Research On The Flow Field And Mass Transfer Kinetics In A Hybrid Oxidation Ditch

In biological wastewater treatment, the establishment of mathematical model andflow field analysis are very important methods to understand the mechanism of thesystem and control the reactor. Although activated sludge and biofilm processes havetheir fully mathematical models, it does not have any fully mathematical models for thenovel hybrid biological system. For the hybrid biological system, the research ofmathematical models mostly focuses on the analysis ofK Laor substrate degradation.Thus the research on the whole system is relatively few. And because there are twokinds of microbial cells existed (suspended state and attached state) in hybrid biologicalsystem, it cannot directly uses any of the existing activated sludge and biofilmmathematical models. Therefore, it has a great significance to establish mass transferkinetics model of hybrid biological system and flow field analysis for understanding itsmechanism and assisting the process control and technology development.In use of procedure analysis and hypothesis on hybrid biological system, this papersimplified hybrid biological system to a mass transfer-reaction process withgas-liquid-solid three-phase relationship, in this context, achieved the generalmathematic model of hybrid biological system; combined the hybrid oxidation ditch’sactual situation to simplify the general mathematical model and established to a moresuitable one-dimensional diffusion-reaction kinetics model, the basic mathematicalequations are as follows:Basic equation of mass transfer between gas-liquid:Basic equations of mass transfer and reaction in gas-liquid-solid three phases: By analysis established model of hybrid oxidation ditch system. It can be get themain factors on mass transfer and reaction of hybrid oxidation ditch system aredissolved oxygen, biomass and hydraulic retention time. By clear water oxygenationexperiment and orthogonal experiment, the optimal condition for system on masstransfer and reaction is that volume radio of suspended biological fillers is30%,HRT=10h, SRT=25d, use joint aeration (revolving speed of down-umbrella aeration is58.5r/min, microporous oxygen is80L/h),and use intermittent aeration at night.By numerical simulation and testing the flow flied, after adding fillers, it has agreat effect on original flow field, which has increased local of turbulent dynamic andthe hydraulic shear force of the system, changed speed distribution system original.However, most points on speed changed trend of the system are close, which still existvelocity distribution. It can be know that natural flow of the oxidation ditch is still inworking.By analysis on flow field and mass transfer reaction, it can be found that suspendedfillers flowing with mixed liquid in the oxidation ditch mobile rather than fixed incertain areas are more conducive to mass transfer and reaction of gas-liquid-solid threephases in system. Hybrid oxidation ditch can be met without increasing energyconsumption, and promoted mass transfer and reaction of gas-liquid-solid three phasesin system, which has a significance for upgrading of original oxidation ditch system.