Experimental Study On Scale-up Stacked Microbial Fuel Cells

Microbial fuel cell (MFC), which can take advantage of the microbes to catalystthe organic chemical directly into electricity, is an innovative wastewater treatment andenergy recovery technology.In this study, based on the analysis of the ohmic resistance and the flow state of thelarge size packing-type microbial fuel cell (L-MFC), a stacked L-MFC with a totalvolume of72L was designed. Besides, we made a study on the performance of itsvarious aspects, aimed to promote the engineering enlarge application of microbial fuelcells.The results included:(1) Due to the surface oxide film, titanium mesh had a decline in its conductivity;with the smallest contact area,0.45mm×20mesh titanium mesh had a minimumcontact resistance; when connected in parallel, L-MFC had a maximum power densityof34.62W/m3, higher than that of other connections; in the ohmic resistance of L-MFC,electrical conduction resistance was generally greater than the ion migration resistance,whose main source was the contact resistance between collecting material and electrode.(2) The actual hydraulic retention time (HRT) of L-MFC was generally longer thantheoretical one, due to the actual mass transfer between the electrode pore was notevenly distributed while the theoretical HRT was based on a fixed porosity. The flowstate in L-MFC was a kind of non-uniform flow that between plug flow and completelymixed flow, and the greater the flow rate was, the less degree the flow mixed, the moreclose to plug flow it was.(3) The internal resistance of stacked L-MFC in start-up period was about0.19.The maximum power density of MFC in parallel system, three-resistance system andfive-resistance system was47.25W/m3,30.55W/m3and50.45W/m3, respectively.When each MFC unit individually supply the power, the stacked L-MFC gets thehighest efficiency of electricity production. At the same time, when in parallel system,“internal current” could appear due to the difference in performance of each anode orcathode, and result in MFC unit’s polarity reversal. In addition, the higher the external resistance was, the greater the chance of polarity reversal there was.(4) The power density of MFC increased with the increase of the concentration ofCOD. When dealing with high or low concentration COD sewage, MFC infive-resistance system had the highest power density. When in continuous flow mode,the coulombic efficiency of MFC in five-resistance system was generally higher thanthat in parallel system, while the COD removal loads in two systems didn’t have muchdifference. The electrodes would block when packing type MFC in long time running.We could figure out the blocking situation and solve the problem with the method oftesting the waterhead in each cavity.