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Thomas Soerens University of Arkansas Mechanical Treatment of Storm Water Slide 2 Outline Fundamentals of Settling Catch basin sizing examples Alternative mechanical treatment technologies Slide 3 Settling Example Regulation Storm water treatment should remove 80% of Total Suspended Solids (TSS). vague: what size solids? System 1: Removes 80% solids with d 50 of 50 microns System 2: Removes 80% solids with d 50 of 100 microns System 2 not remove 80% of solids with d 50 of 50 microns In comparing systems, must see data side by side and compare apples to apples Example Basin (next slide) Slide 4 A rectangular settling tank processes 48,000 m 3 /day, is 6 m wide, 36 m long, and 4 m deep. What is the average hydraulic retention time in the tank (hr)? t 0 = Vol/Q = (6m x 4m x 36m) / 48000 m 3 /day = 0.018 day = 0.432 hr = 26 min Assuming horizontal flow, what is the flow (approach) velocity (m/d)? v x = Q/(w x h) = Q / (6m x 4m) = 2000 m/day = 1.4 m/min What is the overflow rate for the tank (m/d)? v 0 = Q/(w x L) = Q / (6m x 36m) = 222 m/day = 0.15 m/min note: v o = 4 m / 0.018 day = depth / retention time Slide 5 Does a particle settle out? If it enters 4 m above bottom, it has to drop 4 m in 26 min to hit bottom If particle has a settling velocity greater than the overflow rate (0.15 m/min), it will settle out. example: v s = 0.20 m/min in 26 minutes, it drops 0.20 x 26 = 5.2 m > depth to drop 4 m, it takes 4/0.20 = 20 min < t 0 in 20 minutes, it travels 20 x 1.4 m/min = 28 m < L If the settling velocity is less than the overflow rate, it doesnt hit bottom example: v s = 0.10 m/min in 26 minutes, it drops 0.10 x 26 = 2.6 m < depth to drop 4 m, it takes 4/0.10 = 40 min > t 0 in 40 minutes, it travels 40 x 1.4 m/min = 56 m > L Slide 6 If it doesnt hit bottom? Approximately v s /v o fraction of particles will settle out example: v s = 0.10 m/min Removal =~ 0.10/0.15 = 0.65 = 65% removal note: this is for horizontal clarifiers note: turbulence happens Slide 7 Settling Velocity Stokes Law Stokes law for settling velocity of spheres: v s = [( p w )d 2 g]/18 p, w = density of particle, water d = diameter of particle g = gravity = viscosity A 100 micron particle will have a settling velocity 4 times that of a 50 micron particle side note for water or wastewater treatment: In Stokes Law, what can be changed? Do you see why we coagulate and flocculate Slide 8 Basin Sizing Approaches Using d 50 Set overflow rate of basin at design flow equal to d 50 of a grain-size analysis of dirt you want to remove. Can have v 0 up to 1/0.8 = 1.25 of settling velocity 100 micron particle Slide 9 for Q = 0.17 m 3 /sec (6 cfs) choose aspect ratio: Length = 4 x width set v o = Q/A surface = Q/(w x 4w) = 0.015 m/sec w = 1.7 m (5.5 ft), L = 6.7 m (22 ft) will a 5 ft x 20 ft basin work? v o = Q/wL = 0.018 m/sec v s /v o = 0.015/0.018 = 0.82 82% removal okay for 80% removal disclaimer: the above process is a principle, not a regulation or a standard. Slide 10 Wait, how deep is it? depth not involved in calculation choose depth based on practical considerations of separating clean water from dirt. 1 inch deep? 1.7 second retention time - solids only have to fall 1 in to reach bottom cant separate 100 feet deep? 34 min retention time - solids fall 100 feet in 34 minutes impractical 4 feet deep? 1.4 min ret time, velocity = 16 ft/min, might be good Slide 11 Another method: from settling data Slide 12 For an overflow rate of 7m/24 min (depth/t o ) at 24 min, 45% of particles have hit bottom (7m) 60% of particles have settled to 2 m; 75% to 0.6m avg settling velocity of 15% of particles between 45% and 60% contours is about 3.4 m in 24 min; for next interval its 1.3m/24min. removal rate = v s /v o overall removal = 45% + 15% x (3.4m/24min)/(7m/24min) + 15% x (1.3/7) + = 45% + 7.3% + 2.8% =~ 55% note: could also take this approach with grain size analysis data Slide 13 Questions? next: examples of mechanical storm water treatment systems Slide 14 Advanced Drainage Systems (ADS) Water Quality and Underground Detention/Infiltration Units Slide 15 ADS system 2 units in series Water Quality Unit (WQU) series of weirs from 60-in diameter HDPE pipe. two manholes for maintenance Detention/Infiltration Unit (DIU) three 40-ft sections of 48 in perforated HDPE pipe top and sides of excavation are wrapped in geotextile flow 1 cfs or less though WQU then DIU > 1 cfs bypass WQU and go into DIU prevents resuspension Slide 16 ADS system WQU: WQU size: 5 ft x 20 ft catchment area: 1 acre peak flow 1 cfs treatment volume 3264 cf $50k per acre requires high maintenance Slide 17 ADS system - DIU Slide 18 ADS performance Slide 19 Slide 20 WAL-MART SITE SUSTAINABILITY INITIATIVE WATER GROUP Thomas Soerens University of Arkansas 479-575-2494 Mechanical Treatment Scott Franklin PACLAND 503-659-9500 Slide 21 OBJECTIVE Identify existing and emerging mechanical storm water treatment technologies and describe design and decision parameters. Slide 22 EXISTING TECHNOLOGIES Mechanical Treatment Manholes Stormceptor Downstream Defender Continuous Deflective Separation (CDS) Slide 23 EXISTING TECHNOLOGIES Mechanical Treatment Manholes Aquafilter and Aquaguard BaySeparator and BayFilter Slide 24 EXISTING TECHNOLOGIES Mechanical Treatment Manholes V2B1 StormGate Slide 25 EXISTING TECHNOLOGIES Mechanical Treatment Vaults Stormfilter Stormvault Storm Water Quality Unit Slide 26 EXISTING TECHNOLOGIES Mechanical Treatment Vaults StormTreat Contech Vortech Crystal Stream Vault Slide 27 EXISTING TECHNOLOGIES Mechanical Treatment Inserts Fabco StormX inserts SmartSponge (AbTech) Skimmers, inserts, or vault EcoSense filters Slide 28 EXISTING TECHNOLOGIES Mechanical Treatment Other various inserts and screens Slide 29 EXISTING TECHNOLOGIES Mechanical Treatment Other ADS Retention Systems Kleerwater Oil/Water Separators More, see: http://www.epa.gov/ne/assistance/ceitts/stormwater/techs.html http://www.epa.gov/ne/assistance/ceitts/stormwater/techs.html Slide 30 Proprietary Units by Treatment Type Mechanical Treatment Wet VaultsStormCeptor BaySaver StormVault ADS Retention System Constructed WetlandsStormTreat Hydrodynamic/Vortex Separators Vortechs Aquafilter V2B1 Downstream Defender CDS Unit Inert/Sorptive Media FiltersStormFilter High-Flow Bypass (Flow Splitter) StormGate Slide 31 DESIGN PARAMETERS Mechanical Treatment Constituent parameters design for % removal of Trash Solids Oil and grease Organics Nutrients Metals Pathogens Slide 32 DESIGN PARAMETERS Mechanical Treatment Concrete manhole possible retrofit Downstream Defender SmartSponge Vault Designed in or major reconstruction concrete manholes BaySaver Stormceptor Larger vaults Designed in or major reconstruction Slide 33 EMERGING TECHNOLOGIES Mechanical Treatment Emerging Technologies: Membrane Processes - microfiltration Dissolved Air Flotation for oils and grease Revolving Drum Screens Other wastewater process Example: Santa Monica Urban Runoff Recycling Facility Slide 34 34 SMURRF Santa Monica Urban Runoff Recycling Facility Joint Santa Monica-Los Angeles Project l Reuse a local water resource. l Keep a pollution source out of Santa Monica Bay. l Reduce imported water & impacts on other watersheds. l Open, walk-through facility to educate the public. l Up to 500,000 gallons/day l 325,000 average l 3% of Citys daily water use. l $12 Million for 0.3 MGD l $175,000 O&M Slide 35 Dissolved Air Floatation Grit Chamber Rotating Drum Screens Membrane Microfiltration UV Disinfection SMURRF Process Slide 36 DESIGN LIMITATIONS Mechanical Treatment Advance processes applications (e.g., SMURFF), are demonstration projects paid by grants Not economically feasible at this time Retrofit and construction issues Inserts can be placed in, but are not as effective Some manhole applications can be retrofit with relatively minor reconstruction Slide 37 DESIGN LIMITATIONS Mechanical Treatment Vault applications Must be designed in. Retrofit is difficult. Stormfilter and some other applications may allow changing or expanding treatment processes in the future. Flexibility and upgradeability of systems should be considered. Slide 38 PROS / CONS Mechanical Treatment Pros: more reliable, flexible than natural treatment or infiltration Not sensitive to climate, soil, season can remove hydrocarbons, metals, nutrients designed for desired constituents and removal rates Cons: The most effective systems are expensive O & M cost and effort can be considerable difficult retrofits for the most effective systems Slide 39 Slide 40 Slide 41 COST / BENEFIT Mechanical Treatment Slide 42 CLIMATE / REGIONAL RESTRICTIONS Mechanical Treatment In general, no climate or regional restrictions Ice, snow, deicing issues dealt with in site-specific design StormTreat is a constructed wetland Not as effective in Winter in some climates A system in California had to be watered Slide 43 RANKING OF ALTERNATIVES Mechanical Treatment Natural treatment and infiltration are preferred when feasible and appropriate. Mechanical systems tend to be more expensive and require more operation and maintenance. Mechanical treatment systems in addition to or instead of natural treatment can be designed to meet specific goals. Vault systems (e.g., StormFilter), if affordable, may offer more flexibility and upgradeability than manhole systems. Inserts can be retrofitted to remove trash, solids, and oils. Slide 44 RECOMMENDED FOR DETAILED STUDY Mechanical Treatment Can a standard protocol be established to evaluate which natural treatment, infiltration, and mechanical treatment alternatives are most appropriate for each site? Can a standard design of a mechanical treatment system be established that can be adapted to different site conditions including hydrology, water constituents, and discharge limits? Slide 45 Discussion?