Design parameters for nitrogen removal by constructed wetlands treating mine waters and municipal wastewater under Nordic conditions.
Sci Total Environ
; 662: 559-570, 2019 Apr 20.
Article
en En
| MEDLINE
| ID: mdl-30699376
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 nitrateâ¯+â¯nitrite-N ((NO3-â¯+â¯NO2-)-N) was low during winter. The first-order N removal coefficient varied from 4.9⯷â¯10-6 to 1.9⯷â¯10-3â¯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-â¯+â¯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-â¯+â¯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-â¯+â¯NO2-)-N, reflecting lower denitrification rate at lower temperature. More than 50% removal was found to require a hydraulic load below 10â¯mmâ¯d-1. In order to achieve 70% of NH4+-N removal, Ntot load lower than 75â¯gâ¯m-2â¯year-1 and a residence time longer than 80â¯d are needed in CWs in cold-climate regions.
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MEDLINE
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2019
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Article