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Thomas Soerens University of Arkansas Mechanical Treatment of Storm Water.

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Presentation on theme: "Thomas Soerens University of Arkansas Mechanical Treatment of Storm Water."— Presentation transcript:

1 Thomas Soerens University of Arkansas Mechanical Treatment of Storm Water

2 Outline  Fundamentals of Settling  Catch basin sizing examples  Alternative mechanical treatment technologies

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)

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) / m 3 /day = day = 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 / day = depth / retention time

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 doesn’t 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

6  If it doesn’t 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

7 Settling Velocity – Stoke’s Law  Stoke’s 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 Stoke’s Law, what can be changed?  Do you see why we coagulate and flocculate

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

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) = 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 = 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.

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  can’t 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

11 Another method: from settling data

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 it’s 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

13 Questions?  next: examples of mechanical storm water treatment systems

14  Advanced Drainage Systems (ADS) Water Quality and Underground Detention/Infiltration Units

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

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

17  ADS system - DIU

18  ADS performance

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20 WAL-MART SITE SUSTAINABILITY INITIATIVE WATER GROUP Thomas Soerens University of Arkansas Mechanical Treatment Scott Franklin PACLAND

21 OBJECTIVE Identify existing and emerging mechanical storm water treatment technologies and describe design and decision parameters.

22 EXISTING TECHNOLOGIES Mechanical Treatment Manholes Stormceptor Downstream Defender Continuous Deflective Separation (CDS)

23 EXISTING TECHNOLOGIES Mechanical Treatment Manholes Aquafilter and Aquaguard BaySeparator and BayFilter

24 EXISTING TECHNOLOGIES Mechanical Treatment Manholes V2B1 StormGate

25 EXISTING TECHNOLOGIES Mechanical Treatment Vaults Stormfilter Stormvault Storm Water Quality Unit

26 EXISTING TECHNOLOGIES Mechanical Treatment Vaults StormTreat Contech Vortech Crystal Stream Vault

27 EXISTING TECHNOLOGIES Mechanical Treatment Inserts Fabco StormX inserts SmartSponge (AbTech) Skimmers, inserts, or vault EcoSense filters

28 EXISTING TECHNOLOGIES Mechanical Treatment Other various inserts and screens

29 EXISTING TECHNOLOGIES Mechanical Treatment Other ADS Retention Systems Kleerwater Oil/Water Separators More, see:

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

31 DESIGN PARAMETERS Mechanical Treatment Constituent parameters – design for % removal of Trash Solids Oil and grease Organics Nutrients Metals Pathogens

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

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

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 City’s daily water use. l $12 Million for 0.3 MGD l $175,000 O&M

35 Dissolved Air Floatation Grit Chamber Rotating Drum Screens Membrane Microfiltration UV Disinfection SMURRF Process

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

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.

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

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41 COST / BENEFIT Mechanical Treatment

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

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.

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?

45 Discussion?


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