To investigate the kinetic behaviors of nitrate removal from groundwater using constructed wetlands, this study set up two flow-through pilot-scale constructed wetlands with the same areal size but various flow patterns (free water surface flow (FWS) and subsurface flow (SF)) to receive a synthetic nitrate contaminated groundwaterat a target concentration of 20 mg NO3-N L-1. These two wetlands were operated at nearly identical hydraulic loading rate (HLR) in every trial and sequentially run in various trials with different HLRs ranging from 0.02 to 0.27 m d-1. Nitrate removal rates of both wetlands increased with increasing hydraulic loading rate until a maximum valus was reached. The maximum removal rates, occurred at HLR of 0.12 and 0.07 m/d, were 0.910 and 1.161 g N/m2/d for the FWS and SF wetland, respectively. After the maximum values were reached, further increasing HLR led to a considerable decrease in nitrate removal rate. Nitrate removal efficiencies remmained high (>85%) and effluent nitrate concentrations always satisfied drinking water standard (<10 NO3-N/L) when HLR did not exceed 0.04 m/d for both FWS and SSF wetlands. As HLR was greater than 0.4 m/d, effluent nitrate significantly increased and removal efficiency cinsiderably decreased with the increase of HLR. The longitudinal transect nitrate data show that the SF wetland exhibited a frist-order plug-flow reactor profile, while the FWS watland diverged from a plug flow response. The first-order nitrate removal rate constant, determined either from longitudinal transect data or influent-effluent data, tends to decrease with increasing HLRs, which may be due to increase of nitrate loading rate decreasing the denitrification rate in wetlands. The FWS wetland provided significantly higher (p<0.05) organic carbon in effluent than the SF wetland, while the SF wetland exhibited significantly (p<0.05) lower effluent DO than the FWS wetland. However, there was no significant difference (p>0.5) in nitrate removal performance between the two types of constructed wetlands in this study except in one trial operating at HLR of 0.06~0.07 m/d.
