Light-Driven Ammonium Oxidation to Dinitrogen Gas by Self-Photosensitized Biohybrid Anammox Systems

Abstract

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 present the 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 photo-excited holes as electron acceptors to directly oxide NH4+ to N₂. Here we constructed an anammox-semiconductor biohybrid system by coating biocompatible cadmium sulfide nanoparticles (CdS NPs) on the anammox cell surface. The photo-induced holes from the CdS NPs could be utilized by anammox bacteria to oxidize NH₄ ⁺ to N₂ without N₂O, NO₂- or NO₃- accumulation. 15N-isotope labelling experiments demonstrated that NH