Experimental Study On Oil Wastewater Treatment By Two Stages Type Biological Aerated Filter

As the development of oil prospecting and petroleum chemical industry, oil wastewater has been one of the most important industrial pollution source. Oil wastewater has some characteristics such as high toxicity, high COD and weak biodegradability and it is harmful for the water environment, soil and the health of animals and plants. In order to solve these problems, it is widely significant to seeking for a technique which is effective feasibility, credible economy, convenient for management.In this paper, with respect to some characteristics of oil wastewater above mentioned, the "HOBAF" two stages type system which means the combination of Hydrolyzing and Acidification reactor, and the Biological Aerated Filter has been used to treating the oil wastewater after filtration from certain oil field of Shanxi. The running behavior of hydrolysis stage and aerobic stage was inspected respectively. At the same time, the most optimum operating condition was determined and the main factors affecting the running behavior of the systems were studied thoroughly by experimental investigation and theoretical analysis.The main results in this paper are listed as follows:(1) It is demonstrated that by the experimental results, as pretreatment device, the hydrolysis stage can enhance the biodegradability of oil wastewater significantly, intercepting SS of the influent, and it can resist the shock loading and provide stable water quality to aerobic stage. When the HRT of the two stages type system is kept in 7 hours, the BOD/COD of effluent of hydrolysis increased from 0.24 to 0.43 averagely, the SS removal rate can reach 80%. Besides, hydrolysis stage has certain contribution to the removal of oil and COD. On this condition above mentioned, removal rate of oil and COD can reach 23.7% and 34.5% respectively.(2) Hydraulic loadings, influent COD concentration and g/w ratio were leading factors affecting the running behavior of the BAR By the experiment, the optimum operating condition was be determined as follows:hydraulic loading is 0.2m3/m2.h, g/w ratio is 5:1. The ranking order of these leading factors was determined by orthogonal experiment as follows:hydraulic loading, g/w ratio and influent COD concentration. On the optimum operating condition, pollutants removal rate of different range of height layer of BAF is differ from one another. In the scope of the first 30cm of filter, the efficiency of COD removal rate is at the peak and the rate of the degradation is the fastest of the whole filter, accounting for 45.7% of the total removal rate.(3) It can be determined by the COD and petroleum types rate under combination of different operating condition that the most optimum parameters of two stages type system is HRT=12h,(hydrolysis stage is kept in 7h, aerobic stage is kept in 5h), the g/w ratio of aerobic is 5:1.On this condition, removal rate of COD and petroleum type can reach 94.7% and 92.44% respectively, effluent COD concentration is in the scope of 36.4-47.1mg/L, effluent petroleum type is in the scope of 3.47-4.86 mg/L, both of two can satisfy the request of the first grade standard about oil wastewater of GB8987-1996. In addition, when the influent oil is not exceeding 70mg/L, the two stages type system has good tolerance to the petroleum type. Meanwhile, the two stages type system has excellent ability to resist shock loading formed by sudden change of salinity, then the system can ensure the effluent water quality effectively.