Coupling Of Anodic And Cathodic Modification In Microbial Fuel Cells And Electrogenic Characteristics During Livestock Wastewater Treatment

In today’s world, renewable energy exploitation and environmental pollutioncontrol are the main problems to be faced for sustainable development. The swinewastewater is a typical kind of high-concentrated organic wastewater. And in China ithas become the third largest pollution sources following industrial pollution anddomestic pollution. Microbial fuel cell (MFC) is a novel device that useelectrochemical activity microorganism as catalysts to convert chemical energy oforganic compounds to electric energy directly, it has advantages such as high energyconversion efficiency, moderate reaction conditions and less pollution. The uniquepower generation mode of this technology makes it can recover electrical energy andcomplete waste disposal simultaneously, thus provides a new idea to resolve theenergy crisis and environmental contamination, and finally realizes win-win situation.Currently, MFC technology is still in its infant and its future is full of manychallenges. Among them, the main obstacle limiting the commercial and practicalapplication of MFC technology is the low power output. Therefore, it is essential toreduce the anode overpotential and cathode overpotential by modification of electrodematerials, further optimize and improve the MFC’s performance to achieve theexpected purpose.In this study, we tried to enhance performance of single-chamber air-cathodemicrobial fuel cell from modification of the anode and cathode. We also disscussedthe performance of swine wastewater treatment and electricity generation utilizingthis technology, and studied the synergistic effect of cellulose and swine wastewateron waste degradation and electricity generation，to ensure its early application in thefield of wastewater treatment and biomass utilization.First of all, the effect of properties of wastewater (COD concentration, pH, andconductivity) and external resistant on the performance of MFC was investigated. Theoutput voltage of MFC increased with COD concentration, and the operated periodalso prolonged. When the COD concentration increased from1240mg/L to8248mg/L, the maximum output voltage heightened70mV, the cycle time prolonged from 17h to77h. The power density enhanced with the increase of pH. Meanwhile, CODremoval efficiency and coulomb efficiency improved. When the pH value of thewastewater was6.0,8.0and10.0, COD removal efficiency was64.7%,71.2%and78.6%, respectively. Compared to the performance of MFC at pH=6.0, the maximumpower density and the coulomb efficiency was enhanced by75.8%and131%separately. The addition of electrolyte increased the solution conductivity whichresulted in a higher power density. Power output was enlarged by1.26times when theNaCl concentration increased from0mM to200mM. The smaller the externalresistance, the greater the current in the circuit, and the higher COD removalefficiency. The COD removal efficiency reached the best (71.5%) in short circuit.Secondly, we optimized the chemical reduction modified method of the carbonmesh anode by hydrazine hydrate and compared with the anode which was modifiedby nitric acid. The MFC which using30%hydrazine hydrate-modified anode(CM-30%) showed the best performance. Compared to the unmodified control(CM-0%), the acclimation time of MFC with CM-30%anode was reduced by30%,the maximum power density increased by30.7%, and the coulomb efficiencyimproved by24.3%. The internal resistance decreased from231to176. Insubsequent experiments, the maximum power density of MFC which using the anodemodified by nitric acid (CM-NA) and the optimized hydrazine hydrate (CM-HA)increased by24%and19%, respectively. According to analysis, the modificationincreased the specific surface area of carbon mesh, added the reaction active sites,changed the nitrogen oxygen functional groups on the surface of material, improvedthe electrochemical performance of the electrode, accelerated the rate of electrontransfer between the anode and the microbes. Consequently, the overpotential of theanode was decreased and the overall performance of MFC was enhanced. CV testsshowed that the anodic biofilms on the modified electrodes had better electrochemicalactivity.We also used nitric acid or hydrazine hydrate to modify the air-cathode with Pt.LSV tests showed that the air-cathodes after modification had larger current response.These results illustrated that the modified cathodes had excellent catalytic activity forthe oxygen reduction reaction. The cathodic reaction rate was accelerated, the overpotential of the cathode was decreased. And therefore the electricity productionperformance of MFC was improved. The maximum power density of unmodifiedMFC reactor (CM-CC/Pt) was655±7mW/m~2，that of the MFC reactors with nitricacid-modified cathode (CM-NA/Pt) and hydrazine hydrate-modified cathode(CM-HA/Pt) increased by24%and21%, respectively.Using the modified anode and the modified cathode in the same MFC reactor, itwas proved that there was coupling function between anode and cathode. Comparedto cathodic modification alone or anodic modification alone, the electricity generationperformance of MFC could be further improved. The maximum power density of theNN reactor with both anode and cathode modified by nitric acid was905±15mW/m~2,which increased by38%compared with the unmodified MFC reactor (CC,655±7mW/m~2). That of the HH reactor with both anode and cathode modified by hydrazinehydrate increased by31%. The electrochemical activity of the anodic electricigens inthe MFC reactor with both anode and cathode modified was higher than that ofanode-or cathode-modified alone MFC reactors. Moreover, this coupling MFCreactors could further improve the treatment efficiency of swine wastewater and theability of electricity generation. When pH was10.0, the performance of MFC forwastewater treatment and electricity generation achieved optimal. The maximumpower density of CC reactor, NN reactor and HH reactor were573mW/m~2、792mW/m~2、759mW/m~2, respectively. So far, the highest power density was obtained bythe NN reactor using swine wastewater as substrate.In addition, we also proved the synergistic effect which was exist betweencellulose degradation bacteria in the swine wastewater and electricigens on the anode.Compared with the MFC reactor using swine wastewater as single substrate, althoughthe highest output voltage were both about350mV, the operational cycle of thesystem was prolonged from94h to199h after adding cellulose, and the degradationefficiency of cellulose was over90%. This study is important to recycle and utilizeswine wastewater and straw as resources in the future.