactor can reduce the bubble diameter,increase the contact area between bubbles and water,and extend the ozone residence time,thus improving the ozone utilization rate and wastewater treatment efficiency,but with the increase of water volume in the reactor,the ozone volume mass transfer coefficient and the average ozone concentration in water show a decreasing trend,and the ozone concentration in water is a key factor for the treatment of difficult to degrade organic matter,so increasing the water depth It is necessary to find a balance between ozone utilization and treatment effect.In this paper,the main structural parameters of the ozone bubble tower were optimized by numerical simulation(CFD)method with gas content,turbulence energy and ozone volume mass transfer coefficient in the reactor as the evaluation indicators,and on this basis,a new structure form of standpipe ozone bubble tower was proposed.The main research results are as follows:(1)Simulation and optimization of the main structural parameters of the continuous flow ozone bubble tower were carried out,including the height-to-diameter ratio(H/D),aeration head to bubble tower diameter ratio(d/D),and outlet location(left-in-left-out,leftin-bottom-out,and left-in-right-out on the basis of reverse flow),and the gas content,turbulent energy,and ozone volume mass transfer coefficient in the bubble tower were analyzed and compared under different structural parameters.It was clarified that the gas content rate and turbulence energy were most favorable to ozone mass transfer and the average ozone volume mass transfer coefficient was the highest when the height-to-diameter ratio was 3:1,the aeration head to reactor diameter ratio was 1:4 and the outlet was left inlet and outlet.(2)The simulation optimization of setting a partition in the bubble tower was carried out,including the partition spacing,position,installation angle and length.By comparing the changes of gas content,turbulence energy and ozone volume mass transfer coefficient in the bubble tower with different solutions,it was clear that the highest ozone mass transfer efficiency was achieved when a partition was installed at 1/2 of the total height of the bubble tower,the installation angle was 30° and the length was 1/2 of the diameter of the bubble tower,and the average ozone volume mass transfer coefficient was increased by 22.3%compared with that of the empty tower.(3)A new structure form of standpipe type ozone bubble tower is proposed.By setting a standpipe on the reaction column at a certain height,the height of the standpipe can be adjusted according to the aeration pressure,and the water is fed and discharged from the standpipe,which has the feature of increasing the water depth but not the water volume,and the average ozone concentration in the reactor increases instead of decreasing,thus improving the treatment efficiency.(4)The numerical simulation of a standpipe ozone bubbler was carried out for three schemes with 6,4,and 2 m standpipes on a reaction column of 2,4,and 6 m height,respectively.The results showed that the gas content,turbulence energy,percentage of high efficiency zone,and average ozone volume mass transfer coefficient in the ozone bubble column with standpipe were better than those without standpipe,and the average ozone volume mass transfer coefficient of the three schemes were improved by 23.2%,20.4%and 18.2%,respectively.(5)The experiments compared the treatment efficiency of the above three schemes of standpipe ozone contact reactor.The results showed that when the aeration flow rate was 15 L/min,the influent flow rate was 1 L/min,the ozone concentration was 55 mg/L,and the reaction time was 40 min,the average ozone concentration in the water was increased by 9.6%,7.4%,and 5.8%,and the COD removal rate was increased by 13.0%,9.9%,and 4.9%,respectively,compared with the ozone bubble tower without standpipe.13.0%,9.9%and 4.9%,and the time to achieve the same decolorization rate was shortened by 19.2%,23.3%and 11.1%,respectively.Among them,the average ozone concentration and hydraulic retention time in water of the bubbler column with 4 m standpipe on a 4 m high reaction column were moderate,and the highest COD removal rate was achieved,which may be due to the better balance between the average ozone concentration in water and the hydraulic retention time of this solution. |
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