Efficiency And Mechanism Of Microbial Fuel Cell Coupled Fenton System For Simultaneous Degradation Of Excess Sludge And Organic Pollutants

With the increasing of waste water treatment plants in operation year by year in China,the production of excess sludge also increases.Effective disposal of excess sludge and advanced treatment of organic pollutants treatment have become an urgent environmental problem.The excess sludge in the anode chamber of microbial fuel cell（MFC）can be utilized by electroproducing bacteria attached to the electrode,and the electrical energy transferred to the cathode chamber for electro-Fenton（EF）reaction treatment of the target pollutants in the cathode chamber.A microbial fuel cell powered electro-Fenton（MFC?EF）system is formed to realize simultaneous sludge degradation and treatment of refractory pollutants in the cathode chamber.In order to strengthen the target pollutant treatment in the cathode chamber of the coupling system,as well as the anode electricity generation and sludge degradation,a new Fe-Mn-Mg/CF composite electrode was prepared by introducing Fenton-like catalyst manganese and alkaline earth metal magnesium on the basis of Iron Fenton catalyst.In addition,2-bromoethyl sulfonate（BES）and lysozyme（LZ）were introduced into the anode chamber to optimize the anode substrate additives,and the influence of their single/combined addition on the system performance was discussed.The enhancement effects of cathode materials and anode substrate additives on the performance of MFC?EF coupling system were investigated from the aspects of electrochemical performance,organic matter removal,anode microbial community structure and metagomenome.In the study of the influence of different types of cathode materials on the system,a novel Fe-Mn-Mg/CF composite electrode was innovatively proposed.The new composite electrode has larger loading capacity and surface roughness,which is beneficial to increase the contact area and mass transfer efficiency,and improve the efficiency of electricity generation and pollutant treatment.The working voltage of the MFC?EF coupling system where the Fe-Mn-Mg/CF composite electrode is located has a significant increase,indicating that the addition of iron,manganese and magnesium in the Fe-Mn-Mg/CF composite electrode has a more significant increase in the working voltage of the coupling system than the single/bimetal iron load.Fe-Mn-Mg/CF composite electrode improves the cathode potential and the voltage of the battery by improving the cathode performance.The Fe-Mn-Mg/CF composite electrode effectively reduces the cathode reaction resistance,increases the output power of the battery,and improves the power generation efficiency of the coupling system.Fe-Mn-Mg/CF composite electrode has the highest hydrogen peroxide production rate,increased the rate and cumulative concentration of H₂O₂ production in-situ in the cathode chamber,thus improving the production efficiency of H₂O₂.In addition,due to the loading of Mg,it promotes the generation of superoxide radical in the system,thus accelerating the degradation of the target pollutant at the cathode.After optimized operation conditions,the aeration rate was 400 m L/min,the initial p H value of the cathode chamber was 3,and the external resistance value was 100ohm.Under these conditions,the degradation effect of the new Fe-Mn-Mg/CF composite electrode was only reduced by 7.1%after continuous operation for 100h.It is of great significance to reduce the actual operating cost and improve the application of the system.In the study of the influence of different anode substrate additives on the system,from the point of view of the system electricity production performance,adding BES as substrate additive alone has the best performance,MFC?EF startup time shortened by 42.3%,the maximum battery voltage increased by 23.1%,and the system has the highest coulomb efficiency.Adding LZ can adjust p H and conductivity of the anode sludge to a certain extent,which is beneficial to microbial growth and anode electricity generation.CCD model calculation shows that the coulomb efficiency of MFC?EF coupling system is the highest（14.81%）when LZ dosage is40.41 mg/g TS,BES dosage is 27.03 mmol/L and LZ+BES dosage is 7.95 d.The addition of LZ can quickly trigger the acid production of residual sludge,and the acetic acid concentration can reach 1048.25 mg/L on day 6.In the combined LZ+BES strategy,LZ could release more low carbon volatile fatty acids from sludge degradation,and BES could inhibit the growth of methanogens and provide more available small molecule acids for electrogens.H₂O₂ concentration in the cathode chamber reached the highest（18.06 mg/L）when adding LZ+BES.It is 58.12%,35.29%and 98.19%higher than that of LZ,BES and control group alone.It only takes 6h to reach the highest H₂O₂ concentration,so as to achieve fast and efficient electricity generation at the anode through the cooperative regulation of sludge and microorganism,and reach the cathode through the external circuit to participate in the electrofenton reaction,and produce a large amount of H₂O₂ at a high rate.Complete the system level of electron generation,transfer and utilization process.The species diversity of anode biofilm decreased slightly after substrate additives were added.The microbial community structure was affected by different substrate additives.Proteobacteria related to electricity generation,Firmicutes,Chlorobacteria and Actinobacteria related to organic degradation are the dominant bacteria in anodic biofilms.Adding LZ+BES can effectively accelerate the formation of anode biofilms and stabilize the community structure,and domesticate the electricity-producing bacteria to the dominant bacteria,thus improving the performance of the system.The new cathode produced more·OH in the electro-Fenton reaction in the cathode chamber,which promoted the degradation of the target pollutants in the cathode chamber.When the new cathode material was loaded,hydroxyl radical and superoxide radical were formed at the cathode interface in the electro-Fenton reaction.·OH’s contribution to SA degradation was 3.76 times that of·O₂^-,which was the main free radical for the degradation of target pollutants in the cathode chamber of the system.COG and KEGG pathways and methanogenesis annotation demonstrated that the combination of LZ+BES significantly inhibited the compilation of heterodithiulatase A subunit responsible for final methanogenesis,thus inhibiting methanogenesis in the MFC?EF coupling system in the metabolic pathway.LZ+BES adsorbed specifically on the electrode surface and improved the abiotic capacitance of the electrode.The Frumkin effect produced by adding LZ+BES could accelerate the electrochemical reaction of the anode.The results show that the new Fe-Mn-Mg/CF composite cathode can greatly enhance the degradation of the target pollutants in the cathode chamber,while the combined addition of 2-bromoethyl sulfonate and lysozyme to the anode sludge can enhance the power generation capacity of MFC?EF and sludge degradation.This method provides a new idea and method for enhancing the simultaneous degradation of residual sludge and refractory pollutants in catalytic oxidation secondary effluent by MFC?EF system with residual sludge as substrate.