Removing Dissolved Pollutants from

Stormwater Runoff

Andy Erickson, Research Fellow

St. Anthony Falls Laboratory

March 8, 2012

http://stormwater.safl.umn.edu/

Outline

• Why should you care about

dissolved pollutants?

• Current treatment methods

• New treatment

technologies

• Field applications and

results

• Questions

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Why Dissolved Pollutants?

• More Bioavailable

• Nutrients eutrophication

• Metals bioaccumulation, toxicity

• Petroleum hydrocarbons toxicity

Pictures source:

www.pca.state.mn.us

Source: Sharpley, A.N., Smith, S.J., Jones, O.R., Berg, W.A. and Coleman, G.A. (1992) The Transport of Bioavailable Phosphorus in Agricultural Runoff.

Journal of Environmental Quality 21(1), 30-35. U.S. EPA. (1999) Preliminary data summary of urban storm water best management practices, U.S.

Environmental Protection Agency, Washington, D.C.

http://stormwater.safl.umn.edu/

Pollutant Spectrum

• Varies by:

– Pollutant

– Location in management system

2 μm

0.45 μm 75 μm 4250 μm

0.2 μm 0.005 μm

Soluble / Dissolved

Colloids

Cla

y

Silt Sand Gross

Solids

Organic / Float

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0 5 10 15 20 25 30

Arsenic

Cadmium

Chromium

Copper

Lead

Nickel

Median Pollutant Concentration

Total (Dissolved + Particulate)

Dissolved

0 50 100 150 200 250 300

Phosphorus

Zinc

Dissolved Fraction Dissolved

Fraction

45.5%

50.0%

29.7%

50.0%

18.9%

44.4%

44.4%

45.5%

Source (adapted from): Pitt, R., Maestre, A., Morquecho, R., Brown, T., Schueler, T., Cappiella, K., and Sturm, P. (2005). "Evaluation of NPDES Phase 1

Municipal Stormwater Monitoring Data." University of Alabama and the Center for Watershed Protection.

http://stormwater.safl.umn.edu/

0.01

0.1

1

10

100

1000

0.01

0.1

1

10

100

1000

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

Tota

l Ph

osp

ho

rus

Load

(k

g/e

ven

t)

Tota

l Ph

osp

ho

rus

Co

nce

ntr

atio

n (

mg/

L)

Dissolved Percent (of total phosphorus)

Concentration Load

0%5%

10%15%20%

Pe

rce

nt

of

Dat

a (%

)

Source (adapted from): Brezonik, P. L., and Stadelmann, T. H. (2002). “Analysis and predictive models of storm water runoff volumes, loads, and pollutant

concentration from watersheds in the twin cities metropolitan area, Minnesota, USA.” Water Res., 36, 1743–1757.

Distribution of Phosphorus

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Current Treatment Methods

• Pollution Prevention

– Target pollutants at the source

• Most stormwater treatment practices provide:

– Filtration (solids)

– Infiltration (solids, dissolved?)

– Sedimentation (solids)

– Biological or chemical (organics, dissolved?)

• Most urban watersheds need:

– 80+% capture of solids and dissolved pollutants

http://stormwater.safl.umn.edu/

0% 20% 40% 60% 80% 100%

Dry Ponds

Wet Ponds

Constructed Wetlands

Sand Filter

Filter Strips/Grassed Swales

Percent Removal

% TSS Removal

% TP Removal

Current Treatment Practices

Source (adapted from): P.T. Weiss, A.J. Erickson and J.S. Gulliver. 2007. “Cost and pollutant removal of storm-water treatment practices,” Journal of Water

Resources Planning and Management,133(3),218-229, 2007.

http://stormwater.safl.umn.edu/

Treatment Train

NOTE: Estimated Values.

45% 2% 28% 25%

0% 20% 40% 60% 80% 100%

Untreated

Percent of the Total Concentration

Dissolved Clay Silt Sand

100% Untreated

0% 20% 40% 60% 80% 100%

Untreated

Percent of the Total Concentration

Dissolved Clay Silt Sand

100% Untreated

80% Untreated

0% 20% 40% 60% 80% 100%

Untreated

After Sweeping

Percent of the Total Concentration

Dissolved Clay Silt Sand

100% Untreated

80% Untreated

55% Untreated

0% 20% 40% 60% 80% 100%

Untreated

After Sweeping

After Ponds

Percent of the Total Concentration

Dissolved Clay Silt Sand

100% Untreated

80% Untreated

55% Untreated

50% Untreated

0% 20% 40% 60% 80% 100%

Untreated

After Sweeping

After Ponds

After Filters

Percent of the Total Concentration

Dissolved Clay Silt Sand

100% Untreated

80% Untreated

55% Untreated

50% Untreated

15% Untreated

0% 20% 40% 60% 80% 100%

Untreated

After Sweeping

After Ponds

After Filters

After Chem/Bio

Percent of the Total Concentration

Dissolved Clay Silt Sand

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Dissolved Pollutant Removal

Processes

• Vegetative processes: plant uptake and rhizospheric activity (microbes, etc.) that use and convert dissolved pollutants

• Sorption: surface sorption or complexation, ion exchange, etc. to capture dissolved pollutants

• Biodegradation: bacteria conversion of nitrates to nitrogen gas or petroleum hydrocarbons to carbon dioxide

http://stormwater.safl.umn.edu/

Phosphorus Sorption with Iron

• Sand Filtration

– Particulate

– capture > 80%

• Enhanced Sand

Filtration

– Steel wool increases dissolved phosphorus capture via surface sorption to iron oxide

Photo Courtesy: A. Erickson

Source: Erickson, A.J., Gulliver, J.S. and Weiss, P.T. (2007) Enhanced sand filtration for storm water phosphorus removal. Journal of Environmental Engineering-

ASCE 133(5), 485-497.

http://stormwater.safl.umn.edu/

18.4%

78.6%88.3%

0

0.1

0.2

0.3

0.4

Dis

solv

ed P

ho

sph

oru

s C

on

cen

trat

ion

(m

g/L)

Influent 100% Sand 0.3% iron 2% iron 5% iron

Experimental Results

Detection limit

http://stormwater.safl.umn.edu/

“Minnesota Filter” (sand with 5%

iron filings, Maplewood, MN)

Photo Courtesy: A. Erickson

http://stormwater.safl.umn.edu/

“Minnesota Filter” (sand with 5%

iron filings, Maplewood, MN)

Photo Courtesy: Ramsey Washington

Metro Watershed District

http://stormwater.safl.umn.edu/

75.1% Removal 29.2%

Removal

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

Total Phosphorus Dissolved Phosphorus

Ph

osp

ho

rus

Co

nce

ntr

atio

n

(mg

/L)

Influent Effluent

Field Monitoring Results

(5% iron filings)

Detection limit

http://stormwater.safl.umn.edu/

Minnesota Filter Trenches

(adjacent to wet detention ponds)

Photo Courtesy: A. Erickson

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Filter Trenches around wet

detention ponds (Prior Lake, MN)

Normal Water

Surface

Elevation

Drain

tile Minnesota Filter

Water Level

Control

Weir

Overflow

Grate

Drain tile

Volume Treated

by Trenches

(Filter Volume)

http://stormwater.safl.umn.edu/

73.1% Removal

0

0.02

0.04

0.06

0.08

0.1

Dis

solv

ed

Ph

osp

ho

rus

Co

nce

ntr

atio

n (

mg

/L)

Influent 7% Iron Filings

Field Testing Results

(Minnesota Filter Trenches)

Detection limit

http://stormwater.safl.umn.edu/

Designing for Phosphorus

Capture with Iron

• As iron rusts, sorption sites for phosphorus are created, therefore:

– Design Minnesota Filter (iron + sand filtration) systems for watersheds with significant dissolved phosphorus fraction

– Ensure the system is oxygenated to ensure iron oxides remain aerobic

– Design systems with 8% or less iron by weight to prevent clogging

http://stormwater.safl.umn.edu/

Conclusions

• Dissolved Stormwater Pollutants are important – Approx. 45% of total concentration is

dissolved

• Physical methods are not enough – Chemical and biological mechanisms can be

used to capture dissolved fractions

• There are field-tested solutions! – Minnesota Filter (iron-enhanced sand)

phosphorus

http://stormwater.safl.umn.edu/

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Photo Courtesy: A. Erickson

For more information, contact:

Andy Erickson (eric0706@umn.edu)