Funded in part by the soybean checkoff

2015 SWCS Conference

July 27, 2015Greensboro, North Carolina

Managing Denitrification Wood Chip Bioreactors for Maximum Nitrate Removal and Minimum Carbon

ExpendedKeegan Kult1 and Dr. Chris Jones2

Iowa Soybean Association1 and University of Iowa, IIHR-Hydroscience and Engineering2

Drivers

• Limited conservation funding, high public demands• BMP’s need placed using precision conversation

– BMP’s need to be optimized

• Do bioreactors perform more efficiently when operated for higher flow volumes or longer retention times?

• Removes nitrate-N from field tiles

• Divert water through wood chips

• 30 – 100 acre drainage areas

• Small footprint• 10 – 15 year lifespan

Denitrifying Bioreactors

Image from John Petersen

• State Nutrient Reduction Strategies– Reduce nitrogen export by

45%– Edge of field practices play

critical role

• ISA has been part of 20 installations

Implementation

Hamilton County

2010 2012 2013 2014 Total

Nit

rate

-N L

oa

d,

kg

0

100

200

300

400

500

600

Performance

LWFC

2012 2013 2014 Total

Nit

rate

-N l

oad

, kg

0

250

500

750

1000

1250

Potential Load

Actual Load

Greene County

2009 2010 2011 2012 2013 Total

An

nu

al N

itra

te-N

Lo

ad, k

g

0

250

500

750

1000

1250

To

tal N

itra

te-N

Lo

ad, k

g0

500

1000

1500

2000

2500

3000

20 – 32% 12 – 76%

12 – 42%

Greene County Monthly Performance(2009 – 2013)

Month

Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Nitr

ate-

N,

kg

0

200

400

600

800

1000

1200

Potential Actual

Study

• Flow management• Nitrate removal/carbon usage• 3 high retention times• 3 low retention times

Funding from Iowa Nutrient Research Center

Diversion Structure (Upper) Flow Control Structure (Lower)

Low retention time higher flow rateHigh retention time lower flow rate

Bioreactor Flow

• Weekly to bi-weekly sampling April – August of 2014

• NO3-, TOC, alkalinity

(inorganic carbon)• Flow tracked with pressure

transducer

Monitoring

Bioreactors Monitored

  Bioreactor  Location Date Installed Dimensions, ft Acres 

drainedYears 

monitored

1 UWFC Wright Co., IA Dec. 2011 98 x 8 25 2

2 LEC Wright Co., IA Sep. 2012 98 x 10 40 2

3 LC Hamilton Co., IA July 2012 100 x 20 80 1

4 Fisher Wright Co., IA Aug. 2011 115 x 25 30 --

5 Voss Wright Co., IA Aug. 2012 113 x 8 25 --

6 Tesdell Polk Co., IA Sep. 2013 80 x 6 NA --

Back-up Plan

Bioreactor HRT Actual HRT

Tes Low Low

Greene Low Low

LEC 2 Low High

Hamilton Low High

LC High High

LWFC High Low

UWFC High High

2014 Results

Bioreactor Nitrate removed, kg

% Load Reduction

Tes 43 54

Greene 33 13

LWFC 49 33

Bioreactor Nitrate removed, kg

% Load Reduction

UWFC 24 12

LC 38 11

LEC 2 50 6

Hamilton 24 13

Low HRT, high flow volume

High HRT, low flow volume

UWFC Bioreactor

2014

Apr May Jun Jul Aug Sep Oct

Flo

w m

3 d-1

0

200

400

600

800

1000

Nitr

ate-

N,

mg

L-1

0

5

10

15

20

25

Bioreactor flowBypass flowUWFC InUWFC Out

Week Flow treatedLoad 

Reduction4/2- 4/8 100% 96%4/9 - 4/15 100% 97%4/16 - 4/22 100% 97%4/23 - 4/29 100% 97%4/30 - 5/6 100% 87%5/7 - 5/13 78% 51%5/14 - 5/20 100% 73%5/21 - 5/27 100% 82%5/28 - 6/3 100% 93%6/4 - 6/10 100% 96%6/11 - 6/17 37% 19%6/18 - 6/24 7% 3%6/25 - 7/1 5% 3%7/2 - 7/8 3% 2%7/9/ - 7/15 100% 67%7/16 - 7/22 100% 72%7/23 - 7/29 100% 81%7/30 - 8/5 100% 90%8/6 - 8/12 100% 98%

Total 14% 6%

• 2014 LEC 2 Results

Hydraulic Retention Time

Low High

HR

T,

days

0.01

0.1

1

10

Difference of measured vs. predicted alkalinity, kg

Management Samples Median

High retention 27 0.191

High flow 29 0.203

Carbon usage during denitrification

Nitrate-N load removed, kg

0 1 2 3 4 5 6 7

Tot

al a

lkal

inity

gen

erat

ed a

s C

aCO

3,

kg

-2

0

2

4

6

8

10

High retention bioreactorsHigh flow-volume bioreactorsPredicted alkalinity generated

2014 Bioreactor Carbon Usage

Bioreactor

Tes Greene LWFC UWFC LC LEC 2 Hamilton

Un

it C

arb

on g

ener

ate

d p

er

Nitr

ate-

N u

nit

rem

ove

d

-2

0

2

4

6

8

10

12

Low Retention TimeHigh Retention Time

Cost Effectiveness

Bioreactor Annual N removed, lbs

Projected 10 year removal, lbs

Projected 15 year removal, lbs Installation cost

Hamilton 143 1,430 2,145 $6,800

Greene 271 2,710 4,065 $10,500

Practice Cost per lb of N removedBioreactors $2.58 - $4.75

Soil testing & side dressing $1.15 Saleh et al. (2007)

Drainage water management $2.71 Jaynes & Thorp (2008)

Wetlands $3.26 Hyberg (2007)

Fall cover crops $11.06 Saleh et al. (2007)

• Low flow 6 – 13% load reduction

• High flow 13 – 54% load reduction

• Differing flow regimes removed similar loads of N

• No difference in carbon usage

Summary

• Know tile system before installing

• Difficult to control flow• Large events drive

performance more than management

Lessons Learned

Acknowledgements

• Project was funded by the Iowa Nutrient Research Center and supplemental data was used from projects funded by an USDA-NRCS Conservation Innovation Grant as well as contracts with private landowners.

• This presentation was prepared by K. Kult and C. Jones under grant number C5-52718-00 from the Iowa Nutrient Research Center. Any opinions, findings, and conclusions or recommendations expressed are those of the authors and do not necessarily reflect the views of the Iowa Nutrient Research Center or Iowa State University.