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

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Volumetric water content (m3/m3)

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• 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 soils

Roadside 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)

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

Wat

er F

low

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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 SummaryResults for 57 Rain Events

• Average Peak Stormwater Runoff Rate Reduction:

46.74% (Std Dev: 64.06%)

• Average Cumulative Stormwater Runoff Volume Reduction:

66.70% (Std Dev: 24.41%)

Results – Soil Moisture Content 

• 0‐15cm Depth: 83% Increase

• 15‐30cm Depth: 50% Increase

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2/10/2016 12:00 4/20/2016 12:00 6/29/2016 12:00 9/7/2016 12:00 11/16/2016 12:00

Volu

met

ric W

ater

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tent

, (m

3 /m3 )

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NFWF Soil Moisture Content

0-15 cm Front Control 15-30 cm Front Control

0-15 cm Back Control 15-30 cm Back Control

0-15 cm Front Biochar 15-30 cm Front Biochar

0-15 cm Back Biochar 15-30 cm Back Biochar

Results – Infiltration

• Tillage: 102.37% Increase

• Biochar: 199.27% Increase

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Undisturbed Control 4% Biochar

K sat

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Saturated Hydraulic Conductivity

Results – Compaction

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epth

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Compaction Testing Summary

Existing 11/15/15

Biochar 12/08/15

Control 12/08/15

Biochar 7/31/16

Control 7/31/16

Biochar 11/18/16

Control 11/18/16

Existing 11/18/16

Root Growth Limit

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

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2/10/2016 12:00 4/20/2016 12:00 6/29/2016 12:00 9/7/2016 12:00 11/16/2016 12:00

Tem

pera

ture

, (oC

)

Date

NFWF Soil Temperature

Control

Biochar

Future Work

• Instrument swales – Spring 2017• Monitor and test throughout 2017• Conduct water quality experiments• Author recommendations for regulatory credit applications for use of biochar

• Model the hydrodynamics of stormwater flow and infiltration using Richard’s equation and results from lab and field experiments

Acknowledgements:

• Advisor: Dr. Paul Imhoff, Dr. Gerald Kauffman• Consultants: Charles 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