Simultaneous Pollutants Removal And Electricity Generation Of Different Electron Acceptors In Microbial Fuel Cell

Environment pollution and energy shortage are two major challenges for human survival today.It is necessary to control environment pollution and develop clean energy for social sustainable development.Microbial fuel cell（MFC）is a new treatment technology,which has attracted much attention because it can simultaneously reduce pollution and generate electricity.For MFC,the cathode electron acceptor has a great influence on the performance of power generation and the pollutants degradation.In this work,two kinds of different acceptors are selected and then the corresponding MFC systems are established.The performance of power generation and degradation for the refractory wastewater was studied.Also,cathode modification was introduced to improve the degradation efficiency and then achieve the sustainable wastewater treatment.Firstly,based on the problem of low C/N ratio wastewater treatment with aerobic denitrifying bacteria,the BCS1-MFC system,which was denitrification system of oxygen resistant,was established with NO₃^-as electron acceptor and high efficiency aerobic denitrifying bacteria Cupriavidus sp.S1 as biocathode catalyst.In this paper,the nitrogen removal and electricity generation were investigated under different low C/N ratios and different external resistance when the concentration of NO₃^-was 100 mg/L,and then its mechanism was analyzed.The results showed that the performance of nitrogen removal and power production of the system were related to the C/N ratios and external resistance.At the R_ext of 1000Ω,TN of nitrogen-containing wastewater with C/N≥4 was almost completely removed,and the denitrification rate is greatly improved.However,the nitrogen removal was poor due to the limitation of organic concentration and electronic transmission at C/N=2.The external resistance was 100Ωat C/N=2 in this study,with an optimal total nitrogen（TN）removal efficiency of 95.71%,and a maximum current density and power density of 7583.89 m A/m³ and 932 m W/m³,respectively.The maximum tolerance of the system at R_extof 100Ωwas C/N=1,with a TN removal efficiency of 90.87%.Compared with the open circuit,the TN removal increased by approximately 21.60%and 52.02%at C/N=2 and 1,respectively.This study initially confirmed that the domesticated aerobic denitrification bacteria Cupriavidus sp.S1 can obtain electrons from the electrode for NOx reduction,which made up for the deficiency of organic shortage.Additionally,the system exhibits the obvious merits of less sludge production,low energy consumption,simple operation and the recovery of some energy.Based on these results,the nitrogen removal with aerobic denitrifying bacteria in low C/N nitrate-containing wastewater was achieved succefully by heterotrophic denitrification and electrochemical denitrification.Secondly,considering that low electricity production of the biological cathode,the potassium monopersulfate（PMS）with high oxidation-reduction potential was chosen as the cathode electron acceptor.A new idea of in-situ electrochemical activation of PMS in the cathode was proposed,and the PMS-MFC system was first constructed to improve the electricity generation performance of MFC.In this work,pure PMS（PPMS）and compound PMS（CPMS）were used as cathode electron acceptors of dual-chamber MFC.The effects of concentration and initial p H of PMS electrolyte on the electricity generation were examined.Also,the reduction mechanism of PMS was discussed,and finally the the simple application of the system was developed.The results demonstrate that the concentration and initial p H of PMS had an effect on the electricity generation,which increased with higher PMS concentration and lower catholyte p H.In the PPMS-MFC system,the maximum voltage（0.972 V）and power density（16.37 W/m³）were reached at 10 m M PMS and p H 3.0.However,the maximum power density（8.60 W/m³）was exhibited at 70 m M PMS and p H 3.0 in the CPMS system.Additionally,high COD removals of 99.41%and 98.71%in anode chambers were obtained in the two systems,respectively.Furthermore,Sulfate radicals（SO₄·^-）and hydroxyl radicals（·OH）were generated in stiu in the cathode to promote the reduction,which played significant roles in the improvement of electricity generation.Finally,the application of refractory organic pollutant removal in PMS-MFC system was carried out.When 500 mg/L Rh B was added to the cathode chamber at 10 m M PMS,Rh B was removed successfully with removal efficiency of100%and apparent rate constant of 0.058 min^-1 in PPMS-MFC system.The maximum voltage of 0.950V and power density of 15.22 W/m³ was obtained.This work confirmed that PMS,as an efficient electron acceptor,was actived by microbial electrochemical method in a MFC,and the system had great energy recovery potential in wastewater treatment.Thirdly,other factors on the power generation performance of PMS-MFC system were studied because of the difference of actual wastewater and operation conditions.The effects of inorganic anions,organic matter concentration and species of anode chamber,external resistance and high concentration Na Cl on the electricity generation performance of the system were investigated.The results indicated that different inorganic anions had different effects on the electricity generation of the system.The voltage output increased with higher organic matter concentration.Macromolecular organic matter had an inhibitory effect on the voltage output of the system at first,and then the power generation rose gradually due to the adaptability of microorganisms.The voltage decreased with the decrease of external resistance.However,the current,coulombic efficiency and the pollutants degradation increased with the decrease of external resistance.The effect of 100 m M Na Cl addition on voltage and power density output of CPMS-MFC system shows different trends.The maximum voltage output was related to the concentration ratio of Cl^-/PMS.When the ratio was 2～10,Na Cl played a positive role in maximum voltage output.Yet the negative effect was shown when ratio of Cl^-/PMS was less than1.5.Additonally,100 m M Na Cl addition caused adverse effect on maximum power output owing to faster PMS decomposition.These factors provided theoretical basis for PMS-MFC system in the actual wastewater treatment process.Finally,based on high power generation of PMS-MFC system,the coupling system of PMS/Cu Co₂S₄-MFC was established by modifying the cathode electrode with Cu Co₂S₄catalyst to improve the degradation rate of Rh B,which realized the sustainable and efficient degradation of Rh B and the recovery of electricity energy.The results showed that Cu Co₂S₄ synthesized by hydrothermal method was three-dimensional nano flake structure,which provided more active sites for redox reaction.The results of cyclic voltammetric curve demonstrated that Cu Co₂S₄（1:2:4）exhibited the best electrochemical performance.The loading amount of Cu Co₂S₄ catalyst,the p H of catholyte and the amount of PMS affected the degradation of Rh B.The high Rh B removal of99%and the maximum apparent rate constant of 0.118 min^-1 were achieved when 5 m M PMS at p H 7.0 was added in cathode chamber with 1.0 mg/cm²Cu Co₂S₄ adhered to cathode electrode after 45 min reaction.In addition,the stability of Cu Co₂S₄catalyst was evaluated.The service life of Cu Co₂S₄ catalyst in PMS activation was prolonged by the drive of MFC.After 5 cycles of operation,more than 99%Rh B removal could still be maintained,which was attributed to situ regeneration of Cu²⁺and Co³⁺by receiving cathode electrode electrons.In addition,the maximum voltages and power densities of the coupling system were 0.896 V and 0.804 V,4.75 W/m³ and 3.86 W/m³,when10 m M and 5 m M PMS were added in cathode chamber at p H 7.0,respectively.During the process of Rh B degradation,sulfate radical was the main active species,which is mainly activated by Cu Co₂S₄ and electrode electron.Therefore,PMS/Cu Co₂S₄-MFC coupling system provides a new strategy for the efficient and durable treatment of RhB dye wastewater.