Study On Dynamic Behaviors Of Fluid Flow And Phenol Biodegradation Characteristics In Gas-Liquid-Solid Three-Phase Bioreactors

Phenol is a common pollutant in many industrial effluents, whose damage to the environment as well as to human beings has given rise to the worldwide concern about its effective treatment. Bio-treatment method, which can degrade phenol and then transform it into harmless substances through microorganisms'metabolism effect, has become one of the most popular phenol wastewater treatment methods. The experimentation, theoretical modeling and numerical simulation study on the local transient multi-phase fluid flow, interfacial mass transfer and biodegradation characteristics of the batch phenol biodegradation by immobilized Candida tropicalis in the gas-liquid-solid three-phase bubble column and airlift loop bioreactors, will definitely find its wide application in the field of phenol wastewater bio-treatment, as well as in the aspect of scientific learning of the complicated multi-phase bio-reaction process modeling.Firstly, the three-dimensional (3D) transient computational fluid dynamics (CFD) model has been set up for simulating the dynamic behaviors of the local hydrodynamics in the gas-liquid-solid three-phase bubble column and airlift loop reactors respectively, with multi size group (MUSIG) model adopted to describe the bubble size distribution behaviors. The local time-averaged hydrodynamics such as gas holdup and axial liquid velocity changing with the varied operating conditions such as superficial gas velocity, axial position and solid loading in the three-phase bubble column and airlift loop reactors are calculated through model simulations respectively, and the reliability of the model is validated through the experimental results obtained by conductivity probe and 3D Laser Doppler Anemometry. At the same time, the time and space distributions of the local transient hydrodynamics such as gas holdup, solid holdup, liquid velocity and bubble size in the three-phase bubble column and airlift loop reactors are reasonably predicted by the developed CFD model respectively.Secondly, the 3D transient CFD model has been set up for simulating the dynamic behaviors of the batch phenol biodegradation characteristics by immobilized Candida tropicalis in the gas-liquid-solid three-phase bubble column and airlift loop bioreactors respectively, coupling of the interactions of the three-phase fluid flow, species interfacial mass transfer and intrinsic bio-reaction, with the MUSIG model adopted to describe the bubble size distribution behaviors. The volume-averaged hydrodynamics, species mass concentrations and species interfacial mass transport source differences changing with the varied operating conditions such as superficial gas velocity, initial phenol concentration and solid loading in the three-phase bubble column and airlift loop bioreactors are calculated through model simulations respectively, and the reliability of the model is validated through the experimental results of the liquid phase oxygen and phenol mass concentrations obtained by DO electrode and HPLC. It is found that the species interfacial mass transfer is the rate-limiting step in the process through comparison between the species interfacial mass transport sources. At the same time, the time and space distributions of the local transient dynamic behaviors of the immobilized batch phenol biodegradation such as gas holdup, Sauter mean bubble diameter, liquid velocity, gas, liquid and solid phase oxygen mass concentrations, liquid and solid phase phenol mass concentrations, solid phase cell concentration and bubble size in the three-phase bubble column and airlift loop bioreactors are reasonably predicted by the developed CFD model respectively.At last, phenol biodegradation behaviors between the three-phase bubble column bioreactor and the three-phase airlift loop bioreactor are compared through CFD model simulations, which confirm that the airlift loop bioreactor has a more regular flow pattern, and a better phenol biodegradation performance compared with the bubble column bioreactor.