Research On In-situ Bioremediation For Oil-contaminated Soil In Oilfields

Oil-contaminated soil is one of the environmental problems resulting from petroleum production, and one desirably solved by petroleum companies. For traditional physical or chemical methods, a lot of fixed facilities are often necessary for remediation for oil-contaminated soil, in which chemical regents are added into the process for some cases, and temperature, pressure, electric power supply and other conditions are needed with a high dispose cost and additional pollution. Therefore, the removal of oil by utilizing the degradation function of microbes is one of effective technologies for the remediation for oil-contaminated soil. Bioremediation is a kind of remedying technology for the ecological system of oil-contaminated soil by making use of the degradation function of microbes. The cost is from about one fifth to one third compared to the traditional physical and chemical methods. This technology has being developed recently in the field of environmental protection. Due to its advantages in a low cost, free additional pollution and moderate conditions, the method has been studied and developed extensively in the world. However, the technique is still in the stage of laboratory experiments, and only small scale of field tests is in operation because the process is not stable and the effect for high-oil soil is difficulty to work. According to the recent situations of Daqing Oilfields, a kind of microbial remediation composed by four types of substances with different functions was developed based on the study of the native microbes for crude-oil degradation. In this research, the aim was focused on the enhancement of the rate and effect for the soil bioremediation by probing the efficient microbe seeds for crude oil degradation. By determining the microbial regents and method, a suit of in-situ bioremediation techniques fitting for local oil-contaminated soil were exhibited. Compared by a commercial OILGATOR, the US patent product of microbial regent, performances of the developed microbial regents were higher. This research was approved by the Science & Technology Department of Heilongjiang Province. The appraisal results showthat the technology has reached international advanced level. This technique surely provides an economical and feasible method for the bioremediation of oil-contaminated soil in Daqing Oilfields or the other oilfields.This research mainly includes three parts, which are briefly introduced as followings:1. A study of evaluation method of the in-situ bioremediation for oil-contaminated soilAn accurate analysis for oil content of the soil was put forward by dealing with problem existed in the weighing method for incomplete extraction of oil in the soil. It was found by research that the measuring value is evidently linear to the standard value, and the linear correlation degree is 0.9993. Therefore, a method was used for amending measuring results with the correction coefficient is 1.1625. The correlation was obtained in Creal = 1.1625Cmeasured. The accuracy of the corrected method is enhanced from 88% to more than 94%. The relative standard error of the corrected measurement is 0.43%, which indicates themethod has a good reproductivity.Based on plate count method for bacterial colonies, a technique was developed for a microbial observation in the bioremediation application. The operating process was determined for the selection, identification and dynamic analysis of bacterial colonies.2. A study of microbial identification and in-situ bioremediation regent for oil degradationBy using of the developed method for bacterial colonies, microbial identification was successfully carried out. 42 bacteria seeds, 8 fungi seeds and 10 actinomycetales were separated and identified from the contaminated soil according to bacterial colony characteristics, seed and spore structure, and physiological and biochemical properties. It was found that the dominant bacteria existed in soil include micrococcus, arthrobacter, bacillus, acaligenes, acetobacter, and flavobacterium; the dominant fungi do aspergillus Niger Nan tieghem, aspergillus aersicolor tirabaschi, penicillium chrysogenum thom, penicillium freguentans westling, tichoderma viride pers. Ex Fr., cepha esosp orium oud., aureobasidium pullulans (deBary) arnaud, and fusarium Lk.; the main actinomycetales do streptomyces. In the active microbial bacteria seeds for oil-degradation, the degradation activity of fungi seeds is higher than that of bacteria or streptomyces, which shows that the bioremediation for oil-contaminated soil is mainly controlled by fungi. Based on the above works, 8 fungi seeds, 3 bacteria seeds and 2 streptomyces seeds, well growing in the substrates containing crude oil, were selected.By using the defining dominant bacteria seeds taking wheat bran as carrier, a novel bioremediation regent, named by ZL-1 type, was developed. It was obtained by appropriate match of four kinds of substances, i.e., microbe, nutriment, surface-active regent and remedying soil material. The composition and usage were also determined..3. An experimental study of the in-situ bioremediation for oil-contaminated soil Aimed at actual applications, the experimental study on the factors, such as mineralization degree, PH value, and sulfide content, was carried out. It indicates that:I. The waters, including from polymer-flooding, water-flooding and tap in Daqing Oilfields, exhibited ineffective on the microbial degradation.II. The mineralization degree influenced the oil degradation. With the existence of mineralized materials in the water, the oil degradation rate was decreased with minor extension.III. In the weak acidic condition, the degradation rate is high while the rate is low in the weak basic condition with small differences.IV. Compared to the experimental results obtained by diluting with sulfide-free and oil-contaminated water, the existence of sulfides could improve the effect of microbial oil degradation while it is basically the same whether in 100 mg/L or in 30000 mg/L of the sulfide.In contrast with the commercial OILGATOR imported from the USA, the laboratory study of the ZL-1 type in-situ bioremediation regent demonstrated that as follows:I. For in-situ bioremediation regent of the OILGATOR, under room temperature ( 18~20℃from Marchto May; 20~25℃from June to September), the oil content in soil was decreased to 0.3% of original 5% through microbial degradation 0f 3 - 6 months, which fulfills the national discharge standard; the oil content was done to 2.9% of original 15% through microbial degradation 0f ~ 6 months.The initial degradation rate is higher while the speed decreases evidently in the following progress, and the level of oil content kept constant when the initial oil in soil reaches a certain value (e.g., 1% for 5% oil; 3% for 15% oil).II. For in-situ bioremediation regent of the ZL-1, under room temperature ( 18~20℃from March to May; 20~25℃from June to September), the oil content in soil was decreased to 0.3% of original 5% through microbial degradation 0f 3 - 6 months, which fulfills the national discharge standard; the oil content was done to 2% of original 15% through microbial degradation 0f ~ 6 months.The initial degradation rate is higher while the speed decreases evidently in the following progress, and the level of oil content kept constant when the initial oil in soil reaches a certain value (e.g., 1% for 5% oil; 2% for 15% oil).It was found by contrast that the developed microbial product had reached the treating effect of imported products.4. An field test of the in-situ bioremediation techniques for oil-contaminated soil Under the local condition in Daqing oilfield, the field test was carried out by using the OILGATOR and the ZL-1 type in-situ bioremediation regent, focused on three types of solid oily soils in the oilfield, the following results were probed by the field test:I. For the in-situ bioremediation treatment of contaminated well site, the oil content was reduced to 2.103% after 2-month degradation and 1.057% after 1-year degradation from initial content of 13.628% only by using the OILGATOR while the oil content was lowered to 1.654% after 2-month degradation and 0.298% after 1-year degradation from initial content of 8.231% only by using the ZL-1 type in-situ bioremediation regent, and the oil content was degraded to 0.854% after 2 months and 0.286% after one year from initial content of 9.132% by using both the OILGATOR and the ZL-1.II. For the in-situ bioremediation treatment of the oil-contaminated sludge discharged from treatment stations, the oil content was reduced to ~1% after 6 months and OILGATOR degradation from the initial content of 13.54% under the above 10℃while the oil content was lowered to 0.185% after same period and ZL-1 degradation from the initial content of 6.10% , which meets the requirements in the national standard.III. For the in-situ bioremediation treatment of the oil-contaminated sludge in the treating site for fall-to-the-ground crude oil, the bad effect was shown due to its high oil content with heavy composition. After nearly 3-month tests, the oil content in the oil-contaminated sludge was reduced to 6% from 40% by using the OILGATOR while reduced to 2% from 10% by using the ZL-1.It indicates that the ZL-1 product is feasible for the bioremediation treatment of crude-oil contaminated soil and sludge. The effect can reach the technical level of the advanced OILGATOR regent.5. The innovations of this dissertation are focused on that:I. For the first time, the effective soil remedying regent was applied for the amending the oil-contaminated soil in salty/alkaline land. Introduction of the bioremediation technology for oil-contaminated soil improved the remedying effect to a great extent.II. The ZL-1 in-situ bioremediation regent of oil-contaminated soil was produced by Effective combination of the native microbial bacteria in crude oil with a microbial surface-active, soil remedying and nutriment regents. The treating effect in the application of oilfields was over one of the imported patent product.III. The continuous supplement of nutriment and soil remedying regents during the bioremediation process was adopted to ensure to keep microbial nutriment balance and to improve microbe-growing activity.IV. The accurate method of analyzing the oil content in soil was established for providing effective means for real-time monitoring and evaluation during bioremediation process.