Modeling Nitrogen Transport in Duckweed Pond for Secondary Treatment of Swine Wastewater

• Published in: Journal of environmental engineering (New York, N.Y.) Vol. 129; no. 8; pp. 731 - 739
• Main Authors: Chaiprapat, Sumate, Cheng, Jiayang, Classen, John J, Ducoste, Joel J, Liehr, Sarah K
• Format: Journal Article
• Language: English
• Published: Reston, VA American Society of Civil Engineers 01.08.2003
• Subjects: Accuracy; Ammonia; Applied sciences; Biological and medical sciences; Biological treatment of waters; Biotechnology; Calibration; Coefficients; Computer simulation; Diffusion; Environment and pollution; Environmental engineering; Exact sciences and technology; Finite difference method; Fundamental and applied biological sciences. Psychology; Industrial applications and implications. Economical aspects; Lagoons; Mathematical analysis; Mathematical models; Nitrogen; Nutrients; Other wastewaters; Pollution; Ponds; Recovering; Spirodela punctata; Statics; TECHNICAL PAPERS; Uptakes; Variations; Wastewater treatment; Wastewaters; Water treatment and pollution; Monocotyledones; Ammonium; Stabilization pond; Lemnaceae; Animal slurry; Livestock farm; Biological purification; Transport process; Vertebrata; Mammalia; Swine; Angiospermae; Numerical simulation; Spermatophyta; Agriculture; Artiodactyla; Aquatic plant; Diffusion coefficient; Waste water purification; Ungulata; Nitrogen Compounds; Concentration distribution; Finite difference method
• ISSN: 0733-9372; 1943-7870
• DOI: 10.1061/(ASCE)0733-9372(2003)129:8(731)

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.