The start-up of mainstream anammox process is limited only by nitrite supply

In this study, we investigated start-up of an Anammox bioprocess from a secondary activated sludge seed fed primary effluent from a domestic used water reclamation plant (WRP). To test the hypothesis that an anammox-enriched sludge could still be achieved under such conditions given enough nitrite and ammonium, nitrite was supplemented at a molar ratio of 2:1 to ammonium. Anammox activity was observed within 50 d of operation and the relative abundance of Anammox bacteria increased from <0.1% gradually up to 4% after 100 d of operation, concomitant with complete ammonium removal. Despite consumption of chemical oxygen demand (COD) by heterotrophic denitrifiers, the Anammox biomass continued to accumulate up to 20% of relative abundance, contributing to biofilm and granule formation in the reactor. Thus, a high influent COD concentration is not inhibitory to the start-up of an Anammox system as long as sufficient nitrite is provided.