The Configuration And Performance Of Microbial Desalination Cell Under Continuous Flow

The shortage of water resources and water pollution have restricted theeconomic and social sustainable development. Although seawater desalinationtechnology can increase the supply of fresh water, high energy consumptionrestricts its application and enlargement. Traditional wastewater treatment processesalso needed large amount of fossil energy. The desalination of low energyconsumption, directed transfer of organic matter in water and energy collection isthe development trend of sustainable water treatment.A microbial desalination cell (MDC) is a new type of bioelectrochemicalsystem (BES) that can simultaneously desalinate water, produce electrical current,and treat waste water. The ions in the salty water are transported through therespective AEM and CEM membranes when current is generated by theexoelectrogenic bacteria to balance charge in the anode chamber from release ofprotons, and in the cathode chamber by the consumption of protons. This results indesalination of the salty water without the use of any external energy source.However, a low pH can develop in the MDC anode chamber that inhibits bacterialactivity and the higher catholyte pH also can result in potential losses, limiting theextent of water desalination and electricity generation. Dissolved oxygen has beenshown to adversely affect reactor performance. These all restricts its futureapplications. In present thesis, research works were performed focusing on the newreactor configuration, seawater desalination, pollutant removal and influence ofdissolved oxygen.In this study, we designed and operated a recirculation microbial desalinationcell (rMDC) that recirculates the solutions between the anode and cathode chambers.This recirculation avoided pH imbalances and bacterial respiration inhibition. Acomparison of the anode potentials and anode pH suggests that a pH<5.0substantially reduced MDC performance due to adverse effects of low pH onmicrobial activity. Both maximum power density and COD removal of rMDC werehigher than that of MDC. The extent of desalination using the rMDC is a48%increase in performance compared to reactors operated in MDC mode with25mM PBS, although it is slightly less (13%) than that compared with the MDC with50mM PBS. The reduction in performance results from a potential losses when thesolutions were mixed between the electrode chambers, with a greater effect for thehigher PBS concentration. The lower concentration of PBS in rMDC with betterdesalination efficiency showed well potential in the practical application.A series of hydraulically connected MDCs was designed based on rMDC andoperated under continuous flow. The power densities of each unit reactor are muchgreater than those previously obtained using three-chamber MDCs when they wereoperated under fed batch conditions. COD removal of series of hydraulicallyconnected MDCs was improved compared to a single MDC. The NaCl removal was76±1%at an HRT=1d, and increased to97±1%at an HRT=2d. These results showthat increasing the HRT enhanced NaCl removal as a result of the longer period oftime for desalination. The most abundant sequences were most similar to Klebsiellaornithinolytica, which is a facultative anaerobe that can ferment D-xylose to mixedacids and butanediol. This suggests that this microbe would have been able toconsume dissolved oxygen and help maintain anaerobic conditions forexoelectrogenic bacteria in the air-cathode MDCs while degrading the xylose.Corn silage and beer brewery wastewater was demonstrated as substrate inseries of hydraulically connected MDCs. The maximum power densities were847±3mW m-2using corn silage washing liquid as carbonsource and609±3mWm-2as carbon and nitrogen sources in air-cathode MFC. When the series ofhydraulically connected MDCs was fed with corn silage washing liquid, the NaClremoval was74±2%at an HRT=1d and96±2%at an HRT=2d. The COD removaland NaCl removal is75%-83%and50%-55%, respectively, when the substratesolution was change to brewery wastewater without any buffer.A air-cathode MFC for pure culture was developed to study the nteraction ofmicroflora. Oxygen has been shown to adversely affect current generation by otherexoelectrogens. When the co-culture reactors were operated with a closed circuit,the dissolved oxygen in the bulk solution was rapid decrease.But no electricity wasproduced by pure cultures of G. sulfurreducens or E. coli. These results show thatoxygen consumption by E. coli created sufficiently anaerobic conditions for currentgeneration by G. sulfurreducens.