Inhibition of anaerobic ammonium oxidation (anammox) bacteria by addition of high and low concentrations of chloramphenicol and comparison of attached- and suspended-growth

Inhibition of anammox activities was tested with two ranges of chloramphenicol (CAP) concentration (5, 10, 20, 50, and 100 mg L⁻¹) and (100, 500, and 1000 μg L⁻¹). In a short-term study, strong inhibition of activity was dependent of CAP concentration in both attached-growth (SBR-A) and suspended-growth (SBR-S) systems. The activities of attached-growth cultures at all CAP concentrations were reversible after 1 day, while activities for suspended-growth cultures were only gradually reversible dependent on the CAP concentrations. In long-term studies with daily additions of 6 mg L⁻¹ CAP, the anammox activity on day 41 in SBR-A had decreased to 18% baseline (SAA reduced from 0.528 to 0.096 mg N mg⁻¹ VSS d⁻¹). More rapid reduction of anammox activity was observed in SBR-S, down to 17% baseline after only 27 days (SAA decreased from 0.576 to 0.096 mg N mg⁻¹ VSS d⁻¹). Inhibition was irreversible in both SBR-S and SBR-A after the long-term study. With lower CAP additions (100–1000 μg L⁻¹), the activities in both reactors were stable during daily CAP addition for two weeks. Attached-growth cultures tended to be more tolerant of CAP addition than suspended-growth cultures. Both un-competitive and non-competitive models could be used to compare anammox activities with the higher CAP concentrations. The SAA_max [fx] (the maximum specific anammox activity) and _h K_i (the inhibition constant) of SBR-A were 0.48 mg N mg⁻¹ VSS d⁻¹ and 98.3 mg L⁻¹, respectively. The SAA_max[fx] and K_i of SBR-S were 1.25 mg N mg⁻¹ VSS d⁻¹and 71.1 mg L⁻¹, respectively.