Screening And Application Of Salt-tolerant Mixed Exoelectrogens

Microbial fuel cells（MFCs）are energy conversion devices that convert biomass into electrical energy using anodic exoelectrogens as catalysts.These exoelectrogens can generate electricity using a variety of substrates,ranging from simple small molecule compounds to complex organic compounds.At present,wastewater known as the most widely used electron donor in MFC system,because the organic matter contained in wastewater can be used as the substrate of MFC.At the same time,the wastewater with high ionic strength that can improve the electrical conductivity of MFC,which provides a reliable idea for the treatment of industrial high-salt wastewater.In order to research the efficient of salt-tolerant exoelectrogens,this experiment took the salt lake soil as the initial bacteria source and small molecule sodium acetate as the only carbon source.The exoelectrogens in the salt lake soil screened,enriched and purified by three-electrode system.Meanwhile,the related electricity-producing properties and properties of the obtained electricity-producing bacteria researched in this study.The results show that:（1）Salt lake soil was used as inoculation source,sodium acetate was used as substrate,and 2%Na Cl was added to preliminarily enrich and screen the mixed exoelectrogens.The mixed exoelectrogens were screened for subculture,and finally the stable mixed exoelectrogens were obtained.The maximum current density was 450μA·cm^-2under the conditions of 28℃,p H 7.2 with 2%salt concentration,while the model strain G.sulfreducens PCA did not have the ability to generate electricity under these conditions.The delay time of carbon sheet electrode as working electrode was 80～100 h,When the carbon cloth electrode is used instead of the carbon sheet electrode,the lag time is shortened to about 1/3 of the original and the maximum current density was 900μA·cm^-2.The mixed exoelectrogens can grow well when the concentration of Na Cl was in the range of 2%～5%and they can be seriously inhibited when the concentration of Na Cl exceeded 6%.At the same time,the mixed exoelectrogens had good electricity-generating capacity under the Na Cl conditions of 3%,4%and 5%,which were 650μA·cm^-2,670μA·cm^-2and 325μA·cm^-2,respectively.The results showed that the salt-tolerant exoelectrogens with strong electricity-producing ability under the condition of salt concentration up to 5%.（2）The results of physicochemical properties and application of the mixed electricity-producing bacteria showed that the mixed electricity-producing bacteria were moderately salt-tolerant bacteria and could grow under the condition of 2%-5%salt concentration.The optimum temperature and p H of exoelectrogens under the condition of2%Na Cl concentration were 35℃and 7.2,respectively.Sodium acetate and CMC（sodium carboxymethyl cellulose）can be used to generate electricity when using carbon cloth as the working electrode and the maximum current densities were 900μA·cm^-2and 200μA·cm^-2,respectively.In addition,the mixed exoelectrogens could reduce Cr（VI）in the medium when the concentration was lower than 4×10^-4mol/L with 2%Na Cl,which provided the possibility o degrade the wastewater containing heavy metals by using the mixed exoelectrogens.（3）In the experiment of determination of Cl^-concentration,AgNO₃Titration and Ion Chromatography were used to analyze the changes of Cl^-concentration in the medium contaning the mixed exoelectrogens during the process of electricity generation.It showed that the salt concentration in the medium did not change significantly after running the electricity generation by using the salt-tolerant mixed exoelectrogens through two methods.