Characteristic Of Cr(?) Transformation By Lysinibacillus Fusiformis And Remedation Of Cr(?)-Lubricating Oil Combined Polluted Soil

With the rapid development of industrialization and the continuous improvement of people's cognition level,the problem of combined pollution of heavy metals and petroleun hydrocarbons has begun to receive more attention.In the past,there were obvious shortcomings in the research and treatment of ignoring the interactive stress effect of pollutants and only focusing on a single pollutant.In this study,the effect of carbon source?nitrogen source and environmental parameters on Cr(?)reduction by Lysinibacillus fusiformis were evaluated through single factor optimization,and the optimal reduction conditions were obtained by response surface method.Based on the optimal condition,the capacity of oil resistance?Cr(?)reduction and the co-removal capacity were investigated and the form of Cr(?)reduction products were detected by XPS ? FTIR.Simultaneously,the bioremediation of simulated contaminated soil and chemical plant contaminated soil were carried out by adding bacterial liquid and culture medium.The main conclusions are as follows:(1)Through the domestication of the contaminated soil collected from the chemical plant in Shapingba District,Chongqing for more than one month,several strains with oil resistance and Cr(?)reduction capacity were isolated and screened,and three strains with strong Cr(?)reduction capacity were identified as Microbacterium keratanolyticum ? Lysinibacillus fusiformis and Bacillus tropicus.By exploring the growth conditions and functional characteristics of three strains,Lysinibacillus fusiformis was selected as experimental strain.(2)Lysinibacillus fusiformis was able to tolerate 50-350 mg/L of Cr(?)in LB medium containing 500 mg/L of lubricating oil and completely reduce 50 mg/L of Cr(?)in 24 h.The strain failed to achieve metabolism and Cr(?)reduction simultaneously in the mineral salt medium with lubricating oil as the only carbon source.Through adding small amount of tryptone,the strain could reduce 50 mg/L Cr(?)to9.94 mg/L within 6 days.(3)The medium carbon source,nitrogen source and environmental factors were optimized.Glucose has the best promotion effect on the reduction of Cr(?)by strains among different carbon source accessory ingredient.Organic nitrogen sources have better promotion effect than inorganic nitrogen sources,ammonium oxalate was finally selected as the nitrogen accessory ingredient due to cost control and its good promotion effect.Lysinibacillus fusiformis was able to tolerate 500 mg/L of lubricating oil and completely reduce 50 mg/L of Cr(?)in 6 d while 8 g/L glucose and ammonium oxalate were added to the mineral salt medium.Through single factor experiment and response surface methodology,the optimal conditions for reducing Cr(?)of the strain were optimized as p H: 7.5,temperature: 34.13?,rotational speed: 158.05 rpm and inoculation amount: 10.63%.The final reduction coondition parameter was set as temperature: 35?,rotational speed: 160 rpm and inoculation amount: 10%.(4)Under optimized conditions,Lysinibacillus fusiformis was able to tolerate500-14000 mg/L lubricating oil in the presence of 50 mg/L Cr(?)and reduce 50-120mg/L Cr(?)while tolerant 500 mg/L lubricating oil.In addition,the strain was able to co-remove 30-70 mg/L Cr(?)and 250-1250 mg/L lubricating oil.(5)Under the stress of Cr(?),Lysinibacillus fusiformis strain grew well with complete morphology,but its surface appeared folds and depression and some cell surfaces were attached with sticky substances.According to XPS,the reduction products of Cr(?)existed in the form of trivalent states,indicating that the removal of Cr(?)by bacterial strains was mainly reduction.FTIR analysis suggested that EPS may participate in the process of reduction of Cr(?),and the reduction products of Cr(?)may exist in the form of Cr(?)-EPS compound.(6)When the concentrations of lubricating oil and Cr(?)are 1000 and 360,3000 and 360,5000 and 160,5000 and 360 mg/kg respectively,Lysinibacillus fusiformis was able to reduce both Cr(?)and lubricating oil concentrations to the screening concentration value of class ? land(826 mg/kg ?3.0 mg/kg)of soil environmental quality-Risk control standard for soil contamination of development land(GB36600-2018).The Cr(?)concentration decreased from 812 mg/kg to 361 mg/kg and the petroleum hydrocarbon concentration decreased from 7920 mg/kg to 4650 mg/kg within 35 days when the Lysinibacillus fusiformis was added to the contaminated soil of chemical plant.