Study On Performance And Mechanism Of Bioelectrochemical System For Fluorinated Nitrobenzene Treatment

Fluoro-nitrobenzene derivatives,as a kind of typical biorefractory fluorine-containing pollutant,have characteristics of three-consistency and fat-solubility.Compared to the equivalent structure of chloro-nitrobenzene derivatives,fluoro-nitrobenzene derivatives have less biodegradability and higher ecology poison.The fluorine-containing wastewater without proper treatment will cause the serious harm to the human and environmnent.Therefore,it is necessary to develop an environmentally friendly,efficient,economical technology of organic fluorine wastewater treatment.In this study,bioelectrochemical systems(BESs)were set up for enhancing fluoro-nitrobenzene-containing wastewater treatment.Meanwhile,the effect of fluorine-substituent on o-fluoronitrobenzene(o-FNB),m-fluoronitrobenzene(o-FNB)and p-FNB degradation in BES were investigated.Meanwhile,the specific mechanism of p-FNB degradation involving p-FNB reduction by biocathodes,oxidative defluorination by bioanodes and electron transport in BESs were also discussed.The main conclusions are as follows:(1)When p-FNB was used as the simulated pollutant,the time needed for 100%p-FNB removal was shortened from 36 d(Biological system,BS)to 18 d(BES)during the acclimation to the stable operation phase,approximately a 50%reduction.In the stable operation phase,the first-order kinetics of the removal of p-FNB in BES was 0.078 h-1,which was 1.625 times that in BS(0.048 h-1).The results of GC-MS indicated that the reduction of nitro group was the key step for p-FNB removal in the BES;however,in the BS,oxidative elimination may be the principal degradation step.Further microbial community analysis showed that the dominant bacteria in the BES(20.8%Anaerolineae,15.9%Flavobacteriia,and 14.8%Alphaproteobacteria)were strikingly different from that in the BS(32.8%Flavobacteriia,24.1%Clostridia and 19.2%Ignavibacteria).(2)The removal of defluorination performance of o-FNB,m-FNB and p-FNB showed significant difference in the BES.The difficulty of monofluoronitrobenzene degradation in the BES was as follows:o-FNB>m-FNB>p-FNB.The removal of p-FNB,defluorination and TOC removal effiencicy were 99.7%.50.1%and 84.8%,which were higher than that of o-FNB(22.6%,3.6%and 5.4%)and m-FNB(50.2%,5.2%and 10.7%).The results of quantum chemistry showed that the charge density of N atoms in o-FNB was the strongest,followed by m-FNB and p-FNB.After the reduction of fluorinated nitrobenzene to the corresponding fluorinated aniline,the barrier of m-FNB(?Eb=47.69 kcal mol-1)defluorination was strongest,while there were no siginifant difference between o-FNB(AEb=15.68kcal mol-1)and p-FNB(?Eb=18.19 kcal mol-1).Further microbial community analysis showed that when o-FNB was chosen as the sole carbon source for microbial community evolution in the BES,the microbial community structures were similar in some regrards,particularly the presence of Proteobacteria(58.0%),Firmicute(14.0%)and Bacteroidetes(9.6%)when compared with that in the BES using m-FNB as the sole carbon source(Proteobacteria(47.6%),Firmicutes(19.3%)and Bacteroidetes(10.3%).However,the dominant bacteria in the BES(Proteobacteria(26.49%),Bacteroidetes(24.5%)and Chloroflexi(13.0%))using p-FNB as the sole carbon source differed greatly from those using o-FNB and m-FNB as the sole carbon sources.(3)The reduction ofp-FNB to p-FA was the predominant process for p-FNB removal on the cathode in the single chamber reactor and defluorination process after this reaction.Taken together,p-FNB was degradated by an integrated reduction and oxidation metabolism.Microorganisms can only use oxygen but nitrate and sulfate as an electron accepter to degrade p-FNB.p-FNB can be converted to p-FA under the condition of electron donor,but further defluorination was difficult without electron accepter.