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Mechanical Treatment of Storm Water. Thomas Soerens University of Arkansas. Outline. Fundamentals of Settling Catch basin sizing examples Alternative mechanical treatment technologies. Settling. Example Regulation Storm water treatment should remove 80% of Total Suspended Solids (TSS).

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Thomas soerens university of arkansas

Mechanical Treatment of Storm Water

Thomas Soerens

University of Arkansas


Outline
Outline

Fundamentals of Settling

Catch basin sizing examples

Alternative mechanical treatment technologies


Settling
Settling

Example Regulation

Storm water treatment should remove 80% of Total Suspended Solids (TSS).

vague: what size solids?

System 1: Removes 80% solids with d50 of 50 microns

System 2: Removes 80% solids with d50 of 100 microns

System 2 not remove 80% of solids with d50 of 50 microns

In comparing systems, must see data side by side and compare apples to apples

Example Basin (next slide)


A rectangular settling tank processes 48,000 m3/day, is 6 m wide, 36 m long, and 4 m deep.

What is the average hydraulic retention time in the tank (hr)?

t0 = Vol/Q = (6m x 4m x 36m) / 48000 m3/day = 0.018 day = 0.432 hr = 26 min

Assuming horizontal flow, what is the flow (approach) velocity (m/d)?

vx = 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)?

v0 = Q/(w x L) = Q / (6m x 36m) = 222 m/day = 0.15 m/min note: vo = 4 m / 0.018 day = depth / retention time


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: vs = 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 < t0

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: vs = 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 > t0

in 40 minutes, it travels 40 x 1.4 m/min = 56 m > L


If it doesn’t hit bottom?

Approximately vs/vo fraction of particles will settle out

example: vs = 0.10 m/min

Removal =~ 0.10/0.15 = 0.65 = 65% removal

note: this is for horizontal clarifiers

note: turbulence happens


Settling velocity stoke s law
Settling Velocity – Stoke’s Law

Stoke’s law for settling velocity of spheres:

vs = [(rp – rw)d2g]/18m

rp , rw = density of particle, water

d = diameter of particle

g = gravity

m = 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


Basin sizing approaches
Basin Sizing Approaches

Using d50

Set overflow rate of basin at design flow equal to d50 of a grain-size analysis of dirt you want to remove.

Can have v0 up to 1/0.8 = 1.25 of settling velocity

100 micron particle


for Q = 0.17 m3/sec (6 cfs)

choose aspect ratio: Length = 4 x width

set vo = Q/Asurface = 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?

vo = Q/wL = 0.018 m/sec

vs/vo = 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.


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



For an overflow rate of 7m/24 min (depth/to)

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 = vs/vo

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


Questions
Questions?

next: examples of mechanical storm water treatment systems


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


ADS system Underground Detention/Infiltration Units

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


ADS system Underground Detention/Infiltration Units

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


ADS system - DIU Underground Detention/Infiltration Units


ADS performance Underground Detention/Infiltration Units


ADS performance Underground Detention/Infiltration Units


WAL-MART SITE Underground Detention/Infiltration UnitsSUSTAINABILITY INITIATIVEWATER GROUP

Mechanical Treatment

Thomas Soerens

University of Arkansas

479-575-2494

Scott Franklin

PACLAND

503-659-9500


OBJECTIVE Underground Detention/Infiltration Units

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


EXISTING TECHNOLOGIES Underground Detention/Infiltration UnitsMechanical Treatment

  • Manholes

  • Stormceptor

  • Downstream Defender

  • Continuous Deflective Separation (CDS)


EXISTING TECHNOLOGIES Underground Detention/Infiltration UnitsMechanical Treatment

  • Manholes

  • Aquafilter and Aquaguard

  • BaySeparator and BayFilter


EXISTING TECHNOLOGIES Underground Detention/Infiltration UnitsMechanical Treatment

  • Manholes

  • V2B1

  • StormGate


EXISTING TECHNOLOGIES Underground Detention/Infiltration UnitsMechanical Treatment

  • Vaults

  • Stormfilter

  • Stormvault

  • Storm Water Quality Unit


EXISTING TECHNOLOGIES Underground Detention/Infiltration UnitsMechanical Treatment

  • Vaults

  • StormTreat

  • Contech Vortech

  • Crystal Stream Vault


EXISTING TECHNOLOGIES Underground Detention/Infiltration UnitsMechanical Treatment

  • Inserts

  • Fabco StormX inserts

  • SmartSponge (AbTech)

    • Skimmers, inserts, or vault

  • EcoSense filters


EXISTING TECHNOLOGIES Underground Detention/Infiltration UnitsMechanical Treatment

  • Other

  • various inserts and screens


EXISTING TECHNOLOGIES Underground Detention/Infiltration UnitsMechanical Treatment

  • Other

  • ADS Retention Systems

  • Kleerwater Oil/Water Separators

  • More, see: http://www.epa.gov/ne/assistance/ceitts/stormwater/techs.html


Proprietary Units by Treatment Type Underground Detention/Infiltration Units Mechanical Treatment


DESIGN PARAMETERS Underground Detention/Infiltration Units Mechanical Treatment

  • Constituent parameters – design for % removal of

    • Trash

    • Solids

    • Oil and grease

    • Organics

    • Nutrients

    • Metals

    • Pathogens


DESIGN PARAMETERS Underground Detention/Infiltration Units 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


EMERGING TECHNOLOGIES Underground Detention/Infiltration Units 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


Smurrf

SMURRF Underground Detention/Infiltration Units

Santa Monica Urban Runoff Recycling Facility

Joint Santa Monica-Los Angeles Project

  • Reuse a local water resource.

  • Keep a pollution source out of Santa Monica Bay.

  • Reduce imported water & impacts on other watersheds.

  • Open, walk-through facility to educate the public.

  • Up to 500,000 gallons/day

    • 325,000 average

  • 3% of City’s daily water use.

  • $12 Million for 0.3 MGD

    • $175,000 O&M


Dissolved air floatation
Dissolved Air Floatation Underground Detention/Infiltration Units

SMURRF Process

Rotating Drum Screens

Grit Chamber

Membrane Microfiltration

UV Disinfection


DESIGN LIMITATIONS Underground Detention/Infiltration Units 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


DESIGN LIMITATIONS Underground Detention/Infiltration Units 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.


PROS / CONS Underground Detention/Infiltration Units 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


COST / BENEFIT Underground Detention/Infiltration Units Mechanical Treatment


CLIMATE / REGIONAL RESTRICTIONS Underground Detention/Infiltration Units 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


RANKING OF ALTERNATIVES Underground Detention/Infiltration Units 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.


RECOMMENDED FOR DETAILED STUDY Underground Detention/Infiltration UnitsMechanical 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?


Discussion
Discussion? Underground Detention/Infiltration Units


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