Multistage treatment of industrial ethylene glycol (EG) effluent: integrating chemical extraction, coagulation/precipitation, and decolouration for enhanced wastewater remediation

Abstract

Industrial wastewater containing high concentrations of ethylene glycol (EG) represents a major treatment challenge due to its high solubility, elevated chemical oxygen demand, and limited removal by conventional treatment systems. In this study, a multistage treatment strategy is proposed to overcome the demonstrated limitations of an existing industrial wastewater treatment plant for EG removal. The approach integrates solvent-assisted phase separation, coagulation–precipitation, and nanomaterial-based polishing. An external solvent-assisted phase separation step was applied as a pretreatment stage, achieving substantial reduction of the organic load (≈ 75–80% COD removal) and enabling partial recovery of an EG-rich fraction through association-driven co-extraction mechanisms rather than classical liquid–liquid extraction. Subsequent coagulation–precipitation removed suspended and colloidal matter, while tertiary polishing using nano zero-valent aluminum (nZVAl) achieved complete decoloration (100%). Kinetic analysis indicated that color removal followed Avrami-type behavior, reflecting a heterogeneous and multistep adsorption mechanism. Pilot-scale validation using real industrial wastewater confirmed the robustness of the proposed system. A preliminary techno-economic screening showed that the multistage process can operate at a net treatment cost comparable to conventional high-strength industrial wastewater treatment systems, with solvent recovery and partial EG reuse contributing to operational cost reduction rather than direct profit. Overall, the proposed framework provides a practical and scalable upgrade for industrial EG-laden wastewater treatment.