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Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
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Volume 20, issue 1 | Copyright
Hydrol. Earth Syst. Sci., 20, 109-123, 2016
https://doi.org/10.5194/hess-20-109-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Review article 18 Jan 2016

Review article | 18 Jan 2016

Carbon and nitrogen dynamics and greenhouse gas emissions in constructed wetlands treating wastewater: a review

M. M. R. Jahangir1,2, K. G. Richards2, M. G. Healy3, L. Gill1, C. Müller4,5, P. Johnston1, and O. Fenton2 M. M. R. Jahangir et al.
  • 1Department of Civil, Structural & Environmental Engineering, Trinity College Dublin, Dublin 2, Ireland
  • 2Department of Environment, Soils & Land Use, Teagasc Environment Research Centre, Johnstown Castle, Co. Wexford, Ireland
  • 3Civil Engineering, National University of Ireland, Galway, Co. Galway, Ireland
  • 4School of Biology and Environmental Science, University College Dublin, Belfield, Dublin, Ireland
  • 5Department of Plant Ecology (IFZ), Justus-Liebig University Giessen, Giessen, Germany

Abstract. The removal efficiency of carbon (C) and nitrogen (N) in constructed wetlands (CWs) is very inconsistent and frequently does not reveal whether the removal processes are due to physical attenuation or whether the different species have been transformed to other reactive forms. Previous research on nutrient removal in CWs did not consider the dynamics of pollution swapping (the increase of one pollutant as a result of a measure introduced to reduce a different pollutant) driven by transformational processes within and around the system. This paper aims to address this knowledge gap by reviewing the biogeochemical dynamics and fate of C and N in CWs and their potential impact on the environment, and by presenting novel ways in which these knowledge gaps may be eliminated. Nutrient removal in CWs varies with the type of CW, vegetation, climate, season, geographical region, and management practices. Horizontal flow CWs tend to have good nitrate (NO3) removal, as they provide good conditions for denitrification, but cannot remove ammonium (NH4+) due to limited ability to nitrify NH4+. Vertical flow CWs have good NH4+ removal, but their denitrification ability is low. Surface flow CWs decrease nitrous oxide (N2O) emissions but increase methane (CH4) emissions; subsurface flow CWs increase N2O and carbon dioxide (CO2) emissions, but decrease CH4 emissions. Mixed species of vegetation perform better than monocultures in increasing C and N removal and decreasing greenhouse gas (GHG) emissions, but empirical evidence is still scarce. Lower hydraulic loadings with higher hydraulic retention times enhance nutrient removal, but more empirical evidence is required to determine an optimum design. A conceptual model highlighting the current state of knowledge is presented and experimental work that should be undertaken to address knowledge gaps across CWs, vegetation and wastewater types, hydraulic loading rates and regimes, and retention times, is suggested. We recommend that further research on process-based C and N removal and on the balancing of end products into reactive and benign forms is critical to the assessment of the environmental performance of CWs.

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Removal efficiency of carbon and nitrogen in constructed wetlands is inconsistent and does not reveal whether the removal processes are from physical attenuation or transformation to other reactive forms. Previous research did not consider "pollution swapping" driven by transformational processes. Herein the biogeochemical dynamics and fate of carbon and nitrogen and their potential impact on the environment, as well as novel ways in which these knowledge gaps may be eliminated, are explored.
Removal efficiency of carbon and nitrogen in constructed wetlands is inconsistent and does not...
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