| BES?Bioelectrochemical System?is a new technology came up in recent years which could be used to treat sewage and recover energy,including the MFC?microbial fuel cell?which could converted the biomass energy in low concentration wastewaters and lignocellulosic into electrical energy directly and the MEC?microbial electrolysis cell?which could converted to hydrogen.In this paper,double chamber MFC and single chamber MEC were constructed.A series of eletrochemical test such as cyclic voltammetry?CV?,anode EIS test and polarization curve were proceeded to study the optimum substrate concentration and temperature of anode biofilm growth and required.Hydrogen generating performance including the gas production,gas production rate and the coulombic efficiency were check and calculated to search the optimal applied voltage in MEC.Metagenomic sequencing technology was used to compared the anode community structure and evolution in Inoculum,MFC and MEC and the community structure difference between biological anode and cathode structure differences in single chamber MEC.Reaction conditions like substrate concentration,temperature and the other factors have greatly effect on the electric transfer from anode biofilm bacteria to anode.The sewage inoculated MFC with sodium acetate as substrate was constructed,set the substrate concentration is 0.25 g/L,0.50 g/L,1 g/L,1.25 g/L,the maximum output power density reached 385.58 mW·m-2,474.82 mW·m-2,573.94 mW·m-2,533.39 mW·m-2.Set the operating temperature is 15?,25?,35?,45?,the maximum output power density reached 323.96 mW·m-2,489.20 mW·m-2,573.94 mW·m-2,515.64 mW·m-2.Electrochemical test was used to inspect the anodic electrochemical activity,the result showed that the concentration of 1 g/L,the temperature is 35?is the best reaction conditions which could keep high activity of anode and achieved maximum power density.Study the anode potential and electrochemical activity of the anode biofilm after MFC converted to MEC.Due to the same metabolic process and the electron transfer process of anodic microorganisms,the steady anode potential of MFC and MEC were both at-0.38 V?vs Ag/AgCl?.Study the optimized applied voltage on hydrogen production in MEC.Set applied voltage is 0.5 V,0.6 V,0.7 V,0.8 V and 0.9 V,found the applied voltage of 0.7 V can obtain the highest purity hydrogen gas production and ensure high gas production volume at the same time.The biggest volume is 15 mL,gas chromatography was used to detect the hydrogen purity reached 70%.Metagenomic sequencing results showed that microbial distribution came up large difference among the Inoculum,MFC and MEC.The dominant bacteria in MFC,MEC are mainly focus on the Proteobacteria,Bacteroidetes and Chloroflexi.Proteobacteria take the highest proportion,38.02%in Inoculum,74.68%in MFC,72.61%in MEC.It appeared Planctomycetes,Verrucomicrobia and other new phylum in MEC.Significant difference came out in the genus level,Inoculum,the purity of bacteria is gradually increased in Inoculum,MFC and MEC,the biodiversity is lossed.Geobacte is the dominant genus in MFC?29.62%?,and MEC?58.88%?.Single room Bio-cathode was constructed.The gas production rate was0.04 mL/min,0.06 mL/min,0.11 mL/min at the applied voltages of 0.5 V,0.7 V and 0.9 V.The purity of hydrogen is 15%,55%and 33.4%.Therefore,0.7 V was identified as the optimal applied voltage.Charge transfer direction on the cathode,the electron donor and acceptor was reciprocal with the anode,electron transfer from the electrode to the cathode microorganism.Metagenome sequencing showed that microbial community structure appeared differences between the anode and cathode.The main phylum of anode and cathode bacteria are proteobacteria,accounting for 56.20%in the anode,decreased to 39.63%in the cathode.Bacteroides in the anode accounted for 10.98%,increased to21.29%in the cathode.Biodiversity of anode and cathode was large at genus level,the unclassified species accounting for more than half.Cathode appeared Desulfovibrio genus and some new species. |
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