Nitrogen removal performance in planted and unplanted horizontal subsurface flow constructed wetlands treating different influent COD/N ratios

Wang, Wei; Ding, Yi; Ullman, Jeffrey L.; Ambrose, Richard F.; Wang, Yuhui; Song, Xinshan; Zhao, Zhimiao

Nitrogen removal performance in planted and unplanted horizontal subsurface flow constructed wetlands treating different influent COD/N ratios

2016

Microcosm horizontal subsurface flow constructed wetlands (HSSFCWs) were used to examine the impacts of vegetation on nitrogen dynamics treating different influent COD/N ratios (1:1, 4:1, and 8:1). An increase in the COD/N ratio led to increased reductions in NO₃ and total inorganic nitrogen (TIN) in planted and unplanted wetlands, but diminished removal of NH₄. The HSSFCW planted with Canna indica L. exhibited a significant reduction in NH₄ compared to the unplanted system, particularly in the active root zone where NH₄ removal performance increased by up to 26 % at the COD/N ratio of 8:1. There was no significant difference in NO₃ removal between the planted and unplanted wetlands. TIN removal efficiency in the planted wetland increased with COD/N ratios, which was likely influenced by plant uptake. NH₄ reductions were greater in planted wetland at the 20- and 40-cm depths while NO₃ reductions were uniformly greater with depth in all cases, but no statistical difference was impacted by depth on TIN removal. These findings show that planting a HSSFCW can provide some benefit in reducing nitrogen loads in effluents, but only when a sufficient carbon source is present.

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