Isolation Of PAHs-Degrading Predominant Strains, Study On Their Biodegradation Properties And Kinetics

Polycyclic aromatic hydrocarbons (PAHs) are a class of ubiquitous toxic recalcitrant organic pollutants. They are widely distributed in various environmental media including atmosphere, water, sediment, soil and organism. And they have done harm to human health by biological-chains accumulation. Based on the review of related study in the worldwide, microbial degradation of PAHs is considered to be the major decomposition process for these contaminants in nature, and which is a complicated systematic project concerning many aspects. Thus, the further study on bioremediation aspects of PAHs is of theoretical and realistic significance.In this paper, firstly, some predominant strains for biodegradation of PAHs were successful isolated. Then, the competitive metabolism of mixed PAHs and the interaction relationship between mixed cultures were investigated respectively. Subsequently, the mass transferring process and degradation kinetics of PAHs were studied. The main results were as follows:(1) Ten strains isolated were of different morphological character and of different cell surface hydrophilicity, which showed a certain microbial diversity. Based on modern molecular identification results, CY4 were identified as Aeromonas salmonicida, which was a new strain in PAHs biodegradation reports to our best known; HY7 was identified as Pseudomonas stutzeri. The two strains could utilized extensive carbon source and had a higher pyrene degradation rate over 35% after inoculated 5days.(2) PAHs biodegradation under the condition of mixed substrate by single strain showed that there were obviously competitive metabolism phenomenon between different kinds of PAHs, and the more simple molecular structure it was or the higher solubility it had, the stronger competitive ability it displayed. Moreover, the metabolic rate of some PAH could be enhanced compared with biodegradation under the condition of single substrate. The results showed a gradually decreased order of competitive ability according to fluorine, phenanthrene, anthracene, fluoranthene and pyrene. For HY7 strain, the anthracene biodegradation rate could be enhanced by 12.7% and the pyrene biodegradation rate could be enhanced by 5.5%.PAHs biodegradation by mixed strains showed that there were interactional relationship among them, and it could be synergism or inhibition. Among it, HY7 strain was a most predominant bacteria, its biodegradation could be enhanced under the existing of HY3 strain and HY6 strain.(3) Analysed intermediates from poly cyclic aromatic hydrocarbon biodegradation using GC/MS, it showed that the mixed intermediates including chemical species with. Dihydroxyl, carbonyl or carboxyl. It had higher content of phenolic compounds in the previous period and of carboxylic acid in the later period, it displayed promoting effect of intermediates on further biodegradation of PAHs. The removing rates of anthracene were increased 3.07-6.10% within 156h, and those of phenanthrene were 13.14-30.35% within 60h.(4) There were at least five steps involved in PAHs biodegradations:the dissolution of PAHs, the sorption of PAHs, dissolved into cell wall, across cell membrane into cells, oxidized by endoenzyme. The experimental results show that the steps in mass transformation had large effects on degradation rate. The adsorption rate of PAHs by strain was much larger than the degradation rate, as a result, that PAHs could exist on the cell surface, within cell wall or inside cells for some time. The apparent degradation rate of PAHs was much larger than the dissolution rate, thus, the dissolution process was the ratelimiting step of the degradation process.(5) In the biodegradation process, the PAHs captured by cells was investigated. Take pyrene for instance, pyrene could exist on the cell surface, within cell wall or inside cells during the biodegradation process. And it always had the most amount of pyrene on the surface of cells, which accounted forl.1～2.9%of the pyrene total amount of biodegradation system. There were little difference between the cell wall and the inside cells of pyrene content, was about 0.3～0.6% of the pyrene total amount of biodegradation system.That pyrene would’t continuously accumulation on cell surface but continuously transferred into the cells and was biodegradated there.(6) The dissolution process could be described by a first-order model Ct=Cs+Ce-kAC, and the kinetic parameters Cs and kA could be determinated by experiment data, the maximum dissolution rate could be calculated by vmax=kACs.by adding biosurfactant, the solubility and the maximum dissolution rate of anthracene could be enhanced by 1.23 tines and by 3.15 times respectively, that of phenanthrene could be enhanced by 1.47 tines and by 1.62 times respectively, and that of pyrene could be enhanced by 4.50 tines and by 7.51 times respectively.(7) The kinetics experiments of PAHs adsorption on cell surface showed that, the adsorption process of phenanthrene or pyrene could rapidly up to the adsorption equilibrium, and the adsorption process could be described by a quasi-second order kinetic equation and the kinetic parameters k2 and qe could be determinated by experiment data.The above experimental results, providing a further understanding on the PAHs biodegradarion process, and was meanful to realizing the bioremediation of PAHs-polluted environment.