Research On The Reductive Decolorization And Mechniam Of Acid Orange7by Shewanella Oneidensis MR-1Biocathode

Coupling bio-catalytic process and the electrochemical redox reactions,bio-electrochemical systems (BESs) has the advantages of high-efficiency, low cost,environmentally friendly as well as producing valuable compounds and transformingmultiple pollutants, therefore, BESs has been widely investigated as a newbiotechnology. At present, one of the research focuses is the reduction of a variety ofelectron acceptors by the cathode biofilm formed by pure cultures in the BESs. Thisresearch focuses on the removal of azo dye Orange Acid7(AO7) by the electrotrophicmicroorganism Shewanella oneidensis MR-1in the cathode chamber of BESs. Wecompared the AO7removal efficiency between the abicathode and the strain MR-1biocathode, as well as the potential mechanisms of electron sources and transfer at twocircumstances, and this will provide theoretical guidance for the pollutants removal inthe cathode chamber of BESs.When cosubstrate sodium lactate exists in the catholyte and the external voltagewas0.3v (the anode electrogenic bacteria contributes the other-0.45reductive potential),the AO7removal efficiency of biocathode was higher than that of abiocathode and opencircuit biocathode control. AO7in the biocathode can be reduced95.8±4.65%in46h,while in the abiocathode and the open circuit the AO7removal efficiency is77.77±0.0.96%and72.96±5.87%in46h respectively.Besides, the biocathode product(Sulfanilic Acid, SA) recovery is higher than that abiocathode and open circuit control.The AO7removal rate constant (κ) of biocathode is more than twice than that ofabiocathode and open circuit control. Therefore, we concluded that biocathode wasbetter than the abiocathode and open circuit control when supplied with cosubstratesodium lactate. The major electron donor in the biocathode was sodium lactate, whichwas oxided to acetate and provided83.34%electrons for the AO7reduction, andelectrode offered the remaining electrons needed for AO7reduction. The AO7removalefficiency of strain MR-1biocathode (with and without cosubstrate sodium lactate) wasalmost equal, while SA recovery of biocathode with sodium lactate was larger than thatof biocathode without sodium lactate.When the sodium lactate didn’t exist in the catholyte, the AO7removal efficiencyof biocathode was higher than that of abiocathode. AO7in the biocathode can bereduced86.44±2.01%in46h while in the abiocathode the AO7removal efficiency was78.80±2.16%in46h and the biocathode product SA recovery is higher than that ofabiocathode. The AO7removal rate constant (κ) of biocathodeis is larger than that ofabiocathode. In the following research, we controlled the cathode potential at-650mv(Vs saturated calomel electrode) under which hydrogen cannot produce. Under thiscondition, the AO7removal efficieny of biocathode is higher than that of abiocathode in each time segment, which elucidated strain MR-1can directly capture electrons fromthe electrode to reduce AO7without the potential mediator hydrogen. Eventually weeduced that strain MR-1can directly capture electrons form the cathode electrode toreduce AO7when electrode was the sole electron donor, which further expand the ideathat electrotrophic microorganism strain MR-1can reverse the anodic electrogenesisprocess and deoxidize azo dyes at the cathode chamber. SEM(Scanning ElectronMicroscopy) and Live/Dead Staining of strain MR-1cathode showed that strain MR-1can form biofilm and maintain active on the cathode material carbon cloth, whichfurther demonstrated strain MR-1can capture electrons from the cathode electrode forthe reductive degradation of azo dye AO7.The cyclic voltammetry (CV) analysis showed that the biocathode reaction currentis higher than that of the abiocathode and the biocathode lowered the two-step azo bond(—N=N—)reductive potential. AC impedance analysis showed that the abiocathoderesistance is more than five times than that of biocathode and the dominate limit duringthe AO7removal process wasn not the reactor configuration but the charge transfer anddiffusion resistance. Moreover, strain MR-1made the anode charge transfer anddiffusion resistance of the biocathode reactor less than that of the abiocathode reactor.