Preparation of microencapsulated coagulants and application to oil–water separation under gravity coagulation conditions

If untreated, oilfield sewage generated during the oil exploitation process can lead to severe environmental pollution. The coagulation/flocculation process plays a pivotal role in the comprehensive treatment of oilfield sewage on a large scale, yet traditional methods exhibit significant limitations. To address the disparity between laboratory experiments and large-scale implementation, this study introduces an innovative coagulant microcapsule. Prepared under gentle conditions, these microcapsules effectively eliminate colloidal particles from water when introduced at the coagulation tank inlet. Featuring a core–shell structure, coagulant microcapsules demonstrate controlled content release upon contact with water. The coagulation process occurs as sewage enters the coagulation tank. The core of the coagulant microcapsule consists of the inorganic polymer coagulant (PASS-C16) with hydrophobic association capabilities. Upon contact with sewage at a specific flow rate, the coagulant is released gradually from the microcapsule. Upon reaching the bottom of the coagulation pool, the coagulant comes into full contact with colloidal particles, influenced by gravity. Ultimately, through integration with Fluent simulation and analysis of floc particle size changes, it was determined that the primary mechanisms of coagulant capsules in aquatic conditions involve charge neutralization and bridging adsorption. The sweeping action is effective only when the test water tends to be static. This technology is viable for application in the coagulation sedimentation tanks of diverse sewage treatment plants. Gravity coagulation demonstrates potential as a replacement for conventional mechanical mixing methods, offering increased efficiency and potential energy savings in various water treatment processes.