Demulsification of Oily Wastewater with the Electro-Enhanced Coagulation Process

Abstract

To enhance floc size and accelerate floc formation during the coagulation treatment of highly emulsified oily wastewater (HEOW), a novel electro-enhanced coagulation (EEC) process was developed by integrating an external electric field with conventional coagulation. This process was optimized based on various operating parameters, including electrolysis time and coagulant dosage. The Turbiscan Stability Index (TSI) and floc size were measured throughout the process. The EEC process substantially improved floc formation compared with conventional coagulation. The TSI and floc size increased and then plateaued as the electrolysis time increased to 240 s. Under optimal conditions of 240 s electrolysis time and 50 mg/L Fe₂(SO₄)₃ dosage, the TSI reached 59.87 ± 0.47 and floc diameter expanded to 473.8 ± 34.1 μm. Additionally, continuous operation experiments achieved an oil removal efficiency of 94.9% ± 1.75%. The energy consumption of this process was 0.29 ± 0.01 kWh/m³. The ζ potential decreased as the electrolysis time increased from 180 to 300 s. This decrease was attributed to charge neutralization facilitated by an external electric field. Furthermore, the pH increased with prolonged electrolysis, promoting Fe³⁺ hydrolysis and facilitating the formation of iron hydroxide species, thereby contributing to enhanced floc formation during the demulsification process.