Hydrazine production by anammox biomass with NO reversible inhibition effects

Abstract

We explored the production of hydrazine from NO and ammonium by anammox biomass, which normally converts ammonium and nitrite to N₂ gas under anaerobic conditions. The key step was reversibly inhibiting cytochrome c in anammox biomass via exposure to NO gas or NO-EDTA. The conformation of cytochrome c was changed through exposure to NO or NO-EDTA, and this is what interrupted the oxidation of hydrazine to N₂, leading to hydrazine accumulation. Experimentally, the maximum hydrazine production climbed to 12 000 and 7800 μg L⁻¹ with the addition of NO and NO-EDTA, respectively. Because the inhibition by NO-EDTA and NO gas was reversible, the normal anammox capacity for nitrogen removal via N₂ recovered within 32 and 24 h after NO and NO-EDTA (respectively) were replaced with ammonium and nitrite substrates. These results demonstrate the promise of producing hydrazine via microbial conversion of NO and ammonium.