Production Of Acetate From Inorganic Carbon Reduction And Influential Cr(Ⅵ) Stress In Serratia Marcescens Catalyzed Cathode Of MES Under Magnetic Field Conditions

Magnetic field has been proved to have positive effect on the electrochemical activity of anode microorganisms in bioelectrochemical systems（BESs）,thereby reducing the internal resistance of the system and increasing electricity harvest.However,the effect of magnetic field on the biocathode is rarely studied and needs to be further explored.Microbial electrosynthesis system（MES）developed from BESs using microorganisms as catalysts shows a promising prospect to reduce inorganic carbon to organic acids.This study explored the effect of magnetic field strength on the production of acetate from inorganic carbon in MES cathode with Serratia marcescens Q1.Moreover,under stressful Cr（Ⅵ）conditions,this MES was explored for simultaneously efficient Cr（Ⅵ）removal and acetate production.Main results included:（1）An optimal magnetic field strength of 100 mT achieved production of acetate of 550±22 mg/L with acetate efficiency(CE_acetate)of 57±2%and acetate conversion efficiency(β_acetate)of 84±2%at an operational time of 12 day,increasing by 2.2（acetate production）,1.2(CE_acetate)and 1.2(β_acetate)times compared with that in the absence of magnetic field..This was attributed to the reduction of the internal resistance of charge transfer,confirming the magnetic field in developing the electrotrophic catalysis activity for reduction of bicarbonate.While the external magnetic field and the circuital current had synergistic stimulating effects on the release of extracellular polymeric substances（EPS）,the circuital current was more influential than the magnetic field on the amount of EPS with a compositional diversity.（2）A magnetic field（100 mT）moderated Cr（Ⅵ）stress and enhanced production of acetate（1.48±0.01 mg/L/h）with simultaneous Cr（Ⅵ）removal（1.67².42 mg/L/h）in the S.marcescens catalyzed cathode of MES under periodical addition of bicarbonate and Cr（Ⅵ）,increasing by1.35 times（acetate production）and 1.34¹.46 times（Cr（Ⅵ）removal）over that in the absence of magnetic field,and 1.05 times（acetate production）over that in the absence of both magnetic field and Cr（Ⅵ）.This efficient acetate production and Cr（Ⅵ）removal was regulated by the magnetic field and the stressful Cr（Ⅵ）,which induced S.marcescens to release additive amounts of EPS with a compositional diversity.This study provides the first experimental indication for an alternative approach to rapidly fabricate controllable MES for not only efficient acetate production from inorganic carbon,but also for simultaneous efficient acetate production and Cr（Ⅵ）removal in MES,from organics-barren waste water contaminated with heavy metal of Cr（Ⅵ）.