SESSION 8 City of Phoenix Mixed Oxidant Trials for TTHM Reduction Brian Fayle City of Phoenix Over the past 23 years, Brian’s worked at every Phoenix operated water treatment plant. He’s currently the Process Control Specialist at the 24th Street and Deer Valley Water Treatment Plants. Contact Information: Email: [email protected]
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SESSION 8
City of Phoenix Mixed Oxidant Trials for TTHM Reduction
Brian Fayle
City of Phoenix Over the past 23 years, Brian’s worked at every Phoenix operated water treatment plant. He’s currently the Process Control Specialist at the 24th Street and Deer Valley Water Treatment Plants. Contact Information: Email: [email protected]
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City of PhoenixMixed Oxidant Trials for TTHM Reduction
Deer Valley WTPAugust - November 2011
Deer Valley & 24th Street WTP’sMay – December 2012
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Definition
Mixed Oxidants – Water treatment strategy of adding chlorine and chlorine dioxide in close proximity to each other, upstream of GAC filters, for the purpose of finished water TTHM reductions.
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Mixed Oxidants Overview
Mixed oxidants reduced finished water TTHM’s by 30 to 50% without additional steps to remove more TOC.Mixed oxidants increased the volatile percentage of the TTHM speciation.A 1:1 ratio of chlorine to chlorine dioxide is the ideal feed ratio.How long will mixed oxidants continue to reduce finished water TTHM’s? Is there an end in sight?
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Canal Raw WaterPumps
Pre-SedBasin
RapidMix
SandBallasted
Flocculation(SBF)
GACFilters
Reservoir #220 MG
Reservoir #120 MG
EPDS
Deer Valley Process SchematicPAC
Ferric Chloride
Sulfuric Acid
PolymerChlorine Dioxide
PAC
Chlorine Dioxide
Chlorine
Ferric Chloride
Chlorine Dioxide
Chlorine
SBF Polymer A-210P
Post SBF Ferric Chloride
Chlorine
FluorideCaustic
ChlorineChlorine
Caustic
Entry Point Dist. System
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#1 1 PPM Additional Cl2 Added Through the ClO2 Generator#2 1 PPM Additional Cl2 Added Through a Separate Chlorinator#3 .5 PPM Additional Cl2 is Not Enough
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5
10
15
20
25
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358/
16/1
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8/18
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8/24
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8/26
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8/28
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8/30
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9/1/
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9/19
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TTH
M's
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
ClO
2 & C
l 2 D
osag
e PP
M..
EPDSTTHM's
Pre-Sed Eff.ClO2Dose
Pre-Sed Eff.Cl2Dose
Pre-Sed Inf.Cl2Dose
#1 #2 #3
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Mixed Oxidants Produced Lower SBF Eff and EPDS TTHM’s versus Cl2By itself. Mixed Oxidants Upstream of GAC had a Beneficial Synergistic
Effect to Reduce Finished Water TTHM’s
0
5
10
15
20
25
30
358/
16/1
1
8/19
/11
8/22
/11
8/25
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8/28
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8/31
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9/3/
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9/6/
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9/9/
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9/12
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9/15
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9/18
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9/21
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TTHM
's
0.0
0.3
0.6
0.9
1.2
1.5
1.8
2.1
ClO
2 & C
l 2 Do
sage
PPM
..
EPDSTTHM's
SBF Eff.Total THM's
GAC Eff. TTHM's
Pre-Sed Eff.ClO2Dose
Pre-Sed Eff.Cl2Dose
Pre-Sed Inf.Cl2Dose
#1 #2 #3
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Exploring Other Scenarios…#1 Mixed Oxidants (M.O.) .5 PPM Additional Cl2 Not Enough#2 1.5 PPM Cl2 By Itself Partially Worked, But Had Consequences#3 M.O. ClO2 at Pre-Sed Inf and Cl2 at Pre-Sed Eff Partially Worked#4 M.O. ClO2 & Cl2 at Raw Water with Additional Cl2 at Pre-Sed Eff Worked
#1 #2 #3 #4
Baseline of .8 PPM ClO2
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9/13
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9/16
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9/25
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9/28
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10/1
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10/4
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10/7
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10/1
0/11
10/1
3/11
10/1
6/11
TTHM
's
0.0
0.3
0.6
0.9
1.2
1.5
1.8
2.1
2.4
ClO
2 & C
l 2 Do
sage
PPM
..
EPDSTTHM's
Pre-Sed Eff.ClO2Dose
Pre-Sed Eff.Cl2Dose
Pre-Sed Inf.Cl2Dose
Raw WaterClO2Dose
Raw WaterCl2Dose
#1 #2 #3 #4Baseline of .8 PPM ClO2
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Mixed Oxidant Versus Chlorine Dioxide Cycles With Corresponding EPDS TTHM's
GAC FiltersExhausted from aTOC RemovalPerspective at117 Average FilterRun Days
Increased Chlorine Dioxide Dose
Placed 2 RegeneratedFilters Online at atime
Early Sign of ChloriteRemoval Exhaustion at210 Average Filter RunDays
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Optimum Mixed Oxidant Dosages and Locations
Best THM Reductions If Dosed at the Same Location• Chlorine & Chlorine Dioxide Dosed at ≈ 1 to 1 Ratio
If Dosed at Different Locations• Chlorine dosed first, enough to carry a slight free
residual to the chlorine dioxide feed point still worked.
• However, chlorine dioxide dosed first only partially worked. The chlorine dioxide residual dissipated before the chlorine feed location.
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TTHM Reductions Using Mixed Oxidants Upstream of GAC Filters
• EPDS TTHM’s were reduced by 43% to 53% WITHOUT Additional Steps to Remove More TOC
• TTHM’s in the far reaches of the distribution system were reduced by 30%
• Mixed Oxidants altered the TTHM speciation to allow a greater percentage of the TTHM’s formed to be volatilized, which should also improve the THM reduction efficiency of aeration methods
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Cost Savings• Deer Valley’s GAC has continued to adsorb THM’s a
year after its been considered exhausted from a TOC removal perspective, which has allowed mixed oxidants to continue to reduce finished water TTHM’s.
• GAC Regeneration frequency can now be based on either a TOC exhaustion frequency or a THM exhaustion frequency.
• Deer Valley regenerated 6 GAC filters during their first year based on projected TOC removal exhaustion rates. Due to the overall THM reductions seen while using mixed oxidants, Deer Valley will only regenerate 4 filters this year, and the potential exists to reduce that further the following year.
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Deer Valley GAC Regeneration And Mixed Oxidants Costs per Year