Recent progress in the advanced oxidation of wastewaters using recycled fly ashes as alternative catalytic agents.

In this study, a comprehensive literature review is conducted with regard to recent advances in using recycled fly ashes as alternative and cost-effective reagents than as wastes in the advanced oxidation of wastewaters. Fly ashes are powdery solid residues that are produced in enormous quantities in coal/lignite-fed power stations and also from waste incineration. Novel applications of these industrial by-products in the field under examination, toward sustainable use of resources and circular economy, are discussed and summarized. Since fly ashes contain useful metal oxides, they can actually be considered as alternative catalytic agents in wastewater treatment, depending on their surface properties and the elements solubility rate in the aqueous media. Beyond the possible contribution of these secondary materials to the oxidation of wastewaters, their potential for concurrent beneficial adsorption of substances present in the effluent to be treated also enhances the significance of the current scientific work. For that purpose, fly ashes and several fly ash-based composite catalysts were examined for their effectiveness in advanced oxidation processes that are summarized in three main categories, namely photocatalysis, Fenton/Fenton-like oxidation, and combined mechanisms. Principal system parameters affecting the degradation of wastewaters were considered, including the dosage of each catalytic agent used, the initial dye concentration, the solution pH, and the reaction time and temperature. [ABSTRACT FROM AUTHOR]