Red mud-efficient catalyst for the treatment of real olive mill wastewater through advanced oxidation toward greener and sustainable practices

Abstract

Recirculation of red mud residue as an efficient catalyst for treating real olive mill wastewater (OMW) via Fenton and photo-Fenton-like processes presents a sustainable approach to addressing environmental challenges in the aluminum industry. To be precise, the large storage areas required for disposal and the likelihood of spills and groundwater contamination should be reduced. Red mud (RM) has a metal composition on a dry weight basis of 82.2 %, with iron compounds (α-Fe³⁺O(OH) and Fe₂O₃) having compositions up to 31 %. RM showed a heterogeneous particle size distribution, mainly with particle sizes ranging from 100 to 600 μm. Adsorption, heterogeneous Fenton, and photo-Fenton-like reactions were employed to remove the organic matter, including phenolic compounds in the OMW, demonstrating significant removal efficiencies. The highest removal efficiencies were observed in the oxidation system under the following conditions: RM concentrations above 1 g/L, agitation rate of 460 rpm, pH 3, ambient temperature, and H₂O₂ concentration at 10 % w/v (131.2 mL/L). Under these conditions, the removal percentages were as follows: TC_removal = 80.9 %, TOC_removal = 75.7 %, IC_removal = 99.8 %, TN_removal = 48.5 %, COD_removal = 58.3 %, and TPC_removal = 70.6 %. The reuse of RM (minimum 6 times) as a catalyst contributes to waste minimization and enhances the sustainability of the aluminum industry by providing a cost-effective and environmentally friendly solution for wastewater treatment.