Adsorption/desorption processes using palygorskite clay mineral for table olive fermentation brine treatment and phenols recovery

Table olive fermentation brine (TOFB) is an acidic, organic-rich agro-industrial effluent containing elevated concentrations of phenolic compounds that pose significant environmental risks due to their toxicity and resistance to biodegradation. Nevertheless, these compounds constitute valuable bioactive molecules exhibiting antioxidant and anti-inflammatory properties. This study investigates TOFB treatment via adsorption onto palygorskite (Pal), emphasizing simultaneous pollutant removal, recovery of phenolic constituents (TPC) and Pal reusability. Raw Pal exhibited a characteristic fibrous morphology, high specific surface area (233 m²/g), and mesoporous structure, as confirmed by SEM and N₂ physisorption analyses. Adsorption performance was evaluated through batch and continuous-flow experiments under varying operational conditions. In batch systems, decreasing the initial phenolic concentration from 5200 to 40 mg/L increased removal efficiency from 58.5% to 88.3%, while increasing Pal dosage from 2.5 to 100 g/L enhanced removal from 50.6% to 75.6%. Continuous-flow operation achieved 37.5% TPC removal, with column saturation occurring after approximately 20 h. Equilibrium and kinetic analyses indicated that adsorption followed the Freundlich isotherm, whereas fixed-bed performance was adequately described by the Clark model. Desorption experiments enabled phenolic recovery up to 76% using water and a 50% (v/v) ethanol-water solution, with UHPLC-MS/MS-DAD confirming tyrosol and hydroxytyrosol among recovered compounds. Thermal regeneration did not affect the removal efficiency at the initial reusability cycle. However, it was found that the removal efficiency decreased to 30% of the initial capacity at the third time of reusability. Structural evolution throughout adsorption-desorption-regeneration cycles was evaluated using XRD and XPS analysis, supporting an integrated and sustainable TOFB management strategy aligned with circular economy principles.