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 (NH4+) to dinitro-gen gas (N-2) 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 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 NH4+ to N-2. N-15-isotope labeling experiments demonstrated that NH2OH instead of NO was the real intermediate. Meta-transcriptomics 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.

Automated summary

In this study, a biohybrid system containing cadmium sulfide nanoparticles (CdS NPs) was constructed, and it was found that photoinduced holes from CdS NPs could be utilized by anammox bacteria to oxidize NH4+ to N-2. This provides a promising and energy-efficient alternative for nitrogen removal from water/wastewater.