The Strain Screening And Influence Factors Of Bioremediation Of Petroleum Polluted Soil In Northwest Loess Area

The exploitation and utilization of petroleum in northwest loess area has a long history of more than 90 years. Due to large aera of oil field and numerous oil wells, there are large quantity of waste petroleum hydrocarbon in the process of petroleum production, storage, transportation, refinement, processing and use. All of this can create oil pollution in large area, which causes the frail natural environment to be originally wicked. Under this background highly efficient petroleum-degrading bacteria were screened, isolated from oil-polluted soil, and they have been identified primarily. The nutritional conditions and the environmental factors which affect its degeneration performance were studied.The main conclusions of the study were as follows.1. Five strains of highly efficient petroleum degrading bacteria, GX1, GX2, GX3, GX4andGX5, were isolated from oil-polluted soil in aerobic condition. They have been identified respectively as Pseudomonas sp. Plesionmonas sp. Xanthomonas sp. Pseudomonas sp. and Zoogloea sp. .2. the pH value, nutrients and oil concentration that affect the bacteria growth and oil degradiation were studied. The experimental results indicated that the five bacterial strains was efficient under initial pH of 7⁹, the best nitrogen source of ammonium nitrate (NH₄NO₃), the ratio of nitrogen/phosphorus of 4 :1. With the low initial concentration of petroleum, the degrading rate had a tiny increase along with increasing oil concentration;it decreased when the oil concentration reached a certain value. Different bacterial strains had different capability for petroleum tolerance.3. Regarding to petroleum hydrocarbon biodegradation, it is necessary to add nutrients to contaminated soil, which intensifed indigenous fungus in oiled soil and improvedits microorganism activity, at the same time increased predominant bacterial strains quantity;It promoted petroleum hydrocarbon biodegradation process by the addition of highly efficient petroleum degrading bacteria and its nutrients.4. In the initial period of the degradation, petroleum hydrocarbon biodegradation effect was better in the upper layer soil, because the upper layer of soil had the better permeability when the initial humidity was almost same. Then enhanced microorganism activy and promoted petroleum hydrocarbon biodegradation. But in the middle, last period, petroleum hydrocarbon biodegradation effect was better in the center, lower layer soil. This is because of the high moisture content in the lower layer soil, it supplied the full moisture content for the microorganism that promoted cell activeness and speeded up metabolism speed, thus enhanced degradation effect.5. The total number of microorganisms and the dehydrogenase activity were closely related to the petroleum hydrocarbon biodegradation, which indicated that they were both good indexes of the contaminated soil bioremediation. However the dehydrogenase activity which compared with the microorganism quantity can reflect microorganism's active condition in contaminated soil's bioremediation.