Sustainable iron-olive stone-based catalysts for Fenton-like olive mill wastewater treatment: Development and performance assessment in continuous fixed-bed reactor operation

Abstract

Iron oxide catalysts supported on activated carbon prepared from olive stones (OSAC–Fe) were used for the catalytic wet peroxide oxidation of refractory polyphenolic solutions and real olive mill wastewater (OMW) in a fixed-bed reactor (FBR). Catalysts were prepared with different precursors and Fe-loadings. The resulting catalysts were essentially microporous materials with well-developed surface areas (SBET = 588–689 m2/g), whereas the nature and distribution of metallic nanoparticles were found to be strongly dependent on the precursor used.The stability and catalytic performance were screened in a batch reactor using a synthetic solution and the most promising catalyst – prepared at 5 wt.% Fe using Fe(NO3)3 as the precursor – was selected for the operation of a continuous FBR. Different operational conditions were evaluated through a parametric study. At 60 °C, [H2O2]feed = 1.5 g/L and Q = 0.75 mL/min, 87% total phenolic content removal (TPh), 28% mineralization and 88% H2O2 conversion were achieved at steady-state. Real OMW samples were then treated at a fixed [H2O2]/[COD] in the feed, and TPh removals of 57–71% and COD (chemical oxygen demand) reductions of 26–34% were attained. The resulting effluents showed an overall reduction of eco-toxicity and improvement of biodegradability indices.