Study On Oxidation Of BTEX Coupled To Microbial Dissimilatory Fe(Ⅲ) Reduction

BTEX are the common organic pollutants of groundwater contamination causedby the leak of oil tank and the waste discharge of petroleum industry. BTEX haveserious threat to ecosystems and human health because of their carcinogenicity,mutagenicity and easy migration. BTEX have high toxicity even though theirconcentrations are very low, therefore, the study on remediation method ofgroundwater contaminated by BTEX has very important significance.Geochemistry and biogeochemistry role have natural remediation function oncontaminated underground environment, in particular, iron biogeochemistry plays acentral role on the attenuation of contaminants in the underground environment. Thereare a large number of Fe（Ⅲ） minerals in the underground environment, and theoxidative degradation of organic contaminants such as benzene and toluene underanaerobic conditions is enhanced during the microbial dissimilatory Fe（Ⅲ） reductionprocesses, the metabolic activity of iron reducing bacteria may further enhance thenatural or engineered bioremediation of BTEX contaminated sites.On the base of domestic and foreign research situation, a series staticexperiments were conducted to explore the kinetics and affect factors of microbialdissimilatory Fe（Ⅲ） reduction and the BTEX degradation based on Fe（Ⅲ） reduction,study the effects of groundwater chemical characteristics on BTEX degradation basedon Fe（Ⅲ） reduction, further simulate the process of BTEX degradation based onFe（Ⅲ） reduction in contaminated groundwater, add microorganism and cosubstratecitric acid to analysis remediation effect, and the results indictated that:（1） Iron-reducing bacteria that was isolated and purified had relatively stableFe（Ⅲ） reduction ability with the increase in the number of passage, microbialdissimilatory Fe（Ⅲ） reduction process can be described as first-order kinetics, afterthe period of14reaction days, the rate constants of Fe（Ⅲ） reduction were respectively0.180、0.156、0.130、0.116d^-1 in the order of the first, second, third, fourthpassage.（2） Under the electron acceptor of akaganeite, microbial dissimilatory Fe（Ⅲ）reduction under the effect of carbon source showed that citric acid＞peptone＞glucose; The types of electron acceptor had a certain effect on the reduction of Fe（Ⅲ）,the Fe（Ⅲ） reduction efficiency was relatively high under the electron acceptor ofakaganeite and goethite in three carbon systems, hematite was not easily utilized bymicroorganisms yet, after reacting40days, Fe（Ⅲ） reduction efficiency was under12%, Fe（Ⅲ） reduction level were different because of different composition andcrystal structure of these three Fe（Ⅲ） minerals; The initial concentration of Fe（Ⅲ）minerals had a certain effect on its reduction, the reduction efficiency of Fe（Ⅲ） wasthe highest under the concentration of0.106g/L in the akaganeite and goethite system,after reacting40days, Fe（Ⅲ） reduction efficiency were respectively84.91%,69.86%,then, Fe（Ⅲ） reduction efficiency gradually droped with the increase of Fe（Ⅲ）minerals’ concentration.（3） BTEX degradation based on dissimilatory Fe（Ⅲ） reduction can be describedas first-order kinetics, under the condition of the BTEX concentration150mg/L andthe electron acceptor of akaganeite, the rate constants of BTEX degradation based onFe（Ⅲ） reduction showed that xylene＞ethylbenzene＞toluene＞benzene; The initialconcentration of BTEX had a certain effect on its degradation, the degradationefficiency of BTEX was the highest under the concentration of100mg/L, afterreacting40days, BTEX degradation efficiency were respectively benzene46.34%,toluene58.14%, ethylbenzene59.22%, xylene69.64%, the degradation efficiency ofBTEX was the lowest under the concentration of200mg/L because of its biologicalactivity inhibition, the degradation efficiency of toluene, ethylbenzene, xylene wereall higher than benzene under the same concentration of BTEX; The degradationefficiency of BTEX was improved after adding cosubstrate citric acid, the degradationefficiency of BTEX was the highest under the citric acid concentration of4g/L.（4） Groundwater geochemical compositions had a certain effect on BTEX degradation, BTEX degradation efficiency was improved under the concentration ofHCO₃^-≤200mg/L, calcium and magnesium hardness50mg/L; BTEX degradationefficiency was improved under the concentration of SO42-≤200mg/L, however, theFe（Ⅲ） reduction efficiency was early inhibited and later promoted; BTEXdegradation efficiency was obviously improved under the concentration of NO3-≤50mg/L, however, the Fe（Ⅲ） reduction efficiency was inhibited.（5）During simulating the process of groundwater contaminated by BTEX, BTEXdegradation efficiency due to external microbial showed that benzene17.81%,toluene30.50%, ethylbenzene32.63%, xylene45.63%; The adjunction of citric acidpromoted the Fe（Ⅲ） dissolution of thin sand and the growth of indigenousmicroorganisms, after reacting40days, BTEX degradation efficiency wererespectively improved benzene14%, toluene21.37%, ethylbenzene17.65%, xylene36.97%; After inoculating iron-reducing microorganisms in citric acid system, ionicFe（Ⅲ） was easily utilized by microorganisms, after reacting40days, BTEXdegradation efficiency were respectively improved benzene22.05%, toluene27.9%,ethylbenzene33.34%, xylene25.34%; BTEX degradation was enhanced under theadjunction of citric acid in iron-reducing microorganisms system, BTEX degradationefficiency were respectively improved benzene18.24%, toluene19.22%, ethylbenzene18.36%, xylene16.68%.