Experimental Study On Biological Treatment Of Disposal Oily Water

Sazhong oilfield has come into a high water cut stage, polymer flooding production has been applied on a large scale to sustain its high and stable production. For polymer flooding efficiency, polymer should be prepared and diluted with fresh water, so a great deal of oilbearing sewage treated has to be piped out. The method of preparing polymer solution with oilbearing sewage is being tested in some areas, but the oil displacement efficiency is not satisfying and can't be developed in the whole oilfield. Although other reasons can cause oilbearing sewage to be piped out, such as periodical water flooding, maintenance in multi-purpose stations, accidental water release and shutting off of water injection wells, the main reason is still caused by polymer flooding. Oilbearing sewage needs to be treated to meet Government Discharging Standard by disposal technology which can be applied in the cold areas in Sazhong Oilfield and decrease the environmental pollution. The early waste water treatment process didn't apply the biological process because of the speciality of the oilfield production. With the increasing of the waste water discharge as well as more and more complicated waste water components, it's a trend to attach importance to and apply the biological process in the foreign oilfield lately. By analyzing the sorts of organic contaminants in waste water disposals, we know that oilbearing sewage with medium degradation can be bio-treated and degraded, in which polymer is the most difficult to be degraded. After proper pretreatment, it's necessary to improve its ability of bio-treatment properties and then to treat it with the biological process. Aerobic membrane biological process is suitable to the extremely cold zone in Sazhong Oilfield, the advantages of which are to take up less experimental areas, high efficient process and low cost. The temperature is not a problem in treating oilbearing sewage from the experience in the north area, but the oxidation pond process can't. Experiments between activated sludge process and aerobic membrane biological process under the same inlet condition are as follows: First, the oilbearing sewage from the gravity pots comes into the anaerobic hydrolysis pool where the organisms and suspensions in the oilbearing sewage are removed by anaerobic microbe. The effluent flows to the activated sludge pool and the aerobic membrane biological pool respectively to have an aerobic degradation to the residual organic contaminants and then to be piped out through the secondary precipitation tanks. After secondary settlement, the water is piped out. The sludge in the secondary settling tank needs to flow back or be treated periodically. The temperature of the whole system is adjusted between 30℃and 40℃to simulate the sludge condition of the in-situ oilfield. After extensive survey on oilbearing sewage treatment technology both domestic and abroad, a further study is made aiming to the practical situation of the field. It explores the feasibility of the biochemical treatment by indoor bacterium cultivation experiments. By comparison of anaerobic process and aerobic process under different conditions, it is feasible to adopt high efficient microorganism treatment technology and pick out a waste water treatment process which combines anaerobic hydrolysis with aerobic biochemistry. Furthermore, by comparing activated sludge process with the aerobic membrane biological process, we reach a conclusion that the latter has more practical value. By experimental study, the conclusions are as follows: I. It is feasible to adopt high efficient microorganism treatment technology in Daqing oilfield. The advantages of low salinity and moderate temperature of the oilbearing sewage are favor of biochemical treatment , but the BOD/COD ratio is around 0.3, the water contains long chain polymers which are hard to be degraded . So we must improve its biochemical degradation by technology method. The experimental result shows that the bacterial strains with a special function can degrade the contaminants in the waste water. II. The treated waste water can meet the second grade of integrated wastewater discharge standard by combination of anaerobic and aerobic process. The test shows that neither anaerobic nor aerobic can process the oilbearing sewage to meet the qualified drainage standard, because the produced water contains much oil hydrocarbons and chemical addictives which are the main source of COD. By adopting the anaerobic process alone, it is hard to decompose the substances mentioned above in a short time; and in the anaerobic experiment, there are many kinds of microorganisms and the reaction is complicated, acid producing bacteria can decompose long chain polymers and infusible high molecular organisms to low molecules and fusible organisms with the aid of exoenzyme. It improves the BOD/COD ratio, increases the ability of bio-treatment properties and wipes off some organisms. According to the features of the oilbearing sewage (temperature 40℃～50℃) and environmental conditions( low temperature in winter), it is feasible to adopt the combination of anaerobic and aerobic process under...