Process Impact And Mechanism Analysis Of Natural Organic Matter And Iron Ore On Cr(?) Reduction And Fixation By Microorganisms

Cr???pollution is common in the environment.Bioreduction or abiotic reduction of strong toxicity Cr???to less toxicity Cr?III?are important methods to control Cr???pollution.Cr???pollution remediation is mainly based on in-situ biological reduction and fixed remediation,while in the actual environment,there are few chrome-resistant microorganisms and the reduction rate is slow.Studies have shown that iron ore and natural organic matter are expected to promote the microbial reduction process of Cr???.Therefore,the actual pollution environment and the factors affecting the biological reduction process were combined,intended to investigate the impact of microbial species,natural organic matter addition,iron ore species and other factors on the migration and transformation process of Cr???.In the mechanism study of Cr???reduction and fixation,.firstly,the Cr-reducing strains were isolated,screened and identified,and the reduction of Cr???was analyzed.Secondly,combined with the actual polluted environment,the influence of the widely existing Fe-reducing bacteria on the Cr???reduction process was studied,and the environmental factors such as iron ore?clay minerals and iron oxides?,electron transporters?AQDS and natural organic matter?and Cr???concentrations were analyzed.The main results are as follows:?1?To obtain Cr-reducing strains,direct method and enrichment method were used to extract from the surface Cr-contaminated soil?0¹0 cm?of Dongdagou watershed of Baiyin city,Gansu province and the surface and deep?30 m?mixed Cr-contaminated soil of Shushan district,Hefei city,Anhui province.The results showed that there are 32 strains with Cr???reducibility,among which CrB3 had strong ability.The strain of CrB3 was rod-shaped with smooth surface by SEM.And the strain was identified as bacillus sp.by 16S rDNA sequence comparison.?2?To further clarify the Cr???tolerance and reducibility of CrB3,different concentrations of CrB3(4×10⁷,6×10⁷ and 1×10⁸ cell·ml^-1),natural organic matters addition,different concentrations of Cr???(0.1².0 mmol·L^-1)was studied to analyze.The results showed that CrB3 had a certain degree of chromium tolerance and reducibility,and grow well with Cr???(0.1⁰.8 mmol·L^-1).When Cr???was reduced by different concentrations of CrB3,the bioreduction rate was improved with the increase of bacteria concentrations,and the reduction degree reached 46.1%,69.2%and 85.5%respectively at 46 h.The addition of AQDS enhanced the bioreduction of Cr???(0.1¹.2 mmol·L^-1).When Cr???concentration is from 0.1 mmol·L^-11 to 0.8mmol·L^-1,AQDS significantly promoted Cr???bioreduction?enhancement factors>1.5?,When the concentration of Cr???was 1.2 mmol·L^-1,the enhancement factor decreased to 1.39.Therefore,well Cr???tolerance and reducibility are possessed by CrB3,and AQDS significantly promoted Cr???(0.1⁰.8 mmol·L^-1)bioreduction.Therefore,the presence of Cr-reducing strain CrB3 plays an important role in the remediation of Cr-contaminated soil and water.?3?Due to the complicated conditions in the actual polluted environment,the influence of the widely existing Fe-reducing bacteria MR-1 on the migration and transformation process of Cr???under different Cr???pollution levels was studied,and the complex system of clay mineral NAu-2 and electron transmitter AQDS were analyzed.The results showed that:solely NAu-2 have no effect on the promotion of Cr???bioreduction.Whereas solely AQDS significantly promoted Cr???bioreduction with the enhancement factor from 1.33 to 3.90.The enhancement factors are ranged from 2.02 to 10.49 indicating that coupling of NAu-2 and AQDS also significantly imporved Cr???bioreduction.In addition,it shows a significant synergistic effect under the concentration of Cr???from 0.8 mmol·L^-11 to 2.0mmol·L^-11 and the synergy factor increased first and then decreased,reaching a maximum of 2.98.Therefore,the effects of AQDS and NAu-2 on Cr???bireduction in soil and water were significantly at different Cr???concentrations.?4?Iron mainly exists in the environment as clay minerals and iron oxides.This part focuses on the analysis of the influence of iron oxide?ferrihydrite?on Cr???migration and transformation process,while the natural organic matter?ESHA?that exist in the actual environment was adopted as electron transport.The results showed that the adsorption capacity of 0.5 mmol·L^-1Cr???by ferrihydrite reached 38.4%.The results showed that ESHA promoted the bioreduction of Cr???and the bioreduction of ferrihydrite;Compared with MR-1+0.5 mmol·L^-1Cr???group,the addition of ESHA and ferrihydrite both promoted the removal of Cr???,and the enhancement factor were 1.20,1.18 and 1.49,respectively.Based on different bioreduction of Cr???researches,and combined with the actual environment analysis of complex system,the process and mechanism of Cr???migration and transformation that complex system include iron ore?clay minerals NAu-2,ferrihydrite?and natural organic matter and its pattern compounds AQDS were analyzed,to explore the method of enhancing Cr???fixation by microbial reduction,and provide new repair ideas and data reference.