Study On The Treatment Process Of Oilfield Polymer Flooding Produced Wastewater Using Codgulation-ultrafiltration

In recent years, the moisture content of oil has reached80%to90%,which resultsin nearly1billion tons of oil produced wastewater needing to process, with the most ofthe oil field has entered the stage of late mining. The wastewater generated by oilfieldpolymer flooding can not all be used for reinjection due to its large amount,so part ofthe wastewater need to treat before discharge to the environment. Nowadays, thegeneral treatmeant of oil wastewater can not meet the requirements of water quality,sothe coagulation-ultrafiltration combined treatment process of oilfield polymer floodingproduced water was investigated.In the study,the treatment of oil wastewater by means of ultrafiltration directlyand coagulation+ultrafiltration combined process were investigated respectively, thecoagulation+ultrafiltration combined process was choosen after comparing. The effectsof flocculant type and dosage,, pH, temperature, water conservancy stirring,transmembrane pressure on treatment effect were investigated. The removalefficiency content of oil, turbidity, HPAM, COD could achieve92.7%,94.6%,87.5%,95.2%respectively under the optimum operating conditions: polyaluminium chloride（PAC）concentration of400mg/L, pH wih no adjustment, temperature40°C, quickstir time1min under the speed of400rpm, slow stir time10min under the of90rpm,static settling time0.5h, ultrafiltration pressure0.04MPa, membrane surface flow rate0.7m/s, temperature40°C, backwash cycle40min.In several small experiments, the coagulation+ultrafiltration combined treatmentprocess was conducted to treat unstable quality of oilfield polymer flooding producedwater under the optimum operating conditions. The result showed that the processedeffluent quality reached the daqing oilfield "water flooding of injected water qualitycontrol index" and "the integrated wastewater discharge standard" level1Bstandard.The treatment effect is good and the removal efficiency of suspended solids,content of oil, COD, HPAM, turbidity were90.14%,98.5%,92.70%,93.51%,94.89%respectively.For the downward trend of the membrane flux in ultrafiltration,The process ofmembrane cleaning methods was invetigated:physical or chemical cleaning methods,chemical cleaning agents, cleaning time, different agents.The result indicated thatchemical cleaning method was selected,and the cleaning agents for0.05mol/L NaOHsolution+0.05mol/L HNO3. The membrane flux recovery coefficient in each stage wasalso studied,which indicated that the hydraulic cleaning and0.05mol/L NaOH cleaningplayed a leading role in membrane flux recovery.Four membrane filtration dynamics models were used to speculate the downwardtrend of the membrane flux. The results shown that filter cake filtering model and strong bad polarization model were more in line with the membrane fouling.The proportion of film itself resistance, reversible membrane pollution resistance,irreversible membrane pollution resistance in the total resistance were studied too, Theresults indicated that the irreversible resistance occupied the smallest percentage,and thereversible membrane pollution resistance the largest.The new membrane and pollutedmembrane wre characterized by AFM, SEM, EDX.