Enhanced separation of emulsified oil from alkaline-surfactant-polymer flooding produced water by Gordonia sp. TD-4: From interactions to mitigation strategies and bio-demulsifying mechanisms

The complexity of emulsions from petroleum industries hinders the application of bio-demulsification. This study revealed the interactions between flooding agents in emulsified alkaline-surfactant-polymer (ASP) flooding produced water (PW) and carbon sources-mediated bio-demulsifiers (byproducts and bacterial cells of Gordonia sp. TD-4). The results demonstrated that synergistic and antagonistic effects existed between flooding agents (surfactant, alkali, and polymer) and bio-demulsifiers. Among these, petroleum sulfonate (PS) mediated emulsifying stability of ASP flooding PW was the dominant factor to affect bio-demulsifying performance. The solubilization of oil-soluble surface-active lipopeptide in micelles and the reduction of bacterial suspensibility constituted two dominant inhibitory mechanisms of PS. Based on the proposed inhibitory mechanisms, two enhanced bio-demulsifying methods toward PW stabilized by a high concentration of PS were established. Partly hydrolyzed polyacrylamide could hinder the solubilization of oil-soluble surface-active lipopeptides and enhance the competitive adsorption-derived bio-demulsification. The suspensibility of cells of TD-4 in the solution of PS could be improved by stimulating the stress response of TD-4, which in turn enhanced the bio-flocculation-derived bio-demulsification. The oil-soluble and membrane-like surface-active lipopeptides produced by TD-4 using oil-soluble carbon sources could sweep the suspended crude oil droplets and decrease the viscoelasticity of interfacial film. The bacterial cells grown in water-soluble carbon sources mainly served as hydrophobic adsorption sites to adsorb and flocculate the suspended nanometer-sized crude oil droplets. This study will innovate the application of biological-based technologies toward the emulsified PW from the petroleum industry.