Zero Fenton sludge discharge: a review on reuse approach during wastewater treatment by the advanced oxidation process

The substantial growth of industrial development and challenging regulations associated with environmental protection demands new and advanced technologies for the effective treatment of the effluents. The applications of the classical Fenton process are versatile and effective particularly for the treatment of recalcitrant compounds among advanced oxidation processes. However, the classical Fenton process possesses some shortcomings like the requirement of a narrow pH range, production of a high amount of iron sludge, and high chemical involvement. These drawbacks are the environmental barriers that restricted its widespread application. Several modifications have been adopted by many researchers as possible solutions to overcome these restrictions. Although several types of research and reviews have been reported in the literature on Fenton's types and applications, nevertheless, a review with emphasis on the restrictions of the Fenton process and their possible solutions is lacking. The present review delineates the restrictions of the classical Fenton process and recent approaches to overcome these limitations with a special focus on Fenton sludge reuse systems as a sustainable approach. The Fenton sludge reuse systems for various wastewater treatment are also highlighted. The sludge reuse systems without regeneration, with optimized addition of reagents dosage, are the most effective method for treatment. To the best of our knowledge, this is the first review article focusing Fenton sludge reuse system for wastewater treatment. The review also addresses the possible areas for future research as reported in the literature, to make the process cost-effective, environmentally friendly, and its feasibility for large-scale applications.