Carbon supplementation and bioaugmentation to improve denitrifying woodchip bioreactor performance under cold conditions

Authors: Feyereisen, Gary; WANG, HAO - University Of Minnesota; WANG, PING - University Of Minnesota; ANDERSON, EMILY - University Of Minnesota; JANG, JEONGHWAN - Jeonbuk National University; GHANE, EHSAN - Michigan State University; COULTER, JEFFREY - University Of Minnesota; ROSEN, CARL - University Of Minnesota; SADOWSKY, MICHAEL - University Of Minnesota; ISHII, SATOSHI - University Of Minnesota

Submitted to: Ecological Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/2/2023
Publication Date: 3/17/2023
Citation: Feyereisen, G.W., Wang, H., Wang, P., Anderson, E.L., Jang, J., Ghane, E., Coulter, J.A., Rosen, C.J., Sadowsky, M.J., Ishii, S. 2023. Carbon supplementation and bioaugmentation to improve denitrifying woodchip bioreactor performance under cold conditions. Ecological Engineering. 191. Article 106920. https://doi.org/10.1016/j.ecoleng.2023.106920.
DOI: https://doi.org/10.1016/j.ecoleng.2023.106920

Interpretive Summary: Nitrate removal from agricultural tile water by woodchip bioreactors is negatively impacted during colder seasons. In this study, two approaches were taken to improve cold performance. First, microbes collected locally were screened for cold tolerance and added to woodchip beds. Second, a readily available carbon source (acetate) was added to the inlet water to other beds. The two approaches were compared to woodchips only. The experimental approaches were tested for two years in an on-farm experiment near Willmar, Minnesota, USA. The addition of acetate showed dramatic reduction in nitrate removal in one of four field campaigns and significantly better performance in a second campaign. Over time, the microbes produced bioslime, which reduced the amount of carbon that could be added and thus diminished the benefits. In one of campaigns, improvements due to addition of the selected microbes were observed for a two-week period; however, the effect was short-lived. We concluded that the addition of carbon performed better than addition of selected microbes. A method of carbon addition must be developed to avoid bioslime build up, and better inoculation techniques and community survival strategies must be developed for microbial additions to woodchip bioreactors. Both approaches need improvement before field implementation is warranted. These findings provide insight into how bioreactor performance may be improved and is pertinent to researchers, practitioners, academics, and agency personnel with interest in using denitrifying bioreactors to remove nitrate-N from water.

Technical Abstract: Cold temperatures limit nitrate-N load reductions of woodchip bioreactors in higher-latitude climates. This two-year, on-farm (Willmar, Minnesota, USA) study was conducted to determine whether field-scale nitrate-N removal of woodchip bioreactors can be improved by the addition of cold-adapted, locally isolated bacterial denitrifying strains (bioaugmentation) or dosing with a carbon (C) source (biostimulation). In Spring 2017, biostimulation removed 66% of the nitrate-N load, compared to 21% and 18% for bioaugmentation and control, respectively. The biostimulation nitrate-N removal rate (NRR) was also significantly greater, 15.0 g N m-1 d-1, versus 5.8 and 4.4 g N m-1 d-1, for bioaugmentation and control, respectively. Bioclogging of the biostimulation beds limited dosing for the remainder of the experiment; NRR was greater for biostimulation in Fall 2017, but in Spring 2018 there were no differences among treatments. Carbon dosing did not increase outflow dissolved organic C concentration. The abundance of one of the inoculated strains, Cellulomonas sp. strain WB94, increased over time, while another, Microvirgula aerodenitrificans strain BE2.4, increased shortly, returning to background levels after 42 days. Shortly after inoculation in Spring 2017, outflow nitrate-N concentrations of bioaugmentation were sporadically reduced compared to the control for two weeks, but were insignificant over the study period. The study suggests that biostimulation and bioaugmentation are promising technologies to enhance nitrate removal during cold conditions. A means of controlling bioclogging is needed for biostimulation, and improved means of inoculation and maintaining abundance of introduced strains is needed for bioaugmentation. In conclusion, biostimulation showed greater potential than bioaugmentation for increasing nitrate removal in a woodchip bioreactor, whereas both methods need improvement before implementation at the field scale.