Energy Generation And Wastewater Treatment Of The Coupled System Based On Single Chamber Microbial Fuel Cells

Energy crisis and environmental pollution are the two bottlenecks threatening thedevelopment of human society. To address these limitations, the research anddevelopment of the environmental-friendly renewable energy have received wideattention of scientists. Among lots of renewable power sources, the microbial energyconversion technology has shown great potential for practical application due to itsadvantage of tremendous substrate （fuel） versatility, cleanness, high conversionefficiency, and capability of converting the organic waste water in clean energy.However, the performance and degradation efficiency are still insufficient for practicalusage due to the product inhibition during the microbial energy conversion process.In order to mitigate the product inhibition effect during microbial energyconversion, a single chamber MFC was coupled in two typical microbial energyconversion systems, i.e. microbial fuel cell （MFC） and photosynthetic biohydrogenreactor （PBR） in this thesis. The experimental results indicated that simultaneousphotosynthetic hydrogen production, electricity generation and continuous waste watertreatment can be realized in the coupled systems. We also demonstrated that the overallpower density, COD removal efficiency and energy recovery efficiency of the coupledPBR-MFC system were also greatly improved when compared with the individual PBRand MFC systems. In addition, it has been found that power density and COD removalefficiency of the double-single-double chamber MFC coupled system （DSD） establishedin this study was significant enhanced due to the improvement of the performance of thedownstream MFC. The main conclusions are as follows:1) A PBR-MFC coupled system was established and its capability of hydrogen/electricity generation was demonstrated by using glucose under continuous feedingcondition. Compared with individual PBR and MFC system, the coupled systemshowed an increased wastewater treatment efficiency as well as the energy recoveryefficiency. Additionally, the effects of substrate concentrations and flow rates on thesystem performance were also investigated in this study. The results showed that theenergy recovery and wastewater treatment efficiency of the system exhibited differenttrends because of the different operating conditions at peak performance. The substrateconcentration and flow rate had a great influence on the system’s power density and energy recovery efficiency, but a minor effect on the COD removal efficiency. Thesystem showed the highest energy density of6.13×10⁵J·m^-3·h^-1at the flow rate of10mL·h^-1when the substrate concentration was6.0g·L^-1. In addition, the peak energyrecovery efficiency （11.2%） was achieved at the flow rate of10mL·h^-1and the substrateconcentration of4.0g·L^-1.2) In this study, we also compared the performance of PBR-MFC andPBR-WCMFC （MFC using a WC modified anode）. The results showed that thePBR-WCMFC system had a higher wastewater treatment efficiency and energyrecovery efficiency due to the enhanced the performance of the WCMFC. Theexperimental results also showed that at a substrate concentration of4.0g·L^-1, themaximum power density of WCMFC was2.79×10⁵J·m^-3·h^-1, nearly1.6times largerthan that of the MFC. And the highest power density of the PBR-WCMFC system was6.79×10⁵J·m^-3·h^-1, when the substrate concentration was6.0g·L^-1. The PBR andWCMFC reached the best performance at the flow rate of60mL·h^-1. The maximumpower density of the WCMFC and the coupled system were3.33×10⁵J·m^-3·h^-1and6.79×10⁵J·m^-3·h^-1, respectively. The highest COD removal efficiency （77.8%） wasobtained When the substrate concentration was4.0g·L^-1and the flow rate was20mL·h^-1. The peak energy recovery efficiency of11.73%can be reached when thesubstrate concentration was4.0g·L^-1at the flow rate of10mL·h^-1.3) In order to verify the buffer effect of a single chamber MFC, we compared theperformance of the two double chamber MFC in the SD （single-double chamber MFC）and DD （double-double chamber MFC） systems. The results showed that theperformance of the double chamber MFC in SD system was higher than that in DDsystem at the pH from5.5⁸.5, due to the buffer effect of the single chamber MFC onthe effluent of the substrate. In this thesis, the performance difference between the DSD（double-single-double chamber MFC） and the DDS （double-double-single MFC）system was also compared. It was found that the acidic effluent produced by the firstdouble chamber MFC （D1cell） in the DSD system can be adjusted to be nearly neutralbefore feeding to the second double chamber MFC （D2cell）, making the performanceof the D2cell showed minor performance difference with that of D1cell. By contrast,for DDS system, the performance of the D2cell was only55.5%of the D1cell due tothe acidification effect of D1on the influent of D2. In this study, the two doublechamber MFCs （D1and D2） of the DDS and DSD systems were also connected in parallel and series to form a MFC stack. The results indicated that the performance ofthe two systems were minor difference at low current densities, but with the currentdensities increased, the performance and COD removal efficiency of the DSD systemwere significantly higher than that DDS system when DMFC in series and parallelconnected style.