Simulation and optimization of a constructed wetland for biomass production and nitrate removal

Nutrient-intensive agriculture involving nitrogen application rates exceeding crop requirements results in excessive loads in surface waters, contributing substantially to hypoxia in coastal ecosystems and violations of EPA drinking water nitrate standards. There is growing interest in the cultivation of perennial grasses for bioethanol production, which may address these problems and reduce greenhouse gas emissions. Some of these grasses can be grown in constructed wetlands, which offer additional nitrate removal by denitrification in the wetland benthos. The present work simulates and optimizes a hypothetical wetland system near Camargo, Illinois. The wetland system is assumed to draw water from the Embarras River and is designed to treat non-point-source nutrient loadings and produce harvestable biomass for ethanol production. An integrated model of biomass production, nutrient removal, and cost is developed to assess and optimize the relationship between wetland cost and nutrient removal. The wetland shows a profit only when some costs are excluded from the analysis; however, consideration of the environmental benefit could change the cost-benefit outcome.