Performance of a continuous micro-oxygen up-flow sludge bed reactor for assimilation of partial nitrification/anammox sludge into a CANON granular-floc system

CANON process was established in a micro-oxygen up-flow sludge bed reactor through one-step inoculation of partial nitrification/anammox sludge. The process was divided into three stages according to the influent NH+4-N concentrations. The position of aeration played a vital role as low DO concentration and sludge loss showed evident negative effects. Placing the aeration device above the sludge bed significantly enhanced the stability of the system, and the DO concentrations were maintained between 0.4 and 0.8 mg/L. The total nitrogen (TN) removal efficiency reached ∼70% within 5 days in stage I, yet the reaction stoichiometric ratios deviated from theoretical values. As the activity of anaerobic anammox bacteria (AnAOB) exceeded ammonia oxidizing bacteria (AOB) in stage III, the maximum TN removal rate reached 350 mg N/ L·d and the TN removal efficiency was retained at a relatively high value of 83%. Flocculent sludge converged into a granular-floc hybrid system with the percentage of sludge mass for particle size between 0.4 and 1 mm increased from 0% to 43.48%, and the percentage of sludge mass for particle size between 0 and 0.2 mm remained at 22.76%. Following 135 days of continuous operation, an interaction balance between AOB and AnAOB was reached with high activities and dominant abundance while nitrite oxidizing bacteria (NOB) were suppressed.