Oil-water separation strategy in oilfield oily sewage based on the APAM resource extraction-reuse mechanism

With the continuous advancement of oilfield extraction technologies, the volume of oily sewage generated has increased substantially. Such wastewater typically contains high concentrations of suspended solids and emulsified oil. At present, coagulation–flocculation remains the fastest and most practical purification method. The traditional coagulants mainly achieve the destabilization of colloidal particles by introducing a large amount of positive charges. However, this method will result in the formation of excessive flocs, thereby increasing the complexity of the subsequent separation process. To address these limitations, an innovative strategy was proposed in which the quaternary ammonium salt surfactant (OTAB) was incorporated to prepare a novel composite coagulant. At an optimal dosage of 90 mg/L, the residual turbidity of the oily sewage decreased to 16.7 NTU, while the demulsification rate reached 92.44 %. During the coagulation process, the Zeta potential increased but remained below the isoelectric point. Unlike traditional flocculants, OTAB promotes the partial precipitation of anionic polyacrylamide (APAM), and the precipitated APAM continues to participate in flocculation in the presence of polyaluminum silicate sulfate (PASSi). By analyzing changes in polymer content, hydrodynamic radius, molecular weight, and heat absorption–release behavior of APAM after coagulation treatment, the interaction mechanism between ionic species and APAM was elucidated. Furthermore, variations in floc size, morphology, and water surface tension were examined to clarify the action mechanism of the prepared flocculant. The results indicate that the coagulation process is dominated by bridging adsorption, accompanied by partial charge neutralization.