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Creating a financial return-on-investment for constructed treatment wetlands

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org

Citation:  21st Century Watershed Technology: Improving Water Quality and Environment Conference Proceedings, 21-24 February 2010, Universidad EARTH, Costa Rica  701P0210cd.(doi:10.13031/2013.29480)
Authors:   Dawn M Reinhold
Keywords:   Treatment wetlands, duckweed, anaerobic digestion, bioenergy

Constructed wetlands are cost-effective treatment alternatives for high-strength agricultural wastewaters. Even though constructed wetlands are relatively low-cost, their adoption is frequently cost-prohibitive to many agricultural operators. However, research has indicated that aquatic plant biomass grown on agricultural wastewaters can be used to help recover the costs associated with wetland construction. This proceeding paper provides a brief review of applications for duckweed biomass that could be developed within the next five years to provide a return-on-investment for duckweed-based treatment wetlands. Additionally, a model that combines equations for hydrologic flows, wetland treatment, and duckweed growth was developed and examined to evaluate the predicted relationships between wetland design, effluent concentrations, and biomass production. Model results indicated that addition of recycle to wetland design decreased the conflict between maximizing biomass production and minimizing effluent concentrations. Maximum biomass production was achieved at harvest frequencies of 3 5 week, with little effect of percentage of duckweed harvested on biomass production. Research to better characterize treatment rate constants, temperature dependency of wetlands on duckweed biomass growth, and wastewater inhibition of duckweed biomass growth is needed to improve the presented model. With addition of information on the economic value of produced biomass and treated effluents, the presented model will improve wetland design by assisting in optimization for water quality benefits and financial return-on-investments.

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