Simulation and Optimization of a Constructed Wetland for Biomass Production and Nitrate Removal

constructed wetland;nitrate;biomass;biofuels;water quality;non-point source pollution;biomass simulation model;wetland denitrification model

Zygas, Aras J. ; Cai ; Ximing ; Eheart ; J. Wayland

关键词: constructed wetland;    nitrate;    biomass;    biofuels;    water quality;    non-point source pollution;    biomass simulation model;    wetland denitrification model;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/18458/Zygas_Aras.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Recently there is growing concern about high nutrient loadings in surface waters as a result of intensive agriculture, resulting in hypoxia in costal ecosystems. There is simultaneous growing interest in the cultivation of perennial grasses for bio-ethanol production. Constructed wetlands offer a promising nutrient removal mechanism while also providing an ideal environment for the growth of such grasses. In the present work, a hypothetical wetland system is designed to treat non-point source nutrient loadings and produce harvestable biomass for ethanol production in central Illinois. Through the integration of a biomass production model, a nutrient removal model and a cost model, the relationship between the costs of wetland construction, benefits from biomass sales, and mass nutrient removal can be seen for various wetland sizes and water throughput capacities. Using genetic algorithms, the Pareto-optimal frontier showing the tradeoff between nutrient removal and the net cost of the wetland system, (accounting for revenue from biomass harvest) can be visualized. This analysis is demonstrated for a hypothetical wetland site near Camargo, Illinois which is assumed to draw water from the Embarras River. Through the simulation of several cost scenarios, the wetland is found to show a profit only when construction, operation and maintenance costs are excluded from the analysis. Results show a tradeoff between the amount of nitrate removed in the wetland via denitrification and biomass production For the example case, a 33.8 ha wetland with a 2.3 m3/s design pumping capacity was found to have the maximum cost efficiency with a cost of 4.8 $/kg of NO3-N removed. The results indicate that there is a unique efficiency-maximizing design for a wetland at a particular site. These results also indicate that a subsidy of at least 4.8 $/kg of NO3-N removed is necessary (assuming the biomass is sold for $58/ton) in order for a wetland at the hypothetical site to break even. Furthermore, if a market for nitrogen exists or if nutrient trading between point dischargers is allowed, it might be possible for a constructed wetland designed for biomass production to be profitable while providing water quality benefits.