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ARS Home » Midwest Area » Ames, Iowa » National Laboratory for Agriculture and The Environment » Agroecosystems Management Research » Research » Publications at this Location » Publication #314273
Title: Woodchip denitrification bioreactors: Impact of temperature and hydraulic retention time on nitrate removal

Author
item HOOVER, NATASHA - Iowa State University
item BHANDARI, ALOK - Kansas State University
item SOUPIR, MICHELLE - Iowa State University
item Moorman, Thomas

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/7/2015
Publication Date: 4/25/2016
Citation: Hoover, N., Bhandari, A., Soupir, M., Moorman, T.B. 2016. Woodchip denitrification bioreactors: Impact of temperature and hydraulic retention time on nitrate removal. Journal of Environmental Quality. 45:803-812. doi: 10.2134/jeq2015.03.0161.

Interpretive Summary: Midwestern agriculture lands are extensively tile-drained which contributes to the excessive loss of nitrate into streams. Woodchip denitrification bioreactors, a relatively new technology for edge-of-field treatment of subsurface agricultural drainage water, have shown potential for nitrate removal. However, very few studies have evaluated the performance of these reactors under controlled conditions similar to the field. This study investigated: (1) the release of total organic carbon during reactor start-up; (2) nitrate removal at hydraulic retention times (HRT) of 2, 4, 8, 12, and 24 hours; (3) nitrate removal at influent Nitrate-nitrogen (NO3-N) concentrations of 10, 30, and 50 ppm (mg/L); and (4) nitrate removal at 10, 15, and 20°C. Greater total organic carbon was released during the first 25 days of bioreactor operation with fresh woodchips, whereas organic carbon release was low when the columns were packed with naturally weathered woodchips. Nitrate-Nitrogen concentration reductions increased from 8 to 55% as hydraulic retention time increased. Nitrate removal on a mass basis (grams NO3-N per cubic meter per day) was also increased as HRT increased from 2 to 24 hours. Comparison of mean NO3-N load reduction for various influent nitrate concentrations showed lower reduction at an influent concentration of 10 ppm, and higher NO3-N reductions at influent concentrations of 30 and 50 ppm. Nitrate-Nitrogen removal showed a stepped increase with temperature. A temperature coefficient (Q10) factor of 2.28, calculated from NO3-N removal rates at 10 and 15°C allows scaling the results to warmer or colder temperatures. The results of this study are useful for informing field-specific design of denitrification woodchip bioreactors.

Technical Abstract: Woodchip denitrification bioreactors, a relatively new technology for edge-of-field treatment of subsurface agricultural drainage water, have shown potential for nitrate removal. However, very few studies have evaluated the performance of these reactors under controlled conditions similar to the field. This study investigated : (1) the release of total organic carbon during reactor start-up; (2) nitrate removal at hydraulic retention times (HRT) of 2, 4, 8, 12, and 24 hours; (3) nitrate removal at influent NO3-N concentrations of 10, 30, and 50 mg/L; and (4) nitrate removal at 10, 15, and 20°C. Greater total organic carbon was released during the first 25 days of bioreactor operation with fresh woodchips, whereas organic carbon release was low when the columns were packed with naturally weathered woodchips. Nitrate-N concentration reductions increased from 8 to 55% as hydraulic retention time increased. Nitrate removal on a mass basis (g NO3-N/m3/day) was also increased as HRT increased from 2 to 24 hours. Comparison of mean NO3-N load reduction for various influent nitrate concentrations showed lower reduction at an influent concentration of 10 mg/L, and higher NO3-N reductions at influent concentrations of 30 and 50 mg/L. NO3-N removal showed a stepped increase with temperature. A temperature coefficient (Q10) factor of 2.28, calculated from NO3-N removal rates at 10 and 15°C, provided a reasonable agreement with the achieved removal rates measured in this study at 21.5°C. The results of this study are useful for informing field-specific design of denitrification woodchip bioreactors.