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Strategies for Using Tank Aeration for

Stage 2 DBP Compliance

David S. Briley, P.E. – Hazen and Sawyer

Tiffanie Hawley – Cape Fear Public Utility Authority

Erik Rosenfeldt, Ph.D, P.E. – Hazen and Sawyer

Allison Reinert – Hazen and Sawyer

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Drivers for Tank Aeration

• Challenges of Stage 2 DBP Rule

• Shifts in compliance sites

• Increasing bromide levels in some water sources

• Cost-effective Stage 2 DBP Compliance options • Most options focus on removal of DBP precursors

• Limit DBP formation (i.e. chloramines)

• Aeration removes formed THMs

PAX TRS System Medora SolarBee

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Brominated DBP Challenges

0

50

100

150

200

250

300

350

400

0

20

40

60

80

100

Dec-02 Sep-05 Jun-08 Feb-11 Nov-13

Ra

w W

ate

r B

rom

ide

RA

A (

mg

/L)

Loca

tio

na

l R

un

nin

g A

nn

ua

l A

ve

rag

e (

pp

b)

Raw Bromide RAA

Echo THM LRAA

Crosswinds LRAA

Echo HAA LRAA

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Brominated DBP Challenges

� Bromide in Source Waters provide challenges for THMs

0

20

40

60

80

100

120

0 20 40 60 80

TT

HM

Co

nce

ntr

ati

on

(u

g/L

),

Ch

loro

form

(%

)

Time (h)TTHM, 100 ug/L Br- TTHM, 300 ug/L Br-

% Chloroform, 100 ug/L Br- % Chloroform, 300 ug/L Br-

Kinetics Mass

Chloroform (CHCl3): 119.4

Bromodichloromethane (CHCl2Br): 163.8

Dibromochloromethane (CHClBr2): 208.3

Bromoform (CHBr3): 252.7

CHBr3/CHCl3 = 2.1

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Several Approaches for Aeration

Q

CQ

Cin

QRP

C

youtyin

Air

Compressor

Diffusers

QinCin

QoutCout

yinyout

10 –

15’

Q

CQ

Cin

QRP

C

youtyin

Diffused Bubble Aeration

(air-in-water)

Fixed Spray Aeration

(water-in-air)

Floating Spray Aeration (water-in-air)

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Aeration – Henry’s Law

For Comparison,

� HAAs: 1.8 – 3.8 x 10-7

� HOCl: 0.05 – 0.06

� OCl-: 5.3 x 10-18

� NH2Cl: 0.008

� NHCl3: 8.6x10-6

CompoundHenry’s Law

Constant at 20oC

Chloroform 0.127

Bromodichloromethane 0.076

Dibromchloromethane 0.035

Bromoform 0.0175

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Aeration Techniques: Diffused Bubble

% T

HM

Rem

oval

Air to Water Ratio

Removal of THMs at Several

Air:Water Ratios

Adapted from: Brooke and Collins, JAWWA, 2011

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Aeration Techniques: Spray AerationP

erc

en

t T

HM

red

ucti

on

Apparent Air:Water Ratio

Reduction of DBPs with Spray Aeration

Adapted from: Brook and Collins, JAWWA 2011

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Holistic Approach to Aeration

1. Review of historical THM data to

establish reduction goals.

2. Assessment of THM formation kinetics

in the distribution system.

3. Evaluate where aeration is required

4. Establish design criteria through

aeration performance modeling

5. Evaluation of tank influence areas

using a calibrated distribution system

hydraulic model.

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Quarterly THM Results at Stage 2 SitesT

TH

Ms (

pp

b)

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TTHM Reduction Goals

LocationMax THM

LRAA (ppb)

THM Reduction To Achieve Goal

of 64 ppb (%)

B01 62 0%

B02 72 11%

B03 75 14%

B04 77 17%

B05 69 7%

B06 74 14%

B07 86 26%

� Goal of 80% of MCL on

LRAA basis

� Provides buffer for:

� Variable water quality

(DOC, bromide)

� Water demands and water

age

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Aeration Performance Modeling

� Impacting factors:

� Recycle rate

� No. and design of

nozzles or aerators

� Ventilation of head

space

� Distance from nozzle

to max water surface

� Hydraulic detention

time

� Temperature

� Process Modeling

� Establish design

criteria

� Assisted by Dr. Robin

Collins, Univ New

Hampshire

TT

HM

, p

pb

Time from Initial Conditions, hr

41%

33%

27%

18%

13%

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Where to Aerate?

� Clearwell Aeration

� Larger aeration system and higher capital and O&M costs

� Provides TTHM reduction for entire system

� Effectiveness depends on THM formation in WTP

� Tank Aeration in Distribution System

� Smaller aeration system and lower capital and O&M costs

� THM levels usually higher due to higher water age

� Provides TTHM reduction for a targeted area

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Prelim Spray Aeration Results (4 MG Clearwell)T

HM

S (

PP

B)

TIME (HOURS)

Based on 60% Recycle - ~25% THM reduction

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Assessment of Clearwell Aeration

� Sweeney WTP has two clearwells in series.

� Concept is allow THM formation in 12 MG clearwell and then

aerate in 4 MG clearwell

12 MG

Clearwell

4 MG

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Modeling of 4 Million Gallon Clearwell Aeration

� Aeration at the WTP could still result in some high THMs in

higher water age areas

LR

AA

(p

pb

)

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Water Age Simulation Water Age Simulation

� Water age is low

(3-4 days max in

most areas)

� 24 automatic

flushers in system

help reduce water

age in localized

areas

� Even with clearwell

aeration, predict

higher TTHMs in

higher water age

areas

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Tank Influences in Distribution System

� To assess aeration

performance in

elevated tanks, need

to understand

hydraulic patterns

� Used calibrated

hydraulic model to

determine influence

on each elevated tank

� Factored in tank

influence (i.e. how

much water in a

certain area went

through the tank)

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Tank Influences in Distribution System

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17th Street and Dawson Street Tank Aeration

Location of

Aeration System

(Tank)

Percent THM

Reduction at the Tank

Average Impact on

the Stage 2

Monitoring Location

(%)

Modeled Reduction

at Site with Tank

Aeration (%)

17th Street

Dawson Street

40%

40%

26% (BO7)

18% (BO4)

10.4% (BO7)

7.2% (BO4)

Example calculation for evaluating tank aeration

performance

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Combined 4 MG Clearwell and Tank Aeration

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Aeration System Optimization

� Plan to assess further evaluate TTHM formation and

reduction trends with aeration to assess seasonal

operation and scaling back

� CFPUA is collecting baseline data using an online THM

analyzer (Foundation Instruments)

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Preliminary Costs – Aeration System

Spray Aeration Capital Cost Annual O&M Costs

2 Elevated Storage Tanks $610,000 $30,000

4 MG Clearwell $2,100,000 $95,000

Total Aeration Cost $2,710,000 $125,000

• CFPUA is proceeding with spray aeration installation• Elevated tanks - Summer 2015• 4 MG clearwell – Fall 2015

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Summary

Multiple aspects should be considered

before installing mixing and/or aeration:

� Effectiveness for THM Reduction:

� Modeling of THM Reduction Available and

Helpful

� Consider speciation of TTHM in selecting

an aeration system

� Impact of WQ Improvement must be

considered

� At Stage 2 sites

� Area of influence

� Improvement possible?

� Must weigh localized treatment vs. full

treatment

� Cost implications and efficiencies

� Obligations for improved WQ to entire

system

� Both localize and full treatment?

� Remember: Only effective for THMs

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David S. Briley, P.E.

Hazen and Sawyer, P.C.

dbriley@hazenandsawyer.com

Questions???

www.hazenandsawyer.com

mailto:chopkins@hazenandsawyer.comhttp://www.hazenandsawyer.com/

Drivers for Tank AerationBrominated DBP ChallengesBrominated DBP ChallengesSeveral Approaches for AerationAeration – Henry’s LawAeration Techniques: Diffused BubbleAeration Techniques: Spray AerationHolistic Approach to AerationQuarterly THM Results at Stage 2 SitesTTHM Reduction GoalsAeration Performance ModelingWhere to Aerate?Prelim Spray Aeration Results (4 MG Clearwell)Assessment of Clearwell AerationModeling of 4 Million Gallon Clearwell AerationWater Age Simulation Tank Influences in Distribution SystemTank Influences in Distribution System17th Street and Dawson Street Tank AerationCombined 4 MG Clearwell and Tank AerationAeration System OptimizationPreliminary Costs – Aeration SystemSummaryQuestions???