Isolation Of Di(2-Ethylhexyl) Phthalate-Degrading Bacteria And Study On Its Degrading Function

Di(2-ethylhexyl)phthalate(DEHP) is a typical kind of Phthalic acid esters(PAEs) with high production,serious toxicity and difficult degradation characteristics. DEHP is widely used industrial chemicals, serving as important additives with impart flexibility in polyvinylchlride(PVC) resins. DEHP is also used to vary degree in resins such as polycinyl acetates, cellulosics, polyurethanes, and is produced in very large quantities. DEHP has received extensive attention in recent years due to its wide spread use and ubiquity in the environment. It is widely distributed in air,sediment,natural water,waste water,soil and living organics. Research suggests that metabolic breakdown of DEHP by microorganism is considered to be one of the major route of environment degradation for these widespread pollutants due to their low rate of the hydrolysis and photolysis. DEHP is degraded by a wide range of bacteria under both aerobic and anaerobic conditions in natural circumstance, but the natural degradaing ability of bacteria cann't be satisfied with the needs of DEHP treatment in environment,so it's time to find out effective degrading bacteria to deal with it. Two DEHP-degrading bacteria strains were isolated from polluted environment using the gradient pressure acclimatization technique, and its biodegradation were studied in this paper.(1) Acclimatization,isolation,identification of DEHP-degrading bacteria: Two strains CQ0110Y and CQ0110G were isolated from activated sludge in sewage treatment factory and soil in a plastics plant sewage outlet using the gradient pressure acclimatization technique. Both of the two strains were able to grow by utilizing DEHP as sole carbon and energy sources. By the study of morphological and physio-biochemical characters,two strains were identificated as L.coryniformis and L.viridescens, respectively.(2) Study on optium degrading conditions: The optimized degrading conditions were obtained by detecting the degrading efficiency of DEHP under different conditions of pH,temperature and so on. Results showed that the optimized pH of the two strains for degrading DEHP were 6.0～8.0 and 6.0～7.5, and the temperature were 20～35℃ and 25～35℃, respectively.(3) Study on degrading knetics:Kinetics of degradation reaction had been performed by detecting the degrading efficiency of DEHP with different initial concentration atdifferent time. After statistics with SPSS10.0 software, the degradation of DEHP by the two strains can be described as the same exponential model respectively when the initial concentration of DEHP was lower than 1350 mg/L, with the degradation half-life of DEHP: CQ0110Y, 1.59 days; and CQ0110YG, 2.00 days. The results showed that both of the two strains had power capability to degrade DEHP.(4) Comparison of degrading behavior: The degrading behaviors were studied and compared by detecting the degrading efficiency of different PAEs(DMP,DEP,DBP,DOP,DEHP) at different time. Results showed that the degrading efficiency of CQ0110Y was superior to that of CQ0110G; both of the two strains were more efficient to DEHP than to others; the degradation of PAEs would be more difficult with the increase of its carbon chain.(5) Study on degrading enzyme: The properties of the DEHP-degrading enzyme had been investigated. The results showed that both of the enzymes were intracellular enzyme. The crude enzyme of CQ0110Y was stable in pH6.0-8.0 and that of CQ0110Y was pH6.0-7.5. Both the crude enzymes were stable in 10℃, at the same time,they could hardly maintain their DEHP-degrading activity at 50℃.(6) Study on degrading pathway: By detecting the degradation product of DEHP at different phase, the degrading pathway could be described: DEHP was Hydrolyed to MEHP and phthalic acid by the action of esterase, then to benzenecarboxvlic acid, hydroxybenzoic acid would form by oxygenase. Then hydroxybenzoic acid was degraded to phenol and to pyruvic acid and succinate, after the tricarboxylic acid cycle, the terminal degradation products were CO2 and H2O.(7)...