Effects Of The Typical Electron Acceptors On The Current Generation By Shewanella Decolorationis S12

The nature of power production from microbial fuel cells (MFC) is microbial anaerobic respiration using electrode as electron acceptor coupling the oxidation of organic compounds. The ultimate aim of developing this kinds of technology is to achieve a wide range of applications to solve the environment and energy problems. However, little is known about the effects of the typical electron acceptors which are commonly presented in the natural environment, especially in the contaminated environment (such as NO3-, SO42-, Fe3+ and azo dyes), on the microbial electricity generation.In this study, we use Shewanella decolorationis S12 as the experimental bacteria and sodium lactate as the electron donor in dual-chamber microbial fuel cells to study the effects of several typical electron acceptor on the S12 MFC power production and the potential mechnisms underlying these processes.In the case of nitrate presented in the S12-catalyzed MFC, experiments with sufficient electron donor showed that nitrate could prevent current generation at the initial phase, and the nitrate reduction at this phase enhanced the anodic cell growth which could result in higher current generation subsequently.In the MFC added with 2 mM nitrate, the biofilm biomass density was 40% higher than those in the MFC without nitrate. The maximum voltages were also increased by adding 2 mM nitrate (0.035 vs 0.024 V). These results suggsted that nitrate was more preferably reduced than electrode by strain S12 and resulted in more biomass producted. With the depletion of nitrate, the accumulated S12 cells switched from nitrate reduction to current generation and generated higher voltage than the MFC without nitrate. However, higher nitrate,10 mM in this study, could significantly prevent current generation and cell growth of S12. When sulfate presented in the MFC, higher concentration of sulfate (7.5 mM) could prevent current generation although lower concentrations of sulfate (less than 2.6 mM) had no effect on the cell growth and current genration of S12.For the case with ferric, the addition of soluble ferric (ferric citrate) increased the growth of planktonic S12 cells but decreased the biofilm growth. The Fe3+ concentrations and the anodic planktonic cell densities were positively correlated. Similarly with the nitrate experiment, the addition of soluble Fe3+ stimulated the current generation at the initial phase compared to the current genration in Fe3+-free MFC. The addition of insoluble Fe3+(Fe2O3) could also increased the current genration at the initial phase, but decrease the maximum voltage compared to the MFC without Fe2O3. It is interesting that the Fe2+ generated from Fe3+ reduction was decreased after a accumulation period in the anode chamber which might be due to the reoxidizatio of Fe2+ to Fe3+ by the oxygen diffused from cathode, or the transfer of Fe2+ accross Nafion membrane to the cathode chamber. Low concetration of Fe2+/Fe3+ couple might function as redox mediator and contributed to the current generation. However, high concentration of Fe3+ seemed likely to prevent current generation by competing for electrons.When using azo dyes as additional electron acceptor, we found that azo dye reduction could enhance the current generation by S12 and the voltage increased with the azo dye concentration. Simultaneously, the azo reduction was also enhanced in the presence of current generation compared with the non-current generation condition. In electricity production conditions, the azo dye tolerance and decolorization capacities of S12 were greatly improved. To underestand the potential mechanisms of co-enhanced azo reduction and current generation, we analyzed the electrochemical activity of the azo-reduction products and found that the azo reduction products P1 and P2A could promote electricity production by increasing the anode biomass and acting as electron mediators to accelerate the azo reduction and current generation by strain S12. Interestingly, the cells of strain S12 became longer in the azo-reducing MFC, which suggested that some toxical compounds to the strain could be produced during azo reduction.