in-reservoir tthm surface aeration · 2/2/2012  · treatment plant enhanced coagulation ... las...

Jeanne M. Jensen, P.E. Steve Acquafredda, P.E.

Jacobs Engineering Group, Inc.

February 2, 2012

In-Reservoir TTHM Surface Aeration: A year of results, experience and lessons learned

Presentation Outline

Introduction TTHM Surface Aeration Strategies Design and permitting considerations

Surface Aeration Full Scale Implementation Phoenix, AZ: 7.5hp aerator in a 2MG reservoir Mesa, AZ: 1hp aerator in a 0.25MG reservoir

Lessons Learned Conclusions

Regulatory Drivers

Drinking Water: Stage 2 DBPR MCL same as Stage 1 DBPR

○ 80 µg/L TTHM ○ 60 µg/L HAA5

Compliance based on Locational Running Annual Average (LRAA)

Monitor sites with highest DBP concentrations

Wastewater: THM discharge compliance Surface discharge limits Aquifer Protection Permits for groundwater

injection

DBP Control Options

Treatment Plant Enhanced Coagulation GAC Adsorption PAC Adsorption MIEX Process Advanced Oxidation River Bank Filtration Chloramination

Distribution System Reduce water age Blending with lower

TOC/DBP water Remote DBP control

GAC/BAC Aeration

DBP Control: Distribution Systems

Effective in isolated areas of high DBPs

WTP

Low DBP

High DBP

Implement Remote DBP Control

TTHM Aeration Strategies

THMs can be removed by air stripping

Efficiency depends on volatility (Henry’s Constant)

TTHM reformation after re-chlorination should be evaluated

Aeration does not remove HAAs THM Species Henry’s Constant (m3 atm mol-1, 20°C) Chloroform (3.0 ± 0.1) x 10-3

Bromodichloromethane (1.6 ± 0.2) x 10-3

Chlorodibromomethane (8.7 ± 0.2) x 10-4

Bromoform (4.3 ± 0.3) x 10-4

TTHM Aeration Strategies In-Reservoir Aeration Strategies

Bubble ● Spray ● Surface

External Aeration Strategies

Tray / Packed Tower

Spray / Bubble Vessel

Liqui-Cel Membrane Contactor

● ●

Design and Permitting Strategies

Identify contributing sources to TTHM-challenged sites

Apply aeration models (e.g. ASAPTM)

Determine “wire-to-water” or air-to-water ratio needed to achieve needed TTHM reduction

Compare available aeration strategies Consider local VOC air emission requirements

Early discussion with permitting agencies Novel application requires more interaction to inform

agency Can reduce re-submittals and clarification responses

TTHM Aeration Strategy Evaluation Tools

Aeration Modeling Aeration System Analysis

Program (ASAP) ○ Bubble, Surface, Packed Tower

Spray aeration calculations ○ Based on AWWA Water Quality Treatment Handbook

Tray tower TTHM reduction ○ Based on WaterRF Project No. 3103 Localized Treatment of

Disinfection By-Products, Las Vegas Valley Water District, South Central Connecticut Regional Water Authority, and City of Phoenix Water Services Department, 2009

ASAP

Applied Aeration Impact on Chlorine Residual

Predominant chlorine species in water around neutral pH are HOCl and OCl- Species are less volatile than Cl2

Literature and recent testing have mixed results Some show no chlorine residual loss Some show up to 40% chlorine residual loss

All aeration strategies should consider impact on chlorine residual

Aerator Batch Test Chlorine Residual Impacts

0

0.5

1

1.5

2

2.5

3

3.5

0 10 20 30 40 50 60

Aerator Run Hours

Chlo

rine

Resid

ual (

mg/

L)

Test conducted at end-of-line reservoir where chlorine demand had been previously met within

distribution system

Phoenix, AZ: 7.5-hp aerator in a 2 MG reservoir

Case Study: City of Phoenix, AZ Evaluation criteria: TTHM reduction, lifecycle

cost, constructability, ease of operation, impact on operation, required time out of service, mixing

Aeration methods evaluated Bubble, Spray, Surface, External Methods Surface aeration capital and O&M costs lower than

for other strategies (25% lower lifecycle cost) Non-cost surface aeration advantages ○ Capability to access and maintain equipment

without entering reservoir

Case Study: City of Phoenix, AZ

Distribution system downstream sample site

Surface aeration reservoir test site • Fills from Zone 2S • Drains to Zone 2S • Pump station to Zone 3S • Flow through reservoir varies throughout the day

Case Study: City of Phoenix, AZ

After start of aeration 23% avg. TTHM reduction achieved Model estimate of 29% reduction at 1.3 MGD

0

10

20

30

40

50

60

70

80

90

100

Jun-1 Jun-6 Jun-11 Jun-16 Jun-21 Jun-26 Jul-1 Jul-6

Conc

entra

tion

(µg/

L)

TTHMs Distribution SystemSample Site 0750HAAs Distribution SystemSample Site 0750

Before start of aeration

After start of aeration

Case Study: City of Phoenix, AZ

TOC was relatively constant over test period TTHM variability partially attributed to chlorine residual

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Jun-1 Jun-6 Jun-11 Jun-16 Jun-21 Jun-26 Jul-1 Jul-6

Conc

entra

tion

(mg/

L)

TOC Distribution SystemSample Site 0750"Cl2 Distribution SystemSample Site 0750"

Before start aeration

After start of aeration

Case Study: City of Phoenix, AZ

Comparing model estimates with test results Reservoir residence time fluctuated between

about 5 to 25 hours due to variations in: Water storage level Flow rate through reservoir

Extent of mixing Aerators float at water surface Reservoir inlet and outlet located near bottom

Variable air flow and turnover within headspace

Headspace Ventilation Air turnover dependent upon

Water storage level Air filter clogging ○ Design air flow rate: 700 scfm ○ Clean filter air flow rate: 1,055 scfm ○ Air flow rate after haboob 7/5/2011: 519 scfm ○ Air filter selection for protection & clogging prevention ○ Air supply fan with filter

Air Filter MERV Rating Controlled Particulate Size 1 to 4 > 10 µm

5 to 8 3 to 10 µm

9 to 12 1 to 3 µm

13 to 16 0.3 to 1 µm

17 to 20 < 0.3 µm Source: HPAC Engineering, February 2006

Further Study

Impact of variable flow rates, storage level, and residence time on TTHM reduction

Monitoring parameters to assess reservoir mixing (temperature, chlorine residual)

Optimization of filter selection

Mesa, AZ: 1-hp aerator in a 0.25 MG reservoir

Case Study: City of Mesa, AZ Target reservoir 40% TTHM reduction Aeration methods evaluated

Bubble, Spray, Surface Surface aeration capital and O&M costs lower than

for other strategies ○ Reduced maintenance for very remote facility ○ Achieved high TTHM reduction

1-hp aerator installed Sizing analysis indicated 0.5-hp aerator needed

400 scfm air supply

Approx. 78% of flow to be aerated in larger of 2 onsite reservoirs

Case Study: City of Mesa, AZ

0

20

40

60

80

100

1206/

14

6/16

6/20

6/22

6/24

6/28

6/30 7/

5

7/7

7/11

7/18

7/22

7/27 8/

1

8/5

8/10

8/22 9/

7

9/14

9/19

9/23

9/28

10/3

10/7

10/1

2

10/1

7

10/2

1

10/2

6

10/3

1

TTH

M (u

g/L)

HLR OOS Period Inlet TTHM HLR2 Top TTHM HLR2 Bottom TTHM

3249 N 91st St 4225 N Pinnacle Ridge Hydrant 214-16

Aeration Off

DBPR Compliance Site DBPR Compliance Site

Case Study: City of Mesa, AZ Test observations

Similar TTHM results for top and bottom of reservoir indicator of good mixing

Mesa has been able to optimize fill and drain times ○ Maximize aerator contact with water

Lessons Learned Access hatches

Material construction to avoid dissimilar metals Intrusion alarm Common Hatch? Dedicated Hatch? Size vs. Weight

Reservoir Modifications Coating condition Penetration placement Structural reinforcement Cathodic protection

Lessons Learned

Truck or Crane access Can access on-site with Davit Crane Boom truck arm distances limited

Maintenance Schedule Semi-annual inspection & greasing Wear bars

Fresh Air Supply Filtered – MCESD Standard Haboobs!

Conclusions & Further Evaluation

Surface Aeration is an effective TTHM reduction approach Site specific technology evaluation

recommended Further Evaluation

Extent of mixing Refine model estimates for dynamic

reservoir flow conditions Optimization of air filter size for protection

and minimal plugging

Acknowledgements

We would like to thank our teaming partners for their important contributions to this work! City of Phoenix, AZ City of Mesa, AZ City of Scottsdale, AZ City of Tempe, AZ Aqua-Aerobic Systems, Inc.

Questions

Jeanne M. Jensen, P.E. Phone: (602) 345-1012 Jeanne.Jensen@Jacobs.com

Steve Acquafredda, P.E. Phone: (602) 650-4007 Sacqua@Jacobs.com

Chad Seidel, Ph.D., P.E. Phone: (303) 820-4846 Chad.Seidel@Jacobs.com