Modeling Nitrogen Transport in Duckweed Pond for Secondary Treatment of Swine Wastewater |
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Authors: | Sumate Chaiprapat Jiayang Cheng John J Classen Joel J Ducoste Sarah K Liehr |
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Affiliation: | 1Lecturer, Faculty of Environmental Management, Prince of Songkla Univ., P.O. Box 50 Kho Hong, Hat Yai, Songkla?90112, Thailand. 2Assistant Professor, Dept. of Biological and Agricultural Engineering, 275 Weaver Labs, North Carolina State Univ., Raleigh, NC?27695-7625 (corresponding author). 3Associate Professor, Dept. of Biological and Agricultural Engineering, 179 Weaver Labs, North Carolina State Univ., Raleigh, NC?27695-7625. 4Assistant Professor, Dept. of Civil Engineering, 208 Mann Hall, North Carolina State Univ., Raleigh, NC?27695-7908. 5Research Associate Professor, Dept. of Biological and Agricultural Engineering, 184 Weaver Labs, North Carolina State Univ., Raleigh, NC?27695-7625.
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Abstract: | A mathematical model was developed to describe nitrogen transport in duckweed-covered static ponds for nutrient recovery from swine lagoon water. A finite difference technique was used to solve the partial differential equations describing the ammonia transport and concentration in the pond. The key parameters in the model include the diffusion coefficient of ammonium in the medium (D) and kinetic constant of nitrogen uptake by duckweed (k). Using one order of magnitude parameter variations, the simulations showed that the model was clearly much more sensitive to D than to k, indicating the process of nitrogen removal in a static pond by duckweed is diffusion limited. Laboratory testing was conducted with Spirodela punctata 7776, a duckweed strain, to calibrate the model. The calibration of the model with experimental data yielded a new ammonium transport coefficient (T) that is 85 times of D value. Model results showed good agreement with depth-wise experimental ammonium concentration and the model also demonstrates that intermittent mixing every 3 h can enhance ammonium uptake. Additionally, an apparent drop in pH near the duckweed mat at the surface was observed that may explain low rates of ammonia emission from duckweed ponds. |
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Keywords: | Ponds Wastewater treatment North Carolina Mathematical models |
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