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Characteristics Of Biocathode Microbial Fuel Cell And Coupling Models With Photoelectrochemical Catalysis

Posted on:2016-03-07Degree:DoctorType:Dissertation
Country:ChinaCandidate:Y DuFull Text:PDF
GTID:1222330503969750Subject:Environmental Science and Engineering
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With the emergency of energy crisis and environmental pollution, more and more attention has been paid to the development and application of clean and renewable energy, such as solar energy and bioenergy. Semiconductor-based photocatalysis and photoelectrocatalysis are promising technologies for solar energy extraction and pollutant degradation, which hold the same purpose as microbial fuel cells(MFCs). Biocathode microbial fuel cells are devices that are catalyzed by microorganisms both in anode and cathode for organic pollutant removal and simultaneously electricity production. Biocathodes are alternatives for noble catalysts used in MFCs for its high efficiency, low-cost, reproducibility. However, the electron transfer mechanism of biocathode remains challenge recently; also, the low power output and vulnerability to persistent organics limits the pratical applications of MFCs. Based on the advantages and disadvantages of photocatalysis and MFCs, the present study was carried out on the working mechanism and pollutant removal of biocathodes, and the possible coupling models for these two technologies.The maximum power density of nitrifying biocathode MFCs in batch mode was ca. 15.37 W/m3. Almost 100% of ammonia was oxidized to nitrate in the biocathode. The biocathode showed the similar catalytic activity of oxygen reduction reaction and better electrical double-layer capacitances compared with Pt/C cathodes according to the electrochemical analysis. There was close interaction between cathodic reaction and microbial metabolism evolved in the cathode process. Based on the variation of nitrification and cathodic oxygen reduction activity towards the initial NH4 Cl and Na HCO3 concentrations of biocathode medium, it was shown that the oxygen reduction process, to some extent, relied on the nitrification activity of biocathode; the external electrons from cathode in turn might benefit the nitrifying bacteria selected in MFC habitat by entering the electron transfer chains as energy source. Nitrifiers, including Nitrosomonas sp., Nitrospira sp. and Nitrobacter sp. were detected in all biocathodes that cultured in different conditions, even that were cultured without NH4 Cl in the medium. These findings provided valuable insights into the possible working mechanism of biocathode.Simultaneous carbon and nitrogen removal was achieved in the continuousflow biocathode MFC. Anion exchange membrane(AEM) used as separator facilitated the transmission of NO3-–N from cathode to anode, resulting in the enhancement of denitrification and the TN removal from 49% to 80%. However, the AEM was not an ideal separator for MFCs because of the susceptibility to biofouling and higher internal resistance of anion migration compared with cation exchange membrane(CEM). The aeration rate showed little effect on the COD removal and power generation, but greatly influenced the nitrification process of biocathode. The aeration rate of 0.6 L/min was the requirement for efficient nitrification. The COD/TN ration of the influent both influenced the TN removal and power output. The maximum TN removal ratio(87.2±1.9%) was obtained with COD/TN ration 26.5; while the COD/TN ration increased to 33.1, the cathode performance deteriorated obviously.The biocathode coupled photoelectrochemical cell(Bio-PEC) was constructed for the first time to integrate the advantages of photocatalytic anode and biocathode. The voltages of Bio-PEC was ca. 250~290 m V, the maximum power density 211.32 ±3.54 m W/m2, and the methyl orange decoloration rate 0.0120 mg/(L· min). Various kinds of waste water can be treated by photo-anode for electricity generation. The higher p H value and anaerobic condition of wastewater benefited the power generation. The minimum conductivity of wastewater should be 10~15 m S/cm to avoid high internal resistances for ion migration.Two coupling patterns for PEC and MFC were proposed to harvest the electrons generated by both photocatalysis process and microbial oxidation. In the hybrid-cathode photoelectrochemical-microbial fuel cell(HCPMFC), the power density of Pt/C-MFC increased from 780 to 1098 m W/m2 when the Pt/C-PEC was connected. In contrast, the improvement of Pt/C-MFC accompanied with the performance reduction of Pt/C-PEC. The current of Pt/C-PEC declined from 150 to 20 μA, and the methyl orange decoloration rate decreased from 0.0082 to 0.0007 min-1 when the Pt/C-MFC connected.The hybrid-anode photoelectrochemical-microbial fuel cell(HAPMFC) was also constructed to integrate the application of solar energy and bioenergy by installing Ti O2 photoanode next to bioanode in microbial fuel cell(MFC), which shares the same cathode. The connection of Pt/C-PEC results in the elevation of cathode potentials of Pt/C-MFC based on the differences of power output characteristics of Pt/C-MFC and Pt/C-PEC alone. The maximum power density increased from 987 to 1645 m W/m2 as the Pt/C-PEC connected to external resistor of 1000 ?. The significant enhancement of power production of MFC is accompanied with the decline of PEC in a lower magnitude, yielding overall power output promotion of HAPMFC. The roles of hybridanode approach were also confirmed in the biocathode MFC. The fluctuation of biocathode potential that was running in poor condition was relied with the connection of Bio-PEC in hybrid-anode pattern.
Keywords/Search Tags:microbial fuel cell, biocathode, photocatalysis, hybrid-anode, hybridcathode, simultaneous carbon and nitrogen removal
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