Advanced oxidation processes for real effluent treatment: an integrated review of technologies, applications, challenges, and sustainability perspectives

Freshwater scarcity and the increasing discharge of complex wastewaters represent major environmental and societal challenges. Industrial, hospital, mining, and landfill effluents often contain refractory organic pollutants, heavy metals, and emerging contaminants that are only partially removed by conventional treatments. Advanced Oxidation Processes (AOPs), based on the in-situ generation of reactive species such as hydroxyl (•OH) and sulfate radicals (SO4•−), have therefore emerged as effective options for degrading persistent compounds. In this review, we discuss conventional advanced oxidation processes (AOPs) such as ozonation, Fenton and photo-Fenton processes, UV-based systems, electrochemical methods, and sonochemical systems. It also includes next generation approaches such as new catalysts, g-C3N4 based heterostructures, visible and solar light photocatalysis, AOP-adsorption combinations, and hybrid set ups. This study is novel in integrating conventional and novel AOPs for the treatment of real effluent. It emphasizes important points including reactor design, applicability to pilot and large-scale work, operational challenges, toxicity of by-products, and sustainability. The review is concerned with important factors influencing the treatment efficiency such as reactor design and operational parameters, energy and reagent consumption, catalyst stability, sludge generation, and toxic by-products. In conclusion, this points to future considerations on cost-effectiveness, regulatory integration, resource recovery, and the role of AOPs in sustainable wastewater management.