| In recent years,the microbial fuel cell(MFC)has attracted wide attention both at domestic and overseas because of its ability to convert chemical energy into electricity in organic pollutants.At present,the researches of MFC were mainly focused on the removal of pollutants and electricity generation.Although the effective use of the generated electricity of MFC to improve the efficiency of pollutant purification is the important direction of MFC research,the low voltage and current of MFC electricity generation still restrict the research progress in this field.In this paper,a MFC-biofilm electrode reactor(BER)coupled system was established for degradation of the azo dye Reactive Brilliant Red X-3B.In order to ensure a good removal result,BER device requires a certain amount of electricity,while the MFC device produces electricity when degrading the pollutant.The coupled system could reach the self-sufficiency state in electric power so long as to fully utilized these two characteristics.Meanwhile,the BER was used as the pretreatment part of MFC,with the use of electrochemical and biological action of BER to improve the biodegradability of inflow of MFC,the removal efficiency of refractory organic and the electricity production efficiency in MFC would be promoted at the same time,and realized the double coincidence of BER-MFC coupled system in matter and energy finally.In this study,first the X-3B removal efficiencies with different cathodeand anode structures in biofilm electrode reactors with different conditions were investigated;in addition,the electricity generation and removal characteristics of the MFC reactors with different co-substrates type,run time and double anode structure were studied;finally on the basis of the research experience of the above two parts,three different BER-MFC coupled systems were constructed.The system coupling condition and the relationship between electricity generation and removal efficiency were studied.A method for preventing voltage reversal in stacked MFCs was developed at the same time.The conclusions are as follows:1)In order to explore a BER optimal treatment effect,at the same time as the early stage of coupled system,the influences of different structure and materials of anode and cathode on BER were mainly studied;the control conditions for the removal of X-3B in BER were optimized;the degradation mechanism of X-3B in BER was discussed.The results indicate that the main factor influencing the X-3B removal efficiency in the reactors with different cathode structures was the different internal resistances caused by the different cathode constructions.Using the DSA electrode as an anode increased the current in the system and improved the removal efficiency.With the optimized structure and operating conditions,the dye removal efficiency reached 75.70%when the inflow of X-3B was 200 mg/L.2)In order to explore a three-dimensional BER optimal treatment effect.Using the ACF/Ti and ACF/Fe as the anode and the cathode,respectively,to build a three-dimensional BER with the cathode filled with particle activated carbon(GAC).The results showed that the existence of the GAC in the 3D-BERs provided a greater area to which microorganisms could adhere,increasing the total number of microorganisms.Meanwhile,the GAC served as the third electrode,and the reductive reactions occurred on its surface.With the special flowed upstream way,the removal efficiency of 73.4%was still achieved when the influent concentration was 800 mg/L.The results of UV-Vis,FT-Irand GC-MS showed that the conjugated structure of X-3B was destroyed first and ruptured the azo bond,then generated the aniline,benzene rings,triazine rings,and naphthalene rings.Naphthalene rings and triazine rings were further degraded to hydrocarbons,aldehydes,and esters,while aniline was concurrently degraded to phenol.3)In order to assess the performance of electricity generation and removal efficiency,MFC reactors with different co-substrates type,run time and double anode structure were constructed.The results showed that the removal efficiency was higher in double anode MFCs with high X-3B concentration and short HRT than that in singleanode MFCs,while the higher voltage output was observed in doubleanode MFCs with short HRT.However,when the X-3B concentration exceeded 400 mg/L in the double anode MFCs,the activation polarize internal resistance increased that led to the total resistance increased and the maximum power density lowered.The performance of electricity generation was poor due to the metabolite accumulation which lead to internal resistance increased in the MFCs which operated a long time,while the removal efficiency was still higher than that in a new MFC.There was a significant difference in electricity generation rather than removal efficiency with the substrate tpyes.4)In order to reach the stable current output to ensure that the coupled system works properly after the MFCs series connection,electricity generation of two MFC series was investigated.There was an obvious difference in output voltage between the two MFCs,however,the voltage reversal phenomenon that is common in stacked MFCs did not occur.During the acclimatization stage in our study,single MFCs were connected to a smaller external resistance to obtain a higher current and the current change in the MFCs from high to low increased the current capacity to a certain extent was the reason.Therefore,voltage reversal in stacked MFCs can be avoided by increasing the current capacity via an acclimitazation stage,in which a smaller external resistance is connected to single MFCs.5)In order to investigate the running condition and the removal efficiency of BER-MFC coupled system,we constructed the system and investigated the X-3B removal efficiency in the match condition of matter and energy.The total output voltage was relatively stable within a range of 0.72-0.95 V and the current stabilized at approximately 0.20 mA.The highest observed power density was 0.257 W/m3 while the internal resistance was 1279.50 ?.The average X-3B removal efficiencies in the BER and MFC units increased by 14.90%and 14.97%,respectively,after coupling,improving the total removal efficiency by 29.87%.The results of current affected the removal efficiencies of the BER was found by changing the current in the coupled system,it was consistent with the conclusion in the first section.6)In order to investigate the running condition and the removal efficiency of BER-MFC coupled system,we constructed the system.The results showed that the total X-3B removal efficiency in the single MFC coupled BER system was basically the same as BER-series MFC coupled system.However,it had a higher power density.This was mainly due to the low internal resistance of the single MFC coupled BER system and there was no loss of an electron across a single cell.BER units was the pretreatment unit which degrade refractory organics into simple organic matter to maintain the MFC unit have the good electricity generation and removal efficiency with the condition of the co-substrate decreases.The total output voltage was relatively stable within a range of 0.24-0.32 V and the current stabilized at approximately 0.66-0.72 mA.The highest observed power density was 1.052 W/m3 while the internal resistance was 220.69 ? The average X-3B removal efficiencies in the BER and MFC units were 50.05%and 46.02%,the total removal efficiency was 96.07%.7)In order to investigate the running condition and the removal efficiency of three-dimensional BER-MFC coupled system,we constructed the system.The voltage and current of the coupled system stabilized at about 0.45 V and 0.4 mA at the X-3B concentration of 500mg/L.The results showed that the removal efficiency of the coupled system only increased by 7.91%than the control group at low X-3B concentration,while increased by 34.08%at high X-3B concentration.At the same time,the coupled system of three-dimensional BER and the single MFC had the advantage to remove the higher X-3B concentration.8)Combined with the results of UV-Vis,FT-Irand GC-MS showed that X-3B was actually broken down into more than 20 kinds of simple molecules in all three different coupled systems.X-3B was broken down into long-chain compounds in the BER unit initially,and those long-chain compounds continued to be broken down into simpler structures in the MFC.Although some substances existed in both units,the degradation products of X-3B in the MFC unit had simpler structures with lower molecular weights.The two units exhibited not only a coupled energetic relationship but also a progressive relationship in terms of the degradation of X-3B. |
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