Hydrodynamics Of Double-chamber Bioelectrochemical Systems Reactor

Bioelectrochemical system(BES)have received extensive attention as a new type of technology in the field of wastewater treatment.The basic principle of BES is that microorganisms act as catalysts to convert the chemical energy of organic matter in wastewater into electrical energy.Therefore,BES has the dual advantages of energy recovery and wastewater treatment.It is well-known that hydrodynamics plays an important role in electricity production performance of the BES.However,only scarce information is available to date.Considering that the mechanism of hydrodynamics affecting the performance of BES reactors is relatively complicated,the numerical simulation combined with experimental research is more helpful to illustrate the mechanism.In this work,residence time distribution(RTD)technology and computational fluid dynamics(CFD)simulation are adopted to study the hydrodynamics of the anode chamber,and the gas-liquid two-phase flow model is adopted to study the hydrodynamics of the cathode chamber.The major contents and conclusions of the research are as follows:1.Hydraulic characteristics of the anode chamber of BES reactors.The RTD curves obtained from the tracer experiments were conducted by both statistical quantitative analysis and qualitative analysis at four different hydraulic retention times(HRTs)to obtain the flow regime information of the anode chamber.It could be concluded that the large proportion of the dead zone existed inside the anode chamber,to imply that the hydrodynamic performance of the anode chamber were not good.In addition,with the decrease of HRT,the dead zone of the anode chamber got decreased,which suggested better hydrodynamic performance.Computational fluid dynamics(CFD)was used to simulate the flow field distribution inside the anode chamber,and the dead zone location mainly existed in the corner area far from the inlet and outlet.Then some measures,such as adding backflow device and baffle device,were adopted to optimize the flow regime of the anode chamber,resulting in the decrease of dead zone,to imply that hydrodynamics of the anode chamber got better with optimization measures.Finally,the results of the power generation experiment of the BES reactor demonstrated that the performance of the BES reactor got higher with better hydrodynamic performances of the anode chamber.Moreover,the addition of backflow devices and baffle plates could also improve the electricity production performance of the reactor.2.Hydraulic characteristics of the cathode chamber of BES reactors.The cathode chamber was set up for air cathode in which oxygen acted as electron receptor,and oxygen was supplied by aeration.The hydrodynamics of the cathode chamber would signifcantly affect flow field distribution around the electrode,exerting a pronounced effect the mass transfer and reaction process of oxygen near the electrode.The gas-liquid two-phase flow model in CFD simulation was used to simulate the hydrodynamics of the cathode chamber under different aeration conditions.The distribution of gas-liquid flow field and gas holdup rate was obtained by steady-state simulation under the Euler-Euler algorithm system.In this work,the effect of different operating conditions of the cathode chamber on hydrodynamics was investigated from four aspects:aeration intensity,relative spatial position of the electrode(carbon paper),bubble size and the number of aeration device.Combined with the influence of the oxygen diffusion flux through ion exchange membrane in the cathode chamber,the effect of different operating parameters on the hydrodynamics of cathode chamber could be concluded:Within a certain range,moderate aeration intensity(1 m/s),centered tilt angle of the carbon paper(45°),moderate bubble size(0.5 mm)and moderate quantity of aeration devices(two),had a more positive impact on hydrodynamic performance of the cathodic chamber,which was more conducive to oxygen mass transfer and reaction,and thus improved the performance of the cathode chamber..Therefore,it is very important to optimize the aeration conditions for the improvement of hydrodynamics of the cathode chamber.