Decentralized Modular Electrochemical Technologies for Advanced Wastewater Treatment: A Comprehensive Review of Advanced Oxidation and Reduction Processes, Bioelectrochemical Systems, and Photocatalysis

The increasing demand for clean water, coupled with the limitations of centralized wastewater treatment systems, has highlighted the need for sustainable and decentralized treatment solutions. Electrochemical and electrode-based technologies offer a compelling alternative by addressing persistent pollutants and emerging contaminants in a flexible and modular manner. This review provides a comprehensive analysis of advanced oxidation and reduction processes (AO/RPs), bioelectrochemical systems (BESs), and photocatalysis, focusing on their principles, reactor configurations, operational parameters, and technoeconomic considerations. AO/RPs facilitate in situ generation of highly reactive radicals for mineralizing complex pollutants. BESs utilize electroactive microorganisms for the dual purpose of pollutant removal and energy or resource recovery. Photocatalysis utilizes semiconductor materials activated by light to degrade organic contaminants efficiently. The review emphasizes the modular applicability of these technologies, presenting case studies and commercial systems that demonstrate their adaptability to variable wastewater characteristics and site-specific needs. Key challenges such as energy demand, chemical input, system scalability, and maintenance are discussed alongside innovations in reactor design and catalyst development. Techno-economic assessments and statistical insights are included to compare these technologies and guide practical deployment. The integration of these systems into decentralized infrastructures offers advantages such as reduced sludge generation, improved process efficiency, and the potential for on-site reuse and energy valorization. Overall, the review supports the adoption of modular electrochemical treatment systems as viable tools for advanced wastewater treatment in diverse environmental and operational settings.