Competitive adsorption, selectivity and separation of valuable hydroxytyrosol and toxic phenol from olive mill wastewater

Competitive adsorption and selectivity of toxic phenol and hydroxytyrosol were studied on the macroreticular aromatic polymer (FPX66) and the macroporous polystyrene cross linked with divinylbenzene (MN202). The adsorption equilibrium of phenol and hydroxytyrosol as well as other phenolic compounds in olive mill wastewater (OMW) was investigated taking into account the different affinities of these compounds towards the two above mentioned resins. The experimental results showed that the adsorption equilibrium of phenol on FPX66 can be well interpreted by the BET model, indicating a multilayer adsorption, whereas, the adsorption of hydroxytyrosol on MN202 at equilibrium is well fitted by the Sips model. At low FPX66 concentration, phenol exhibited much higher adsorption percentage than hydroxytyrosol, indicating a stronger interaction with the resin. The adsorption selectivity ratio of phenol/hydroxytyrosol was of about 3.215 at 5 g L−1 of FPX66. Thanks to the large affinity of hydroxytyrosol for the MN202 resin, its adsorption and recovery were higher than 90% on this resin. Thus, under suitable operating conditions, phenol was selectively separated on FPX66, while hydroxytyrosol was largely recovered from the OMW residual solution by adsorption on MN202.