Promoting Shewanella Bidirectional Extracellular Electron Transfer By Polyriboflavin Modified Electrode Interface And Its Preliminary Application

Microbial electrochemical technologies(METs)developed on basis of microbial extracellular electron transfer(EET)have attracted great attentions among researchers recently,due to their promising potential of applications in renewable energy production and environmental pollutant treatment.However,their current performance are far from meeting the demand of actual applications.The sluggish EET process between electrochemical active microbes(EAMs)and electrodes is the key limiting factor,thus how to improve the microbial EET rate on the electrode interface is a crucial scientific problem.Riboflavin(RF)that is a kind of endogenous electron shuttles produced by Shewanella spp.(typical EAMs),usual plays an important role in the EET process for Shewanella spp.and even other EAM strains.Thus RF is expected to being employed to modify and functionalize the microbial electrodes for enhancing the EET rate between EAMs and electrodes,and thereby promoting the development and applications of METs in energy recovery,biotransformation and environmental pollutant treatment.In this thesis,an electrochemial pollymerization method for the immonilization of RF on the microbial electrodes has been developed,and the effect of the developed polyriboflavin(PRF)modified electrode interface on the Shewanella bidirectional EET has been studied systematacially when using S.putrefaciens CN32 as the model EAM strain,followed by preliminary investigation on the application prospect in the fields of microbial fuel cell(MFC)anode for bioelectricity generation and microbial cathode for both fumarate reduction and heavy metal removal.The main research contents and results are as follows:1.A cyclic voltammetry approach was adopted to electrochemically polymerize RF on conventional carbon cloth(CC)as the base electrode,the results of fourier transform infrared spectrum,Raman spectrum and electrochemical data indicated that this electrochemical polymerization methode is effective means for the electrode surface modification.In comparison to bare CC electrode,the developed PRF-modified CC electrode(termed as PRF@CC)achieved about 4.3-fold increase in output power density when used as an MFC bioanode and about 3.7-fold increase in cathode current density when used as a biocathode for fumarate reduction,which strongly demonstrated the greatly enhanced bidirectional EET rate of S.putrefaciens CN32 on the PRF modofied electrode interface and the improved ability of bioelectrocatalysis.The result of comparative analysis of the wild-type S.putrefaciens CN32 strain and its mutant strain with deletion of two out-membrane cytochromes(MtrC/UndA)genes indicated that the PRF can not only act as electron shuttles for enhancing mediated electron transfer but also tailor the direct electron transfer through the possible interaction with bacterial out-membrane cytochromes.Apartfrom Shewanella spp.,the PRF modifed electrode interface was also found to improve the EET abilities of a variety of other EAMs to varying degrees,indicating the certain universality.2.In consideration of the relatively poor electrochemical activity of the CC electrode,the improvement of PRF modified electrode interface was further proved based on the highly electrochemical-active graphene/CC(G/CC)electrode that was fabricated by the means of two-step chronoamperometry method.Although a clear enhancements on both anodic electricity production and cathodic fumarate reduction was achieved after the introduction of graphene with great electrochemical property,the bidirectional EET ability of S.putrefaciens CN32 could also be further improved to a greater degree after the modification of G/CC electrode using PRF.Thus the above results substantially demonstrated that the PRF functionalized electrode interface was indeed a reliable and efficient strategy for boosting microbial EET rate and their bioelectrocatalytic abilities.3.Subsequently,the PRF modified G/CC electrode was studied for investigating the effect of PRF interface on the reduction of hexavalent chromium(Cr(VI)),a typical heavy metal,by S.putrefaciens CN32 biocathode.The Cr(VI)exhibited relatively obvious inhibition on the growth of S.putrefaciens CN32 and the inhibition degree is concentration-dependent.The more negative electrode potential was more beneficial for S.putrefaciens CN32 to take up electrons from cathode for increasing Cr(VI)reduction.Particularly,the higher Cr(VI)reduction rate for the PRF@G/CC electrode indicated that the feasiblity of PRF modified electrode interface for enhancing heavy metal bioelectrochemical reduction.In summary,the effect of PRF modified electrode interface on Shewanella bidirectional EET and its mechanism have been studied in details,the applications of PRF modified electrode in Shewanella bioelectrochemical systems for increased renewable energy production(e.g.,bioelectricity generation in MFC),bioelectrochemical transformation(e.g.,fumarate reduction)and heavy metal(e.g.,Cr(VI))removal have been investigated and preliminarily proved.This work is beneficial to promote the development and application of METs.