maximizing polymer value for improved sludge dewatering conference... · maximizing polymer value...
TRANSCRIPT
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Maximizing Polymer Value for Improved Sludge Dewatering
Yong Kim, Ph.D.
Technical Director
UGSI Chemical Feed, Inc.
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Presentation Overview
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Characteristics of Polymer
Effect of Dilution Water Chemistry
Effect of Mixing Energy/Strategy
Two-stage Primary Mixing
Primary Mixing then Post-Dilution
Case Study at Fairfield WWTP
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Coagulation and Flocculation
Coagulation
- Double-layer compression (charge neutralization)
- Enmeshment (sweep coagulation)
Clay suspension + Ferric chloride (40 – 120 mg/L)
3
Flocculation
- Polymer Bridging
Clay suspension + Ferric chloride + Polymer (< 1.0 mg/L)
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Extended cationic polymer molecule attracts negatively-charged suspended particles.
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Flocculation - Bridging by Polymer Molecules
suspended particles
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How to prevent long-chain polymer molecules from being damaged?
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Polymer Structure
• Polymeric Flocculant, Linear Polymer, Polyelectrolyte
• Chained Structure by Repetition of Monomers
… - CH2 - CH - [CH2
- CH]n - CH2 - CH- ... CO CO CO NH2 NH2 NH2
Most polymers in water industry are acrylamide-based.
If molecular weight of polymer is 10 million,
the number of monomers in one polymer molecule, “degree of polymerization”
n = 10,000,000 / 71
= 140,850
(mol. wt. of monomer, acrylamide = 71)
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Measure of Polymer Activation - Polymer Solution Viscosity
0
50
100
150
200
250
4 9 16 22 27
Reduced Specific Viscosity
Sakaguchi, K.; Nagase, K., Bull. Chem. Soc. Japan, 39, p.88 (1966)
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Effect of Dilution Water Quality on Polymer Activation
Ionic strength (Hardness): multi-valent ions; adverse effect
- Soft water helps polymer molecules fully-extend faster
- Hardness over 400 ppm may need softener
Oxidizer (chlorine): detrimental to polymer chains
- Should be less than 3 ppm
Temperature*: higher temperature, better polymer activation
- In-line water heater for water lower than 40 oF
- Water over 100 oF may damage polymer chains
Suspended solids: strainer recommended if > 10 ppm
pH: negligible effect within pH 3 - 10
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*David Oerke (CH2M), et al., 2014 Biosolids Conf. - 20% less polymer with warm water, 40% more polymer with 140oF sludge
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Effect of Chlorine (Oxidizing Chemical)
When effluent is used for polymer mixing, chlorine should be < 3 mg/L
0
200
400
600
800
1000
1200
0 1 2 3 4 5 6 7 8 9 10
Vis
co
sit
y
Cl2 mg/L
8
cP
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Polymer Activation (Mixing, Dissolution)
(I) Initial Wetting (Inversion) Sticky layer formed
High-energy mixing -> No fisheyes
(II) Dissolution
Reptation* or Uncoiling
Low-energy mixing -> No damage to polymer
Sticky Layer
Water Polymer (gel)
* de Gennes, P.G., J. Chem. Phys., 55, 572 (1971)
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Time
(I) (II)
Oil
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Mixing Effect on Polymer Activation
beaker 1
Viscosity of polymer solution
(prepared in 600 mL beakers)
- Beakers 1, 2: one-stage mixing
- Beaker 3: two-stage mixing
beaker 2
beaker 3
Two-stage mixing resulted in polymer
solution of much better quality
* High energy first: prevent fisheye formation
* Low energy followed: minimize polymer damage
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Development of Two-stage Mixer
G-value, mean shear rate (sec-1)
1,700
4,000
1,100
1- stage mixer (EC) 2- stage mixer (PB)
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Mixing Effect on Polymer Activation Two-stage mixing significant increase in polymer solution viscosity
226
427
310
523
0
100
200
300
400
500
600
Anionic Polymer Cationic Polymer
Viscosity of 0.5% Emulsion Polymer Solution, cP
1-stage mixer 2-stage mixer
27% up
18% up
PolyBlend® Technology
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Why Primary Mixing followed by Post-Dilution? Inverting Surfactant helps to invert w/o emulsion to o/w emulsion
Polymer Gel: Polymer 40%
Water 30%
Hydrocarbon Oil: 30%
d
d = 0.1 - 2 µm
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- Stabilizing surfactant - Inverting (breaker) surfactant* To maximize the value of Inverting Surfactant, * 0.75% - 1.0% primary mixing * 0.25% - 0.5% secondary mixing (dilution)
* AWWA Standard for Polyacrylamide (ANSI-AWWA B453-06), 11, 2006
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How to Maximize the Value of Inverting Surfactant?
Primary Mixing
Primary Mixing
Post-Dilution
Primary mixing at high % + Post-dilution at feed %
Polymer 1 gph
Polymer 1 gph
Water 200 gph
Water 100 gph
Water 100 gph
0.5% solution
0.5% solution 1.0%
0.5%
Ideal Design
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PolyBlend Polymer Mixing Systems
Two-stage mixing in mix chamber Primary mixing followed by post-dilution
high-shear zone
low-shear zone
Baffle plate Secondary dilution water
Primary dilution water
Mix chamber
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Dry Polymer Mixing System
High Energy Mixing
(3,450 rpm, < 0.5 sec)
Low Energy Mixing
(60 rpm, 20 min)
(0.5% - 0.75%)
Post-dilution
(0.1% - 0.2%)
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Initial Wetting Mixing Tank Solution Feed
Two-stage Mixing
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Dry Disperser (DD4) for Initial Wetting
Very High-Intensity Mixing for Short Time
G = 15,000 /sec
@ 3,450 rpm
for < 0.5 sec
Disperses Individual Polymer Particles
* No Fisheye Formation
* Shorter Mixing Time in Next Stage
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Water in
Solution Out
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How to Reduce Mixing/Aging Time in Polymer Mixing?
initial high-energy mixing is critical
Polymer dissolution time, ts ~ (diameter)2 Tanaka (1979)*
d
10*d
Assume ts 1 min
ts 100 min
Initial high-energy mixing (DD4) No fisheye formation Significantly shorter mixing time Minimum damage to polymer structure Better quality polymer solution Less Polymer Usage
* Tanaka, T., Fillmore, D.J., J. Chem. Phys., 70 (3), 1214 (1979)
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Mixing Tank for Dissolution of Dry Polymer
Patented Hollow-Wing Impeller
No Weissenberg Effect
Large Impeller, d/D > 0.7
Uniform Mixing Energy
Low RPM, 60 rpm
Low-intensity Mixing
Minimize Damage to Polymer Chain
Shorter Mixing Time – Due to DD4
20 Minutes for Cationic Polymer
30 Minutes for Anionic Polymer
Minimize Damage to Polymer Chain
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Weissenberg Effect
Water (Newtonian)
Polymer Solution (Non-Newtonian, Pseudoplastic)
extremely low mixing
very high mixing
extremely low mixing
* Polymer solution exceeding “critical concentration” climbs up mixing shaft * Extremely non-uniform mixing * Critical factor for conventional polymer mix tank max 0.25% limit for HMW polymer
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PolyBlend® DP Series Tank Mixing
Impeller diameter/ tank diameter > 0.7 Cationic Polymer Solution @ 0.75%
Eye of impeller
Hollow-bladed impeller
PVC sleeve around mixer shaft
PVC sleeve around mixer shaft prevents Weissenburg effect
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Fairfield-Suisan, CA - Sewer District
• Solano County, CA, 40 miles North San Francisco • Design capacity: 24 MGD • Population served: 135,000 • Tertiary treatment/ UV disinfection • Polymer use for dewatering (screw press) and thickening (GBT)
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• Problems with existing polymer system • Struggled to make proper polymer solution • Polymer performance inconsistent • Frequent maintenance issues
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Polymer
Secondary Clarifier
Primary Clarifier
Aeration Basin UV Disinfection
Anaerobic Digester
Gravity Belt Thickener
Dewatering Screw Press
Polymer
Biosolids to Landfill
Final Effluent to Cache la Poudre River
Fairfield-Suisun Wastewater Treatment Plant
WAS
Advanced Tertiary Treatment Facility
RAS Headworks
Tertiary Filter
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Pilot Testing with Two Polymer Mix Equipment
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Existing Polymer System • Initial wetting: educator-type hydraulic mixing • Mixing: two (2) > 3,000 gal mix/age tanks
UGSI PolyBlend Dry Polymer System • Initial wetting: high-energy mechanical mixing • Mixing: two (2) 360 gal mix tanks with hollow-
blade impeller
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Fairfield-Suisan SD – Pilot Test Results
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DP800/DD4 demo trailer at Fairfield
• Dewatering by Screw Press (3/21 – 4/21)
• Less polymer consumption
* Daily usage from 255 lbs to 200 lbs
* 22% polymer savings
• Better cake solids
* 14% - 16% to average 16.4%
• Thickening by GBT (4/24 – 5/23)
• Less polymer consumption
– Daily usage from 29 lbs to 20 lbs
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Various Forms of Polymer Solution
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Broken polymer chains by longer mixing time
Neat polymer
Fisheyes due to poor initial wetting
Ideal polymer chains by two-stage mixing
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Thank You
Yong Kim, PhD UGSI Chemical Feed, Inc. 1901 W. Garden Road Vineland, NJ 08360 Phone: 856-405-5756 E-mail: [email protected]
Please contact Yong Kim with any questions
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How Much Aging Time is Required for Dry Polymer?
0 20 40 60 80 100 120
Vis
cosi
ty (
cP)
Mix Time (min)
stopped mixing
stopped
mixing
stopped
mixing
1.00%
1.00%
0.86%
Rao, M, Influents (WEA Ontario, Canada), Vol. 8, 42 (2013)
PolyBlend® DD4/DP-series do not need additional aging