Degradaiton Of3,3’,4,4’-Tetrachiorobiphenyl By Nanoscale Fe⁰/Fe₃O₄and Microorganism Integrated Treatment System

Polychlorinated Biphenyls （PCBs）, including209congeners and isomers, are a class oftypical, complex, and ubiquitous persistent chlorinated pollutants in the environment. Dueto the ubiquitous contaminants in soil and groundwater, their toxicity and potentialcarcinogenesis have led to the considerable necessity to remove these chlorinated solventsfrom contaminated sites. Degradation of PCBs by a combination of nanoscale Fe⁰/Fe₃O₄and microorganism were stuided. The Fe⁰/Fe₃O₄would eliminate the toxicity byreductively transforming the chlorine of biphenyls to chlorineion. Then the bacterium wasapplied to combine with nanoscale Fe⁰/Fe₃O₄to degrade PCBs. The combinationmechanism was revealed by analysis the relationship between bacterium and nanoscale Fe⁰/Fe₃O₄. The experiment results would provide the theory for remediation of pesticidepollution in groundwater and a new method for fast degradation of residual PCBs in soil.The main research contents and results were as follows:1. The degrading bacteria strains were isolated from the soil contaminated by PCBs.The degrading bacteria strain’s16S rDNA was amplified with bacteria universal primer, theamplified product （about1500bp） was purified and sequenced for phylogenetic analyseswith Genbank. The bacterium was identified as Pseudomonas sp. The cell growth ofbacteria strain and resultant depletion of PCB77showed that the bacterium could degradePCBs efficiently by microbial cometabolism. The PCBs provided carbon sources for thegrowth of microorganism. The degradation rate of PCB9、PCB28、PCB77was69.72%、63.17%、58.63%on the seventh day, respectively.2. The experiment results indicated that the degradation rate of PCB77could reach to58.63%on the seventh day when the culture temperature was30℃, pH7.0, inoculationamount of109cfu·mL-1and the initial PCB77concentration of1.0mg·L-1. The degradationrate of PCB77will increase with increasing of inoculation amount and decrease withincreasing of the concentration of PCB77. The pH of culture medium was ranged from5to9, when pH was7.0as well as external carbon source was2g·L-1, The optimum reactionconditions for PCB77degradation was required.3. Reductive degradation of PCB77by nanoscale Fe⁰was studied. The resultsindicated that the82.99%of PCB77would be degraded by nanoscale Fe⁰on the seventhday. The concentration of Cl-increased to47μmol·L-1from the beginning of18μmol·L-1in solution. The degradation of PCB77by nanoscale Fe⁰was a process of reductive dechlorination which could reach to a significant effect.4. The degradation of PCB77by a combination nanoscale Fe⁰/Fe₃O₄withmicroorganism was studied. As a result, the combination of nanoscale Fe⁰/Fe₃O₄andmicroorganism could accelerate the dechlorination of PCB77compared to the individual.The degradation rate could reach to93.30%by a combination nanoscale Fe⁰andmicroorganism. The combination mechanism between nanoscale Fe⁰/Fe₃O₄andmicroorganism could be described as follows: The cathodic hydrogen which was producedduring the degradation process could be used to energy source for the autotrophic growthof degrading bacterium. Biphenyl produced by a subsequent chemical reductive processwith nano-Fe⁰and nano-Fe₃O₄which was considered as carbon source for degradingbacterium. The results showed that the growth microorganism value of the combinationmechanism was higher than the single.5. The degradation of PCB77in soils by combined nanoscale Fe⁰/Fe₃O₄withmicroorganism was studied. The results showed that the degradation of PCB77in soilscould be described by first-order kinetic equation. The degradation rates varied withdifferent soils. The half-lives （t1/2） of PCB77were133.3d、141.4d and147.4d in red soil,vertisol and alfisol, respectively. When adding nanoscale Fe₃O₄and the microorganism,the half-lives were46.5d、49.4d and43.9d, respectively. When adding nanoscale Fe⁰andthe microorganism, the half-lives were26.3d、29.9d and31.8d, respectively. The resultssuggested that the combination of nanoscale Fe⁰/Fe₃O₄and microorganism couldaccelerate the degradation of PCB77in soils, which might be an effective method for thecleanup of contaminated sites.