Study On Degradation Characteristics Of Thermophilic Microbial Consortium And Cometabolism Of Polycyclic Aromatic Hydrocarbons

In recent years, with the petroleum resources exploitation and regional economic development, the petroleum pollution has become more and more serious, and soil pollution is worsening. This has become a main factor that restricts the sustainable development. Therefore, bioremediation of petroleum contaminated soil and restoration its ecological functions is extremely urgent. Bioremediation technology has been considered as the most viable environmental administration technology until now, with broad prospects for development. Northwest China Oilfields such as Karamay Oilfield have unique climate and environment, besides the oil pollution sources are dispersive. In view of the facts, a thermostable microbial consortium which used crude oil as carbon source was isolated from local oil contaminated soil and its degradation characteristics were investigated to provide technical support and theoretical basis for bioremediation of high temperature arid areas’ petroleum contaminated soil. The main findings and conclusions are as follows:(1) Karamay Oilfield soil subjected to different degrees of oil pollution, and the oil content was between3.13%and10.88%. Petroleum pollution made the microbial populations simplification and functionalization, but common petroleum-degrading bacteria existed in petroleum polluted soils which provided references for the choice of seed sources in process of microbial remediation technology development. The contents of N, P, H2O and petroleum hydrocarbon were the limiting factors in growth and reproduction of petroleum-degrading bacteria which should be improved in the bioremediation process;(2) A thermostable microbial consortium KO5-2was isolated from Karamay oil-contaminated soil and its growth temperature was30-65℃. It contained12separable single strains which came from six different genera, and8single strains had a capability of degrading crude oil, but KO5-2could degrade crude oil better than these single strains. KO5-2-9was able to produce biosurfactant which belonged to Pseudomonas sp.. The key component of the biosurfactant was rhamnolipid which showed great surfactivity and emulsifying capacity over a wide range of pH, temperatures and high salt concentrations. The optimum culture condition was initial pH8, incubation temperature30℃, nitrogen-phosphorus ratio10:1, incubation time10d and inoculation amount1.5%(v/v).(3) KO5-2was able to completely biodegrade saturated hydrocarbon before C19and the long-chain saturated hydrocarbon of C20-C33degradation effect was also obvious, besides with the long-chain alkanes increase the degradation decreased. The biodegradation of four components in petroleum hydrocarbons deceased in the order of saturated hydrocarbon> aromatics> colloid and asphaltene. The degradation effect of fluorene by KO5-2was the best, followed by phenanthrene, and pyrene was the worst. With the benzene ring numbers increase the degradation decreased.(4) The deformation gradient gel electrophoresis (DGGE) was used to investigate the community structure variation of KO5-2in different carbon source. The results showed that the community structure of KO5-2was roughly the same on the condition that crude oil and saturated hydrocarbon was the carbon source respectively, but there was dominant bacteria Bacillus sp. in saturated hydrocarbons as carbon source. There was some difference of the community structure in three different PAH as carbon source respectively, and the composition of the microbial consortium was the most abundant that phenanthrene was the carbon source, in comparison with which the microbial populations became simple when pyrene was the carbon source. Sphingomonas sp. was the predominant genus of degading aromatics and Ochrobactrum sp. was the functional bacteria of degading phenanthrene.(5) KO5-2was able to degrade PAH (fluorene, phenanthrene and pyrene) by a variety of metabolic pathways, and monooxygenase and dioxygenase reactions happened at multiple sites. KO5-2cometabolism mixed PAHs showed that the presence of fluorene and phenanthrene was able to promote the degradation of pyrene completely and rapidly and the removal of pyrene metabolites, besides the presence of pyrene was also able to promote the degradation of luorene and phenanthrene and the removal of these metabolites. After30days bioremediation, the degradation rate of total PAHs in soil by microbial consortium KO5-2 was54.17%, and the degradation rate of four-rings, five-rings, six-rings was71.26%,39.76%,42.86%, respectively. PAHs in contaminated-soil were degraded effectively.(6) KO5-2was made into powdery microbial agent and applied to indoor bioremediation of petroleum contaminated soil. The optimum culture condition that obtained through single factor experiment was:soil porosity55%, moisture content25%, inoculation amount of microbial agent5%(w/w), nitrogen-phosphorus ratio10:1and the addition amount of biosurfactant5%(w/w). After60days bioremediation of oil contaminated soil on this optimum condition, n-alkanes before C27were biodegraded obviously, and the oil content in petroleum contaminated soil droped from4.07%to1.81%with the degradation rate55.53%. In this process, both the microorganism population number and enzyme activities (dehydrogenase activity, catalase activity and polyphenol oxidase activity) in the soil were improved.