Nitrogen removal in micro-polluted surface water by the combined process of a bio-filter and an ecological gravel bed was studied. Sodium acetate was added into micro-polluted surface water as carbon source and the nitrogen removal under different C/N ratio, hydraulic load and temperature were investigated. The results showed that the variations in C/N ratio, hydraulic load and temperature have significant influence on nitrogen removal in bio-filter. It was found that the denitrification rate was above 90% when C/N ratio reached 10; also, the denitrification was inhibited at low water temperature (2–10 °C); at the condition of water temperature above 20 °C, C/N ratio 10, hydraulic load 8 m3/(m2 h), the combined process obtained the nitrogen removal of more than 90%, and the residual organics could be removed in ecological gravel bed.

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