Screening Of Hydrocarbon Degradation Bacteria And Studies On Biochemical Treatment Of Produced Wastewater In Oilfield

With the durative exploitations of the primary oilfields in China, the water content in produced water is higher, as well as water quality is more complex. The traditional wastewater treatments could not meet the developments of oilfield and environmental protection. The adaptability of reinjected water quality was only 57% in Shengli oilfield in 2005. The existing physical and chemical methods have a series of deficiencies, with the low efficiency of eliminating oil, thus the techniques have to be improved exigently. Biological wastewater treatment technology has been paid more attention due to no secondary pollution, high water quality and low cost. The main levels of the oil, sulfate reducing bacteria (SRB) concentration and corrosion rate treated by the biological technique are far better than that treated on other existing processes.The content of this thesis was divided into five parts: the first part was literature summarization; the second part was screening of HDB and their characteristic evaluation; the third part was studing on biodegradation; the fourth part was simulation experiment of biological treatment; the last part was conclusions.In this thesis, we selected Daluhu oilfield as our study object. The systemic simulated experiments were carried out in the laboratories, screening high-temperature hydrocarbon degradation bacteria(HDB), which could be utilized in biological treatments through floatation and contact oxidation, in order to find out economical technics and operating parameters in biological treatments. In addition, mechanism and processes of microbial degradation had also been studied. The main conclusions are as follows:1. A high-temperature, high-efficiency HDB were enriched and isolated from petroleum contaminated water and soil samples, which contained three strains. After the primary test, we know that one was Acinetobacter sp., and the others were Bacillus sp.. Through shaking experiments, the best degradation conditions of mixed bacteria presented as follows: the temperature was 45~60℃, the pH was 5.0~8.0, the mineralized rate was 15000~27000 mg/L, the inoculation was 2%,the initial crude oil concentration was lower than 500mg/L, and the rotating speed was 180rpm.After analyzing the composition of crude oil in degradation, the results were concluded as follows: HDB preferred degraded brief,middle saturated hydrocarbons; HDB mostly degrade saturated hydrocarbons, the degrading rate of normal alkane exceed 90%, the part of PAHs were degraded ,not obviously;biological marker such as menthane, sterane,were not degraded basically.2. In the simulated experiments, oil content, suspended solid and SRB were wiped off distinctly by floatation, oil content which was 8 mg/L averagely could reach the request of biochemical treatment. During culturing stage, the superior strains were utilized to culture biofilm. The matured biofilm exhibits a distinct effect towards produced wastewater. After the treatment, the water quality reached the A2 standard which was required by the oilfield, except for suspended solid. SRB could not reproduce in closed system. The optimum operation time of HRT was 6h.The results of this thesis would provide the theoretical basis and technologic support for the biochemical treatment of produced wastewater of Daluhu oilfield. And it has been put into use in-situ in Daluhu oilfield.