Improving GAC Filter Operations
at SCWA
Joseph Roccaro
Suffolk County Water Authority
NYSAWWA Tifft Symposium
Sept. 18, 2014
GAC Pilot Phase 1 Results
1,1-DCA: Effect of Virgin GAC Type
1.6
1.4
1.2
C/C0
1.0
0.8
0.6
0.4
0.2
0.0
0
3,000
AC (EBCT = 11 min)
6,000
9,000
12,000
Bed Volumes
DC
L
15,000
CS
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.
Low Density, Soft,
World of Raw Materials for AC
Weakly Adsorbing
Vegetable Waste
Rice HullsCorn Cobs
Biomass
Fermentation Residues
Wood Chips and Sawdust
Pine
Oak
Walnut
Teak
Ebony
Pits, Stones, and Kernels
Cherry pits
Peach pits
Palm Kernels
Olive Stones
Nut Shells
Almond
Pecan
Walnut
Coconut Babassu
Coals – Coalification Series
Peat
Lignite
Bituminous
Anthracite
High Density, Hard,
Courtesy of Calgon Carbon Corp.
Strongly Adsorbing
Starting Materials Critical Properties
•
•
•
•
•
Ash level and constituents
Density
Hardness
Inherent Transport porosity (permeability)
Building Blocks for Adsorption Structure
Description of the Two Types of
Activated 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 Structure
Coal based carbon
Aliphatic dislocation of platelet
Graphite
Platelet
100 angstroms
Inter bounding
of plates
Adsorption
pores
40%
Skeleton
35%
Courtesy of Calgon Carbon Corp.
Transport
pores
25%
Carbon Molecular Structure
Coconut based Carbon
Aliphatic dislocation of platelet
Graphite
Platelet
100 angstroms
Inter bounding
of plates
Adsorption
pores
45%
Skeleton
40%
Courtesy of Calgon Carbon Corp.
Transport
pores
15%
Carbon Molecular Structure
Wood based Carbon
Aliphatic dislocation of platelet
Graphite
Platelet
100 angstroms
Inter bounding
of plates
Courtesy of Calgon Carbon Corp.
Skeleton
20%
Transport
pores
45%
Adsorption
pores
35%
Order of Attack on Molecular Structure
Aliphatic dislocation of platelet
3
4
1
2
1
2
2
2
5
4
4
2
4 2
5
3
1. Edge dislocations
5
5
4
4
4
5
3
3
100 angstroms
5
2. Edges of small plates
3. Internal plate dislocations
4
4
5
3
2
3
1
4
Graphite
Platelet
1
4
Inter bounding
of plates
Courtesy of Calgon Carbon Corp.
4. Edges of large plates
5. Edges inter bonded with
other plates
Molecular Structure of 0% Burn off Activated Carbon
Calcined CMS Carbon
Aliphatic dislocation of platelet
Graphite
Platelet
100 angstroms
Inter bounding
of plates
Courtesy of Calgon Carbon Corp.
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 Carbon
AFC-2204 Carbon
Aliphatic dislocation of platelet
Graphite
Platelet
100 angstroms
Inter bounding
of plates
Courtesy of Calgon Carbon Corp.
AD 0.64g/cc,
Iodine No. 600
Adsorption Pore
Volume 0.28 cc/g
Abrasion No. 90,
Ash 3.75%
Molecular Structure of 20% Burn off Activated Carbon
AFC-2204 Carbon
Aliphatic dislocation of platelet
Graphite
Platelet
100 angstroms
Inter bounding
of plates
Courtesy of Calgon Carbon Corp.
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 Carbon
F400 Carbon
Aliphatic dislocation of platelet
Graphite
Platelet
100 angstroms
Inter bounding
of plates
Courtesy of Calgon Carbon Corp.
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 Atom
Adsorbate
Molecule
Carbon Skeletal
Structure
The Adsorption force present at the adsorption site is the sum of all the
individual interactions between carbon atoms and the adsorbate
molecule.
(10,000,000 X Magnification)
Courtesy of Calgon Carbon Corp.
Relationship between Structure
and Adsorption Force
London Dispersion Force Field for One Graphite Plate
Butane Adsorbate Molecule
Graphite Plate of Carbon skeletal Structure
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
Courtesy of Calgon Carbon Corp.
Relationship between Structure
and Adsorption Force
London Dispersion Force Field for Two Graphite Plates
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
Butane Adsorbate Molecule
Graphite Plate of Carbon Skeletal Structure
Courtesy of Calgon Carbon Corp.
GAC Pilot Phase 1 Results
1,1-DCA: Effect of Virgin GAC Type
1.6
1.4
1.2
C/C0
1.0
0.8
0.6
0.4
0.2
0.0
0
3,000
AC (EBCT = 11 min)
6,000
9,000
12,000
Bed Volumes
DC
L
15,000
CS
1,1-DCA
H
H
H
C
C
Cl HCl
1,1 Dichloroethane
(1,1 DCA)
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 vessels
Assume GAC density = 30 #/ft3
40,000 # GAC ÷ 30 #/ft3 = 667 ft3 GAC
667 ft3 x 7.48 Gal / ft3 = 9973 Gal. = 1BV
BV 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
Down flow Adsorption column
Inlet
Outlet
Headspace
Saturated
Virgin
Mass
Transfer
Zone
Courtesy of Calgon Carbon Corp.
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
GAC Pilot Phase 1 Results
Contaminant Breakthrough Order
1.4
1.2
1.0
C/C0
0.8
0.6
0.4
0.2
0.0
0
5,000
10,000
15,000
20,000
Bed Volumes
1-4 dioxane
25,000
30,000
35,000
GAC Pilot Phase 1 Results
Contaminant Breakthrough Order
1.4
1.2
1.0
C/C0
0.8
0.6
0.4
0.2
0.0
0
5,000
10,000
15,000
20,000
25,000
Bed Volumes
1-4 dioxane
1,1-dichloroethane (1,1-DCA)
30,000
35,000
GAC Pilot Phase 1 Results
Contaminant Breakthrough Order
1.4
1.2
1.0
C/C0
0.8
0.6
0.4
0.2
0.0
0
5,000
10,000
15,000
20,000
25,000
30,000
Bed Volumes
1-4 dioxane
1,1-dichloroethane (1,1-DCA)
1,2 dichloroethane (1,2-DCA)
35,000
GAC Pilot Phase 1 Results
Contaminant Breakthrough Order
1.4
1.2
1.0
C/C0
0.8
0.6
0.4
0.2
0.0
0
5,000
10,000
15,000
20,000
25,000
30,000
Bed Volumes
1-4 dioxane
1,1-dichloroethane (1,1-DCA)
1,1,2-trichlorotrifluoroethane (TCTFA)
1,2 dichloroethane (1,2-DCA)
35,000
GAC Pilot Phase 1 Results
Contaminant Breakthrough Order
1.4
1.2
1.0
C/C0
0.8
0.6
0.4
0.2
0.0
0
5,000
10,000
15,000
20,000
25,000
30,000
35,000
Bed Volumes
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)
GAC Pilot Phase 1 Results
Contaminant Breakthrough Order
1.4
1.2
1.0
C/C0
0.8
0.6
0.4
0.2
0.0
0
5,000
10,000
15,000
20,000
25,000
30,000
35,000
Bed Volumes
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)
GAC Pilot Phase 1 Results
Contaminant Breakthrough Order
1.4
1.2
1.0
C/C0
0.8
0.6
0.4
0.2
0.0
0
5,000
10,000
15,000
20,000
25,000
30,000
Bed Volumes
1-4 dioxane
1,1-dichloroethane (1,1-DCA)
1,1,2-trichlorotrifluoroethane (TCTFA)
1,1,1-trichloroethane (1,1,1-TCA)
cis-1,2-dichloroethene (cis-1,2-DCE)
1,1-dichloroethene (1,1-DCE)
1,2 dichloroethane (1,2-DCA)
35,000
GAC Pilot Phase 1 Results
Contaminant Breakthrough Order
1.4
1.2
1.0
C/C0
0.8
0.6
0.4
0.2
0.0
0
5,000
10,000
15,000
20,000
25,000
30,000
Bed Volumes
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)
1,1-dichloroethene (1,1-DCE)
carbon tetrachloride (CT)
35,000
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
GAC Pilot Study - Phase 2
• 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
Coconut
#1
Coconut
#2
Coconut
#3
RBA
Coconut
#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 GAC
Phase 2 GAC Pilot
B.V.
Sb
As
Mo
Ni
Se
V
14
4.22
6.3
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
15.3
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
GAC Pilot Study - Phase 3
• 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
Vanadium Concentration
18
16
14
Vanadium (ug/l)
12
Reactivated GAC
10
AW reactivated GAC
8
6
Common Influent
4
2
0
0
20
40
60
Bed Volumes
80
100
120
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
Adsorption
Pore
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