Isolation And Identification Of Carbon Tetrachloride Degrading Bacteria And Degradation Mechanism

Carbon tetrachloride(CCl₄)is a toxic volatile chloride that has been widely used as an industrial degreaser and fire extinguisher for many years.The presence of CT contamination in groundwater and soil has been found in several regions of China,and the use of microorganisms to degrade CCl₄ is an effective method for environmental protection and energy conservation.In this study,CCl₄ was used as the only carbon source to screen the dominant degrading bacteria with degradation ability,and the growth characteristics and the influence of different factors on the growth of the strain were studied.The degradation mechanism was analyzed by detecting the intermediate products of carbon tetrachloride degradation process,aiming to find the efficient CCl₄degrading bacteria,thus providing a basis for the development of microbial degradation applications in environmental pollution.The results of the study are as follows:(1)A contaminated site in Changzhou City,Jiangsu Province was used as a sampling site to enrich and domesticate the culturable microorganisms,and finally three strains of CCl₄ degradative bacteria were obtained,and WY-C7 is identified as Brucella,WY-C10 is FZW.22(Acinetobacter)?WY-C11 is Cellulomonas Acinetobacter.When the initial concentration of CCl₄ was 450?g/L,the degradation rates of WY-C11 and WY-C7 were 85.64%and 53.60%for CCl₄ after 3 days,and WY-C10 had the strongest degradation capacity of 90.91%,which indicated the potential application of WY-C10 in the treatment of CCl₄.(2)The four factors affecting the growth of the strain,namely the initial concentration of CCl₄,p H,incubation temperature and incubation speed,were selected to study the growth characteristics of WY-C10,and the single-factor and orthogonal experiments showed the same results,with strain WY-C10 having the best growth at a CTC concentration of 450?g/L,p H 7.0,temperature 35?and speed 180 r/min,optimal growth.(3)By culturing WY-C10 under the influence of different factors,it was found that the strain grew better when the H₂O₂ concentration was 30?50 mmol/L,TW?80concentration was 60?100 mg/L,and Fe³⁺concentration was 0.5?0.7 mmol/L.The results of response surface experiments showed that the three factors influenced the test results to the extent of Fe³⁺>Tween-80>H₂O₂,where the interaction between TW-80and H₂O₂ was significant,and the strain grew the most under the conditions of H₂O₂concentration 50 mmol/L,Tween-80 concentration 100 mg/L and Fe³⁺concentration 0.7mmol/L fitting value.(4)The degradation pathway of WY-C10 was studied,and the intermediate products of CCl₄ degradation were determined by GC-MS and ion chromatography,and four products were obtained as CH₂Cl₂,CH₃COOH,HCHO,COCl₂.The possible degradation pathways are presumed to be either continuous dechlorination by CCl₄ or catalytic degradation by methane monooxygenase(MMO),and it is assumed that reductive dechlorination plays a major role in high-chlorinated substitutes,while oxidative degradation is the main role in low-chlorinated substitutes.