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Updated: Jan 30, 2026

Mesocosm-Scale Constructed Wetland Design for Wastewater Treatment
Published on: May 2, 2025
Design parameters for nitrogen removal by constructed wetlands treating mine waters and municipal wastewater under
Katharina Kujala1, Teemu Karlsson2, Soile Nieminen3
1Water Resources and Environmental Engineering Research Unit, Faculty of Technology, University of Oulu, P.O. Box 4300, FI-90014, Finland.
Abstract:
Nitrogen (N) loads from municipal and mine wastewater discharges typically increase N concentrations in recipient water bodies which should get more attention especially in cold-climate regions. This study compared N removal efficiency of six constructed wetlands (CWs) treating mine waters and three CWs polishing municipal wastewater. There were clear impacts of point source N loading to recipient water bodies in all cases studied and >300-fold increase in N was seen in some cases. First-order N removal coefficient was determined for seven of these CWs. All CWs studied were observed to remove N efficiently during the warm growing season but the amount of N released increased significantly during the cold season. Although some year-round purification was achieved by both peat-based and pond-type CWs, removal of nitrate + nitrite-N ((NO3- + NO2-)-N) was low during winter. The first-order N removal coefficient varied from 4.9 · 10-6 to 1.9 · 10-3 d-1 and showed that peat-based CWs were slightly more efficient in N removal than pond-type CWs. However, purification efficiency was steadier and higher for pond-type CWs, as lower hydraulic load or longer water residence time compensated for purification performance. Pond-type CWs showed mean removal efficiency of 59% and 46% for ammonium-N (NH4+-N) and (NO3- + NO2-)-N, respectively, whereas peatland-type CWs had lower removal efficiency for NH4+-N (mean of 26%) and in many cases negative removal for (NO3- + NO2-)-N. Correlation analysis revealed no clear, systematic relationship between temperature and N removal. However, in some CWs the highest correlation was between temperature and (NO3- + NO2-)-N, reflecting lower denitrification rate at lower temperature. More than 50% removal was found to require a hydraulic load below 10 mm d-1. In order to achieve 70% of NH4+-N removal, Ntot load lower than 75 g m-2 year-1 and a residence time longer than 80 d are needed in CWs in cold-climate regions.
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