improving gac filter operations at scwa 8.1 improving gac.pdf · • transport pore structures –...

Improving GAC Filter Operations at SCWA

Joseph RoccaroSuffolk County Water Authority

NYSAWWA Tifft SymposiumSept. 18, 2014

GAC Pilot Phase 1 Results 1,1-DCA: Effect of Virgin GAC Type

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Outline

• GAC Characteristics

• Specifications

• Tracking GAC Performance

• Recent SCWA Work

• Pilot Testing

• Contract Specifications

What is activated Carbon?

• Crude form of Graphite

• Random or Amorphous structure

• Highly porous

• Wide range of pore sizes

Visible and molecular cracks and crevices

45 µm dust particle Cluster of 100 molecules

Courtesy of Calgon Carbon Corp.

High Density, Hard,

Strongly Adsorbing

Low Density, Soft,

Weakly Adsorbing

Peat Lignite Bituminous Anthracite

Coals – Coalification Series

Almond Pecan Walnut Coconut Babassu

Nut Shells

Cherry pits Peach pits Palm Kernels Olive Stones

Pits, Stones, and Kernels

Pine Oak Walnut Teak Ebony

Wood Chips and Sawdust

Rice HullsCorn Cobs Biomass Fermentation ResiduesVegetable Waste

World of Raw Materials for AC


Starting Materials Critical Properties

• Ash level and constituents

• Density

• Hardness

• Inherent Transport porosity (permeability)

• Building Blocks for Adsorption Structure

Description of the Two Types ofActivated Carbon Pore Structures

• Transport Pore Structures– Carbon “Highways”

– Larger Pores which never adsorb– Act as diffusion paths to transport adsorbates– 25% of GAC particle– Dictate adsorption kinetics

• Adsorption Pore Structures– The finest pores in the carbon structure.– Carbon “Parking spaces” – Have adsorption capabilities– 40% of GAC particle – Define adsorption thermodynamics

• Transport Pore:Adsorption Pore– Varies w/ GAC type; activation process– Find the correct parking lot; parking spaces

Carbon Molecular StructureCoal based carbon

Adsorption

pores

40%

Transport

pores

25%

Skeleton

35%

Aliphatic dislocation of platelet

100 angstromsGraphite Platelet

Inter bounding of plates


Carbon Molecular StructureCoconut based Carbon

100 angstroms


Graphite Platelet


Adsorption

pores

45%

Transport

pores

15%

Skeleton

40%


Carbon Molecular Structure Wood based Carbon

100 angstroms


Graphite Platelet


Adsorption

pores

35%

Transport

pores

45%

Skeleton

20%


Order of Attack on Molecular Structure




5. Edges inter bonded with other plates

1

23

4

5

11

2 2 2

2

2

12

3

3

3 3

3

4

4

4

44

4

4

44

4

5

5

5

5

55

1. Edge dislocations

2. Edges of small plates

3. Internal plate dislocations

4. Edges of large plates


Molecular Structure of 0% Burn off Activated Carbon Calcined CMS Carbon




AD 0.80g/cc,Iodine No. <200 Adsorption Pore Volume 0.15 cc/g Abrasion No. 98, Ash 3.0%


Molecular Structure of 20% Burn off Activated CarbonAFC-2204 Carbon




AD 0.64g/cc,Iodine No. 600 Adsorption Pore Volume 0.28 cc/g Abrasion No. 90, Ash 3.75%


Molecular Structure of 40% Burn off Activated CarbonF400 Carbon




AD 0.48g/cc,Iodine No. 1050 Adsorption Pore Volume 0.48 cc/g Abrasion No. 80, Ash 5.0%


What is adsorption?

• Intermolecular attractions in these smallest pores result in adsorption forces that– Cause condensation of adsorbate gases

– Precipitation of adsorbates from solutions

• Adsorption forces are a result of:– Interactions of the carbon structure with outer

bonding electrons of the adsorbate molecules.

– For similar type and size bonds:• The greater the number of bonds per unit volume molecule,

the greater the adsorption force.

Relationship between Structure and Adsorption Force

Carbon AtomAdsorbate Molecule

Carbon Skeletal Structure

(10,000,000 X Magnification)

The Adsorption force present at the adsorption site is the sum of all the individual interactions between carbon atoms and the adsorbate molecule.


Graphite Plate of Carbon skeletal Structure


London Dispersion Force Field for One Graphite Plate

Butane Adsorbate Molecule

Adsorption Force Field Strength for Butane Adsorption= 0.5 Kcal/mole Butane adsorbed= 1.0 Kcal/mole Butane adsorbed= 2.0 kcal/mole Butane adsorbed= 4.0 Kcal/mole Butane adsorbed


Graphite Plate of Carbon Skeletal Structure


London Dispersion Force Field for Two Graphite Plates

Butane Adsorbate Molecule

Adsorption Force Field Strength for Butane Adsorption= 0.5 Kcal/mole Butane adsorbed= 1.0 Kcal/mole Butane adsorbed= 2.0 kcal/mole Butane adsorbed= 4.0 Kcal/mole Butane adsorbed= 8.0 Kcal/mole Butane adsorbed


GAC Pilot Phase 1 Results 1,1-DCA: Effect of Virgin GAC Type

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1,1-DCA

1,1 Dichloroethane(1,1 DCA)

HCl

C

C

HH H

Cl

Common & Useful GAC Specification Parameters

• Size Distribution / Physical Attributes– Apparent Density – Effective Size– Uniformity Coefficient (U.C.)– Moisture content– Ash Content– Hardness/Abrasion

• Adsorptive Performance Tests

Apparent Density

• Density of a packed bed of GAC particles, filled in a standard cylinder in a manner to minimize voids between particles

• Provides info on type of carbon and changes undergone during reactivation. – Bituminous = 28 – 41 lb/ft3 **

– Coconut = 28 – 35 lb/ft3 **

– Lignite = 22 – 26 lb/ft3 **

** - from AWWA B604

Effective Size / U.C.

• Effective Size (E.S.) – Screen Size which holds 90% of the carbon above it (mm)

• Uniformity Coefficient (U.C.) = Ratio of size opening that will pass 60% of material divided by that opening that will pass 10% of same sample

– AWWA B604 – UC ≤ 2.1.

• Effect bed packing; dP; adsorption kinetics

Abrasion Number

• Measure of structural strength

• AWWA B604 – measures loss of MPD when subjected to action of stirrer or steel balls

• Ability to withstand handling; slurrying; hydraulic impacts

Ash Content / Moisture Content

• Ash Content – Helps to identify the type of GAC and indicate quantity of extractable material.

– Non-useable impurities on GAC; paying for weight

– Contributes to metals leaching; ↑pH at start-up

– Indicator of minerals present; often insoluble

• Moisture Content

– Needed to calculate dry wt.; cost calculations

– Paying for weight of water

– AWWA (<8%)

Adsorptive Performance Tests(Activity Parameter Tests)

• BET

• Iodine #

• Butane #

• TCN

• Tannin #

BET Surface Area

• Measure of overall surface area

– Larger surface area = potential for greater adsorption capacity

• Measures the amount of N2 gas adsorbed by GAC

– Known surface area occupied by N2

– Uses Brunauer-Emmett-Teller (BET) isotherm eqn.

– N2 small M.W. & size allows access to adsorption pores

– ASTM D 3037

Iodine (I2) # Activity Test

• Measures the amount of 0.02N I2 solution that will adsorb under specific conditions (ASTMD4607).

• Results expressed as mg iodine / gm carbon

• Test inexpensive, fast, reproducible

• Limitations/problems: – Reacts with ash, adsorbates, oxygen on carbon

– Measures volume present in pores from 10 – 28 Å• May not correlate well with trace contaminant removal

Trace Contaminant Number – TCN

• TCN – Acetoxime– Relatively new test method– Acetoxime – very soluble in water – Measures smallest pore fraction – liquid phase isotherm test;– Measure Acetoxime uptake via UV adsorption – AWWA B604-12 – Few labs perform test

• TCN-G– “G” = gas = CF4 (tetrafluoromethane).– Weakly adsorbed; small MW compound– Measure ∆ wt

Tracking GAC Performance

• How to determine how well GAC performed?

• A few key parameters

– Bed Volumes (BV)

– Empty Bed Contact Time (EBCT)

– Carbon Use Rate (CUR)

– Definition of breakthrough

GAC Bed Volume

• Volume occupied by GAC bed

Example: Two (2) 20K vesselsAssume GAC density = 30 #/ft3

40,000 # GAC ÷ 30 #/ft3 = 667 ft3 GAC667 ft3 x 7.48 Gal / ft3 = 9973 Gal. = 1BVBV Treated ≈ Gallons treated / 10,000 Gal.

Normalizes data w/different Q; vessel size

EBCT & CUR

• EBCT = Empty Bed Contact Time – Volume of GAC Bed ÷ Q

– Expressed in minutes

– Removal of specific contaminants ƒ(EBCT)

– Recommendations for contaminant removal

• CUR = Carbon Use Rate– Amount of GAC used at contaminant breakthrough

– expressed as # GAC/MG; # GAC/KGal ; mg/L

Breakthrough in GAC Filter

Inlet Outlet

Mass Transfer Zone

Headspace

Virgin

Down flow Adsorption column

Saturated


GAC Pilot Study - Phase 1

• WRF Project #4235

• 8 pilot columns – 6” dia.

• GAC bed depth: 8.5 ft (2.6 m)

• GAC mesh size: 8 x 30 U.S. Standard Mesh

• 11 min & 22 min EBCT

• Compared VOC removal:

• virgin vs. reactivated GAC

• direct activated vs. re-agglomerated

• coconut GAC

• lignite GAC

• effect of BW; EBCT

GAC Pilot Study (Avg. Influent Concentrations)

• 1,4 – dioxane = 2.3 ug/L

• 1,1-dichloroethane (1,1-DCA) = 2.2 ug/L

• 1,2-dichloroethane (1,2-DCA) = 0.9 ug/L

• 1,1,2-trichlorotrifluoroethane (TCTFA; Freon 113) = 4.2 ug/L

• 1,1,1-trichloroethane (1,1,1-TCA) = 3.2 ug/L

• cis-1,2-dichloroethene (cis-1,2-DCE) = 1.2 ug/L

• 1,1-dichloroethene (1,1-DCE) = 2.1 ug/L

• Carbon tetrachloride (CT) = 0.9 ug/L

• 1,2,3-trichloropropane (1,2,3-TCP) = 0.8 ug/L

• Tetrachloroethene (PCE) = 3.2 ug/L

• Trichloroethene (TCE) = 3.7 ug/L

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1-4 dioxane

GAC Pilot Phase 1 Results Contaminant Breakthrough Order

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1-4 dioxane 1,1-dichloroethane (1,1-DCA)


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1-4 dioxane 1,1-dichloroethane (1,1-DCA) 1,2 dichloroethane (1,2-DCA)


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1-4 dioxane 1,1-dichloroethane (1,1-DCA) 1,1,2-trichlorotrifluoroethane (TCTFA) 1,2 dichloroethane (1,2-DCA)


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1-4 dioxane 1,1-dichloroethane (1,1-DCA) 1,1,2-trichlorotrifluoroethane (TCTFA) 1,2 dichloroethane (1,2-DCA) 1,1,1-trichloroethane (1,1,1-TCA)


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1-4 dioxane 1,1-dichloroethane (1,1-DCA) 1,1,2-trichlorotrifluoroethane (TCTFA)

1,2 dichloroethane (1,2-DCA) 1,1,1-trichloroethane (1,1,1-TCA) cis-1,2-dichloroethene (cis-1,2-DCE)


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1,1,1-trichloroethane (1,1,1-TCA) cis-1,2-dichloroethene (cis-1,2-DCE) 1,1-dichloroethene (1,1-DCE)


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1,1,1-trichloroethane (1,1,1-TCA) cis-1,2-dichloroethene (cis-1,2-DCE) 1,1-dichloroethene (1,1-DCE) carbon tetrachloride (CT)


Conclusions – GAC Pilot Phase I

• GAC not good for 1,4-dioxane removal.

• 1,1-DCA - least adsorbable of VOCs present.

• 1,2,3-TCP, TCE, and PCE - most adsorbable of VOCs present. No detectable breakthrough after 30,000 BV.

• GAC type important for VOC removal

– Direct activated bituminous - least effective

– Coconut-shell based - most effective

– Bituminous - Re-agglomerated outperformed direct activated

– Lignite - slightly less effective than re-agglomerated coal-based GAC on a bed volume basis, but slightly more effective on a mass-based carbon usage rate

Conclusions – GAC Pilot Phase 1 (cont’d.)

• Reactivated GAC

– Acceptable removal of contaminants: • Agglomerated reactivated outperformed its virgin counterpart for all

adsorbates except 1,1,2-TCTFA & 1,1,1-TCA.

• Direct activated reactivated GAC outperformed its virgin counterpart for all adsorbates except 1,2-DCE & CT.

– Metals leaching a potential problem - Agglomerated Bituminous

• EBCT effect on VOC removal: – ↑ EBCT from 11 to 22 min. = 13% ↓ in CUR

• Backwashing effect on VOC removal – No measurable effect.

• EPA proposed cVOC Rule a major concern

Metal Leaching from Reactivated GAC Phase 1 GAC Pilot


• Virgin vs. reactivated; coconut GAC

• GAC bed depth: 4.25 ft

• GAC mesh size: 8 x 30 U.S.

• 5.5 min EBCT

• Compared VOC removal:

- virgin vs. reactivated bituminous

- coconut GAC:

• Iodine #: 900 – 1300

• Tested “performance predicting” surrogate parameters

• TCN; Dye; TAC TIC

Phase 2 - GAC Performance

Coco-nut # 1

Coco-nut# 2

Coco-nut # 3

RBACoco-

nut# 4

VBA RBD VBD

BV to 50% Breakthrough

of 1,1-DCA 12500 12000 11500 11400 10000 8200 4500 4500

CUR (#GAC/MG)

336 334 362 405 516 625 897 855

I2 # 1130 1190 1432 929 870 832 864 978

TCN # 14.5 15.4 14 12.7 14.9 12.6 6.8 6.7

R = reactivated; B = bituminous;V = virgin; D = direct activated;

A = agglomerated

Metal Leaching from Reactivated GACPhase 2 GAC Pilot

B.V. Sb As Mo Ni Se V

14 4.22 6.3 15.3

30 2.56 3.56 1.51 10.2

50 1.28 1.79 2.3 5.78

85 2.91 4.12

115 3.19 3.1

190 2.9 1.38

Conclusions – GAC Pilot Phase 2

• Reactivated Bituminous GAC

– Confirmed acceptable removal of contaminants

– Confirmed metals leaching in agglomerated GAC a potential problem for SCWA. Different sources for spent GAC also had metals carryover.

– TCN appears to be good predictor of performance

• Coconut GAC

– confirmed as effective for VOC removal

– I# is good predictor of performance


• Looking @ reactivated vs. acid washed reactivated GAC

• GAC bed depth: 4.25 ft

• GAC mesh size: 8 x 30 U.S.

• 5.5 min EBCT

• Study underway

• AW Reactivated performing better than non-AW Reactivated

Phase 3 Metals Results

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adiu

m (

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l)

Bed Volumes

Vanadium Concentration

Reactivated GAC

AW reactivated GAC

Common Influent

SCWA – Current GAC Spec’s.

• Contractor: previous experience; mechanical capability

• GAC:

– Virgin bituminous & coconut (8 x 30)

– Iodine # = 1000 (coconut) / 900 (bituminous)

– Water Soluble Ash – 1% (max.)

– Abrasion # - 75 (min.)

– Leachable metals after specified rinse:As = 2.5 ppb

Sb = 0.4 ppb

Others not above background

Best Surrogate for GAC Performance?

CS R-AC L AC R-DC DC

CUR #/MG 460 590 600 730 930 1900

Iodine # 1174 812 659 847 899 870

TCN # 15.4 15.6 2.8 13.5 7.5 9.1

TAC TIC 2.4 2.36 1.08 2.26 1.42 1.71

Dye # 35.5 41.3 95.6 47.3 41.9 36.3

BET (m2/g) 855 550 611 626 716 742

A.D. (g/cc) .494 .595 .386 .593 .49 .507

AdsorptionPore

39% 32% 31% 37% 34% 35%

Transport Pore

23% 23% 39% 18% 29% 25%

Improvements to GAC Use @ SCWA

• 2014: – Began full-scale use of coconut GAC

– Began dividing up zones by contaminants present; not fixed geographic zones

• 2015:– Include TCN # for bituminous GAC in specs.?

– Leave I2 # for coconut GAC in specs.?

– Approval for use of Reactivated GAC?• Under Regulatory Review • Specifics: Pooled use required; WQ Sampling as per DOH• Potential 30% cost savings over virgin GAC

improving gac filter operations at scwa 8.1 improving gac.pdf · • transport pore structures –...

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