| Oily wastewater from oil exploitation contains much oil, large amounts of suspended solids, bacteria as well as Ca2+, Mg2+ and SO42-. It caused severe damage to the environment and ecology and production of oilfields. The best way of dealing with oily wastewater is re-injection and re-use after advanced treatment. Ultrafiltration(UF) can well remove pollutants in oily wastewater such as:suspended solids, oil, bacteria and part of COD. The permeate of UF can meet the quality of injection water for low-permeability oilfield. To reuse oily wastewater and save water resources, nanofiltration (NF) can reject scaling ions such as Ca2+, Mg2+, SO42-, Sr2+, Ba2+, and reduce salinity and alkalinity, making the treated oily wastewater available for polymer flooding water and boiler make-up water.With the dual purpose of oily wastewater re-injection and reuse, integrated membrane system (IMS) of UF and NF were designed to treat oily wastewater. The membrane types, membrane fouling, influencing factors of the IMS process were tested. The stability of IMS to deal with oily wastewater from different oil blocks was investigated. Last the feed water indicators for treating oily wastewater with IMS was presented.When experiment in situ, pretreatment process of IMS was investigated firstly. According to the effect of removling oil, suspended solid and turbidity, different pretreatment processes were selected. Pre-tretreatment with two stage microfiltration (MF-1+MF-2) was designed to treat oily wastewater in Le'an sewage station, Pre-tretreatment with oil remover and bag filter was chosed to treat oily wastewater with high salinity in Biyi sewage station for guaranteeing better quality of treated feed water.Based on determined the pre-processing procedures, oily wastewater was treated by IMS was studied. In this part, the respective performance characteristics of ultrafiltration and nanofiltration were systematically explored. The results showed that: permeat flux of polysulfone (PS) and polyether sulfone (PES) ultrafiltration membranes (No.UFâ… and No.UFâ…¡) increased as the rise of operating pressure, however the flux decay rate showed a increased tendency gradually. Period of physical backwash showed better effect for membrane flux recovery, the backwash is generally less than 40 minutes. Two kinds of ultrafiltration membrane with different materials had good effects for removal of suspended solids and oil. Both of permeat from two kind ultrafiltration membrane can basically meet the water quality requirements for low-permeability oilfield injection. Compared with UFI, UFII with better hydrophilic had higher flux.When nanofiltration membrane treated with the oily wastewater different salinity property, the flux changed greatly. The permeat flux of NF increased as the rise of operating pressure, however the ratio of the increased fluxes reduced when the pressure was over a certain value. The retention rate of salinity and hardness was also different, when dealing with different mineralized oily wastewater, but retention rate of scaling ions such as Ca2+, Mg2+, SO42- remained stable and the rejection rate of hardness, salinity and COD respectively reaches as high as 97%,91% and 81%.The study on membrane fouling of UF and NF was carried out. SEM, AFM and EDX were used to identify the surfaces of new membrane, washed membrane and fouled membrane.The result showed the main pollution materials causing ultrafiltration fouling were organic pollutants such as oil and COD. For NF membrane are fouled mainly by organic fouling.To conclude, for oily wastewater purification by IMS is a feasible technology purified by intergrated membrane easily. The IMS can be run well and stably for long time, and can supply fine quality water for polymer flooding and steam-injection boiler. This study has found ground foundation for its wide application in this area.
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