Study On Bio-treatment Of Heavy Oil Sewage Reused In Thermal Steam Generators

Today, most of oilfields in our country have already entered into the mid or late stage, so a large number of viscous crude oil has been exploited. During the exploitation and refinement of crude oil, a lot of heavy oil wastewater will be discharged. Owing to short of water in China, how to treat this wastewater successfully and use them during production has been the problem needs to be solved urgently. After treatment, the crude oil wastewater mainly used in thermal steam generator, reinjection and released.Physical,chemical and bio-chemical methods are major kinds of techniques used to treat heavy oil wastewater. The main problems of physical and chemical techniques are low efficiency and high cost, compared with those methods, the bio-chemical technique has many advantages, such as high efficiency, low cost and no secondary pollution, due to these reasons, the bio-chemical technique is paid more attention.The content of this thesis is divided into five parts: the first part is literature summarization; the second part is screening of HDB tolerable with heat and salt, the evaluation of their functions, the construction of degradation community; the third part is the research of petroleum hydrocarbon biodegradation; the fourth part is laboratory simulation experiment and pilot plant research; the fifth part is conclusion and advice.In this thesis, four bacteria tolerable with heat and salt were screened from the heavy oil wastewater and the soil contaminated with oil in Chenzhuang, Shengli oil field. The oil and COD degradation community was also constructed, which was used in the laboratory simulation experiment to treat the wastewater. The combination technique of bio-contact oxidation and UF-RO was used in the laboratory simulation experiment, the produced water reached the aim to replace fresh water used as boiler feedwater. The parameters were optimized in the pilot plant research. Beside these, the mechanism of oil biodegradation was studied by GC-FID and GC-MS. The main conclusions are as follows:(1)Four oil-degrading strains tolerable with salt and heat were screened from heavy oil wastewater and the oil-contaminated soil in Chenzhuang, named as HD-1, HD-2, HD-3 and HD-4. HD-1 and HD-3 were identified as Pseudomonas sp. primary, HD-2 and HD-4 were identified as Bacillus sp.. The degradation ability of every bacterium was studied; the best condition of the growth and degradation of each strain was researched. The results showed that the ability to degrade oil and reduce COD of these strains was very high, the oil degrading rate of HD-1, HD-2, HD-3, HD-4 was as follows: 42.0 %, 47.6 %, 55.6 %, 43.4 %; the remove rate of COD is 6.1 %, 39.2 %, 41.3 %, 35.2 %。(2)The oil and COD degradation community is constructed by orthogonal test, the community is 0.5 % HD-1, 1.0 % HD-2, 0.1 % HD-3, 0.5 % HD-4. The oil degrading rate of this community was 68.01 %, the remove rate of COD was 52.9 %, which was better than other communities and the single bacterium.(3)Based on the analysis of the variation of normal alkanes and polycyclic aromatic hydrocarbons (PAHs) before and after degradation, the mechanism of degrading was studied by GC-FID and GC-MS. The results showed that the degradation ability of the single strain was high and the mixed strains were more effective. The single strain's average degradation rate of the normal alkanes which carbon chain is shorter than 30 was more than 50 %, the average degradation rate of the normal alkanes which carbon chain is from 30 to 33 was 20 %; the short chain alkanes can be degraded almost completely by mixed strains, the average degradation rate of the normal alkanes which carbon chain is longer than 30 was 50 %, the average degradation rate of the mixed strains reached to 65 % after adding the biosurfactant released by HD-2. The average degradation rate of PAHs by single strain was 35 %; the average degradation rate of mixed strains was 40 %, after adding the biosurfactant released by HD-2 the degradation rate was more than 55 %.(4)The experimental process in simulated experiment was designed based on bio-contact oxidation and UF-RO. In experiment, firstly, the wastewater was treated by floatation and two stage bio-treatment, then, the it was treated by the UF and RO. The results showed that this technology can replace fresh water used as boiler feendwater and it can be used in actual production. The effects of DO and HRT were studied and it showed that the optimization DO was 3.5 mg/L to 4.0 mg/L and the HRT was 8 h. Under this condition, the process would meet the demand of the feedwater and the actual production.(5)Based on the results of the lab simulation experiment, the pilot test was carried on, the optimum parameters were also studied. As the temperature is very high, the cooling procedure was added in the test. The temperature, the kind and the concentration of the flocculants were optimized. The results showed that when the HRT was 8 h, the temperature was between 45℃and 50℃and the flocculant was PAC, its concentration was 80 mg/L, the removal rate of turbidity reached to 95.6 %, which can satisfy the requirement to feed UF, the product water of RO can replace fresh water used as boiler feedwater.