Ecological Effects And Bioremediation Of Petroleum-contaminated Soil

Oil-contanminated soil could considerably influence the normal function of the soil, the ecological enviroment and the human health. People are paying more and more attention to the study of contamination mechanism, ecological effects and bioremediation technology of petroleum-contanminated soil. Biological treatment of petroleum-contanminated soil has many advantages, for example, low cost, mild conditions, no second pollution. So the method has caused wide public concern and developed rapidly. In view of the present situation of the petroleum-contanminated soil in Northern Shaanxi Province, the characteristics of absorption, desorpton, vertical migration and degradation of petroleum pollutants in loess medium have been revealed through the laboratory experiments and field tests. Effects of petroleum-contanminated soil on the growth of microorganism and the microbial community in ecological system of the soil-plant have been systematically investigated. Oil degrading microorganism is isoled firstly in this thesis, bioremediation technologies of phytoremediation and plant-introduced microbes of petroleum-contanminated soil are constructed on the basis of the research of the dynamics and the most suitable ecological conditions in biological degradaton of petroleun pollutants. The evaluaton system of the bioremediation of oil-contaminated soil is set up, the efficacy and safety of the bioremediation technology is evaluated preliminarily according to this standard after the field trial had been finished. The achievments of the research are as follows:1. The study of the adsorption and desorption of petroleum pollutants in batch tests have discovered that the distributes of petroleum hydrocarbon in loess phase-water phase conforms to the Freundlich equation, the adsorption dynamics may be described by the logarithm equation approximately, the organic matter content is major factor affecting the adsorption capacity. The desorption of petroleum pollutants in the loess can balance quickly,but the release quatity is very small,it increases along with the pH.The vertical transport characteristics of petroleum pollutants in the loess has been studied by column penetration tests. The results show that this process is very slow, and the most of the petroleum pollutants are intercepted in the surface soil. The result of shaking cultivation and stacked experimentation shows that biodegradation is a major removal way of petroleum pollutants in the loess naturally.2. The study of the characteristics of the growth of microorganism and plants in petroleum-contanminated enviroment shows that the lag phase of bacterium's logarithmic growth curve has shortened remarkably than that of the fungi, the colony numbers of bacterium in stationary phase has been higher than the fungous numbers, the bacterium is the main body of the microflora in petroleum polluted enviroment. oil-philic microorganism are increasing in number greatly and there are remarkable increase difference for different plants in the petroleum-contanminated ecological system of the soil-plant. When the initial concentration of the petroleum in soil is 300 mg/kg～50000 mg/kg, the germination-percentage of the alfalfa is decreased 24%～78%. In treatment with petroleum concentration of 10000 mg/kg, chlorophyll contents and superoxide dismutase (SOD) activities are decreased remarkably,malondialdehyde (MDA) contents are increased obviously, the physiological characters of plants can be significantly affected by petroleum, the biomass of the corn, the sunflower and the soybean decrease 14.5%,21.2%,7.6% respectively, the plant's growth can be inhibited. Residual petroleum hydrocarbon has been discovered in different parts of the plants, Petrolic residual quantity is the highest in the root, next in the seed or stem. When the petroleum density in the soil achieves 10000 mg/kg, petrolic residual quanlity of the corn,the sunflower, the soybea can reached 3.82 mg/kg,4.64 mg/kg and 1.14 mg/kg respectively in seed, benzo[a]pyrene(BaP) content in the corn is 5.78μg/kg, which is more than the government-required standard (<5μg/kg). The food stafety is threatened.3.28 predominant strains for degradating oil have been isolated from the petroleum-contaminated medium,and identified results show they are 5 Micrococcus sp.,6 Arthrobanter sp.,3 Acinetobacter sp.,2 Baccillus sp., a Microbacterium sp.,a Pseudomonas sp. and 2 Aspergillus sp., a Cephalosporium sp.,a Mucor sp.,a Saccharomyces sp., and a Trichoderma sp..10 strains of high-efficient petroleum hydrocarbon degradation bacteria have been obtained by the study of their degradation rate for petroleum hydrocarbon. The study of single-factor experiments and multifactoral experiments has indicated that the best ecological conditions of petroleum-contaminated soil biodegradation are that nutrition material C:N:P= 40:2:1, electron receiver body H2O2 (the liquid of 30%)joining quantity amount to 9000 mg/kg, water content is 50%, suitable surface-active agent is Sodium Dodecyl Benzene Sulfonate. the relation of primary and secondary factor of the bioremediation is water concent, surface-active agent, nutrition material, and electron receiver respectively.4. The study of the in-situ bioremediation experiments for two years time showed that the systems consisting of the corn, the sunflower, the alfalfa and the soybean had obvious repair function to the petroleum-contaminated soil, the petroleum biodegradation efficiency of 4 phytoremediation systems were 42.5%,46.4%,44.7% and 40.6% respectively with initial concentration of 10000 mg/kg within 150 days. The petroleum biodegradable efficiency were 95.5%,96.1%,92.4% and 87.6% respectively within 500 days. The union bioremediation systems of "corn-exogenous Arthrobacter-DX-9" and "sunflower-exogenous Arthrobacter---DX-9" had made the petroleum pollutants of initial concentration of 10000 mg/kg to reduce 72.8% and 76.4% within 150d, increasing by 71.3% and 64.6% compared with controlled field, which there was no exogenous Arthrobacter. The petrolic content in the soil of the experimented fields had been remved 97.6% and 98.9% within 500 days. The union bioremediation systems consisting of "alfalfa-the mixed strains", which make up of Bacillus, Pseudomonas, Arthrobacter and Microbacterium, and "soybeans-the mixed strains" had made the petroleum pollutants of initial concentration of 10000 mg/kg reduce 63.5% and 51.7% within 150d, increasing by 27.3% and 42.1% compared with controlled field.The petrolic content in the soil of the experimented fields had been removed 98.8% and 92.7% within 500 days. The union bioremediation has achieved satisfactory efficiency.5. The growth indexes, the quality characters for seeds, the residue of petroleum in different parts of the plants and the physic-chemical properties, microbial distribution and respiration intensity of the soils in experimented fields are not significant difference compared with controlled fields. Eco-toxicity of petroleum-contaminated soil to plant is eliminated. The contaminated soil has been restored to health by the bioremediation for two years time. The bioremediation technology established by the plants and exogenous bacteria is safe and effective for the treatment of the non-point source petroleum-contaminated soil.