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

Abstract

The anaerobic ammonium oxidation (anammox) process exerts a very vital role in the global nitrogen cycle (estimated to contribute 30%-50% N2 production in the oceans) and presents superiority in water/wastewater nitrogen removal performance. Until now, anammox bacteria can convert ammonium (NH4+) to dinitrogen gas (N2) with nitrite (NO2-), 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 NH4+ to N2. 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 NH4+ to N2. 15N-isotope labeling experiments demonstrated that NH2OH instead of NO was the real intermediate. Metatranscriptomics data further proved a similar pathway for NH4+ conversion with anodes as electron acceptors. This study provides a promising and energy-efficient alternative for nitrogen removal from water/wastewater.