The reuse of tailwater as recycled water requires an advanced nitrogen removal treatment, during which carbon source is added based on the tailwater quality. This study conducted an advanced nitrogen removal model test in constructed wetland to evaluate the effects of influent NO3--N loading on denitrification and carbon releasing. In the constructed wetland, bark was used as filler and carbon source for nitrogen removal. The results showed that nitrogen removal was steady in the constructed wetland filled with bark. Denitrification velocity followed the Monod equation, and it increased as the influent NO3--N loading increased. The saturation constant KS was 19.10 mg·L-1. NO3--N removal rate decreased as the influent NO3--N loading increased. During the early periods of operating the constructed wetland filled with bark, the carbon releasing amount and velocity increased as the influent NO3--N loading increased. Both factors were positively linearly correlated with the influent NO3--N loading. The static carbon releasing velocity was 0.2 mg·(g·d)-1. Compared with the hollow and loose plant carbons, such as rotten wood, bark had a better performance and a longer cycle of carbon releasing, which made bark a good slow-release carbon source.
Keywords: NO3--N loading; bark; carbon source releasing; constructed wetland; denitrification.