| Energy crisis and environment pollution is two crucial problem that affectinghuman survival and social developing. China‘s energy structure rely on traditional fossilfuel, especially coal, and leads to serious air pollution, such as smog and excessiveemissions of greenhouse gases. A revolution in waste water treatment is in urgentlyneed.Microbial fuel cells（MFCs） rely on electrochemically active bacteria as catalyststo capture the chemical energy contained in organic or inorganic matter and convert itinto electrical energy, which is widely draw attention from the scientists all over theworld. Variety of organic waste could be oxidized by anode bacteria, thus making MFCa promising technology to make profit from wastewater treatment.However, in practice a typical air cathode MFC could only produce a workingvoltage of around0.5V and a current of several mA, which is insufficient for most ofpractical use. In order to expend the application of MFC, we design a MFC stack whichcombined single chamber MFCs and double chamber MFCs (stack DS). Stackperformance was investigated under varieties of condition. Its shows that stack DScould efficiently control the pH of medium, but still encountered with voltage reversal.Thus, we further investigated the voltage reversal behavior of MFC stack and measuresfor improving output current and voltage was proposed. It also finds that the singlechamber microbial fuel cell plays a crucial role in pH control of stack DS. Thus weapply the single chamber microbial fuel cell between series connected photosyntheticbio-hydrogen reactors. The single chamber microbial fuel cell remove the organic acidand improved hydrogen production of downstream reactors. The main research findingsare listed below：(1) The performance of SCMFC-DCMFC combined MFC stack was investigated.MFC stack unit was structured by connecting SCMFC and DCMFC in series.. Stackunit DD has longer batch operation time, but the current output was limited by acidmedium. Downstream MFC was limited by acid medium. While stack unit DSeffectively control the medium pH above6.6, making the voltage show a plateau above0.5V. Steady voltage behavior not only improved the power output of MFC stack butalso enhanced the waste water treatment efficiency. The reason of pH control was theconsumption of proton by cathode biofilm on SCMFC cathode. MFC stack unit was further scale up by connecting in series, constitute a four cells MFC stack. Theperformance of the stack was tested in continuous mode and recycle-batch mode. Itshows that the medium pH of stack DSDS was controlled above6.8, thus leading to anuniform performance of each stack unit and making a longer effective working period.(2) A series of experiment was made to investigate the reason of voltage reversal.A MFC stack consist of DCMFC was established and its performance and performancestested. The voltage behavior of stack was investigated and the reason of voltage reversalwas analyzed. The limited current of branch MFC regulated the reversal current of thestack. MFC stack constructed by MFCs started under lower resistance will show aimproved performance.(3) SCMFC was further combined with PBR to form a PBR-MFC-PBRsystem.The HPR value of PBR2in PBR1-MFC-PBR2achieved a hydrogen productionrate of0.44±0.22mmol L h-1, which was15and4times higher than those obtained byPBR1-PBR2and PBR1-pH regulation-PBR2, respectively. In addition, thePBR1-MFC-PBR2exhibited the highest substrate utilization (ηs) of97.6±2.1%, whilePBR1-PBR2and PBR1-pH regulation-PBR2showed lower ηs values of75.6±2.2%and70.1±1.2%. These improvements can be attributed to the continuous inhibitorybyproduct removal and pH regulation in the MFCs. |
PDF Full Text Request