Microbial photoelectrotrophic denitrification: Development, mechanisms, and applications in wastewater treatment

Photoelectrotrophic denitrification (PEDeN) has emerged as a promising strategy for sustainable and high-efficiency nitrogen removal from wastewater by coupling solar energy with microbial denitrification. This review summarizes the development of PEDeN from conventional chemotrophic and electrotrophic denitrification, and synthesizes its system configurations, electron-transfer mechanisms, key influencing factors, and application potential. Current PEDeN systems can be classified into electrode-based and hybrid-based modes, which differ in device dependence, photosensitizer-denitrifier coupling, and practical application orientation. Recent advances in photosensitizer engineering, reactor design, and electron-transfer regulation have improved nitrogen removal and product selectivity, while expanding PEDeN applications to low C/N wastewater treatment, co-transformation of contaminants, and light-assisted nitrogen conversion in natural environments. However, practical implementation remains limited by material safety, light attenuation, system stability, and insufficient validation under real-wastewater conditions. Overall, this review provides a systematic framework for understanding PEDeN and highlights key directions for its future optimization and engineering application.