| The large-scale application of alkali-surfactant-polymer(ASP)flooding oil production technology can help the construction of China’s oil and gas safety assurance system.However,the application of ASP flooding oil recovery technology produces a large amount of emulsified and bio-sour(H2S-producing)produced water.The conventional technologies used for ASP flooding water demulsification and bio-souring control often have problems such as complex equipment operation procedures,enormous amounts of chemical agents(demulsifying agents,flocculants,biocides,etc.),and a high risk of secondary pollution.How to achieve the green,efficient,and intensive treatment of ASP flooding produced water has become an urgent problem to be solved to promote the industrialization of ASP flooding oil enhanced recovery technology.Bio-demulsification and nitrate-based bio-souring control have received widespread attention in recent years.There is still no large-scale industrial application due to the limitation of bio-demulsifying bacteria(agents),i.e.,the single function of bio-demulsifying bacteria,high production and usage costs,and poor adaptability to the complex industrial wastewater.Nitratemediated bio-souring control also faces bottlenecks of short-term effectiveness.To solve the above-mentioned engineering and technical problems,this study innovatively proposed a technical scheme of using bio-demulsifying bacteria with nitrate-reducing ability to synergistically realize demulsification and durable bio-souring control of ASP flooding produced water.This study conducted systematic research from four perspectives:the screening of multifunctional bio-demulsifying bacteria,the gene regulation of bio-demulsification,the interactions between bio-demulsifiers and flooding agents,and the exploration and utilization of the sulfur-autotrophic nitrate reduction function of bio-demulsifying bacteria.The main research contents and results were as follows:(1)In order to solve the problem of single function of bio-demulsifying bacteria,multifunctional bio-demulsifying bacteria with alkane degradation and nitrate reduction abilities were isolated from municipal activated sludge and oily kitchen waste.The effects of carbon sources on the bio-demulsification of bio-demulsifying bacteria were investigated using potassium nitrate as sole nitrogen source.The results not only found the phenomenon that carbon sources can regulate bio-demulsifying performance and bio-demulsifying mechanism of Gordonia sp.TD-4,but also revealed the bio-demulsifying mechanism of ASP flooding produced water by TD-4.Cell-bound bio-demulsifying bacteria TD-4 could use many kinds of oil-soluble carbon sources to yield oil-soluble,membrane-like,and surface-active lipopeptides,which can not only sweep the suspended crude oil droplets,but also be competitively adsorbed at the oil-water interfacial film,and decrease the viscoelasticity of interfacial film.This kind of bio-demulsifying mechanism that mediated by oil-soluble carbon sources was defined as interface competitive adsorption-derived bio-demulsification.Water-soluble carbon sources(such as glucose,sodium citrate and sodium acetate)could not induce TD-4 to yield surfaceactive lipopeptides,and only bio-demulsifying bacteria grown in sodium acetate could effectively demulsify ASP flooding produced water.The bacterial cells of TD-4 grown in sodium acetate with high suspensibility of bacterial cells,high cell-surface hydrophobicity,and cation-dependent bio-flocculating ability mainly served as hydrophobic adsorption sites to adsorb and flocculate the suspended nanometer-sized(average particle size 65 nm)crude oil droplets.This kind of bio-demulsifying mechanism that mediated by water-soluble carbon sources was defined as bio-flocculation-derived bio-demulsification.(2)Transcriptomics techniques were used to reveal the genetic regulatory mechanisms of the carbon source-mediated bio-demulsification mechanism of TD-4.The results showed that carbon sources regulated the bio-demulsification mechanism of TD-4 by mediating the process of dissimilatory nitrate reduction to ammonium(DNRA)and the assembly of cell surface protein-containing complexes.Water-soluble carbon sources affected the process of DNRA of TD-4 and resulted in the accumulation of nitrite.The accumulated nitrite(>180 mg-N/L)could induce the stress response of TD-4,which resulted in the upregulation of associated genes encoding chaperones.The overexpressed chaperones could increase the cell surface hydrophobicity,the cation-dependent bio-flocculating performance,and bacterial cells’suspensibility.The oil-soluble carbon source regulated the synthesis of surface-active lipopeptides by influencing the fatty acid β oxidation pathway of bio-demulsifying bacteria,and then regulated the interface competitive adsorption-derived bio-demulsification.(3)In response to the poor adaptability of bio-demulsifying bacteria to complex wastewater,the effects of emulsifying stability of ASP flooding water that mediated by flooding agents(alkalis,surfactants,and polymers)on the two main bio-demulsifying mechanisms(bioflocculation-derived bio-demulsification and interface competitive adsorption-derived biodemulsification)of TD-4 were investigated.Synergy and antagonism were found between flooding agents and bio-demulsifiers.Petroleum sulfonate was the dominant factor affecting bio-demulsification.The solubilization of oil-soluble surface-active lipopeptides in micelles and the reduction of bacterial cells’suspensibility constituted two dominant inhibitory mechanisms of petroleum sulfonate.The adaptability of TD-4 to complex wastewater could be enhanced by increasing the concentration of HPAM or increasing the suspensibility of bacterial cells of TD-4.Interface competitive adsorption-derived bio-demulsification is suitbale for ASP flooding produced water with high concentration of HPAM,while bio-flocculation-derived biodemulsification is suitable for ASP flooding produced water with low concentration of petroleum sulfonate and high oil content.(4)In response to the short-term potency of nitrate-mediated souring control,the effects of bio-augmentation with bio-demulsifying bacteria(TD-4)that possessing DNRA-driven sulfide-oxidizing ability on the durability of nitrate-mediated souring control were investigated.The results revealed that nitrate amendment after souring could effectively control souring,while nitrate amendment before souring failed to effectively control souring.Nitrate amendment combined with bio-augmentation with TD-4 after souring could effectively enhance the durability of nitrate-mediated souring control.When the dissolved sulfide was depleted,the rapid growth of denitrifying bacteria and their heterotrophic denitrification activities constituted key factors responsible for the short-term potency of nitrate-mediated souring control.Pulsed injection of nitrate combined with bio-augmentation with DNRA-driven SOB was proposed as a potential method to improve the durability of nitrate-mediated souring control.(5)ASP flooding produced water was treated with bio-demulsifying bacteria(TD-4)grown in water-soluble carbon sources,and the synergy of bio-augmented nitrate-mediated souring control and bio-demulsification was realized.After 24 h treatment of biodemulsification and souring control,the emulsified crude oil in ASP flooding produced water could be decreased to 48.15 ± 9.46 mg/L,and the sulfide could be decreased to 15.94 ± 3.20 mg-S/L.The oil removal efficiency could be achieved at 93.42 ± 1.35%,and the sulfide removal efficiency could be achieved at 79.86± 3.85%.The suspensibility of bio-demulsifying bacterial cells in ASP flooding produced water played key roles in the synergy of bio-demulsification and souring control.To solve the problems caused by emulsification and biological souring on the green,efficient,and intensive treatment of ASP flooding produced water,this study focused on the carbon,nitrogen,and sulfur metabolism characteristics of bio-demulsifying bacteria,invented a new technology for durable souring control and bio-demulsification,and initially established a theory and methodology for the treatment of sour and emulsified ASP flooding produced water,which can provide a solid theoretical basis to the technological innovation of the treatment of ASP flooding produced water. |
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