Central composite design for optimal technology of concentrating vanillic acid using foam fractionation

Hydrophilic phenolic compounds in olive-mill wastewater (OMWW) evince high potential for use in pharmaceutical, nutraceutical and cosmetic products due to their bioactivities. However, up-to-date, effective and low-cost extraction techniques suitable for large quantities of OMWW are still wanting. This lack turns the by-product OMWW into problematic waste, instead of a value-added product. Foam fractionation has not yet been studied with regard to its potential for extracting polar phenolics from OMWW. In this study, this was investigated in a simple model system with oxidative-insensitive vanillic acid. The influence of four process parameters (concentration of vanillic acid, concentration of cetyltrimethylammonium bromide, pH value and gas flow rate) on enrichment factor and percentage recovery was analyzed with design of experiments. Analysis of the central composite design revealed that the concentration of the cationic surfactant and the gas flow rate are diametrically opposed for high enrichment factor in the foamate and simultaneous low percentage recovery in the residue. Low vanillic acid concentration and pH of 6-7 were found to be advantageous in terms of good extraction performance. Foam fractionation of vanillic acid under the optimized process parameters led to an enrichment factor of 22.24 in the foamate and 55.88% recovery in the residue.