A Field Study of Biochar Amended Soils: Water Retention and Nutrient Removal from Stormwater Runoff

Funded through the Chesapeake Bay Stewardship Fund by a National Fish and Wildlife Foundation grant

Joseph D. Brown, Sr., P.E.University of Delaware, Department of Civil and Environmental Engineering

Outline

• Background• Research Hypotheses• Experimental Methods• Preliminary Results• Future Research

What is Biochar?

• Produced from the pyrolysis of wood or waste biomass

• Important properties– High surface area– High porosity– Significant cation exchange capacity– High adsorption capacity– Stable carbon structure

Biochar’s Potential Benefits:

• Decreased overall stormwater runoff rates & volumes

• Reduced soil erosion and sedimentation

• Reduced nutrient & metal loading• Improved groundwater recharge• Reduced flooding

Background Research• Biochar Impact on Soil Hydraulic

Properties:

• Impact on Nutrient Removal

0.0 0.1 0.2 0.3 0.4 0.5

-70

-60

-50

-40

-30

-20

-10

0 Ctrl-wet Exp-wet Ctrl-dry Exp-dry

Volumetric water content (m3/m3)

Dep

th (c

m)

0

10

20

30

40

50

60

70

Cap

illar

y pr

essu

re h

ead

(cm

H2O

)

• Ksat Increased 4X

• Water Retention Increased 30%

• 43% NO3 Reduction

• 6.1% increase in NO3 in control cell without biochar

Jing Tian, Jing Jin, Paul T. Imhoff, Pei C. Chiu, Daniel K. Cha, MingxinGuo, Julia A. Maresca

Research Hypotheses:Roadside Filter Strips:• Biochar increases

– water retention – unsaturated hydraulic conductivity – hydraulic residence time of

pollutants in soilsRoadside Swales:• Biochar increases

– water retention – hydraulic residence time

Project Site: Rt 896 & Bethel Church RoadMiddletown, De

Experimental Methods - Filter Strips

Test Equipment:• Soil Moisture sensors• Water potential &

temperature sensors• Automated water samplers• Ultrasonic flow sensors• Rain gauge

Experimental Methods - Filter Strips

Experimental Methods – Roadside Filter Strips

Control Strip 4% Biochar Strip

Experimental Methods - SwaleTest Equipment:• Soil Moisture sensors• Rhizon Pore Water Samplers• Rain gauge

Experimental Methods - Swales

Experimental Methods - Parameters:Soil Data:• Volumetric Water Content• Soil Water Potential• Soil pH and Temperature• Electrical Conductivity• Soil Compaction• Unsaturated Hydraulic Conductivity• Nitrogen Compounds in Pore WaterSurface Water Data:• Stormwater Runoff Rate and Volume• Influent and Effluent N Loading

(Total N, NH3, NO3, NO2, TOC, etc.)• Total Suspended Solids

Results – Runoff Profile (Typical Rain Event)

0

200

400

600

800

1000

1200

6/24/2016 12:36 6/24/2016 13:04 6/24/2016 13:33 6/24/2016 14:02

Wat

er F

low

Rat

e, (m

l/s)

Date

Storm Event 27: Area Flow Rates

Sampler 1

Sampler 2

Sampler 3

Roadway Runoff

Control

Biochar

Rainfall, (in/hr)

Results – Cumulative Runoff (Typical Rain Event)

Stormwater Runoff Summary

0

500

1000

1500

2000

2500

3000

3500

4000

4500

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 35 36

Pea

k R

unof

f Rat

e, (m

l/s)

Storm Event

Peak Runoff Rate Summary

Runoff Rate (ml/s)

Control Rate (ml/s)

Biochar Rate (ml/s)

Stormwater Runoff Summary

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 35 36

Cum

ulat

ive

Run

off V

olum

e, (l

)

Storm Event

Runoff Volume Summary

Runoff Volume (l)

Control Volume (l)

Biochar Volume (l)

Stormwater Runoff SummaryResults for 34 Rain Events

• Average Peak Stormwater Runoff Rate Reduction:

43% (Std Dev: 28%)

• Average Cumulative Stormwater Runoff Volume Reduction:

68% (Std Dev: 24%)

Results – Soil Moisture Content

• 0-15cm Depth: 83% Increase

• 15-30cm Depth: 50% Increase

Results – Infiltration

0

1

2

3

4

5

6

biochar control undisturbed

log

Ksa

t(cm

/day

)

Filter Strip

• Tillage: 50% Reduction

• Biochar: 732% Increase

42.6 cm/day

21.4 cm/day

354.4 cm/day

Results – Compaction

0

5

10

15

20

25

30

0 10 20 30 40 50 60 70 80

Dep

th, (

cm)

Cone Stress, (kg/cm2)

Compaction Testing Summary

Biochar 12/08/15

Control 12/08/15

Biochar 7/31/16

Control 7/31/16

Existing 11/15/2015

Results – NO3 –N Concentration(Typical Rain Event)

• 23% NO3 Reduction

Results – NO2 –N Concentration(Typical Rain Event)

• 21% NO2 Reduction

Results – TN (Typical Rain Event)

0

1

2

3

4

5

6

6/24/2016 12:28 6/24/2016 12:57 6/24/2016 13:26 6/24/2016 13:55

NH

4-N

, (m

g/L)

Time

TN: Storm 27

Roadway

Control

Biochar

• 26% TN Reduction(First 80% of Storm)

• 15% TN Increase(Overall)

Results – Grass Growth

Control Strip (4/25/2016) 4% Biochar Strip (4/25/2016)

Results – Dissecting Microscopic Imagery

Existing Soil Existing Soil with 4% Biochar

Results – Soil Temperature

-5.0

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

40.0

2/10/2016 12:00 3/26/2016 12:00 5/10/2016 12:00 6/24/2016 12:00 8/8/2016 12:00

Tem

pera

ture

, (oC

)

Date

NFWF Soil Temperature

Control

Biochar

Future Work

• Construct swales – Summer 2016• Monitor and test throughout 2016• Author recommendations for regulatory credit applications for

use of Biochar• Model the hydrodynamics of stormwater flow and infiltration

using Richards equation and results from lab and field experiments

Acknowledgements:

• Advisor: Dr. Paul Imhoff• Consultants: Chuck Hegberg, Larry Trout• Funded By: National Fish and Wildlife Foundation thru the

Chesapeake Bay Stewardship Fund• Fellow Researchers: Sriya Panta, Seyyed Ali Akbar Nakhli,

Susan Yi, Tian Wenling, Jing Jin, Fang Tan• In Cooperation with: DelDOT