Mechanisms For Pyrogenic Carbon-Enhanced Bioreduction Of Nitroaromatic Compounds By Shewanella

As a typical exoelectrogen,Shewanella can transfer electrons extracted from in-tracellular organic carbon substrates to extracellular electron acceptors,e.g.organic compounds or metal oxides,vir different electron transport pathways,which may de-pend on their molecular structure.It‘s of guiding significance for regulating microbial degradation of organic compounds to reveal the electron transport pathways,through which organic compounds with different structure were reduced by Shewanella.In this study,we selected 13 nitroaromatic compounds?NACs?with different structures to test the electron transport pathway emplied by S.oneidensis MR-1 to reduce dif-ferent NACs,and further elucidated the mechanism for pyrogenic carbon-mediated NAC degradation.The main findings of this thesis are summarized as below:?1?We found that the molecular weight,van der Waals volume,and log K_ow dif-ference are the factors determining whether NACs were reduced inside the S.onei-densis MR-1 cells or not,among which the van der Waals volume was the main factor.Among the tested NACs,those with a van der Waals volume larger than 16.41,in-cluding 2,5-ditertbutyl-nitrobenzene,2-nitrobiphenyl,and 2,2‘-dinitrobiphenyl were reduced outside of the cells via the Mtr respiratory pathway,while the compounds with a van der Waals volume smaller than 15.60?e.g.,4-nitrotoluene and2,4-dinitrotoluene?,were reduced through both the Mtr transport pathway and the ox-ygen-inactive nitroreductase Nfn B involved pathway?inside the cells?.?2?We illustrated the mechanism by which pyrogenic carbon mediated nitroben-zene degradation by S.oneidensis MR-1 under different phase states.Nitrobenzene was simultaneously reduced in both the liquid and sorbed phases by S.oneidensis MR-1 in the presence of pyrogenic carbon.The reductions followed first-order kinet-ics model and zero-order kinetics model and the reduction rates are of?0.023 h^-1and?0.003 m M?h^-1,respectively.Oxidation of pyrogenic carbon with nitric acid in-creased the content of quinone,thus improving the reaction rates by 4.2-fold and rais-ing pyrolysis temperature stimulated the growth of aromatic ring structure,promoting the reaction rates by 1.4-fold.It indicated that the anthraquinones and condensed ar-omatic structures are mainly responsible for nitrobenzene reduction in both the liquid and sorbed phases by S.oneidensis MR-1.?3?Pyrogenic carbon significantly promoted the extracellular reduction of dense non-aqueous phase 2,2‘-dinitrobiphenyl by S.oneidensis MR-1.The reduction rate was increased by more than 50%,and higher the pyrolysis temperature is,faster is the reduction rate.The large capacitance of pyrogenic carbon is the main factor leading to the high reduction performance of the insoluble 2,2‘-dinitrobiphenyl.