Effect of organic matter on the performance and N2O emission of a granular sludge anammox reactor

Abstract

A continuously fed bubble column granular sludge anammox reactor was operated for 405 days to investigate the effect of organic matter on the reactor performance and N₂O emission. Results showed that influent COD improved the nitrogen removal of the anammox reactor at low influent COD/TN ratios (ca. 0.1); however, a concurrent increase in N₂O emission was observed. The average N₂O emission increased by 2.5 times (p < 0.05) with increasing influent COD concentration, accounting for up to 0.46% of the incoming nitrogen load. A generalized method was demonstrated and applied to derive the anammox stoichiometry from experimental data for improved mass balance. Mass balance revealed that approximately 18% of the nitrate produced from anammox conversion was reduced via heterotrophic denitrification to nitrite, and 29% of this produced nitrite was further released as N₂O. In addition, it was found that the experimentally measured anammox biomass yield in the overall metabolic reaction has been mistakenly used as the catabolic yield in many modelling studies. Solutions were proposed.