Study On Treatment Technology Of Oil Production Wastewater In Liaohe Oilfield

Wastewater from tertiary oil recovery is currently a critical point in the treatment of wastewater from oil production in China.In the process of oilfield exploitation,a large amount of wastewater that contains large amount of pollutants is generated,which has a significant environmental impact on water bodies,soil,ecological environment,and humans.Therefore,taking cost-effective treatment measures to ro reduce the contaminants concentration to meet the standards for discharge or reuse has important practical significance for the sustainable development of the current petroleum industry.Based on the characteristics of water quality,the SBR biochemical+depth treatment process route was selected,which can be divided into three technical routes:BCB(Biochemical pretreatment-Chemical oxidation technology-Biochemical post-treatment),BC(Biochemical process-Chemical oxidation technology)and BA(Biochemical process-Activated carbon adsorption).The most suitable treatment path is determined by comparing the treatment effect and economic cost of each technical route and treatment process.The operation cycle of primary SBR was 24 h(instantaneous inlet and outlet water,aeration 22 h,sedimentation 1 h,idle 1 h),and the hydraulic retention time was 38.5 h.For the influent water with COD of 260-360 mg/L,the removal rate could reach 40%-56%after stabilization,and the effluent COD after reaction was 138-167 mg/L.The effluent COD remained stable after 8 h of SBR stabilization operation,so the operation cycle of the SBR in practical projects can be set to 8 h.SBR process mainly removed organic matter with molecular weight<1 kDa,including small molecule protein-like and humus-like organic matter in wastewater.To further treat the wastewater,physical and chemical methods were subsequently applied.Route 1 aimed to apply the BCB process route,comparing the degree of improvement of O3 oxidation and Fenton oxidation technologies on biochemical properties of the primary SBR effluent,and selecting the appropriate process for the secondary SBR reaction.Under the optimal conditions of reaction time of 90 min,adjusted pH=8.0 and O3 concen-tration of 10 mg/L,O3 oxidation degraded the COD and UV254 of primary SBR effluent to 73 mg/L and 0.244 respectively,increased B/C to 0.244 as well.When using Fenton oxidation technology,under pH=4.0,H2O2/Fe2+molar ratio of 1,H2O2 dosage of 150 mg/L,and reaction time was 2 h.COD was degraded to 86 mg/L,UV254 was changed to 0.330,and B/C reached 0.358.Considering the treatment difficulty and cost of the sludge produced by Fenton oxidation,the wastewater after O3 oxidation was selected for secondary SBR reaction,and the effluent COD was at least 59 mg/L,which could not meet the maximum permissible discharge concentration(where COD<50 mg/L)of water pollutants directly discharged in the comprehensive discharge standard of Liaoning Province sewage(DB 21/1627-200).Route 2 adopted the BC process route,two advanced oxidation technologies,O3/H2O2 oxidation and thermally activated sodium persulfate oxidation were selected to treat the primary SBR effluent.The combined O3/H2O2 oxidation treatment of the primary SBR effluent resulted in an effluent COD of 35 mg/L and UV254 of 0.152 at the reaction time of 40 min,without changing the pH of the primary SBR effluent,an O3 concentration of 10 mg/L,and an H2O2 dosing of 60 mg/L.When the primary SBR effluent was treated by thermal activated sodium persulfate oxidation with a reaction time of 2 h,sodium persulfate dosage of 2 g/L,no change in the initial pH,and a reaction temperature setting of 80 ℃,COD degraded to 35 mg/L and UV254 degraded to 0.234.Route 3,BA method,which is an activated carbon adsorption process added after the SBR process,was compared to investigate the effects of the dosage and adsorption time of three kinds of activated carbon,namely,coal powder carbon,coconut shell powder carbon and regenerated granular activated carbon,on the treatment effect.When the reaction time was 15 min and the amount of coal powder carbon was 0.5 g/L,the COD was degraded to 41 mg/L,and the removal rate of COD reached 65%.The adsorption of COD by pulverized coal carbon was in accordance with the Freundlich adsorption model.The wastewater treated by both BC and BA technical routes could meet the standard discharge,activated carbon adsorption was the best process to treat the subject of this study from the cost analysis.The final decision of BA technology route,i.e.SBR+Activated carbon adsorption,was determined.The specific process parameters were:SBR operation cycle of 8 h,hydraulic retention time of 14 h,activated carbon adsorption of 500 mg/L coal powder activated carbon,and contact time of 15 min.The effluent quality of the wastewater after the joint operation was stable and met the requirements of direct discharge,which proved the economic feasibility of this technology route.