Removing Dissolved Phosphorus from Stormwater Peter T. Weiss, Associate Professor Department of Civil Engineering Valparaiso University (USA) International Conference on Urban Drainage Porto Alegre, Brazil 15 September 2011
Outline Dissolved Pollutants Experiments and Model Applications of Dissolved Phosphorus Removal Conclusions Photo Courtesy: A. Erickson
Total Phosphorus Concentration (mg/l) Total Phosphorus Load (kg/event) Percent of Data (%) Dissolved Pollutants: Distribution of Phosphorus 0% 5% 10% 15% 20% 1000 Concentration Load 1000 100 10 1 0.1 100 10 1 0.1 0.01 0.01 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Dissolved Percent (of total phosphorus) Adapted from Brezonik and Stadelmann (2004)
Dissolved Pollutants: Rationale Most urban watersheds need: 80+% capture of solids and pollutants, including dissolved component Precipitation and adsorption are two unit processes that have not been used to treat urban runoff.
Dissolved Pollutants: Enhanced Sand Filter Sand Filtration Particulate capture > 80% - Dissolved capture < 2% Enhanced Sand Photo Courtesy: A. Erickson Addition of elements that would precipitate or adsorb dissolved phosphorus
Experiments and Model: Experimental Setup Column Study (10) 5% iron (3) A,B,C 2% iron (3) D,E,F 0.3% iron (3) G,H,I 100% sand (1) J Reservoir mixed with dissolved phosphorus Mass balance model Photo Courtesy: A. Erickson
Experiments and Model: Model Attributes: Model Derivation Mass balance model between iron and phosphorus in water Predict phosphorus capture of ironenhanced sand filtration Data observed in column experiments Function of contact time (t c ) and total mass of adsorbed phosphorus (SM)
dc dt Experiments and Model: = -ka(c -C*) Model Derivation C C out in dc C C * t contact 0 kadt After integration: C in out kat C C * e c C 1 in and assuming: C* C in 1 e 0 1 M C in 0 C in C* S Mass Removed
dc dt Experiments and Model: = -ka(c -C*) Model Derivation C C out in dc C C * t contact 0 kadt After integration: C in out kat C C * e c C 1 in and assuming: C* C in 1 e 0 1 M by substitution yields: C C M t e e c 1 1 in out 2 Fraction Captured 0 C in
Phosphorus Fraction Retained Experiments and Model: Experimental Results 1.2 5% iron 2% iron 0.3% iron 100% Sand 1 0.8 0.6 0.4 0.2 0 0 20 40 60 80 100 120 140 160 180 200 220 240 Depth Treated (m)
Phosphorus Fraction Retained Experiments and Model: Experimental Results 1.2 5% iron 2% iron 0.3% iron 100% Sand 1 0.8 0.6 0.4 0.2 0 0 20 40 60 80 100 120 140 160 180 200 220 240 Depth Treated (m)
Phosphorus Fraction Retained Experiments and Model: Experimental Results 1.2 1 0.8 0.6 0.4 0.2 0 100% sand 5% iron filings 2% iron filings 0.3% iron filings 0 205 40 10 60 80 15 10020120 140 25 16030180 35 200 220 40 240 Depth Years of Treated Service(m) HLR = 5.6 m/yr
Applications: Sand with 5% iron filings Volume Treated by Filter Overflow Grate Drain tile Sand + Iron Filings
Applications: Sand with 5% iron filings, Maplewood, MN Photo Courtesy: A. Erickson
Applications: Enhanced Sand Filter Trenches around wet detention ponds Volume Treated by Trenches (Filter Volume) Overflow Grate Normal Water Surface Elevation Water Level Control Weir Drain tile Minnesota Filter Drain tile
Prior Lake, MN, Filter Trenches around wet detention ponds Photo Courtesy: A. Erickson
Enhanced Sand Permeable Weir Permeable Weir: Minnesota Filter Coarse Aggregate Natural Soil
Applications: Enhanced Sand Permeable Weir Photo Courtesy: VLAWMO and EOR
Applications: Enhanced Sand to reduce PO4 Release with Bioretention Compost-Amended Sand Iron-Enhanced Sand Gravel Subbase and underdrain Drain tile Natural Soil
Conclusions Dissolved Stormwater Pollutants are important Approx. 45% of total concentration is dissolved Physical methods are not enough Chemical mechanisms (adsorption) can be used to capture dissolved fractions. There are solutions! Minnesota Filter (iron-enhanced sand) adsorb phosphorus onto iron. Dissolved nitrogen is next.
Acknowledgements Collaborators: Andy Erickson (U of MN) John Gulliver (U of MN) Brian J. Huser (Sveriges Lantbruksuniversitet and Barr Engineering Co.) Ross Bintner (City of Prior Lake) Contributors: Global Material Technology, Inc. (Steel wool) Connelly GPM, Inc. (Iron filings) Funding Partners: RWMWD, LRRB, City of Prior Lake, PLSLWD, Scott WMO, VLAWMO, EPA/MPCA
For more information, contact: Andy Erickson (eric0706@umn.edu) Iron Enhanced Sand Filter, Maplewood, MN (photo courtesy A. Erickson)