Performance of pilot-scale vertical-flow constructed wetlands in responding to variation in influent C/N ratios of simulated urban sewage

The performance response of planted and the unplanted wetlands to simulated wastewater with different ratios of carbon to nitrogen (C/N) was studied during a 9-month period in greenhouse conditions. With different C/N ratios for influent water (C/N ratios 2.5:1, 5:1 and 10:1), average removal efficiencies for the unplanted and the planted wetlands were as follows: COD (41–52% and 59–68%), TN (24–48% and 25–62%), TP (35–64% and 59–71%) and TOC (22–37% and 16–33%). At C/N 5:1, both systems performed most efficiently for removal of COD and TP. However, high N removal efficiency only occurred when C/N ratio ranged 2.5–5. Both wetlands exhibited good capabilities of total organic carbon removal at C/N 10:1. Maybe, appropriate control of the carbon or nitrogen source concentration and C/N ratio in the influent can achieve the optimal effect of nutrients removal.