© 2014 HDR, Inc., all rights reserved. © 2015 HDR, Inc., all rights reserved.

Making Clarifiers Do More For

Less

Hany Gerges, Ph.D, PE

July 31, 2015

Presentation Agenda

Background

Primary Clarifiers

Experience - Case Studies

Secondary Clarifiers

1

3

4

5

Grit Removal Technology 2

Background

• Grit Removal Technology

• Field testing is a MUST.

• Know “YOUR” Grit settling

velocity.

• Determine Design Particle

• Select Right Technology

Background

• Field Testing

• Quantity of Grit.

• Particle Distribution.

• Grit settling velocity (300

micron grit particle = 125

micron sand particle)

Grit is Different than Sand….could be much slower

Technology Selection

Mechanically induced vortex grit basins

Multi-tray vortex (headcell)

Aerated grit basins

Large footprint

Complex operation

High life cycle cost

Good flocculation environment

Small footprint

High turndown

Low life cycle cost

Small footprint

High capital cost, low O&M cost

Sole-source

Ask yourself…what size is the majority of incoming Grit

Background

Rectangular Primary

Circular Primary

• Primary Clarifiers

• Hydraulics Improvements

• Minimizing short circuiting

• Reducing sludge re-suspension

• Reducing solids carry over

• Flocculation Improvements

• Chemically Enhanced Primary

Treatment (CEPT)

• Reduce non-settleable solids

• Increasing solids settling velocity

Primary Clarifiers…The Workhorse of Treatment Plants

Pound for Pound…They Remove more

BOD than any other treatment unit at a

treatment plant

Primary Clarifiers Remove Settleable Solids ONLY…

Non-Settle Settle

sBOD pBODRaw

Influent

PSTpBOD

Settle

sBOD pBOD

Non-Settle

sBODPrimary

Effluent

Sludge

Primary Clarifiers – Typical Design

Designer Assumptions

• Over Flow Rate = 800 gpd/ft2.

• TSS Removal = 50 to 60

percent.

• BOD Removal = 25 – 40

percent

Circular Primary

Not always the case…!!!!

Effect of Non-settleable Solids

• Example I

• Inf. TSS = 300 mg/L, TSSnon = 100 mg/L

• Max. Removal Efficiency = 67 %

• Example II

• Inf. TSS = 300 mg/L, TSSnon= 50 mg/L

• Max. Removal Efficiency = 83 %

Effect of Solids Settling Velocity

• Design OFR = 800 gpd/ft2.

• Settling velocity = 0.07 ft/min.

• All particles with velocity greater than 0.07

ft/min will be 100 percent removed.

• What is the percentage of these particles in

the influent…..????......

Settling Velocity Distribution

0

5

10

15

20

25

30

35

40

45

0.00 0.01 0.03 0.05 0.11 0.21 0.42 0.84

Frac

tio

n o

f So

lids

(%

)

Settling Velocity (ft/min)

Typical Primary Influent

Chemically Enhanced Primary Influent

How to Use SVD?

• Computational Fluid Dynamic Models

Simple Modifications Increase Wet Weather Capacity

• Sludge protector

canopy.

• Easy to retrofit to

existing circular

tanks.

• Protects hopper and

direct flows above

blanket minimizing

sludge re-

suspension.

Simple Modifications Increase Wet Weather Capacity

• Sludge protector

canopy.

• Easy to retrofit to

existing circular

tanks.

• Protects hopper and

direct flows above

blanket minimizing

sludge re-

suspension.

Simple Modifications Increase TSS and BOD Removal Efficiency

• About 19 percent

reduction in TSS.

• About 10 percent

reduction in BOD

• More Biogas

production.

Primaries performing well under very high loading rates

Background

Rectangular

Secondary

Circular Secondary

• Secondary Clarifiers

• Hydraulics Improvements

• Minimizing short circuiting

• Reducing sludge re-suspension

• Reducing solids carry over

• Flocculation Improvements

Secondary Clarifiers..The Bottleneck of WWTPs

Last line of defense.

Limited process control (return rate only).

Not Knowing the cause of poor performance.

Very expensive to build.

Causes of Poor Performance

• Poor settling sludge.

• Hydraulic inefficiency.

• Poor flocculation.

• High Blankets.

• Denitrification.

Secondary Clarifier Elements

Effluent Baffle Energy Dissipating Inlet

Covered Launders

TowBro Suction Mechanism Spiral Scraper

16 - 20 SWD

Many Elements..…with One Objective…!!!!

Energy Dissipating Inlet More Than 10 Different Designs

Flocculation Center Well Big or Small? Deep or Shallow?

Effluent Baffles? Needed or Not Needed?

Better Hydraulics – No Short Circuiting

EDI – Everyone has an EDI

• Envirex – Different

configurations

• WETECH – Different

configurations

• LA - EDI

• Multi Layer

• No Bottom Tub

Do You Really Need an EDI?

Performance Enhancement Feature Improves Performance

Secondary Clarifiers

• More than 80 percent of new

technology is for circular seconadries.

• Optimal arrangements for rectangular

secondaries

– Inlet Baffles

– Mid Tank baffles

– Effluent Launders

– Sludge Hopper Canopy

HDR State Of The Art Clarifier

HDR - Optimized Rectangular Secondary Clarifiers

• Santa Fe WWTP.

• Plant 1 - Orange County Sanitation District, CA.

• Michelson Water Reclamation Plant, Irvine Ranch, CA.

• Bethel Park Authority, PA.

• City of Vacaville, CA

• Stage IV- ShaTin WWTP, Hong Kong

Proven Experience

• Santa Fe WWTP.

• Field Testing to

Pinpoint to the

problem

• Modeling to select

fixes

Proven Experience

• Santa Fe WWTP.

• Influent Baffles

• Transversal

Launders

• Partial Blockage of

effluent launders

• RAS modifications

Avoided Building One Additional

Clarifier

Proven Experience

• Michelson WRP – IRWD

– Influent baffles

– Transversal launders

– RAS modifications

Unmodified Modified 40 % Reduction in Effluent TSS

Hong Kong

Q & A

© 2014 HDR, Inc., all rights reserved. © 2015 HDR, Inc., all rights reserved.

Making Clarifiers Do More For

Less

Hany Gerges, Ph.D, PE

July 31, 2015

Settling Velocity Tests

Kemmerer Sampler Measurements

Step 1: Lower Kemmerer sampler below the water surface, and then close by sliding the messenger down the rope.

Step 2: Bring sampler to the surface and collect a sample from the bottom valve (for influent composite sample).

• Step 3: Let sample settle for predefined

time . Tests were conducted for settling

times of 1, 2, 4, 8, 16, 32 and 60 minutes.

Step 5: Store samples in ice

chests and send to

laboratory for analysis.

• Step 4: After settling

time has elapsed,

collect sample through

middle sampling port.

The supernatant TSS of the sample that is settled 60

minutes is considered to be the

Non-Settleable Solids (NSS) concentration.

The contents of the bucket (which contained samples

from each test) were mixed and analyzed for TSS. This

sample was considered to be the influent composite

sample.

Stone Cutter WWTP – One of the Largest Primary Clarification Plant –

1.2 BGD

• 48 Double Deck Primary Clarifiers.

• 1.2 billion gallon a day.

• More than 15 percent increase in TSS

removal.

HDR Engineers have designed and optimized all shapes and

configurations of clarifiers all over the world

Hong Kong