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Plastic Biofilm Carrier after Corn Cobs Reduces Nitrate Loading in Laboratory Denitrifying Bioreactors

Gary W. Feyereisen, Laura E. Christianson, Thomas B. Moorman, Rodney T. Venterea, Jeffrey A. Coulter
Journal of environmental quality 2017 v.46 no.4 pp. 915-920
Zea mays, biofilm, bioreactors, cold, corn, corn cobs, denitrification, denitrifying microorganisms, effluents, genes, laboratory experimentation, nitrate nitrogen, nitrates, nitrogen, nitrous oxide, plastics, pollution control, pollution load, temperature, total organic carbon, wood chips
Nitrate‐nitrogen (nitrate‐N) removal rates can be increased substantially in denitrifying bioreactors with a corn (Zea mays L.) cob bed medium compared with woodchips; however, additional organic carbon (C) is released into the effluent. This laboratory column experiment was conducted to test the performance of a postbed chamber of inert plastic biofilm carrier (PBC) after corn cobs (CC) 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 CC only and CC plus PBC in series (CC‐PBC). Across the two temperatures, nitrate‐N load removal was 21% greater with CC‐PBC than CC, with 54 and 44% 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, although gene abundance at the outlet (PBC) was less than at the inlet (CC). The PBC chamber increased nitrate‐N removal rate and reduced cumulative N₂O production at 15.5°C, but not at 1.5°C. 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 benefits in terms nitrate‐N removal but did not achieve C removal. The presence of excess C, as well as available nitrate, in the PBC chamber suggests another unidentified limiting factor for nitrate removal. CORE IDEAS: A chamber of inert plastic biofilm carrier after corn cobs increased NO₃‐N removal. The added chamber did not achieve aqueous carbon removal. Denitrifiers colonized the plastic biofilm carrier. At 15.5°C, nitrous oxide cumulative production decreased, but not at 1.5°C. Cold temperature performance was unaffected by the added chamber.