| Microbially mediated dissimilatory Fe(?)bioreduction is one of the important driving forces in the process of biological and geochemical cycle of iron in nature.The object of study was the interactions among Shewanella bacteria(Shewanella putrefaciens),lepidocrocite and goethite.The current study discussed microbial reduction influences on process of lepidocrocite mineralline transformation characteristics and goethite microbial reduction influences on the mechanism of pollutants(4-Nitroacetophenone)degradation in the anaerobic environment.Firstly,this paper discusses the characteristics and influence factors of lepidocrocite bioreduction and the mineral transformation process.The process of microbial dissimilation reduction of the fiber containing different components in the system has different effects on the characteristics of the mineral form transformation.1)system containing electron transport carrier(AQS,AQDS),due to the electron transport carrier,it can accelerate the alienation of lepidocrocite reduction process,promote the lepidocrocite mineralline transformation,which can basically complete the process in27 h,when Fe(II)adsconcentration near the 6.0 m M.2)In the system containing AQS after adding the Ortho-phenanthrene,the degree and the rate of the mineral transformation of the lepidocrocite were significantly reduced,and the reaction was not observed after 685 h.Phenanthrene is a very strong coordination agent,and the adsorbed iron was almost complexed(concentration of Fe(II)ads is about 0.10 m M)and transferred into the supernatant,and the content of adsorbed iron was significantly decreased.Similar phenomena were also observed in the system with low adsorption iron content,such as 4-Nitroacetophenone(4-NP).The transformation process was slow until the 441 h,at this time Fe(II)ads concentration was 2.30 m M in the system containing 4-NP.The above phenomena show that the content of Fe(II)ads had an obvious promoting effect on the degree and rate of the transformation of the mineral form,and it is an important controlling factor in the process of the transformation of the mineral form in the system.3)the increase of concentration of electron donor(sodium lactate concentration was 1 m M,5 m M,10 m M,20 m M),can promote the lepidocrocite reduction process,resulted the increase of Fe(II)ads concentration for 2.13 m M,4.77m M,5.11 m M,7.51 m M at 130h,mineral transformation process was also enhanced.The characteristics and mechanism of the interactions of“iron oxide-microbe-pollutants”were discussed.Two groups of experiments were designed,that is,respectively joined the 4-NP after the first day and 5 days in the"microbe-goethite"reaction system.The results showed that:1)in the 0day of 4-NP system,electron carrier(AQS)promotes goethite dissociation.It can be seen that the degradation of organic matter will be accompanied by the consumption of iron,the system of organic matter,and the time delay of the process of the iron dissimilation reduction,but the Fe(II)concentration is basically the same when the two finally reach the equilibrium.Degradation 4-NP was completed within 14 days,and the addition of AQS increased the degradation rate of 4-NP.2)Added at the 5th day of 4-NP set two systems(not including LB based systems and training with LB medium system),containing LB based training system by microorganism have adequate nutrition source and respiration enhancement,promotes the goethite bioreduction,and take advantage of the high concentration of electron carriers.Fe(II)tot,Fe(II)dis concentration increased sharply in LB medium system.The 4-NP in the two systems can be completely degraded in 1day,and the active of electron transfer in the reaction of the goethite dissimilation is active,which can accelerate the degradation process.Finally,the paper discusses influence of“goethite-microorganism”interaction systemand its degradation characteristics,when the system added a higher concentration of 4-NP after reaction 86 h.The 86 h adding different concentrations of 4-NP(0.25?2.0m M)found when 4-NP concentration was low,Fe(II)adsand Fe(II)tot loss to a smaller range.Fe(II)adsand Fe(II)tot recovery growth cycle is shorter,the degradation product4-Aminoacephenone(4-AP)production rate is faster.It is indicated that the degradation reaction of 4-NP is a process of continuous consumption of Fe(II)adsor Fe(II)tot.In degradating the same concentration of 4-NP,the degradation rate of AQS containing system was greater than that of AQDS system.When adding the lower the concentration of phenanthroline,it had the less impact on the dissimilation of goethite,the faster the recovery after Fe(II)ads decreased,the faster the degradation rate of the 4-NP.When phenanthroline concentration is 2.5 m M,Fe(II)was maintained at a relatively low level(0.03?0.05 m M),while 4-NP was almost not degraded under the system.Comprehensived above experiment,1)Fe(II)tot,Fe(II)diswas not change key factors,Fe(II)ads was the key controlling factors of mineral transformation,and concentration of Fe(II)ads more high,lepidocrocite is transformed to magnetite faster.2)The process of degradation 4-NP is continuous consumption of Fe(II)ads,and Fe(II)adsacts as a positive role in the reduction reaction.It was confirmed that the Fe(II)ads with a lower redox potential was the effective active species of 4-NP reduction degradation.Experiments on the characteristics of the dissimilation reduction of both lepidocrocite and goethite have been found that Fe(II)ads is the key factors in the bioreduction process,This provides the further research ideas and theoretical support for the establishment of the bioremediation technology of heavy metal/organic pollutants mediated by iron and its oxide and the establishment of the iron mineral form. |
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