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© 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