Impact of hydraulic residence time on nitrate removal in pilot-scale woodchip bioreactors

E A Martin; M P Davis; T B Moorman; T M Isenhart; M L Soupir

doi:10.1016/j.jenvman.2019.01.025

Impact of hydraulic residence time on nitrate removal in pilot-scale woodchip bioreactors

J Environ Manage. 2019 May 1:237:424-432. doi: 10.1016/j.jenvman.2019.01.025. Epub 2019 Feb 26.

Authors

E A Martin¹, M P Davis², T B Moorman³, T M Isenhart⁴, M L Soupir⁵

Affiliations

¹ Department of Agricultural and Biosystems Engineering, Iowa State University, Ames, IA 50011, USA. Electronic address: eamartin@iastate.edu.
² Iowa State University, Dept. of Agronomy, 2104 Agronomy Hall, Ames, IA 5001, USA. Electronic address: morgand@iastate.edu.
³ USDA-ARS National Laboratory for Agriculture and the Environment, 2110 University Boulevard, Ames, IA 50011, USA. Electronic address: Tom.moorman@usda.ars.gov.
⁴ Iowa State University, Dept. of Natural Resource Ecology and Management, 334 Science II, Ames, IA 50011, USA. Electronic address: isenhart@iastate.edu.
⁵ Iowa State University, Water Quality Research Lab, Dept. of Agricultural and Biosystems Engineering, 3358 Elings Hall, USA. Electronic address: msoupir@iastate.edu.

PMID: 30822646
DOI: 10.1016/j.jenvman.2019.01.025

Abstract

Nitrate (NO₃^-N) export from row crop agricultural systems with subsurface tile drainage continues to be a major water quality concern. Woodchip bioreactors are an effective edge-of-field practice designed to remove NO₃^-N from tile drainage. The NO₃^-N removal rate of woodchip bioreactors can be impacted by several factors, including hydraulic residence time (HRT). This study examined the impact of three HRTs, 2 h, 8 h, and 16 h, on NO₃^-N removal in a set of nine pilot-scale woodchip bioreactors in Central Iowa. NO₃^-N concentration reduction from the inlet to the outlet was significantly different for all HRTs (p < 0.05). The 16 h HRT removed the most NO₃^-N by concentration (7.5 mg L^-1) and had the highest removal efficiency at 53.8%. The 8 h HRT removed an average of 5.5 mg L^-1 NO₃^-N with a removal efficiency of 32.1%. The 2 h HRT removed an average of 1.3 mg L^-1 NO₃^-N with a removal efficiency of 9.0%. The 2 h HRT had the highest NO₃^-N mass removal rate (MRR) at 9.0 g m^-3 day^-1, followed by the 8 h HRT at 8.5 g m^-3 day^-1, and the 16 h HRT at 7.4 g m^-3 day^-1, all of which were statistically different (p < 0.05). Significant explanatory variables for removal efficiency were HRT (p < 0.001) and influent NO₃^-N concentration (p < 0.001), (R² = 0.80), with HRT accounting for 93% contribution. When paired with results from a companion study, the ideal HRT for the bioreactors was 8 h to achieve maximum NO₃^-N removal while reducing the impact from greenhouse gas emissions.

Keywords: Hydraulic residence time; Nutrient removal; Pilot-scale; Water quality; Woodchip bioreactors.

MeSH terms

Bioreactors*
Denitrification*
Iowa
Nitrates
Nitrogen
Nitrogen Oxides

Substances

Nitrates
Nitrogen Oxides
Nitrogen