Gas-liquid Mass Transfer And Influence On Reaction Kinetics Of Ozone-based Advanced Oxidation Process In Bubble Column

The majority of fluid flow in natural world and practical engineering is multiphase flow, which plays an important role in the field of Three wastes treatment and chemical industry. The process of wastewater treatment is a classical multiphase flow system with fluid's mixture, mass transfer and biochemical reaction. So the flow regime, mass transfer and reaction kinetics can directly influence the biological treatment effect of wasterwater. The flow regime, mass transfer and reaction kinetics, of the multiphase flow system were investigated in this study.To study the multiphase flow regime and oxygen transfer in bubbling packed column, the effect of gas distributor style, sponge and ceramisite bio-medias on gas holdupεg, flow regime and gas-liquid mass transfer capacity was investigated. In the range of superficial gas velocity U, three apparent regimes were observed in the case of 81 holes (Φ1 mm) while no obvious transition regime in the case of 25 holes (less hole number) and 225 holes (less hole spacing). In churn-turbulent regime (U>0.118 m/s), there was no significant discrepancies in gas holdup among these three distributors. There was no obvious change in gas holdup as the sponge volume fractionε<25%, whereas the gas holdup reduced and transition regime emerged ahead at 35% volume fraction. In heterogeneous regime, the volumetric mass transfer coefficient kLa enhanced significantly in the presence of sponge. The gas holdup reduced in the presence of ceramisite and there was no obvious difference inεg as a function of volume fraction. In the ceramisite system, kLa reduced as a function ofεs. Compared with several aeration conditions, there were no significant differences in the oxygenation capacity per unit volume air, kLa/εg, which showed a minimal interval in the transition regime with 81 holes distributor indicating a lower oxygen transfer efficiency. At specific operation conditions, kLa/εg was almost constant, which was an important reference on deep understanding of the oxygenation capacity in the system where two kinds of bubble populations coexisted.The ozone treatment technology in two phase or multiphase is not only an advanced oxidation process, but also a process with mass transfer among phases. To study the kinetics of advanced oxidation processes in multiphase flow, Methylene Blue (MB) dye was used as simulated dying wastewater, taking ozone decolorization for example. The influence of activated carbon, buffered pH and hydroxyl radical scavenger on the decolorization was investigated. The results showed that the decolorization of MB was a pseudo-first-order reaction. The phase interface catalytic action of activated carbon could promote the decolorization. The reaction rate of decolorization increased with the concentration of Granular Activated Carbon (GAC) in the range of 3 to 15 g/L, and Powdered Activated Carbon (PAC) surpassed GAC in catalyzing decolorization. It was found that the decolorization rate increased obviously with buffered pH. The apparent rate constant in activated carbon system was twice as large as that in strongly alkaline system. Adding sufficient hydroxyl radical scavengers (0.003 mol/L) into the strongly alkaline buffer system (pH=12.7), the experimental data indicated that HCO3- overmatched t-butanol in scavenging hydroxyl radical. But ozone consumption rate in bicarbonate system is lower than that in t-butanol system.