Enhancing water circularity: Lactic acid-menthol deep eutectic solvent for efficient fats, oils and grease (FOG) removal and recovery from contaminated waters

Water pollution, particularly the contamination of water sources by fats, oils, and grease (FOG), presents a significant environmental challenge exacerbated by climate change. While conventional water resource recovery facilities (WRRFs) address various contaminants, FOG treatment often remains indirect and suboptimal. This study introduces an innovative, environmentally benign approach utilizing deep eutectic solvents (DESs) for the targeted removal and recovery of FOG from contaminated waters via liquid-liquid extraction. A binary DES comprising menthol and lactic acid was synthesized and evaluated for its efficacy in extracting oleic acid, selected as a model fatty acid contaminant. The investigation employed a comprehensive factorial design to optimize key operational parameters, including the molar ratio of DES components, solvent-to-water ratio, contact time, initial contaminant concentration, stirring speed, and phase separation time. Results demonstrated exceptional removal efficiencies exceeding 95 % under optimized conditions, with peak performance approaching 99.5 %. Optimal parameters were identified as a 1:1 molar ratio of menthol to lactic acid, 1:10 DES-to-water ratio, 15-minute contact time, 300 mg L⁻¹ initial contaminant concentration, 500 RPM stirring speed, and 8-hour phase separation. This research establishes a foundation for the application of DESs in water decontamination processes, potentially revolutionizing FOG management and advancing water circularity initiatives. The study's findings align with multiple UN Sustainable Development Goals, including SDG 6 (Clean Water and Sanitation), SDG 14 (Life Below Water), and SDG 12 (Responsible Consumption and Production), offering a promising avenue for sustainable water treatment technologies.