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Estimation of nitrogen dynamics in a vertical-flow constructed wetland

Ouyang, Y., Luo, S.M., Cui, L.H.
Ecological engineering 2011 v.37 no.3 pp. 453-459
Cyperus alternifolius, adsorption, ammonium nitrogen, computer software, constructed wetlands, denitrification, drying, leaching, models, nitrate nitrogen, nitrogen, nutrients, pollutants, roots, stormwater, volatilization, wastewater, water flow
The vertical-flow constructed wetland (VFCW) is a promising engineering technique for removal of excess nutrients and certain pollutants from wastewater and stormwater. The aim of this study was to develop a model using the STELLA software for estimating nitrogen (N) dynamics in an artificial VFCW (i.e., a substrate column with six zones) associated with a growing Cyperus alternifolius species under a wetting (wastewater) -to-drying ratio of 1:3. The model was calibrated by our experimental data with a reasonable agreement prior to its applications. Simulations showed that rates of NH₄ ⁺-N and NO₃ ⁻-N leaching decreased with increasing zone number (or column depth), although such a decrease was much more profound for NH₄ ⁺-N. Our simulations further revealed that rate of NH₄ ⁺-N leaching decreased with time within each zone, whereas rate of NO₃ ⁻-N leaching increased with time within each zone. Additionally, both the rates of NH₄ ⁺-N and NO₃ ⁻-N leaching through zones followed the water flow pattern: breakthrough during wetting period and cessation during drying period. In general, the cumulative amounts of total nitrogen (TN) were in the following order: leaching>denitrification>uptake>settlement. About 54% of the TN from the wastewater flowed out of the VFCW system, 18% of TN lost due to denitrification, 6% of TN was taken up by roots of a single plant (one hill), and the rest of 22% TN from the wastewater was removed from other mechanisms, such as volatilization, adsorption, and deposition. This study suggested that to improve the overall performance of a VFCW for N removal, prevention of N leaching loss was one of the major issues.