Location: Soil and Water Management ResearchTitle: Denitrifying bioreactors for nitrate removal from tile drained cropland
Submitted to: Meeting Abstract
Publication Type: Proceedings
Publication Acceptance Date: 12/5/2014
Publication Date: N/A
Technical Abstract: Denitrification bioreactors are a promising technology for mitigation of nitrate-nitrogen (NO3-N) losses in subsurface drainage water. Bioreactors are constructed with carbon substrates, typically wood chips, to provide a substrate for denitrifying microorganisms. Researchers in Iowa found that for four sites (14 site-years) NO3-N load reduction was 45% for tile drainage flowing through the bioreactor and 32% for total tile flow, including water that bypassed the bioreactor during high-flow events. Nitrate-N removal rate ranged from 0.4 - 8 gN d-1 m-3 and the cost to remove NO3-N ranged from $0.48 - 5.59 lbN-1. Laboratory research was conducted by USDA-ARS-SWMRU on using agricultural residues as the denitrifying bioreactor media. Columns were packed with wood chips (WC), barley straw (BS), corn cobs (CC), corn stover (CS), and a combination of corn cobs followed by wood chips (CC-WC). A synthetic water solution (50 mg L-1 of NO3-N) was pumped through the columns at a 12-h hydraulic residence time. Bioreactors were operated at 16°C (experiment 1) and 1.7°C (experiment 2). At 16°C, NO3-N removal was greatest for the CC treatment (35 g N m-3 d-1), and least for WC (1.4 -5.6 g N m-3 d-1). The BS, CS and CC-WC materials were intermediate in NO3-N removal. At the lower temperature, the same trend was observed with respect to the relative NO3-N removal by the different materials, but the NO3-N removal rate was decreased by 3 - 5X in all treatments (< 10 g N m-3 d-1). The abundance of denitrifying bacteria was assessed by qPCR analysis of the nosZ gene. Gene abundance followed a similar trend as NO3-N removal with CC supporting 3.76 x 1012 gene copies and WC supporting 2.18 x 108 copies g-1. Gene abundance was not reduced in the cold temperature experiment. Estimated cost for NO3-N removal with corn cobs ranged from $0.37 - 2.06 lbN-1.