Reductive Transformation Of Chloronitrobenzenes In The Cathode Of A Dual-chamber Microbial Electrochemical-Enhance Anearobic System

The chlorinated aromatic compounds, which are important chemical raw materialto manufacture various chemical products, exist in pharmaceutical, dyes and pesticidesand some other wastewater. Because of high-risk, long life and non-biodegradable, thechlorinated aromatic compounds have been classified as one of the priorityenvironmental pollutants by EPA. Therefore, the residual and degradation of them haveattract wide attention.This paper preliminary investigated the degradation features and maintransformation products of4-chloronitrobenzene in a MicrobialElectrochemical-enhance Anaerobic System(MEAS). In addition, the effect of the keyfactors on the performance of the MEAS were explored.The bioanode can start-up and the electricigens can be enriched in a short time inthe MEAS. As a result, the potential of anode came to-450mV and the potential ofcathode reached about-920mV.The degradation effect and characteristic of4-CNB were contrasted in MEAS,abiotic cathode reactor and anaerobic biological reactor. When the concentration of4-CNB was15mg/L, the removal rate in MEAS reached93.74%in24h at roomtemperature, which in abiotic cathode reactor and anaerobic biological reactor wererespectively62.89%and88.44%. The order of the reductive transformation reactionkinetic constant accorded with Pseudo-first order kinetic equation wasKMEAS>Kanaerobic-biological>Kabiotic cathode. The MEAS showed a enhanced effect on thedegradation of4-CNB. The reductive transformation characteristic of4-CNB in MEASis stable and can be repeated. The main transformation product was4-CAN andaniline(AN) was produced with the biological action. The transformation ratio of4-CNB to4-CAN was low in abiotic cathode reactor for the formation of diazene,bis(3-chlorophenyl)-,1-oxide and bis-(4-chloro-phenyl)-diazene in the electrochemicalreduction of4-CNB. The possible degradation mechanism inferred by the contrast of4-CNB transformation and electrochemical parameters in MEAS, abiotic cathodereactor and anaerobic biological reactor was:The cathode potential came to certain negative value with the assist of appliedvoltage which can act as a electron source. Some of the electrons can transfer tomicroorganism for metabolic and reduce4-CNB, the others were directly used to reduce4-CNB. Meanwhile, the microorganism in the cathode chamber can degrade the4-CNB with the co-metabolism of glucose. The microorganism played a key role in the electrontransformation and degradation of4-CNB. The biofilm on the cathode was diverse. Themicroorganism were spherical and bacilliform, some of them assembled into catenulate.The effects of the key factors on the4-CNB transformation and performance of theMEAS were investigated. It turned out that when the voltage increased from0.3V to1.0V, the removal rate and removal efficiency were both improved. The production ratioof4-CAN was reduced by the strengthen of the electrochemical action under the voltageof1.0V. Besides, the increase of the voltage made a negative impact on theelectro-microorganism. The microorganism in the MEAS cathode chamber had a goodability to degrade and tolerate4-CNB under the initial concentration of15-75mg/L.When the initial concentration was75mg/L, the removal rate still reached to98.39%in72h and the degrading capability didn’t show degradation. However, the increase ofinitial concentration had a big effect on anaerobic biological reactor. The complexdegradation mechanism in MEAS made it have a better capacity to resist impact load.As a good co-substrate, the glucose affected the degradation of4-CNB. Theperformance of the MEAS would decline without the glucose and the removal ratewould improve with the increase of the glucose concentration. When the concentrationof the glucose reached1500mg/L, the gap between MEAS and anaerobic biologicalreactor was shrunk.