Localized Control of DBPs

By Spray Stripping in

Storage Tanks

March 25, 2014

CA-NV AWWA Spring Conference

Anaheim, CA

Hal Reed, P.E.

American Water

Outline

1. Localized Control of DBPs

2. Spray Stripping of DBPs

3. Bench Scale Testing

4. Full Scale Testing

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3

1. Localized Control of DBPs

When only a small or localized area of

the distribution system will exceed the

Stage 2 DBPR LRAAs ....

Instead of treating all of the flow at the

plant, use “localized treatment” to reduce

DBPs in that area, and

Huntington WV installation saved

$13.0MM in CapEx and $1.8MM in OpEx!

4

Saved $13,000,000 over Centralized Treatment!

ITSS:

CapEx $27K

OpEx$4K

Localized Carbon Contactors:

CapEx $2.6MM

OpEx $205K per year

Centralized treatment:

CapEx $13MM

OpEx $1.8MM per year

ITSS at Huntington, WV (12 MGD)

Localized Control Strategies

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GAC absorption

Air Stripping

Surface aeration

Diffused bubble aeration

Packed tower or tray

aeration

Spray stripping

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“Localized Treatment for DBPs”

Water RF 91254 (2009) Technology TTHM Removal

Packed

towers and

tray aerators

•55-65% at A/W ratio of 30:1

•75-85% at A/W ratio of 45:1

•85-90% at A/W ratio of 75:1

GAC

•80% at 10 min EBCT through 10,000

bed volumes

•20% at 10 min EBCT at 20,000 bed

volumes

•After 20,000 bed volumes, chloroform

begins desorbing

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“Localized Control of DBPs by Spray

Aeration in Storage Tanks”

WaterRF 4413

2. Spray Stripping of DBPS

1. Bench scale testing of nozzles

2. Modeling of In Tank TTHM stripping &

Distribution System TTHMs

3. Full Scale Testing

4. Develop System Cost and O&M Guidance

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Schematic of ITSS System

Advantages of Spray Stripping

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“Simple” technology: pump, pipes, and

nozzles

Minimal O&M requirements

High DBP stripping efficiency

Low Life Cycle Cost

10

At a constant temperature, the amount of a given

gas that dissolves in a given type and volume of

liquid is directly proportional to the partial

pressure of that gas in equilibrium with that liquid.

Henry’s Law:

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Henry’s Law in action:

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Henry’s Law

kH = Caq/Cgas where:

kH - dimensionless Henry’s Constant

Caq - liquid phase concentration (mol/L)

Cgas - gas phase concentration (mol/L)

Note: applies to dilute aqueous solutions, like TTHMs in

drinking water.

William Henry,

1803

Henry’s Law Coefficients for TTHMs

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TTHM Species Henry’s Law Constant

(dimensionless, 20C)

Chloroform 0.127

Bromodichloromethane 0.076

Dibromochloromethane 0.035

Bromoform 0.006

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What does this tell us?

Only one thing: equilibrium concentration

THMs in water tanks are never at equilibrium

Air enters and leaves the tank with each fill and

drain

What controls DBP stripping rate for ITSS?

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Rate of Stripping/Mass Transfer

ITSS is “liquid

side limited”

Stripping rate is

controlled by liquid

phase diffusivity

94% of the

chloroform’s

resistance is in the

liquid phase

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Good News about Stripping

Brominated species strip too!

Liquid phase diffusivity of chloroform and

bromoform in water vary by only 4.5%

Maximize stripping efficiency by minimizing the

liquid diffusion path length

Small water drops are best (SA/V varies as 6/D)

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TTHM removal by Species (all nozzles, 10 psi, 3’ drop)

0%

10%

20%

30%

40%

50%

60%

CHLOROFORM BDCM DBCM BROMOFORM

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Three nozzle types: Full, hollow, fan

Three nozzle sizes: ¾”, 1”, 1-1/2”

Two spray angles: 90º and 120º

Two pressures: 10 & 30 psi

Three drop heights: 1, 2, and 3 feet

(108 combinations)

3. Bench Scale Testing

Spray Nozzles Tested

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Full cone

Hollow cone

Fan

Nozzle Manufacturer Information

Nozzle Manufacturer Information

Bench Scale Testing

800 gallon tank

Pump

Flowmeter

Sampling tap

and pressure

gage at nozzle

Tank heater with

recirculating

pump

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Flow meter

Spray

Aeration

Nozzle

Spray collection basin

Pump

Tank

Pressure gage

Throttling valve

Sample tap

Bench Scale Testing

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TTHM Removal (% at 3' height)

Nozzle type 10 psi Nozzle Pressure

Nozzle Size & Spray Angle

3/4" 1" 1-1/2"

90˚ 120˚ 90˚ 120˚ 90˚ 120˚

Full 45% 62% 29% 45% 35% 48%

Hollow 60% 56% 43% 42% 38% 48%

Fan 47% 47% 21% 33% 20% 20%

30 psi Nozzle Pressure

Full 54% 71% 49% 53% 57% 49%

Hollow 56% 60% 46% 49% 44% 56%

Fan 50% 49% 44% 48% 33% 40%

0%

10%

20%

30%

40%

50%

60%

90˚ 120˚

DBP removal

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TTHM Removal by Spray Angle

0%

10%

20%

30%

40%

50%

60%

Full Hollow Fan

DBP removal

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TTHM Removal by Nozzle Type

0%

10%

20%

30%

40%

50%

60%

3/4" 1" 1-1/2"

DBP removal

26

TTHM Removal by Nozzle Size

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0%

10%

20%

30%

40%

50%

60%

90˚ 120˚ 90˚ 120˚

10 psi 30 psi

TTHM removal by Spray Angle and Pressure

DBP removal

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0%

10%

20%

30%

40%

50%

60%

10 psi 30 psi 10 psi 30 psi 10 psi 30 psi

3/4" 1" 1-1/2"

DBP removal

TTHM removal by Nozzle Size

and Pressure

0%

10%

20%

30%

40%

50%

60%

10 psi 30 psi 10 psi 30 psi 10 psi 30 psi

Full Hollow Fan

DBP removal

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TTHM removal by Nozzle Type

and Pressure

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Is ITSS Appropriate for all systems?

Modeling Phase (EPANet and WaterGEMS®)

• In Tank TTHM stripping with FIFO, LIFO,

CSTR, and Two Compartment

• Resulting TTHM levels in distribution

system

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Spray Stripping Project

Modeling Phase

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4. Full Scale Testing

System constructed Fall 2012

Huntington, WV Greenbottom Tank

Testing Complete; May-Dec 2013

Thanks WVAW staff for their support

System Specifics Oversized tank

14 miles from 12 MGD plant

High water age

TTHMs at Stage 2 DBPR maximum residence time over 120 ug/L in the summer of 2012.

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Greenbottom Tank

Tank Details

300,000 gallons

40 ft high

Welded Steel

Interior and exterior recoated in the last 5 years

Problem: High water age water entering tank

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ITSS System ($27k) Nozzles: Two 1” full cone

Pumps: Two, 5 hp each with VFD

Flow and pressure to SCADA

Piping: 2” Schedule 80 PVC

Tank mounts: Magnetic

Flowrate: 67-116 gpm total

Tank Turnover: 1.8-3.2 days

Electrical Cost: $8.36 per day

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Greenbottom Tank

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Greenbottom Tank

Magnetic Mounts! Saves welding

& coatings repair

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Greenbottom Tank

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Greenbottom Tank

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Greenbottom Tank

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Greenbottom Tank

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Full Scale System Sampling

Monitor TTHM, HAA5, and chlorine for one

high TTHM season (June-October):

1. Point of Entry

2. Entering tank

3. Leaving tank

4. Maximum water age

WQ Sampling

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•Weekly at the POE, tank, and Stage 2

DBP site:

•TTHM,

•pH, temp, TOC, DO, and

•Disinfectant residual prior to

reaching the nozzles

•Weekly downloads of system operating

information including:

•Tank levels & System delivery

•Disinfectant residual and Water

temperature leaving the plant

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Does Chlorine Strip?

Cl2+ H2O ⇌ HOCl + HCl

HOCl ⇌ H+ +OCl-

Henry’s Law Coefficients

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Species Henry’s Law Constant

(dimensionless, 20C)

Chloroform 0.127

Bromodichloromethane 0.076

Dibromochloromethane 0.035

Bromoform 0.006

Hypochlorous acid 0.104

Hypochlorite ion 5.31 x 10-18

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Some chlorine may strip.

Depends on your pH!

No

stripping Limited

stripping

Limited

stripping

No

stripping

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Conclusion

ITSS Works. Proven at numerous installations.

All four TTHMs strip, even bromoform!

Little to no chlorine stripping, depends on pH.

Final report will help designers optimize

designs to minimize LCC.

Questions ?

Comments?

Ideas?

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Harold.Reed@amwater.com

856-727-6166

Thank you for attending.