Rapid in-situ enrichment of anammox bacteria from activated sludge via nitrate induction: pilot-scale demonstration and mechanistic insights.

Abstract

The enrichment of anaerobic ammonium-oxidizing (anammox) bacteria from common activated sludge is slow, greatly limiting the application of anammox-based technologies. Herein, a nitrate-induction strategy was applied during the early enrichment stage to accelerate the enrichment of anammox bacteria. Compared with the control, the nitrate-induced system triggered earlier occurrence of anammox activity and achieved higher anammox activity (50.5 mg N·g-1 VSS·d-1vs. 17.5 mg N·g-1 VSS·d-1) and abundance within 64 days (2.00% vs. 0.31%). The endogenous organic substrates in sludge were used to reduce nitrate for slow and stable nitrite supply that alleviated direct nitrite inhibition on anammox bacteria. Nitrate addition also accelerated depletion of endogenous carbon, suppressing the heterotrophic denitrifier activity. These functions create a favorable environment for anammox bacteria to rapidly proliferate. This strategy was successfully validated in an 8 m3 pilot-scale reactor. Anammox activity emerged within 30 days, and the anammox abundance reached 8.8% by day 129. The pilot-scale results further suggest that utilizing endogenous carbon released from the sludge avoids excessive activity of heterotrophic denitrifiers and facilitates the establishment of an autotrophic anammox-dominated system. This strategy offers a rapid and promising approach for anammox bacteria enrichment from common activated sludge, propelling full-scale implementation of anammox technology.