Removing Dissolved Pollutants from Stormwater Runoff Andy Erickson, Research Fellow St. Anthony Falls Laboratory March 8, 2012
Outline Why should you care about dissolved pollutants? Current treatment methods New treatment technologies Field applications and results Questions
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.
Clay Pollutant Spectrum 0.005 μm 0.45 μm 0.2 μm 2 μm 75 μm 4250 μm Colloids Soluble / Dissolved Varies by: Pollutant Location in management system Silt Sand Gross Solids Organic / Float
Arsenic Cadmium Chromium Copper Lead Nickel Dissolved Fraction Total (Dissolved + Particulate) Dissolved 0 5 10 15 20 25 30 Median Pollutant Concentration 0 50 100 150 200 250 300 Dissolved Fraction 45.5% 50.0% 29.7% 50.0% 18.9% 44.4% Phosphorus Zinc 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.
Total Phosphorus Concentration (mg/l) Total Phosphorus Load (kg/event) Percent of Data (%) Distribution of Phosphorus 0% 5% 10% 15% 20% 1000 Concentration Load 1000 100 100 10 10 1 1 0.1 0.1 0.01 0.01 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Dissolved Percent (of total phosphorus) 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.
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
Current Treatment Practices % TSS Removal % TP Removal Dry Ponds Wet Ponds Constructed Wetlands Sand Filter Filter Strips/Grassed Swales 0% 20% 40% 60% 80% 100% Percent Removal 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.
Treatment Train Percent of the Total Concentration 0% 20% 40% 60% 80% 100% Untreated After Sweeping After Ponds After Filters After Chem/Bio 100% Untreated 45% 2% 28% 25% 80% Untreated 55% Untreated 50% Untreated 15% Untreated NOTE: Estimated Values. Dissolved Clay Silt Sand
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
Phosphorus Sorption with Iron Sand Filtration Particulate capture > 80% Enhanced Sand Photo Courtesy: A. Erickson Filtration Steel wool increases dissolved phosphorus capture via surface sorption to iron oxide 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.
Dissolved Phosphorus Concentration (mg/l) Experimental Results 0.4 0.3 18.4% 0.2 0.1 78.6% 88.3% 0 Influent 100% Sand 0.3% iron 2% iron 5% iron Detection limit
Minnesota Filter (sand with 5% iron filings, Maplewood, MN) Photo Courtesy: A. Erickson
Minnesota Filter (sand with 5% iron filings, Maplewood, MN) Photo Courtesy: Ramsey Washington Metro Watershed District
Phosphorus Concentration (mg/l) Field Monitoring Results 0.14 0.12 0.1 0.08 0.06 0.04 0.02 0 (5% iron filings) Total Phosphorus 75.1% Removal 29.2% Removal Dissolved Phosphorus Influent Effluent Detection limit
Minnesota Filter Trenches (adjacent to wet detention ponds) Photo Courtesy: A. Erickson
Filter Trenches around wet detention ponds (Prior Lake, MN) Volume Treated by Trenches (Filter Volume) Overflow Grate Normal Water Surface Elevation Water Level Control Weir Drain tile Minnesota Filter Drain tile
Dissolved Phosphorus Concentration (mg/l) 0.1 Field Testing Results (Minnesota Filter Trenches) 0.08 0.06 0.04 0.02 73.1% Removal 0 Influent 7% Iron Filings Detection limit
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
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
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Photo Courtesy: A. Erickson For more information, contact: Andy Erickson (eric0706@umn.edu)