Light-driven ammonium oxidation to dinitrogen gas by self-photosensitized biohybrid anammox systems

The anaerobic ammonium oxidation (anammox) process exerts a very vital role in the global nitrogen cycle (estimated to contribute 30%–50% N(2) production in the oceans) and presents superiority in water/wastewater nitrogen removal performance. Until now, anammox bacteria can convert ammonium (NH(4)(+)) to dinitrogen gas (N(2)) with nitrite (NO(2)(−)), nitric oxide (NO), and even electrode (anode) as electron acceptors. However, it is still unclear whether anammox bacteria could utilize photoexcited holes as electron acceptors to directly oxide NH(4)(+) to N(2). Here, we constructed an anammox-cadmium sulfide nanoparticles (CdS NPs) biohybrid system. The photoinduced holes from the CdS NPs could be utilized by anammox bacteria to oxidize NH(4)(+) to N(2). (15)N-isotope labeling experiments demonstrated that NH(2)OH instead of NO was the real intermediate. Metatranscriptomics data further proved a similar pathway for NH(4)(+) conversion with anodes as electron acceptors. This study provides a promising and energy-efficient alternative for nitrogen removal from water/wastewater.