Recovery of low molecular weight phenols through solid-phase extraction

The recovery of polyphenols from olive mill wastewaters (OMWs) decreases the toxicity of the effluent and permits the obtainment of high-added value natural antioxidants. Solid phase extraction (SPE) represents a valuable approach to obtain polyphenols from OMWs, since it relies on simple, cheap and environmental friendly procedures and agents. In this work, five resins with different physical properties, namely Amberlite XAD4, XAD7, XAD16, IRA96 and Isolute ENV+, were tested in parallel for their adsorption and desorption features towards an aqueous solution of ten target phenolic compounds typically occurring in OMWs. Water, methanol and ethanol, also under basic and acidified conditions, were tested as possible desorbing agents. Adsorption isotherms related to the mixture of all phenols and to each single phenol were determined. Experimental data well fitted with Langmuir isotherm model. The highest phenol adsorption (76%) was achieved with IRA96 polar resin. Conversely, non-polar adsorbents allowed higher desorption ratios. Almost 60% of the overall phenols originally occurring in the applied mixture were recovered by employing ENV+ and ethanol as the desorbing phase. Lower performances were achieved with the other recovery and desorption agents. The compound polarity generally influenced the adsorption ratios (the sorption capacities of non-polar resins increased by decreasing the compound polarity, and vice versa), while the desorption ones were not always affected by such a compound feature. These findings are of special interest in the perspective of developing an effective SPE procedure for the recovery of natural phenols from real OMWs.