Degradation Of PCBs In Soil By Combined Use Of Nanoscale Fe⁰/Fe₃O₄ And Aerobic Microorganism

PCBs is a kind of organic chemical pollutants which is toxic,persist and hydrophobic.This paper studied aerobic microorganism combined iron nanoparticles and its compounds degraded PCBs in soil.As alfisol polluted by PCBs was the main tested soil,the best growth temperature,pH,iron,and its compound,nanoscale Fe₃O₄ dosage,aerobic microorganism inoculation amount,the effect of different innitial PCBs concentration,soils with different properties was studied.The products of PCBs dechlorination by nanoscale Fe₃O₄,degradation by aerobic microorganism,the effect of nanoscale Fe₃O₄,bipheyl to aerobic microorganism was analysis.The best degradation condition and mechanism of aerobic microorganism combined iron nanoparticles degradation PCBs was investigated.This paper mainly get the following study conclusions:1.The degradation results of different chlorinated PCBs was different when they were degradated by iron and its compounds.The residual rate of PCB30 was 50.65%,77.84%,70.65%,71.35%,61.10%,49.42%,PCB77 was 57.04%,82.74%,77.94%,78.89%,65.03%,61.38%,when nanoscale Fe⁰/Fe₃O₄ dosage was 25 g·L^-1,and it was not decreased because of mix nanoscale Fe⁰/Fe₃O₄ or change their ratios.2.The degrader growing with PCBs as the sole carbon source was isolated from the contaminated soil by waste electrical machine.It was identified as Pseudomonas sp.primarily,a kind of aerobic microorganism,after purification and sequencing the 1500 bp of16S rDNA that get from degrade strains by using general primer amplification,and 75%homology with Pseudomonas sp.fragi after compare with Genbank.After growth with PCBs as the sole carbon source for7 d,the residual rate of PCB30,PCB77 in mineral salt medium was 67.3%,69.59%.From aerobic growth of Pseudomonas sp.PCBs provided carbon source for Pseudomonas sp.to maintain its growth.Pseudomonas sp.needed 2 d to adaptation into the logarithmic phase,after 5 d enter the decline phase.3.The degradation rates of PCB30,PCB77 increased with increasing the microbial inoculation amount from 0-0.8 mL(1*109 cfu·mL^-1),the nanoscale Fe₃O₄ dosage from0^-16.7 g·kg^-1,and the PCB30,PCB77 initial concentration from 0^-10 mg·kg^-1.When the cells inoculation amount was 0.8 mL,the nanoscale Fe₃O₄ dosage was 16.7 g·kg^-1 and the PCB30,PCB77 initial concentration was 10 mg·kg^-1,in alfisol the residual rates of PCB30,PCB77 was 26.28%,28.22%,in red soil the residual rates of PCB30 was 32.51%,in vertisol the residual rates of PCB30 was 51.32%.The pH of soils played a important role in the degradation of PCBs.4.By studied the effect of nanoscale Fe₃O₄ and biphenyl did to aerobic microorganism Pseudomonas sp.,detected the product of PCBs degradation by nanoscale Fe₃O₄,it was found out that,nanoscale Fe₃O₄ could enhance the rate of degradation for aerobic microorganism Pseudomonas sp..The nanoscale Fe₃O₄ could decrease the toxic of PCBs by dechlorinated PCBs to biphenyl.When the cells inoculation amount was 0.8 mL,the PCB28 initial concentration was 10 mg·kg^-1,the residual rates of PCB28 without biphenyl was 64.87%,with 2 mg·kg^-1 biphenyl was 59.43%,treatment with biphenyl was better than the without one.And aerobic microorganism Pseudomonas sp.needs less time to adaptation into the logarithmic phase.It proved that biphenyl as the product of nanoscale Fe₃O₄ degradating PCBs,is better than PCBs to be the carbon source of aerobic microorganism Pseudomonas sp.,finally growth of aerobic microorganism Pseudomonas sp.could be improved so that the degradation of PCBs could be increased.At the same time the OD600 of the treatment without nanoscale Fe₃O₄ dosage was higher than the treatment with the dosage of nanoscale Fe⁰,lower than the treatment with the dosage of nanoscale Fe₃O₄.It proved that to a certain extent,nanoscale Fe⁰ can inhibit the growth of aerobic microorganism Pseudomonas sp.while the nanoscale Fe₃O₄ can promote.It further prove that nanoscale Fe₃O₄ could improve the aerobic microorganism Pseudomonas sp.degradation PCBs by stimulating the growth and metabolism of it.