Pillared interlayered natural clays as heterogeneous photocatalysts for H2O2-assisted treatment of a winery wastewater

The present research assessed, for the first time, the application of natural pillared clays (PILCs: Al-Cu-ST and Al-Fe-ST) as heterogeneous photocatalysts for the H2O2-assisted treatment of a real winery wastewater (WW), which is characterized by high loads of recalcitrant polyphenolic compounds. The heterogeneous photocatalysts were characterized by XRD, FTIR, N-2 adsorption isotherms and SEM-EDX, and successful immobilization of the active phase on natural smectite (Ca-ST) was confirmed. The influence of various parameters, such as initial pH, H2O2 concentration and catalyst dosage, on catalyst activity and on the metal leaching from the heterogeneous catalysts were investigated. The results demonstrated that Al-Cu-ST exhibits higher activity than Al-Fe-ST, however, lower stability along 3 consecutive cycling processes (pH = 3.0; S:L = 3.00 g/L, [H2O2](0) = 98 mM). Accordingly, the TOC removals varied between 79.3% and 75.2%, and between 67.1% and 57.9%, using Al-Cu-ST and Al-Fe-ST, respectively, from the 1st to the 3rd cycle. The metal leaching concentrations were in both cases lower than the legal limits imposed, along the cycling processes. A lumped kinetic model based on the Fermi's equation was successfully applied in order to describe the kinetics of the photo-oxidation processes. Accordingly, the higher rate process was achieved at pH 3.00, using a H2O2 concentration corresponding to 98 mM, and a Al-Cu-ST dosage of 3.00 g/ L (k(TOC) = 3.76 x 10(-2) min(-1)).