The current study reduces the issues caused by petroleum-based organic solvents, which commonly employed in emulsion liquid membrane (ELM) process. The waste cooking oil as a low-cost easily available nontoxic organic solvent was used in a green ELM (GELM) process without complicated pretreatment stages. Methyl violet 2B (MV) dye was chosen as the sample cationic dye for the study of the ability of waste vegetable oil in water decolorization. The proposed GELM included Span 80 as the surfactant, hydrochloric acid as the internal phase, and waste vegetable oil as the diluent. Initially, Plackett–Burman screening design was employed for the determination of important influencing parameters in dye removal by GELM. Afterward, to achieve the optimal process conditions, Box–Behnken design was used. The optimized factors were Span 80 concentration of 3 wt%, internal phase concentration of 1.43 M, MV concentration of 24.59 mg/L, and organic phase to aqueous phase ratio of 2.07. The maximum achieved MV extraction efficiency was found to be 99.1% under the optimized process conditions and without utilizing the carrier agent. Also, the membrane might be recovered for more than seven times.
