| About 26,700 thousand tons of crude oil is produced in Shengli oilfield each year, of which the yield in low-permeability oilfields is 2,500 thousand tons, about 9.5% of the total amount. Low permeability oilfield requires the high quality injection water because of the small pore throat radius. If the wastewater can't satisfy the requirement of reinjection water, the pore throat of stratum will be blocked easily, which will improve the pressure of reinjection pump, increase the operating costs, even directly influence the crude oil production in severe case.18 water injection stations are equipped with fine filtration treatment systems in Shengli oilfield and it brought positive effect for the exploitation and steady production of the low-permeability blocks in Shengli oilfield in a certain period. However, with the prolonged run under highly erosive and fouling formative recovery water circumstances, many problems appear in the systems and the equipments such as difficult regeneration, serious attenuation of the filtration capacity, and even perforation damage of filter element, which immediately affect the water quality and certainly will have very unfavorable influence on the water injection production. Biological wastewater treatment technology has been paid more attention due to no secondary pollution, high water quality and low cost.The content of this thesis was divided into five parts, including literature summarization, screening and characteristic evaluation of hydrocarbon degradation bacteria, laboratory simulation of oily wastewater biotreatment, pilot plant examination of wastewater treatment, and the conclusions in the last part.The oily wastewater from Bonan low permeability oilfield was selected as our test object in this thesis. The hydrocarbon degradation bacteria was screened out, laboratory simulation and a pilot plant examination were carried out for the treatment of oily wastewater by biocontact oxidation technology . The main conclusions are as follows:1. Two strains of HDB were screened out from oily wastewater by many times enrichment and purification, named as PZ-1 and PZ-2. The strain of PZ-1 was identified as Bacillus cereus and PZ-2 was Bacillus subtilis, which had the oil degradation capability of 47.5% and 41.2%, and 56.8% when the two strains were mixed together. The results of shaking flask experiment showed that removal rates of oil by the mixed strains were above 50 % when pH value of oilywastewater was 7~9, the temperature was 40℃~50℃and salinity was 7000mg/L~12000mg/L. If NH4NO3 was used as the main nitro source the removal effect of oil in wastewater could be improved obviously, the removal rate of oil was about 70%.2. A laboratory simulation was carried out for the treatment of oily wastewater by biocontact oxidation technology. The result showed that the content of oil could be lower than 1 mg/L when the hydraulic retention time(HRT) was 24~8h and 3 ~4 mg/L dissolved oxygen, which is satisfied with the A1 level of injection water quality. The sulfated-reducing bacteria could be restrained by biological competition and high concentration oxygen, the corrosion rate was controlled in less than 0.076mm/a.3. The results of pilot scale test showed that shock resistance of biological treatment unit could be improved when floatation process was used as the biochemical pretreatment, and 40%～60% oil in wastewater could be recycled. The dispersed oil and emulsified oil in wastewater could be effectively removed by biocontact oxidation, the average oil content was below 1.0 mg/L when the HRT was 8h. The pH value of oilywastewate by the treatment of biocontact oxidation increased slightly, which had no obvious effect on the removal efficiency of oil. The biocontact oxidation technology is suitable for the treatement of oily wastewater from Bonan low permeability oilfield.The results of this thesis would provide the theoretical basis and technologic support for the the construction of reinjection sewage station with daily capacity of 1500 m3/d in Bonan oilfield. Currently, the sewage station was put into operation formally in Jannary 2009.
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