Adsorption of phenols from olive oil waste waters on layered double hydroxide, hydroxyaluminium–iron-co-precipitate and hydroxyaluminium–iron–montmorillonite complex

Olive mill waste water (OMWW) contains high concentrations of phenols that are responsible for the high toxicity of the effluent. A one step precipitation process of OMWW by cold methanol yielded a polymeric organic precipitate (polymerin) and a supernatant (OMWW-S) rich in phenols, which were further concentrated in an ethyl acetate extract (OMWW-E). This extract was comparatively adsorbed on: i) a layered double hydroxide of magnesium and aluminium (LDH); ii) the LDH after calcination at 450 °C (LDH-450); iii) a hydroxyaluminium–iron-co-precipitate (HyAlFe); and iv) a hydroxy-aluminium–iron–montmorillonite complex (HyAlFe-Mt). Adsorption behaviour and kinetics of phenols with these materials were investigated. The Langmuir model better described adsorption (R2 > 0.97) in comparison to the Freundlich model (R2 > 0.89). Phenols were sorbed according to the following order: LDH-450 > LDH > HyAlFe > HyAlFe-Mt. Phenol adsorption on LDH matrices was strong, since desorption with simulated soil solution under dynamic conditions never exceeded 20%. Cyclic adsorption conducted with LDH-450 removed most phenols, ~ 94% from OMWW-E, consequently reducing its phytotoxicity. The study evidenced that calcined LDH represented an effective remediation process for OMWW.