canada b&b 2012 grit pres

B&B’s Process Equipment experience includes lines from companies such as

• LIGHTNIN/SPX • SWECO •SMITH & LOVELESS •SPIROFLOW•THERMO FISHER SCIENTIFIC•J&H•V-SEP•PERIFLO•MERRICK/BIF

© Smith & Loveless, Inc. 2010

Grit Presentation

Presented By:Mike Arpin, Smith & Loveless Inc.

& Greg Gurd Black & Baird

• Fundamentals• Grit Removal Efficiencies• Vortex Grit Chambers• Water Level Velocity Control• Grit Testing Methodologies• Grit Study - Grit at WWTP & USGS River Bed Sediment• Grit Pumping• Don’ts• Grit Dewatering/Grit Classifiers & Washers• Packaged Headworks

Outline

• What is grit?What is grit?

• Specific gravitySpecific gravity

• Classifying gritClassifying grit

• VelocityVelocity

Fundamentals

• Grit is heavy mineral matter consisting of a variety of Grit is heavy mineral matter consisting of a variety of particles including sand, gravel, cinder, and other heavy, particles including sand, gravel, cinder, and other heavy, discrete inorganic discrete inorganic materials found in materials found in domestic sewage.domestic sewage.

Reprinted with the permission of Smith & Loveless, Inc. © 2007-2010.

What is Grit?

• The EPA’s Wastewater Technology Fact Sheet (Screening & The EPA’s Wastewater Technology Fact Sheet (Screening & Grit Removal), defines grit as “particles larger than 0.21 mm Grit Removal), defines grit as “particles larger than 0.21 mm (.008 in.) (65 mesh) and (.008 in.) (65 mesh) and with a specific gravity ofwith a specific gravity ofgreater than 2.65.”greater than 2.65.”


What is Grit?

• Correlates to a particle’s settling velocity, which measures the Correlates to a particle’s settling velocity, which measures the speed or time a particle will settle in the water.speed or time a particle will settle in the water.


What is Specific Gravity?

• Grit particles develop a thin coating of iron oxide or iron Grit particles develop a thin coating of iron oxide or iron sulfide when exposed to wastewater.sulfide when exposed to wastewater.

• This coating, does not alter the particle’s specific gravity.This coating, does not alter the particle’s specific gravity.

Grit & Specific Gravity

• Appropriate retention time must be maintained for grit to settle Appropriate retention time must be maintained for grit to settle & be captured.& be captured.



• Settling velocities & retention times Settling velocities & retention times do notdo not apply to forced apply to forced vortex systems.vortex systems.

• Forced vortex systems use Forced vortex systems use hydraulic forces to remove grit. hydraulic forces to remove grit.



• Mesh sizing is a common way to classify grit particle sizes.Mesh sizing is a common way to classify grit particle sizes.

• Increasing mesh values translates into smaller grit particle Increasing mesh values translates into smaller grit particle diameters.diameters.


Classifying Grit Particles

• Typical domestic sewage grit ranges from 20 to 140 mesh.Typical domestic sewage grit ranges from 20 to 140 mesh.

• Majority of grit (90+ %) normally ranges between 50 and Majority of grit (90+ %) normally ranges between 50 and 100 mesh.100 mesh.

• Quantity may vary based upon geographic location.Quantity may vary based upon geographic location.



• Abrasive grit particles (100+ mesh) create the Abrasive grit particles (100+ mesh) create the greatest problems.greatest problems.

• Particles smaller than 140 mesh display buoyant, Particles smaller than 140 mesh display buoyant, silt-like characteristics.silt-like characteristics.



SEPARATE SEWERSAverage 2 to 4 ft3 per 3,785

CMDPeak 8 ft3 per 3,785 CMDCOMBINED SEWERSAverage 8 to 20 ft3 per CMDPeak 40 ft3 per CMD

SEPARATE SEWERSAverage 2 to 4 ft3 per 3,785

CMDPeak 8 ft3 per 3,785 CMDCOMBINED SEWERSAverage 8 to 20 ft3 per CMDPeak 40 ft3 per CMD

Rule of Thumb

• Velocity plays a key role in grit travel through a collection Velocity plays a key role in grit travel through a collection system & WWTP.system & WWTP.


Velocity

The low velocity is near The low velocity is near the left & right walls, the left & right walls, and near the bottom and near the bottom corners. The highest corners. The highest velocity is in the center velocity is in the center of the flume. The high of the flume. The high velocity pushes velocity pushes obstructions towards obstructions towards the low velocity areas.the low velocity areas.


Understanding Flume Flow Dynamics & Velocities

• Range between 0.48m to 1.07m or 1.6 to 3.5 ft./second.Range between 0.48m to 1.07m or 1.6 to 3.5 ft./second.

• Causes grit suspension in the flow, traveling like a Causes grit suspension in the flow, traveling like a

moving bed.moving bed.

• Higher velocities (above 1.07m or 3.5 ft./second), the Higher velocities (above 1.07m or 3.5 ft./second), the

flow becomes turbulent dispersing the grit bed.flow becomes turbulent dispersing the grit bed.

• Lower velocities (below 0.48m or 1.6 ft./second), grit will Lower velocities (below 0.48m or 1.6 ft./second), grit will

settle & have limited movement.settle & have limited movement.

Ideal Flow Velocities

• Multiple straight currents exist within a flume, each with Multiple straight currents exist within a flume, each with varying velocities.varying velocities.

• Grit will generally be found where the lowest velocities occur.Grit will generally be found where the lowest velocities occur.


Flow Velocities


Understanding Flume FlowDynamics & Velocities

Grit Removal Efficiency

-- 95% of 50 mesh grit and larger 95% of 50 mesh grit and larger

-- 85% of 70 mesh grit but less than 50 mesh 85% of 70 mesh grit but less than 50 mesh

-- 65% of 100 mesh grit but less than 70 mesh 65% of 100 mesh grit but less than 70 mesh

• 360 Degree w/ Baffling System360 Degree w/ Baffling System

• 270 Degree or 360 Degree with Weir270 Degree or 360 Degree with Weir

- 95% of 140 mesh- 95% of 140 mesh

Grit Removal Efficiency

Vortex Grit Chambers


270 Degree Layout


360 Degree Layout


Vortex Grit Chamber Design


Gravity Based Vortex Systems

Hydraulic BasedHydraulic BasedHydraulic BasedHydraulic Based Gravity BasedGravity BasedGravity BasedGravity Based


Illustration from Jones & Attwood

Gravity Grit Chamber Design

Photo taken by S&L during site visit.

Water Level / Velocity Control

The minimum The minimum inlet channel inlet channel velocity - 1.6 velocity - 1.6 feet/second.feet/second.

The maximum The maximum inlet channel inlet channel velocity - 3.5 velocity - 3.5 feet/second.feet/second.


Understanding Flume Flow Dynamics & Velocities

Grit Pumping

• Up to 30 MGD, use 250 GPMUp to 30 MGD, use 250 GPM

• 30 MGD Plus, use 500 GPM30 MGD Plus, use 500 GPM

• Option A - Top Mounted Vacuum PrimedOption A - Top Mounted Vacuum Primed

• Option B - Flooded SuctionOption B - Flooded Suction

250 GPM / 500 GPM

• Suction Piping Should be Kept to a Minimum (Less than Suction Piping Should be Kept to a Minimum (Less than 10’-15’)10’-15’)

• Never Use Check Valves, instead use Pinch ValvesNever Use Check Valves, instead use Pinch Valves

• Use Good Screening Equipment Ahead of Grit Process Use Good Screening Equipment Ahead of Grit Process (3/4” max. opening)(3/4” max. opening)

Grit Piping Rules

• Remove All Grit From BasinRemove All Grit From Basin

• Use Water Flush Into Suction Line Use Water Flush Into Suction Line

• May Run Flush Water While PumpingMay Run Flush Water While Pumping

• Do NOT Depend on GravityDo NOT Depend on Gravity

Grit Piping Rules

• Use Dedicated Suction & Discharge Lines for Dual Use Dedicated Suction & Discharge Lines for Dual PumpsPumps

• Eliminate Unnecessary ElbowsEliminate Unnecessary Elbows

• Use 45Use 45oo Elbows if Necessary Elbows if Necessary

Grit Piping Rules

Don’ts

• Watch out for Siphoning - Inlet to the Grit Watch out for Siphoning - Inlet to the Grit Concentrator must be 24 inches above the water level Concentrator must be 24 inches above the water level in the grit removal chamber to prevent siphoningin the grit removal chamber to prevent siphoning

Avoid Siphoning Problems

• Watch out for short inlet flumes, which create unnecessary Watch out for short inlet flumes, which create unnecessary and excessive turbulence which can affect the removal and excessive turbulence which can affect the removal efficiency of a forced or gravity based vortex unit.efficiency of a forced or gravity based vortex unit.

Avoid Short Inlet problems

Grit Dewatering

Inside Look of the Screw Conveyor

Inside Look of the Screw Conveyor

• Growing Landfill Restrictions.Growing Landfill Restrictions.

• Growing Concerns About Odor & Disease Conveying Insects.Growing Concerns About Odor & Disease Conveying Insects.

• More Stringent Regulations, and we see this preference in the More Stringent Regulations, and we see this preference in the Midwest and Northeast.Midwest and Northeast.

Why a Grit Washer?

Grit Washer

Packaged Headwork Technologies

Model 0.5 0.5 MGD 8'-0 Wide x 18'-0 High x 45'-0 LongModel 1.0 1.0 MGD 8'-0 Wide x 18'-0 High x 45'-0 LongModel 2.5 2.5 MGD 8'-0 Wide x 18'-0 High x 46'-0 LongModel 4.0 4.0 MGD 8'-0 Wide x 18'-0 High x 47'-0 LongModel 7.0 7.0 MGD 12'-0 Wide x 18'-0 High x 49'-0 Long

Model 12.0 12.0 MGD 12'-0 Wide x 18'-0 High x 49'-0 Long

ModelPeak System

Flow CapacityInstalled Footprint

PISTA® WORKS™

THANK YOU

canada b&b 2012 grit pres

Technology

mesh grit

grit velocity

permission of smith

grit bed

grit travel

grit presentation

grit willsettle

grit suspension