in-reservoir tthm surface aeration · 2/2/2012 · treatment plant enhanced coagulation ... las...
TRANSCRIPT
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 [email protected]
Steve Acquafredda, P.E. Phone: (602) 650-4007 [email protected]
Chad Seidel, Ph.D., P.E. Phone: (303) 820-4846 [email protected]