Research On Performance Of Microbial Fuel Cell-flowable Electrode Capacitive Desalination

With the lack of fresh water resources,desalination has gradually become one of the important ways to solve the water crisis,the treatment technology of desalination was focused on thermal and reverse osmosis technology,However,the inevitable disadvantage was high energy consumption and high cost.Capacitive deionization technology as a new technology have been widely applied in the field of desalination applications due to a certain theoretical basis,but it’s important to improve the desalination efficiency.Recently the flowable-electrode capacitive deionization technology（FCDI）stands out due to its simple operation and higher desalination rate.The paper mainly explores the law of flowableelectrode capacitive deionization technology,and puts forward the concept of microbial fuel cell denitrification and electrogenesis to drive flowable-electrode capacitive deionization.In this paper,the capacity properties of four kinds of carbon materials as flowable-electrodes were compared with analyzing their specific surface area and pore structure,functional groups and adsorption kinetics.The results showed that the AC80 adsorption capacity of four carbon materials AC80、AC50、G400、AC was 64%,while the AC was 48% under the same operating conditions,The reasons for the discrepancy between AC80 and other materials was rich microporous and mesopores content,more developed pore volume,large specific surface area,less impurity。In contrast to the adsorption models of four carbon materials,the addition of ion exchange membranes of FCDI avoided the same ion effect and the diffusion of anions and cations,so that the amount of desalination and efficiency is larger than conventional CDI,while the addition of ion exchange membranes and the mobility of the carbon material electrode also cause the ions not to be solidly adsorbed on the carbon material,so the correlation coefficient of the simulated first and second kinetics is small.In order to investigate the effect of operating conditions on the desalination effect,the main considerations included voltage,flow ratio（intermediate chamber: cathode chamber: anode chamber）,flow rate,electrode spacing,two carbon materials ratio and multi-stage series or parallel.The results showed the most optimal processing parameters of FCDI were charged voltage of 1.4V,the low flow rate of 2.5ml/min,the flow ratio（intermediate chamber: cathode chamber: anode chamber）of 1: 2: 2,spacing between polar plate of 3mm,the single carbon materialofAC80,the desalination amount of multi-stage series was about 17% higher than that of the single module,however the desalination rate was reduced due to that the increasing distance of the ion.The selective removal of the single cation solution was investigated.The adsorption capacity of AC80 was prioritized by KCl> NaCl> CaCl2> AlCl3.The results showed that the smaller the radius of hydration was adsorbed in the single cation solution.The microbial fuel cell（MFC）was studied by nitrogen-doped graphenecatalyzed cathode,and the mechanism of denitrification,the output energy of microbial fuel cell（MFC）under different dissolved oxygen,the way of fuel cell parallel connection was studied.Experimental results showed: Compared with that of the bare electrode,microbial fuel cell voltage of nitrogen-doped graphene catalytic cathode increased by 50%,power density increased by 80%,electrogenesis was stable in the nitrogen removal process.the removal of ammonia nitrogen rate was the same,the removal time of ammonia nitrogen was shortened and The efficiency of ammonia nitrogen was improved.With the increase of dissolved oxygen（DO）in the cathode chamber,the microbial production performance was improved.After the DO concentration increased from 1mg/L to 4mg/L,stable output voltage of MFC was increased from 362 mV to 446 mV.With the increase of dissolved oxygen,ammonia nitrogen was degraded acceleratedly and nitrate quickly generate,When dissolved oxygen is 4mg/L after 75 h,the removal rate of NH₄⁺ was 91.7% and the accumulation of NO₃^-was 80.9mg/L.In the multi-stage series or parallel microbial fuel cell,the voltage and power density are improved,but the parallel production performance is more stable,combined with the flow electrode capacitive deionization technology,the efficiency of desalination was 30%.