| The dissolution of ozone into the liquid phase is controlled by liquid-film,and the ozone mass transfer efficiency mostly depends upon the interfacial area of ozone-liquid.Thus,microbubbles,which are characterized by huge interfacial areas,low rising velocity and high inner pressure,has received wide attention.However,the large-scale application of ozonation technology has been limited because of the low solubility,instability and high energy consumption of ozone molecule.Thus,this paper aims to compare the ozone microbubble processes via two different intake systems,and ultrasound was introduced into these systems to investigate the enhanced mass transfer mechanisms.The effects of ozone dosage,ozone intake flow rate,initial pH,medium temperature,ultrasonic power under different frequencies on dissolved ozone concentration were discussed.Besides,pCBA mineralization rates and Rct values under optimal operation parameters in each system were calculated to explain degradation mechanism.The study on the membrane aeration ozone microbubbles system showed that the optimal operating parameters are:ozone dosage 32.38 mg/L,intake flow rate 300 L/h,initial pH 7,temperature 293.15 K,and the corresponding KLa value was 0.58 min-1.Then,ultrasound was applied into the membrane aeration ozone microbubbles system,and results showed that the introduction of ultrasound can intensify ozone mass transfer efficiency effectively and a 47.38%of KLa value could be obtained in the presence of ultrasound(20 kHZ,1250 W).A novel ozone microbubble aeration system with a jet flow was designed.In this system,microbubbles can be generated by venturi,and both dynamic and velocity were provided by pump.In this reactor,microbubbles spiral up and the rotate diameter gradually decreased,and then this gas-liquid mixed phase cycle back to the inlet under the action of pump.Results showed:the intake flow rate of ozone is the key factor which can affect the dissolved ozone concentration and KLa value,and this is because the change of ozone intake flow rate can alter both the flow type and the circulation velocity in reactor;the optimal parameters in this system were:ozone dosage 32.38 mg/L,intake flow rate 50 L/h,initial pH 7,temperature 293.15 K,and the KLa value 0.6451 min-1 can be obtained.The saturated ozone concentration decreased but KLa value increased after the introduction of ultrasonic power,the maximum KLa value was 1.2894 min-1,which is about double of 0.6451 min-1.A batch of experiments were conducted to further investigate the ozone mass transfer and oxidation efficiencies in different systems,and the mineralization of pCBA were measured also.Charts showed that ozone and ultrasound have a favorable synergistic effect in both two different intake systems,and the maximum KLa value was 2.941,2.15,respectively.The degradation of pCBA followed pseudo-second-order kinetics equation and the pseudo-second-order kinetics coefficient in membrane aeration and jet flow is 0.2,0.6 mL mg-1 min-1,respectively,and the corresponding values of mineralization are 31.88%,61.95%.These two coefficients can be improved to 0.6,1.3 mL mg-1 min-1 when combined withultrasound(60 kHZ);the corresponding values are 55.58%?77.54%.The ozone decomposition rates in different operation conditions and Rct value in both ozone and ultrasound assisted ozone systems were calculated.Results showed that the introduction of ultrasound irritation can accelerate ozone decomposition rate,and ozone decomposition rate increased with increasement of ultrasonic frequency,which was in accordance with Rct value.The Rmt value in ozone alone system was 5.400×10-9,and when combined with ultrasound,Rct values were 1.180×10-8,1.336×10-8,1.440×10-8 with ultrasonic frequencies of 20,40,60 kHZ,indicating that a large number of OH· was produced with the irradiation of ultrasound,and the amount of OH· in liquid phase increased with increasing ultrasonic frequency. |
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