Shewanella Drives The Circulation Of Fe(?)/Fe(?)in An Electro-fenton Reaction And The Mechanisms

Electro-Fenton technology is a classical advanced oxidation technology,which the Fe???/Fe???cycle is the core reaction step.However,the reaction rate of reduction of Fe???to Fe???is only 1/5000 of that of Fe???oxidation,which becomes the speed limiting step of electro-Fenton reaction.And this reaction produces secondary pollutants such as iron sludge.Dissimilatory iron reducing bacteria such as Shewanella can drive Fe???reduction through extracellular electron transfer,a phenomenon that has been widely demonstrated in natural water bodies such as wetlands.Therefore,this study proposed the following research idea: we loaded Shewanella biofilm on the Fe₂O₃ electrode?F/S?to drive electro-Fenton reaction,with the system of no Fe₂O₃ and biofilm loading?blank?for reference,the systems of only loading Fe₂O₃?F?and only loading Shewanella biofilm?S?as the control groups,and then explored the driving effect and related mechanism of Shewanella on Fe???/Fe???cycle during phenol degradation by electro-Fenton reaction.Dissolved oxygen?DO?is a key factor which affects Shewanella to drive electro-Fenton reaction.It is both an oxidant of Fe???oxidation and able to compete electrons with Shewanella,which weakens the driving reaction.Firstly,the effects of different DO on electro-Fenton reaction were discussed.The results showed that the F/S system had higher phenol degradation rate and COD removal rate than other systems under all DO conditions.Taking DO as 2 mg/L as an example,the removal rate of phenol in F/S system was ⁶7% higher than that of the addition of other three systems,and the removal rate of COD was ⁷2% higher than that of F system and ⁵0% higher than that of S system.The relative content of Fe???in F was 12.59%,while that in F/S was 14.58%.In addition,the I_corrof F/S system was 6.29 times that of F system,indicating that Fe???reduction accelerated the release of Fe²⁺in F/S.The above results confirmed that Shewanella drove Fe???reduction in electro-Fenton reaction.The results of crystal structure analysis showed that Shewanella drove hematite to transform into iron phosphate and iron oxide hydroxide.The cyclic voltammetry curve showed that Shewanella driving electro-Fenton reaction had redox peaks of MtrC,OmcA and flavin,revealing the electron transport pathway of Shewanella.In order to clarify stability of Shewanella driving electro-Fenton reaction,the operating characteristics of the F and F/S system were studied.Compared with F,the COD removal rate of F/S increased by about 17%,and the inhibition rate of luminescent bacteria decreased by about 13%,indicating that the phenol degradation products of F/S were more completely removed and the effluent toxicity was significantly reduced.In addition,the Fe loss in F/S system was slightly higher than that in F by about 1.3%,because more Fe²⁺participated in the electro-Fenton reaction.Iron in the attached state in the F system is still mainly in the form of Fe???,while about 55% of Fe???in the F/S system is gradually transformed into Fe???,which further indicated that Shewanella played a role of dissimilatory iron reducing.This study constructed the Shewanella-electro-Fenton system.Based on the scientific hypothesis that Shewanella could influence the cycle of Fe???/Fe???,we investigated the effect of DO on degradation of phenol in Shewanella-electro-Fenton system.Furthermore,the influence mechanism and electron transfer pathway of Shewanella on Fe???/Fe???cycle during electro-Fenton reaction were analyzed.We provide a theoretical basis for the coupling of electro-Fenton oxidation and bacterial degradation and a new idea for treating refractory pollutants.