1. Trihalomethanes Removal Evaluation
June 26, 2019

2. Introduction & Purpose
Background With the onset of EPA’s Stage 2 Disinfectants and Disinfection Byproducts Rule, the Town was proactive in investigating and implementing process modifications to enhance treatment efficiency and effectively reduce regulated DBPs.
Motivation Although the system is in compliance with the Stage 2 rule, the potential for exceedance still exists particularly of total trihalomethanes (TTHMs) during the summer.
Purpose The purpose of this work was to assist the Town to develop and evaluate alternative DBP control strategies and provide recommendations for an effective DBP control strategy.
1. The modifications worked since the data demonstrates that you are in compliance.
2. But at some locations the concentration are approaching the MCL particularly of total trihalomethanes (TTHMs) during the summer season when higher TOC levels and temperatures can drive their formation.
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3. How Do DBPs Form?
An unintended consequence of chemical disinfection is the formation of DBPs.
Free Chlorine (Cl2)
Dissolved Organics
(TOC)
Disinfection Byproducts
(DBP’s)
Temp Br
Time
Factors Contributing to Higher DBP Formation
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4. Types of DBPs
Trihalomethanes (TTHMs)
Types of TTHMs:
Chloroform
Dichlorobromomethane Dibromochloromethane
Bromoform
Maximum Contaminant Level: 80 μg/L
Haloacetic Acids (HAA5)
Types of HAAs:
Dichloroacetic Acid
Trichloroacetic Acid
Chloroacetic Acid
Bromoacetic Acid
Dibromoacetic Acid
Maximum Contaminant Level: 60 μg/L
Regulatory compliance is based on a locational running annual average (LRAA).
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5. DBP Control Strategies
Flushing
Modified Disinfection
Move Cl2 location
Reduce Cl2 dose and/or time
Use an alternative disinfectant
Remove DBP precursors (aka TOC)
Coagulation Optimization
GAC Adsorption
Biological Active Carbon (BAC)
Ozone-BAC
MIEX / Ion Exchange
Membranes
Remove DBP after formation
Aeration
Biofiltration
DBPs
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6. Treatment Requirement
Water Quality and Treatment Goals
Constituent
Goal Basis
Concentration Goal
Goal Achieved?
Treatment Requirement
TTHM
80% of MCL
64 µg/L No
40% to 50%
HAA5
48 µg/L
Yes
Goal Met
TOC
Meet DBP Goals
≤ 2.0 mg/L
50% to 65%
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7. Technologies Identified & Evaluated
Spray Aeration GAC/BAC Ozone BAC Ion Exchange
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8. Spray Aeration Treatment Integration
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9. Spray Aeration Treatment Overview
Two Key Considerations:
TTHM Speciation 1
TTHM Re-Formation 2
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10. TTHM Speciation
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11. Spray Aeration Treatment Example
80 µg/L THM Limit
TOTAL REGULATED DBPS (µg/L) 
TTHM Formation
WTP SITE BOUNDARY 
TTHM Formation
CUSTOMERS
DISINFECTION
CONTACT TIME (DAYS)
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12. Spray Aeration Treatment Example
80 µg/L THM Limit
TTHM Removal 
TOTAL REGULATED DBPS (µg/L)
WTP SITE BOUNDARY
CUSTOMERS
DISINFECTION
AERATION
CONTACT TIME (DAYS)
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13. Spray Aeration Treatment Example
80 µg/L THM Limit
TOTAL REGULATED DBPS (µg/L)
WTP SITE BOUNDARY
CUSTOMERS
DISINFECTION
AERATION
AERATION
CONTACT TIME (DAYS)
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14. GAC/BAC Treatment Integration
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15. GAC/BAC Treatment Overview
Two Key Considerations:
Empty Bed Contact Time 1
Carbon Change Out Frequency 2
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16. Biologically Active Carbon (BAC)
Absorption
Biological Removal F E C D B A
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17. Ozone-BAC Treatment Integration
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18. Ozone-BAC Treatment Overview
Two Key Considerations:
Empty Bed Contact Time 1
Biodegradable TOC Fraction 2
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19. Ion Exchange Treatment Integration
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20. Fixed Bed Ion Exchange Overview
Two Key Considerations:
Effectiveness 1
How Frequently Does it Have to be Regenerated 2
(1) How frequently do we have to regenerate it
(2)
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21. Treatment Performance
Water Quality/
Treatment
DBP Precursor (i.e. TOC) Removal
TTHM Reduction
Goal Achieved?
Spray Aeration
Does not Remove TOC
20% to 40%
Mostly
GAC
Adsorption
30% to 70%
Yes
BAC
25% Typical (5% to 60% Range)
8% to 50%
Possibly
Ozone-BAC
15% to 50%
Ion Exchange
30% to 60% ≈
Make this into a decision flow chart ≈
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22. Conceptual Cost Opinions
Alternative at 2 MGD Capacity
Construction Cost Opinion ($)
Unit Construction Cost Opinion ($/gal)
Relative Operating cost
Spray Aeration System within Clearwell
$770,000
$0.40/gal
Minimal
$$$$
Spray Aeration System within Bear Hill and Scituate Hill Tanks
$1,600,000
$0.80/gal
GAC/BAC Filtration
$2,000,000
$1.00/gal
Moderate
Ion Exchange
$3,900,000
$1.95/gal
Ozone-BAC
$5,800,000
$2.90/gal
Moderate/High
Based on cost curves, vendor based estimates, and experience with analogous systems.
15% Contractor Overhead & Profit, 7% General Requirements, mobilization and bonding
30% Construction Cost Contingency
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23. Recommendations Phase I: Spray Aeration Phase II: Organic Removal
Perform bench-top evaluation of spray aeration.
Installation of spray aeration within the clearwell.
Installation of additional spray aeration at the Bear Hill and Scituate Hill tanks or proceed with Phase II.
Phase II: Organic Removal
Installation of organic removal technology capable of removing 50%to 65% of the combined filtered water TOC levels.
Install a 1.5 to 2.0 MGD expandable to 3.0 MGD GAC or ion exchange technology.
GAC could be allowed to convert into biological mode during the higher quality winter/spring months.
If GAC/BAC is selected, the design could be phased to allow the subsequent installation of ozonation, if required at a later phase.
Decreased your organic removal capacity with integration of aeration with GAC
To reduce the operating cost of any of the phase II alternatives, you could operate the additional treatment seasonally.
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24. Q&A
June 26, 2019