The Effects On Electricity Generation And Sediment Remediation By Solar Cell-microbial Fuel Cell Systems

Microbial fuel cell(MFC)is an emerging technique which can use organic matter as carbon source by microorganisms to transform the chemical energy in organic matter into electricity.In this study,the contaminated sediment was used as substrate in the anode and the modified carbon felt as electrode.We structured a solar cell-microbial fuel cell system through cascading solar panels into the ordinary microbial fuel cells.Under the synergy of solar cells,electricity generation,the removal efficiency of pollutants in the sediment and microbial communities on the surface of anode carbon felt were all changed greatly.After two runs,the results are showed as follows:(1)The cascaded solar cells could improve the initial voltage within 36 hours at the startup of microbial fuel cells.However,the voltage declined gradually over time and decreased along with the increasing rated voltage of solar cells.The biomass on the surface of the anode was tested by Lipid-P method and the results showed that the biomass of 1V SC-MFC systems was higher than the control group within the sartup 36 hours.In other words,it inferred that cascaded lower voltage solar panels could promote the growth of microorganisms and the formation of biofilms on anode felt.Conversely,the biomass of 2V SC-MFC increased slowly and was lower than the control group,showing that the cascaded higher voltage solar panels would inhibit microbial growth and reduce biomass,thus to block the system startup.(2)The cascaded solar panels in the MFC system and lighted was equivalent to add another directional electric field to the MFC,which would improve the electronic directional migration ability and the electricity generation.In the first run(with different rated voltage cascaded),the output power density of solar cell-microbial fuel cell system with 24 h illumination increased rapidly along with the rising rated voltage of solar panels,such as 86.27 mW·m-2 with 5 V panels in series,which was far more than the ordinary MFC system(2.53 mW·m-2).But it would increase the overall resistance of the system when inserted solar penels as well.In the second period(with different illumination time),under the condition of the same solar cell(1 V)inserted,the output voltage and power density varies greatly because of different illumination time.The output power density of 3h SC-MFC reached 5.08 mW·m-2,lower than the control group(6.30 mW·m-2).(3)It could improve electricity generation with the solar cell inserted.The electron came from the oxidized matrix,so it could also increase the pollutant removal rate in the sediment while we put an adscititious solar panels in the MFC.In the first period,the removal rate of organic matter,total phosphorus,ammonia nitrogen,nitrate nitrogen in the SC-MFC was higher than the ordinary MFC and the maximum removal rate were achieved with low electric field(0.5 V-2 V).In the second period,the removal rates of treatment groups were higher than the control group under the same electric field intensity but different lighting time.The rates of organic matter,total phosphorus,ammonia nitrogen reached the largest with 12 hours light duration.Correspondingly,the maximum removal rate of nitrate nitrogen were 41.5% with 3 hours illumination.(4)It would reduce the microbial community diversity if we added an extra electric field.In the first period,the numbers of OTUs were respectively 2920,3537,3349,2664 with the external 1 V,0.5 V,2 V,5 V solar cells,less than the control group(3558),which showed that the additional electric field lead to less diversity of microbial community.In the second period,we got the same conclusion: the numbers of OTUs were respectively 5585,5664,5676 with 3 hours,12 hours,24 hours illumination,all lower than the control group(6329).(5)The introduction of solar cells had a significant effect to anodic microbial community structure.In the first period,at phylum level,the primary microorganism of all treatment groups and the control group,except with 5V solar cell inserted,were Proteobacteria and the relative abundance was all above 45%.The primary microorganism in 5V SC-MFC was Firmicutes,which relative abundance reached up to 55.94%.At family level,the predominant bacteria from S1 to S4 was Desulfobulbaceae,while S5 was Peptostreptococcaceae and BA008.In the second period,at phylum level,the predominant bacteria of all 12 groups was Proteobacteria and the relative abundance were all above 40%,particularly,the 3 hours SC-MFC reached to 50.26%.At family level,the predominant bacteria of the control group and the 3 hours SC-MFC system was Desulfobulbaceae.Meanwhile,the treatment groups with 12 hours,24 hours illumination,their predominant bacteria were Thermodesulfovibrionaceae.Consequently,the microbial community structure would be influenced by the extra electric field.