Cosubstrates in azo dye decolorization: From conventional anaerobic systems to microbial fuel cells

Cosubstrates play a pivotal role in anaerobic azo dye treatment, including both conventional and emerging microbial fuel cells (MFCs) systems, but their mechanistic roles are often overlooked. Compounding this issue is the persistent shortage of biodegradable cosubstrates in real textile wastewater, emphasizing the need for strategic evaluation and optimization. This review systematically analyzes how cosubstrate types and concentrations affect decolorization performance in both systems, based on a wide range of previous studies. Beyond identifying effective cosubstrates and optimal dosage ranges, this review explores the biochemical and microbiological mechanisms underlying these differences. Furthermore, the potential of waste-derived cosubstrates is discussed as a sustainable strategy to improve treatment efficiency and address the shortage of carbon donors. Cosubstrates are more than just auxiliary carbon sources; rather, they serve as central regulators of microbial coordination, enzymatic activity, and electron flow. Recognizing their multifaceted roles is key to optimizing future treatment strategies.