Enhanced recovery of phenolic compounds from vegetable oil processing wastewater through a synergistic emulsion liquid membrane process

Abstract

Vegetable oil processing wastewater represents an underutilised bioresource rich in phenolic compounds (PCs) with high antioxidant potential. In this study, a synergistic emulsion liquid membrane (SELM) process was investigated to extract and recover PCs from palm oil mill sterilisation condensate by using a synergistic formulation of diluent (palm/sunflower oil), carrier (Aliquat 336/D2EHPA), surfactant (Span 80/Tween 80), and stripping agent (NaOH/Na₂CO₃). A two-level factorial design was first employed to screen the key operational parameters influencing the extraction performance. Then, four most significant parameters (mixed carrier and stripping agent concentrations, agitation speed, feed-to-emulsion ratio) were optimised by using Box-Behnken design to maximise the extraction performance. The effects of octanol as a modifier and feed phase concentration were studied to improve recovery performance. Under the optimal conditions of Aliquat 336/D2EHPA (0.2855/0.0023 M), NaOH/Na₂CO₃ (0.5129/0.0615 M), an agitation speed of 263 rpm and a feed-to-emulsion ratio of 2.94:1, the SELM process achieved an extraction performance of 91.2%. Modification of SELM with 5% w/v of octanol resulted in almost 80% recovery and 9.2 times solute enrichment. The results also demonstrated that the optimum formulation of SELM process remained effective up to 340 milligram gallic acid equivalents per liter (mg GAE/L) of feed phase concentration. These findings indicate that SELM process is promising for the valorisation of agro-industrial wastewater within resource recovery frameworks.