Study On The Treatment Efficiency Of Sulfur Eletron Acceptor Biological Enhanced Saline ASP Flooding Produced Water

With the development of tertiary oil recovery,ASP flooding has been widely used in Daqing oilfield.In the process of oil production,a large amount of produced water is produced by asp flooding,which has the characteristics of high salt content,difficult separation of oil and water,poor demulsification and low biodegradability.In order to enhance the treatment efficiency of ternary sewage,this paper studies the treatment efficiency of sulfur with different valence states on saline ASP produced water,and selects the electron acceptor with the best treatment effect,which is used in the pilot test and evaluates the treatment efficiency.In laboratory experiment,the biological treatment efficiency of sulfur with different valence states as electron acceptor was studied.Add sodium sulfate,sodium sulfite,sodium thiosulfate,ferrous sulfate and elemental sulfur into the water as electron acceptors,so that the carbon-sulfur ratio is 2:1.By adding NaCl to ternary sewage,the salinity of inlet water of the reactor is twice that of ternary sewage.The reactor operation time is 90 days.During the operation of the reactor,the index of ternary sewage is detected,and the community of microorganisms in the stable period is analyzed.The experimental results show that there are differences in the treatment effects of ternary flooding when sulfur with different valence states acts as electron acceptor.When sodium sulfite is the electron acceptor,it has good effect on oil content,suspended matter,COD and polymer,while when ferrous sulfate is the electron acceptor,it has good effect on surfactant,viscosity and salinity.Sodium sulfite was selected as the electron acceptor in field pilot test because oil content and suspended substance were the main re-injection indexes.When sodium sulfate,sodium thiosulfate and sodium sulfite are used as electron acceptors,the treatment effect of organic compounds is better.When sulfur with different valence states acts as electron acceptor,the most difficult substances to be degraded are alkanes.High-throughput sequencing results show that when sulfur in different valence states acts as electron acceptor,microorganisms are mainly composed of 3 genera of Halomonas,Nitrincola and Marinospirillum.And the content of Halomonas microorganism is increasing and gradually occupies the dominant position.In the field test stage,sodium sulfite was used as the electron acceptor to start up the reactor quickly and study the efficiency of stable operation test.The test site is a ASP flooding produced water station of the fourth oil production plant of Daqing oilfield.The test period is 90 days,and the sampling and testing period is 3 days.The polymer content,viscosity,oil content,suspended matter,sulfide,COD and other conventional indexes of produced water in each reaction area of the reactor were detected,and the treatment effect of the reactor was evaluated.Sludge sampling was carried out at the later stage of stable operation of the reactor,and microbial composition was analyzed by high-throughput sequencing.The average contents of oil,suspended matter,COD,polymer,surfactant and viscosity in the effluent were 5.85mg/L,44 mg/L,1924 mg/L,969 mg/L,190 mg/L and 4.410 mPa·s,respectively,with an average removal rate of 95.11%,30.05%,24.16%,15.64%,18.18% and 15.02%.The oil content in the output water meets the re-injection standard,while the suspended substance content fails to meet the re-injection standard,which needs to be filtered before re-injection.The results of GC-MS analysis of water samples in each reaction area of the reactor during the stable operation stage show that the reactor has a good treatment effect on organic matter and can remove most of the organic matter.Only 19 of the 70 organics in raw water are left after treatment,and the most refractory organics are alkanes.The startup stage was mainly composed of microorganisms of Nitrincola and Bacillus,while the stable running stage was mainly composed of microorganisms of Nitrincola,Bacillus and Halomonas.The microbial content of Halomonas gradually increases during the operation of the reactor.