To achieve high nitrification and denitrification rates, step-feed SBR with multiple aerobic and anoxic phases was adopted to study nitrogen removal performance. Theoretical analysis of step-feed SBR was presented first, from which feeding steps and C/N ratio had significant influences on nitrogen removal performance. Total nitrogen removal efficiency would increase with increasing of feeding steps, while the increasing extent was not distinct with feeding steps above 4. At a given feeding step, nitrogen removal efficiency would also increase with increasing of C/N ratio. Experimental work was conducted in a lab-scale SBR to investigate practical effects of these critical factors, using real municipal wastewater. The results showed when C/N ratio was appropriately decreasing influent flow mode could achieve enhanced nitrogen removal with less adding of external carbon source, compared with equal influent flow mode. Three-step equal influent flow mode was recommended to treat common municipal wastewater in view of operation complexity. Non steady-state experiments over about three months confirmed step-feed SBR was an enhanced nitrogen removal process with high efficiency. Total nitrogen in the effluent was under 2 mg/L, the average removal efficiency achieved for TN was over 97% just adding a little external carbon source, and good sludge settleability was obtained.

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