| Water, soil and other natural resources are the basis for human being, plants and animals to survival and development. However, a large number of POPs(persistent organic pollutants) were released into environment with the rapid development of modern chemical industry. In particular, industrial wastewater containing environment hormone compounds had caused serious pollution to ecological environment. Chlorophenols, one of the most widely used POPs, had a cumulative effect. The enriched concentration of chlorophenols in organisms was more than which contained in waste water. Chlorophenols could be strongly adsorbed in the soil, sediment and plants after entering the food chain by bioconcentration, were not easy to be oxidized or hydrolysis under natural conditions and difficult to move through the air for its low volatility. Therefore, eleven kinds of chlorine phenol had been listed in priority pollutants table by EPA. The pollution caused by the distribution of chlorophenols had already become one of the serious problems concerned by today’s China government.2,4,6-trichlorophenol, a kind of typical chlorinated phenolic, was widely used in the production of the fungicides, preservatives, dye, as a kind of organic chemical intermediates. At the same time,2,4,6-trichlorophenol was a byproduct of the chlorination process of drinking water.2,4,6-trichlorophenol had strong toxic effects, which mainly manifested in making protein degeneration, so that the cells lost their activity. In addition,2,4,6-trichlorophenol also had the role of damaging to the nervous system.Now, the treatment methods of2,4,6-trichlorophenol mainly include microbial degradation, photocatalytic oxidation, physical adsorption, etc. Photocatalytic oxidation was such a method of using the light catalyst to speed up the photolysis compounds and achieving rapid removal of pollutants thereby. Relative to microbial degradation, the elapsed time of this method was short, the capacity of processing was larger, but the energy consumption and cost were high. Physical adsorption referred to using adsorbent to transfer compounds from polluted water into the adsorbent. This method could remove2,4,6-trichlorophenol in the wastewater effectively and recycle the compounds adsorbed, which had economic rationality. But the absorbed2,4, 6-trichlorophenol still needed to be converted into innocuous and harmless product. And physical adsorption method was easy to produce of secondary pollution and cost of processing was high. In comparison, microbial degradation method had the advantage of high efficiency, low cost, no secondary pollution. It had plays an increasingly important role in the field of environmental pollution control.In this thesis,2,4,6-trichlorophenol was chose as probe molecular, microbial degradation and immobilized degradation were studied. The following results are obtained:(1)Isolation of a bacterial strain with high degrading efficiency of2,4,6-trichlorophenol. Through domesticating twice activated sludge from Tang Wang sewage treatment plant, and after the steps of isolation, screening and purification, obtain a degrading bacteria T10which could grow with2,4,6-trichlorophenol as the sole carbon source. In the initial substrate concentration of25mg/L, pH7.0, the temperature of30℃condition,90.12%of2,4,6-trichlorophenol was degraded by bacteria T10after5d, which incarnated good degradation effect.(2) Identification of bacteria T10by molecular genetics and phenotype. The degrading bacteria TIO was identified as Bacillus sp, based on physiological and biochemical characteristics, and comparing16Sr RNA sequence and gene pool. Strain T10and Bacillus subtilis EF428238had the highest homology, up to99%. Strain T10showed positive in the test of gram staining, starch hydrolysis and gelatin liquefaction, showed negative in produce H2S test.(3) Optimizing degradation conditions. This thesis mainly talked about the2,4,6-trichlorophenol degradation rate, which was affected by the initial substrate concentration, pH value and temperature. It turned out that strain T10had high physiological activities and degradation rate of5d can reach more than90%, when the initial substrate concentration was5～25mg/L. In the condition of mention above, degradation reaction played a leading role. However, the degradation rate decreased significantly and the inhibition of substrate to degrading bacteria played a leading role gradually, when the initial substrate concentration was more than30mg/L Stain T10had the highest degradation enzyme activity under the condition of pH7.0, and the degradation rate of5d reached90.12%. For the acid and alkali resistant ability, the degradation rate reached36.47%under the condition of pH9.0. The suitable growth temperature range of strain T10was relatively wide, and its degradation rate of5d reached more than90%under the condition of30～40℃. The degradation rate of30℃was90.63%, and which of40℃was97.27%.In conclusion, under the condition of temperature of30℃to40℃, pH was neutral and substrate concentration under25mg/L, the strain T10could keep high degradation characteristics for2,4,6-trichlorophenol.(4) Kinetic analysis of degradation reaction process. The degradation process was fitted into the first order reaction kinetics model. Through the fitting analysis, the half-life of1.26d, the degradation rate constant of0.5678and R2of0.982were obtained, under the condition of substrate concentration of25mg/L, pH7.0, temperature of30℃.(5) Influence of additional carbon and nitrogen source on the degradation efficiency of strain T10. Study different carbon sources, nitrogen sources on the influence of degradation by determining the degradation rate. Sugar, starch, sodium acetate and peptone promoted the degradation of strain T10on2,4,6-trichlorophenol, and the promotion of sugar and peptone was the best, with the degradation rate of3d reached100%. However, adding glucose, maltose, urea, ammonium chloride, ammonium sulfate and potassium nitrate, reduced the degradation rate of strain T10, may be due to the priority of absorption.(6) The analysis of the intermediate products. The degradation products of2,4,6-trimethylaniline,1,2,4,5-tetramethyl benzene and their isomers were obtained after5days through the analysis and detection of GC-MS. It could be inferred that2,4,6-trichlorophenol first removed chlorine, then combination freely with short alkyl chain into new degradation products.(7) The influence of immobilized bacteria on degradation. Choose two groups of carrier materials to prepare immobilized bacteria, and optimized the preparation conditions. The immobilized bacteria, which were embedded with sodium alginate-calcium chloride, had higher degradation rate than the same amount of free bacteria, and the degradation rate in120h reached97%. The adsorptive property of immobilized beads made of polyvinyl alcohol-boric acid was low relatively, and the beads failed to advantage in the process of degradation. |
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