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Treatment Of Oily Wastewater
- Aug 01, 2018 -

Treatment of oily wastewater


There are three kinds of oily wastewater in existence: oil slick, dispersing oil and emulsified oil. The first two are easier to handle, and can be treated by mechanical separation, coagulation sedimentation, activated carbon adsorption, etc., so that the oil content is lowered to a very low level. However, the emulsified oil contains a surfactant and an organic substance that functions in the same manner. The oil is present in water in the form of micron-sized ions. Gravity separation and coarse granulation are difficult, and ultrafiltration membrane technology is used to make water and low molecular organic substances. Through the membrane, COD and BOD are removed while degreasing, thereby achieving oil-water separation.


For example, the oil content of oily wastewater in oil fields is usually 100-1000mg/L, which exceeds the national emission standard (<10mg/L). Therefore, advanced high-pressure balanced shallow air flotation technology and hollow fiber membrane separation technology are used for separation before discharge. When the operating pressure is 0.1MPa and the sewage temperature is 40°C, the water permeability of the membrane can reach 60-120L/(m2 ̇h), the oil content in the effluent is trace, and the average solid content of suspended solids is 0.32mg/L. The median particle size averaged 0.82 μm, which fully met the water quality standard for re-injection water in ultra-low permeability oilfields.


Municipal wastewater reuse


Urban sewage is an important water resource. Foreign countries have begun to use a wide range of English membrane methods for urban sewage reuse. As China's water pollution problems become more serious, the application of ultrafiltration membrane technology to urban wastewater reuse has also caused People's attention. For example, Tang Fanmin et al [5] used CASS and ultrafiltration membrane combination process to treat residential sewage. When the hydraulic retention time is 12h and the CODCr concentration is between 215~677mg/L, the COD of the process effluent is stable at 30mg/L; When the concentration of NH3-N is 22.2~41.2mg/L, the effluent NH3-N can be as low as 0.2mg/L, the removal rate is over 90%, the effluent pH is between 7.26~7.89, the effluent turbidity is less than 0.5, and the effluent quality is effluent. It is superior to the water reuse standard and can be directly reused.