Nitrate removal from tail water by integrated vertical-flow constructed wetlands at a high hydraulic loading rate

Abstract

Nitrate removal rates of two pilot-scale integrated vertical-flow constructed wetlands (IVCWs) treating tail water, under a hydraulic loading rate (HLR) of 250 mm/d with a mean influent NO3--N concentration of 24.4 mg.L-1, were evaluated. Mean NO3--N removal efficiencies of 15.5 and 18.5% with mass removal rates of 1.01 g.m(-2).d(-1) and 1.16 g.m(-2).d(-1) for IVCW 1 (planted with Canna indica and Pontederia cordata) and 2 (planted with Typha orientalis and Arundo donax var. versicolor), respectively, were achieved. The removal rate constants as fitted by the first-order area-based model averaged 0.046 and 0.055 m.d(-1), respectively. Since NO3--N was the dominant nitrogen form in the effluent, denitrification was the limiting step in nitrogen removal despite of favorable pH and anaerobic conditions in the wetland beds. Low availability of carbon source, high HLR, and low temperature could be the probable influencing factors for the observed low NO3--N removal efficiencies. However, IVCW could be used to treat tail water for nitrate removal at a comparable high loading rate.