Location: Soil and Water Management ResearchTitle: Plastic biofilm carrier after corn cobs reduces nitrate loading in laboratory denitrifying bioreactors
|CHRISTIANSON, LAURA - University Of Illinois|
|Venterea, Rodney - Rod|
|COULTER, J - University Of Minnesota|
Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/20/2017
Publication Date: 6/1/2017
Citation: Feyereisen, G.W., Christianson, L.E., Moorman, T.B., Venterea, R.T., Coulter, J.A. 2017. Plastic biofilm carrier after corn cobs reduces nitrate loading in laboratory denitrifying bioreactors. Journal of Environmental Quality. 46(4):915-920. doi:10.2134/jeq2017.02.0060.
Interpretive Summary: Lab testing has shown that nitrate removal performance of denitrifying bioreactors can be improved by using corn cobs as the medium rather than woodchips, however, corn cobs release more carbon into the effluent. The objective of this study was to determine whether a "polishing" filter in series after a corn cob denitrifying bioreactor would enhance nitrate-nitrogen removal and reduce aqueous carbon concentrations and loads compared to using corn cobs with no polishing filter. Water with nitrate-nitrogen was pumped through PVC columns containing corn cobs and corn cobs with an added chamber containing plastic biofilm carrier (PBC) for five months at 60 degF and for 5 months at 36 degF. Over both experiments, total nitrate-nitrogen load removal was 21% greater for corn cobs with PBC than for corn cobs alone. Nitrate removal rates and outlet concentrations were not significantly different, although tendency was for better performance for the corn cobs with PBC. The effluent aqueous carbon concentrations and loads were similar for both treatments, as were nitrous oxide concentrations and loads. The findings of this study inform researchers, policy makers, and conservation practitioners that a polishing filter in series after a denitrifying bioreactor with corn cobs would improve nitrate removal but not reduce aqueous carbon release or nitrous oxide production.
Technical Abstract: Nitrate-nitrogen removal rates can be increased substantially in denitrifying bioreactors with a corn cob bed medium compared to woodchips; however, additional organic carbon (C) is released into the effluent. This laboratory column experiment was conducted to test the performance of a post-bed chamber of inert plastic biofilm carrier (PBC) after corn cobs to extend the area of biofilm colonization, enhance nitrate-N removal, lower total organic C losses, and reduce nitrous oxide (N2O) production at warm (15.5°C) and cold (1.5°C) temperatures. Treatments were corn (Zea mays L.) cobs only (CC) and corn cobs plus PBC in series (CC-PBC). Across the two temperatures, nitrate-N load removal was 21% greater with CC-PBC than CC; 53.7 and 44.5% of total nitrate-N load, respectively. However, total organic C concentrations and loads were not significantly different between treatments. Colonization of the PBC by denitrifiers occurred; gene abundance at the inlet and outlet of the CC-PBC treatment was not significantly different even though PBC was not a respiration substrate. There were no significant differences between treatments in dissolved N2O concentrations or loads at either temperature. Across temperatures and treatments, N2O production was 0.9% of nitrate-N removed. Including an additional chamber filled with PBC downstream from the CC bioreactor provided only marginal benefits in terms of nitrate-N and C removal. The presence of excess C in the PBC chamber as well as available nitrate suggests limitation of some other nutrient, inadequate residence time, or lack of contact with the microbial biofilm.