Amending woodchip bioreactors with corncobs reduces nitrogen removal cost

Ji Yeow Law; Alexis Slade; Natasha Hoover; Gary Feyereisen; Michelle Soupir

doi:10.1016/j.jenvman.2022.117135

Amending woodchip bioreactors with corncobs reduces nitrogen removal cost

J Environ Manage. 2023 Mar 15:330:117135. doi: 10.1016/j.jenvman.2022.117135. Epub 2022 Dec 28.

Authors

Ji Yeow Law¹, Alexis Slade², Natasha Hoover³, Gary Feyereisen⁴, Michelle Soupir³

Affiliations

¹ Dep. of Agricultural and Biosystems Engineering, Iowa State University, 605 Bissell Rd, Ames IA, 50011, USA. Electronic address: jiyeow@iastate.edu.
² Dep. of Agricultural and Biosystems Engineering, Iowa State University, 605 Bissell Rd, Ames IA, 50011, USA; Dep. of Civil and Environmental Engineering, University of Iowa, 4231 Seamans Center, Iowa City IA, 52242, USA.
³ Dep. of Agricultural and Biosystems Engineering, Iowa State University, 605 Bissell Rd, Ames IA, 50011, USA.
⁴ USDA-ARS Soil and Water Management Research, St. Paul, MN, 439 Borlaug Hall, 1991 Upper Buford Circle, 55108, USA.

PMID: 36584471
DOI: 10.1016/j.jenvman.2022.117135

Abstract

Woodchip denitrification bioreactors are an effective agricultural practice to reduce nitrogen (N) export from subsurface drainage via the conversion of nitrate (NO₃^-) to nitrogen gas (N₂), but there are challenges associated with limited woodchip supplies and increasing prices. Previous lab studies indicate that corncobs could be a promising woodchip alternative from the perspectives of N removal rate and cost. This field study aimed to provide early performance and cost assessment of denitrification bioreactors with two woodchip-corncob treatments. The objectives were to i) compare N removal rates of bioreactors with different carbon and hydraulic retention time (HRT) treatments, ii) compare bioreactor N removal costs, and iii) conduct sensitivity analysis on full-scale bioreactors (FBR) N removal costs with varying corncob lifespans and prices. Nine replicated field pilot-scale bioreactors (PBRs) using three carbon treatments and three HRTs were assessed for N removal efficiency. The carbon treatments were woodchip-only (WC100), 25% (by vol.) corncobs + 75% woodchips media (CC25) in series, and 75% corncobs + 25% woodchips (CC75) in series set at HRTs of 2, 8, and 16 h. N concentrations were monitored at each PBR inlet and outlet, and the PBR N removal efficiencies were used to estimate FBR N removal rates and costs. At respective HRTs, the estimated N removal rates of CC75 were 1.6- to 10.1-fold higher than WC100, but CC25 exhibited 0.9-fold lower (at 8-hr HRT) to 2.8-fold higher than WC100. A 15-yr cost assessment indicated CC75 ($10.56 to $13.89 kg^-1 N) was the most cost-efficient treatment, followed by WC100 ($13.30 to $88.11 kg^-1 N) and CC25 ($22.41 to $60.13 kg^-1 N). This assessment showed CC75 as a promising alternative to WC100 in terms of N removal rate and cost, but CC25 did not provide sufficient N removal rate increase for it to be a cost-efficient option. Nonetheless, using corncobs as a bioreactor medium is a relatively new approach, and we encourage more field studies to explore the long-term opportunities and challenges.

Keywords: Alternative carbon source; Best management practices; Denitrification; Economic analysis; Nitrogen removal cost; Woodchip bioreactors.

MeSH terms

Bioreactors
Carbon
Denitrification
Nitrates / analysis
Nitrogen*
Zea mays*

Substances

Nitrogen
Nitrates
Carbon