Plastic carrier polishing chamber reduces pollution swapping from denitrifying woodchip bioreactors

Authors: CHRISTIANSON, LAURA - University Of Illinois; Feyereisen, Gary; LEPINE, CHRISTINE - Freshwater Institute; SUMMERFELT, STEVEN - Freshwater Institute

Submitted to: Aquacultural Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/16/2018
Publication Date: 5/1/2018
Citation: Christianson, L.E., Feyereisen, G.W., Lepine, C., Summerfelt, S.T. 2018. Plastic carrier polishing chamber reduces pollution swapping from denitrifying woodchip bioreactors. Aquacultural Engineering. 81:33-37. https://doi.org/10.1016/j.aquaeng.2018.01.001.
DOI: https://doi.org/10.1016/j.aquaeng.2018.01.001

Interpretive Summary: Denitrification woodchip bioreactors are an established in-field practice for nitrogen (N) mitigation. Their straightforward design and efficient nutrient reduction make this technology an appealing cost effective strategy for meeting established nutrient loss reduction goals. Advanced bioreactor design, however, may improve the N removal ability or reduce pollution swapping of these systems. When combined as a dual treatment approach, a post-woodchip polishing chamber of plastic biofilm carriers, traditionally used in denitrifying moving bed reactors, captured and utilized leached material. Observed during laboratory column study, no additional nitrate removal was detected from the post-woodchip chamber but significant chemical oxygen demand and nitrite reductions occurred. Sulfide production, a process associated with long woodchip retention times, was also alleviated as sulfates re-oxidized in the plastic biofilm carrier chamber. This performance increase may be required of bioreactors located in highly sensitive watershed areas.

Technical Abstract: Denitrifying bioreactors with solid organic carbon sources (i.e., “woodchip bioreactors”) have proven to be relatively simple and cost effective treatment systems for nitrate-laden agricultural and aquacultural waters and wastewaters. However, because this technology is still relatively new, design modifications, such as the addition of a post-bioreactor polishing chamber filled with inert media, may offer potential to increase nitrate removal and mitigate unintended bioreactor by-products. Paired-column configurations filled with woodchips followed by plastic biofilm carrier media showed significant nitrate removal within the woodchip bioreactor columns (37, 26, and 88% nitrate removal efficiencies at woodchip column retention times of 7.1, 18, and 52 h), but no significant additional nitrate removal benefit of the post-processing plastic media chamber (41, 22, and 89% nitrate removal efficiencies, respectively). Releases of chemical oxygen demand from the woodchips were likely not sufficient to fuel significant nitrate removal in the polishing chamber. However, the polishing chamber significantly reduced nitrite releases from the bioreactor columns, and provided some mitigation of reduced sulfate during the 52-h retention time testing period (influent, woodchip effluent, and plastic chamber effluent sulfate concentrations of 23.6, 18.8, and 20.7 mg SO42- L-1, respectively). A full-scale post-woodchip polishing chamber filled with inert plastic media generally may not be worth the added cost unless the receiving waters are particularly sensitive to nitrite or hydrogen sulfide.