Optimizing Oil-Contaminated Wastewater Purification with Aluminum Coagulants

Abstract

The study aimed to optimize the coagulation parameters for treating oil-contaminated wastewater using aluminum coagulants, specifically aluminum sulfate and aluminum hydroxychloride. Laboratory experiments were conducted to evaluate the efficiency and behavior of these coagulants under various conditions. Results showed that the slow hydrolysis and low dissociation rate of aluminum sulfate prolonged floc formation and sedimentation time, creating fine flocs with low hydraulic size that contributed to secondary water pollution. In contrast, aluminum hydroxychloride formed larger, more porous flocs with higher hydraulic size, resulting in faster sedimentation and more efficient removal of oil contaminants. The sedimentation time remained consistent (67–72 min) with aluminum hydroxychloride, whereas it increased significantly (125–229 min) with aluminum sulfate, indicating the latter’s lower efficiency due to the formation of small, suspended flocs. Moreover, aluminum hydroxychloride showed a reduced tendency to lower the pH of the treated water, suggesting a more complete hydrolysis process compared to aluminum sulfate. Experimental findings established that using aluminum hydroxychloride increased coagulation and sedimentation rates by 2–3 times, reduced sediment volume by 1.5 times, and enhanced pollutant removal efficiency, achieving 98.6% removal of suspended solids and 93.6% removal of oil products. Optimal coagulation conditions were identified as a coagulant dose of 21 mg/L, coagulation time of 10 min, and settling time of 60 min. A key contribution of this work is the establishment of regression equations and correlation coefficients that quantitatively describe the relationships between critical process parameters, such as coagulant dose, coagulation time, initial concentration of oil products and suspended solids, and pollutant removal efficiency. The study concludes that aluminum hydroxychloride is a superior coagulant for oil-contaminated wastewater treatment, providing faster, more effective, and stable purification performance compared to aluminum sulfate.