Power generation and organic degradation performance of microbial fuel cell with biogas slurry

A dual-chamber microbial fuel cell (MFC) with biogas slurry from corn stover as anode substrate was studied in this paper to make the biogas slurry decrement, harmlessness and further utilization. The MFCs were constructed by a plexiglass vessel with each volume of 500 mL using carbon felt as anode materials. The deep river sewage was fed as inoculum accounted for 35% in initial cycle of the experiment. The power generation, chemical oxygen demand (COD) reduction and Coulombic efficiency (CE) of MFCs with different concentrations of biogas slurry were compared to investigate the effects of MFCs on degradation of biogas slurry and its energy recovery efficiency. The results showed the MFCs could start normally and remained a stable power generation using the biogas slurry as anode substrate. The maximum power density of the MFCs was 203.4 mW/m2 when the initial COD of biogas slurry was (3 618.6±55.6) mg/L. The other 3 maximum power density of diluted tests were 60.8, 36.6, 3.2 mW/m2, respectively. The maximum power density was decreased by linear with the COD concentration decreasing in biogas slurry, and the result of linear fitting was y = 0.0620x - 29.2348, R2 = 0.9567. With the decrease of substrate concentration, the internal resistance of MFCs was increased from 261 to 1 882 Ω, because the dilution of deionized water led to the decrease of conductivity of anode solution. Another reason was the microbial activity influenced by substrate concentration of anode. The higher substrate concentration could promote the enhancement of microbial electron transfer ability and increase the output power of MFC. The removal rate of COD was gradually decreased from 63% to 45% with the decrease of anode substrate concentration. The CE of the MFCs was 3.9%-7.6%, which were lower than other substrates, such as sugar and brewage waste water. The microbial community and diversity of biogas slurry, deep river sewage, anode carbon felt and anode solution samples were analyzed by Illumina Miseq sequencing. The microbial community analysis indicated the microbial community of the MFCs with biogas slurry from corn stover as anode substrate had a rational construction. In the anode of the MFC, the hydrolyzed bacteria mainly from biogas slurry could break down macromolecule to small molecules organics, mainly including Clostridia, Flavobacteria and Bacteroidia. Meanwhile, the anode biofilm could enrich the electroactive bacteria in the inoculation, and decompose the small molecules organics to generate electricity. The mutualism of two kinds of microorganisms could avoid high concentration inhibition in the MFC. In the anode carbon felt, 5% Pseudomonas was detected, which belongs to Gammaproteobacteria from deep river sewage. The Pseudomonas could generate a chemical intermediary that could transfer electrons to the electrode. For the MFCs with biogas slurry from straw as the anode substrate, the Pseudomonas could be artificially inoculated and enriched, to shorten the start-up time of the MFCs and improve the electrical production efficiency. The study showed that MFCs could effectively degrade organics in the biogas slurry from corn stover and generate electricity, which provides a new approach for utilization of biogas slurry. © 2019, Editorial Department of the Transactions of the Chinese Society of Agricultural Engineering. All right reserved.