Research And Development Of Novel Cathodes For The Scaling-up Of Microbial Fuel Cell

With the increasing concern for energy and environmental problems,microbial fuel cell(MFC)is experiencing rapid development as a kind of novel technology for simultaneous wastewater treatment and energy recovery.There are two strategies for making large-scale MFCs:(1)MFC stacks,which means combining several small or meadium sized MFCs to be a stack,and(2)individual large-scale MFC,which means enlarging the size of an individual reactor.Air-cathode MFC is the optimal choice for scaling-up,and air-cathode is the key factor for system performance and cost.As a result,it's significant to research and optimize the type and structure of cathode during the scaling-up of MFC.In regard to MFC stacks,graphite felt-activated carbon cathode(GF-AC)was prepared with graphite felt(GF)as the matrix and activated carbon(AC)as the catalyst.The loading of catalyst and PTFE in the gas diffusion layer(GDL)was optimized in typical small-scaled MFCs,and the feability for the application of GF-AC cathodes in MFC stacks was examined through water pressure tolerance test and operation in medium-sized MFC reactors.The results demonstrated that the optimal preparation loading for catalyst and PTFE in the GDL were 20 mg·cm-2(AC)and 80 mg·cm-2(PTFE),respectively.Meanwhile,the maximum power density(MPD)of small-scaled MFC(28mL)was 1472.3±10.6 mW·m-2 initially and decreased by 6.0%after 3-months operation.Furthermore,the initial MPD of MFC with GF-AC cathode was 28.7%higher than that with nickel foam-activated cathode(NF-AC),and the cost for per power generation of the former was 220.9 ?·W-1,which was 6.6%lower than the later,indicating the outstanding power generation performance,stability and cost-efficiency of GF-AC cathode.In addition,medium-sized MFC reactor with GF-AC cathode showed impressive stability in long-term operation,as 340mL MFC generated 136.2 W·m-3 after 4-months operation and 4.5L MFC generated 6.5W·m-3 after 2-months operation.Therefore,it's suitable for GF-AC cathode application in MFC stacks.In regard to individual large-scale reactor,stainless steel mesh-activated carbon cathode(SSM-AC)was prepared with stainless steel mesh(SSM)as the matrix and activated carbon(AC)as the catalyst.Meanwhile,a columned pressure MFC reactor was fabricated by connecting water tube with typical 28-mL small-scale MFC in order to imitate large-scale reactor,and the coupling effects of water pressure and binder content in the catalyst layer(CL)were researched.The results illustrated that increasing PTFE binder content appropriately benefited the power generation of pressure MFC and cathodes,while hardly influencing the start-up process of MFC and the performance of corresponding anodes.Furthermore,increasing hydraulic pressure resulted in the improvement firstly but degeneration later of power generation.The existence of optimal hydraulic pressure for the cathodes in LSV and MFC was resulted by oxygen permeability of cathode,consumption of substrate,water flooding of cathode and etc.simultaneously.In addition,the start-up process of MFC was prolonged and anode performance was decreased with the increasing of hydraulic pressure,which was caused by the environmental change for the inoculation bacterium,oxygen permeability,the inhibition of bacterial metabolism,and relatively low substrate,concentration under high hydraulic pressure.Moreover,dual-CLs structure benefited the electricity output and stability of SSM-AC cathode in MFC,and it was beneficial to diminish the effects of hydraulic pressure on cathode performance.The benefic dual-CLs structure was prepared by relatively fewer PTFE binder inthe outer CL(facing the solution side)and relatively more PTFE binder in the inner CL(facing the SSM side).The pressure MFC with dual-CLs cathodes(DP3P2,the mass ratio of AC and PTFE was 12:2 in the outer CL,and 12:3 in the inner CL)generated an average MPD of 1502.7 ± 52.1 mW · m-2 intially,which was 1.7%higher than that with single-CL cathode.Meanwhile,the average MPD of MFC with DP3P2 cathodes decreased by 15.8%after 3-months operation,which was 9.5%higher than that with single-CL cathode,as the average MPD of MFC with single-CL cathodes decreased by 21.7%during that time.What's more,the power generation of DP3P2 MFC reduced gradually with the increasing of hydraulic pressure,and the MPD was 1564.8 ±47.8 mW,m-2 in the 12th day under hydraulic pressure of 250mmH20.Dual-CLs SSM-AC cathode could maintain effective long-term operation under high water pressure of 2000 mmH2O and generated relatively considerable electricity output,as a result,it's suitable for SSM-AC cathode application in individual large-scale MFC.