Photoelectric materials-assisted anammox systems: Performance, microbial community dynamics, metabolic responses and N-removal pathways

Anaerobic ammonium oxidation (anammox) offers a promising low-carbon pathway for nitrogen removal in wastewater treatment. However, its application was limited by inhibited redox reaction and low electron transfer efficiency under adverse conditions, etc. Enhancing the electron transport activity of anammox bacteria is crucial for addressing these challenges. In such a situation, innovative photoelectric materials-assisted anammox systems have been developed for promoting direct transfer of electrons generated by photoelectric materials to the anammox metabolic networks through extracellular electron transfer (EET) and endogenous metabolism. Therefore, this article attempts to offers critical insights into the fundamentals and applications of photoelectric materials-assisted anammox systems, with a specific focus on (i) classification and properties of photoelectric materials; (ii) nitrogen removal performance of photoelectric materials-assisted anammox systems; (iii) photoelectric materials-enhanced anammox activity and N-removal pathways; (iv) microbial community structures in photoelectric materials- assisted anammox system and (v) metabolic responses of anammox community to photoelectric materials. The current knowledge gaps and the perspectives for future research are further outlined. It is expected that this article may trigger further thinking and action on how to develop a new theoretical framework for the photoelectric materials-assisted anammox systems.