The whole pilot experiment mainly included two stages:
Experiment 1: efficient TN removal via SND in the outer channel of the Orbal system through precise control of DO and ORP;
Experiment 2: enhanced nitrogen removal in a modified Orbal oxidation ditch with internal recycle for pre-denitrification at
the optimal DO for SND in Experiment 1. The characteristics of influent wastewater during two experimental stages were summarized in Table 1.