The Effect of Inorganic Carbon Limitation on the Performance of the CANON system

The Completely Autotrophic Nitrogen-removal Over Nitrite (CANON) process can remove ammonia by combining partial nitritation and anaerobic ammonia oxidation (anammox) in one single reactor. Considering that the stability of CANON systems relies on the interactions between three groups of predominantly autotrophic bacteria, the effect of inorganic carbon (IC) limitation on the performance of the CANON process in a moving-bed biofilm reactor was investigated. Upon subjecting the CANON system to IC limitation, the nitrogen removal rate decreased from 80% to 44% after 27 HRTs of 50% stoichiometric IC limitation, but no significant increases in NO and N2O emissions were observed during the limitation. After 4 HRTs of recovery, the removal rate increased back to 62% and the gas emissions experienced a further decline. Based on these results, transient or continuous IC limitation could be deleterious to the performance of autotrophic N-removal systems and needs to be minimized to ensure stable reactor performance.