Effectiveness of Denitrifying Bioreactors on Water Pollutant Reduction from Agricultural Areas

HighlightsDenitrifying woodchip bioreactors treat nitrate-N in a variety of applications and geographies.This review focuses on subsurface drainage bioreactors and bed-style designs (including in-ditch).Monitoring and reporting recommendations are provided to advance bioreactor science and engineering. Denitrifying bioreactors enhance the natural process of denitrification in a practical way to treat nitrate-nitrogen (N) in a variety of N-laden water matrices. The design and construction of bioreactors for treatment of subsurface drainage in the U.S. is guided by USDA-NRCS Conservation Practice Standard 605. This review consolidates the state of the science for denitrifying bioreactors using case studies from across the globe with an emphasis on full-size bioreactor nitrate-N removal and cost-effectiveness. The focus is on bed-style bioreactors (including in-ditch modifications), although there is mention of denitrifying walls, which broaden the applicability of bioreactor technology in some areas. Subsurface drainage denitrifying bioreactors have been assessed as removing 20% to 40% of annual nitrate-N loss in the Midwest, and an evaluation across the peer-reviewed literature published over the past three years showed that bioreactors around the world have been generally consistent with that (N load reduction median: 46%; mean ±SD: 40% ±26%; n = 15). Reported N removal rates were on the order of 5.1 g N m-3 d-1 (median; mean ±SD: 7.2 ±9.6 g N m-3 d-1; n = 27). Subsurface drainage bioreactor installation costs have ranged from less than $5,000 to$27,000, with estimated cost efficiencies ranging from less than $2.50 kg-1 N year-1 to roughly$20 kg-1 N year-1 (although they can be as high as $48 kg-1 N year-1). A suggested monitoring setup is described primarily for the context of conservation practitioners and watershed groups for assessing annual nitrate-N load removal performance of subsurface drainage denitrifying bioreactors. Recommended minimum reporting measures for assessing and comparing annual N removal performance include: bioreactor dimensions and installation date; fill media size, porosity, and type; nitrate-N concentrations and water temperatures; bioreactor flow treatment details; basic drainage system and bioreactor design characteristics; and N removal rate and efficiency

Comparison of Contaminant Transport in Agricultural Drainage Water and Urban Stormwater Runoff

<div><p>Transport of nitrogen and phosphorus from agricultural and urban landscapes to surface water bodies can cause adverse environmental impacts. The main objective of this long-term study was to quantify and compare contaminant transport in agricultural drainage water and urban stormwater runoff. We measured flow rate and contaminant concentration in stormwater runoff from Willmar, Minnesota, USA, and in drainage water from subsurface-drained fields with surface inlets, namely, Unfertilized and Fertilized Fields. Commercial fertilizer and turkey litter manure were applied to the Fertilized Field based on agronomic requirements. Results showed that the City Stormwater transported significantly higher loads per unit area of ammonium, total suspended solids (TSS), and total phosphorus (TP) than the Fertilized Field, but nitrate load was significantly lower. Nitrate load transport in drainage water from the Unfertilized Field was 58% of that from the Fertilized Field. Linear regression analysis indicated that a 1% increase in flow depth resulted in a 1.05% increase of TSS load from the City Stormwater, a 1.07% increase in nitrate load from the Fertilized Field, and a 1.11% increase in TP load from the Fertilized Field. This indicates an increase in concentration with a rise in flow depth, revealing that concentration variation was a significant factor influencing the dynamics of load transport. Further regression analysis showed the importance of targeting high flows to reduce contaminant transport. In conclusion, for watersheds similar to this one, management practices should be directed to load reduction of ammonium and TSS from urban areas, and nitrate from cropland while TP should be a target for both.</p></div

Relationship between daily nitrate load and daily flow depth over the period of the study for City Stormwater (n = 479), Fertilized Field (n = 907), and Unfertilized Field (n = 663).

<p>The lines represent the loads at constant nitrate concentration of 1 and 10 mg-N L^-1.</p

Linear regression relating natural log of load to natural log of flow depth over the period of the study for City Stormwater (n = 479), Fertilized (n = 907) and Unfertilized Fields (n = 663) after adjusting for serial correlation.

<p>Linear regression relating natural log of load to natural log of flow depth over the period of the study for City Stormwater (n = 479), Fertilized (n = 907) and Unfertilized Fields (n = 663) after adjusting for serial correlation.</p

Precipitation from 1 April to 31 October for the City Stormwater and Fertilized Field.

<p>Precipitation from 1 April to 31 October for the City Stormwater and Fertilized Field.</p

Location of the Willmar sub-watershed, Fertilized and Unfertilized Fields in Minnesota, USA.

<p>Location of the Willmar sub-watershed, Fertilized and Unfertilized Fields in Minnesota, USA.</p

Daily flow depth for City Stormwater and Fertilized Field (excluding 2008 and 2013) used for the paired <i>t</i>-test, and daily precipitation at the City Stormwater.

<p>Daily flow depth for City Stormwater and Fertilized Field (excluding 2008 and 2013) used for the paired <i>t</i>-test, and daily precipitation at the City Stormwater.</p

Cumulative flow depth from April to October of 2007 to 2012 (excluding 2008), and paired <i>t</i>-test comparison between Stormwater and Fertilized Field after adjusting for serial correlation (n = 792).

<p>Cumulative flow depth from April to October of 2007 to 2012 (excluding 2008), and paired <i>t</i>-test comparison between Stormwater and Fertilized Field after adjusting for serial correlation (n = 792).</p

Cumulative load from April to October of 2007 to 2013, and paired <i>t</i>-test comparisons of daily loads between Unfertilized and Fertilized Fields after adjusting for serial correlation (n = 1071).

<p>Cumulative load from April to October of 2007 to 2013, and paired <i>t</i>-test comparisons of daily loads between Unfertilized and Fertilized Fields after adjusting for serial correlation (n = 1071).</p

Daily contaminant concentrations from 2007 to 2013 for the City Stormwater (excluding 2008 and 2013), Unfertilized and Fertilized Fields for (a) nitrate, (b) ammonium, (c) total suspended solids, and (d) total phosphorus.

<p>Daily contaminant concentrations from 2007 to 2013 for the City Stormwater (excluding 2008 and 2013), Unfertilized and Fertilized Fields for (a) nitrate, (b) ammonium, (c) total suspended solids, and (d) total phosphorus.</p