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Reducing THM via Aeration: A Case StudyAugust 28, 2014
by Gary Williams, P.E.Jones & Henry Engineers
WEA-AWWA 2014 Technical Conference & Expo
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Agenda
Location History Pilot Implementation Take Away Information
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Location Map3
Water Quality 2008
Raw WaterTotal Hardness 285 mg/L as CaCO3
Total Alkalinity 133 mg/L as CaCO3
pH 8.2Turbidity 3.2Total Organic Carbon 4.5 mg/LFinished WaterTotal Hardness 150 mg/L as CaCO3
Total Alkalinity 36 mg/L as CaCO3
pH 9.2Total Organic Carbon (average) 2.1 mg/LTOC Removal (average) 51%
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THM 2008
Date of Sample
Sample Location Second Quarter 2007 Average RAA
MR002 LRAA
HAA5Average RAA
5/24/2007 RD002 38.9 13.4RD003 40.8 14.4MR002 50.2 43.3 47.8 59.3 11.8 13.2 17.8
7/10/2007 RD002 82.3 16.6RD003 85.3 15.2MR002 102.0 89.9 50.4 60.6 16.7 16.2 14.4
10/11/2007 RD002 54.1 17.3RD003 58.3 16.4MR002 81.7 64.7 58.1 69.3 22.0 18.6 15.9
1/16/2008 RD002 40.6 19.3RD003 40.7 20.8MR002 54.9 45.4 60.8 72.2 20.4 20.2 17.0
4/2/2008 RD002 40.5 13.6RD003 40.6 13.1MR002 60.3 47.1 61.8 74.7 14.2 13.6 17.1
7/8/2008 RD002 85.1 33.1RD003 85.3 32.1MR002 131.0 100.5 64.4 82.0 34.7 33.3 21.4
10/9/2008 RD002 52.0 28.8RD003 55.7 28.8MR002 80.6 62.8 63.9 81.7 33.3 30.3 24.4
Fourth Quarter 2008
Total Trihalomethane & HAA5 2007/2008
Thrid Quarter 2007
Fourth Quarter 2007
First Quarter 2008
Second Quarter 2008
Third Quarter 2008
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Water History
1972 Water Treatment Plant, Low Head Dam, and Reservoir Constructed
1993 Water Treatment Plant Study 1996 Reservoir Study 1999-2000 Water Treatment Plant Expansion $3,000,000 2002 Second Reservoir $2,300,000 2004 Water Distribution System DBP Reduction Study 2005 Chlorine Dioxide Benchtop Study 2005 MIEX Benchtop Study 2006 RSSCT for GAC Benchtop Study 2008 THM Reduction via Aeration Opflow Article
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2008 THM Reduction via Aeration OpflowArticle
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Research
Limited Research Available for Dynamic System One Company Marketed a System $$$$$$$$ Air : Water Ratios (cfm : gpm) 5 to 60 If A:W = 40 and processing water @ 700 gpm =
28,000 cfm blower Approximately 200 hp Blower
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Pilot
Assumed 20:1 A:W ratio or 14,000 cfm Determined Approximate Area Diffusors for 14,000 cfm in
Clearwell 2 Assumed One/half Depth of Clearwell or 7 feet Calculated the Volume over the Diffusors Developed the Detention Times in the Three Celled
Clearwell Influent Cell 60 minutes Aeration Cell 75 minutes Effluent Cell 60 minutes
Scaled down the flows of air and water to match a 4-inch PVC pipe
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Pilot10
Test Pipe Arrangement
Pilot Air Requirements
Air: Water Ratio Required (cfm) Total Air (cf)
2:1 0.1 9.5
5:1 0.25 23.8
10:1 0.5 47.5
20:1 1.0 95
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Pilot Protocol
Two Pilot Steps First Step Test Entire
A:W Range Second Step Optimize
Results of the First Step Goal was to Optimize
Air Required
Parameters Tested TOC THM HAA5 Chlorine Residual Stability pH Total Alkalinity Total Hardness Calcium Hardness TDS Chlorides Sulphates
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Pilot Results
Air: Water Air RateTrihalomethane Results
(ug/L)Ratio (scfm) October 14 November 11
Control N/A 47.1 38.02:1 0.10 16.9 16.75:1 0.25 5.7 9.07:1 0.35 N/A 6.710:1 0.50 2.1 5.720:1 1.00 2.730:1 1.50 2.640:1 2.00 3.050:1 2.50 2.1
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Pilot Results
0.05.0
10.015.020.025.030.035.040.045.050.0
0 5 10 15 20 25 30 35 40 45 50 55
Trih
alom
etha
nes (
ug/L
)
Air to Water Ratio
October 14November 11
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Other Pilot Results
Temperature October 16 deg C November 12 deg CControl Sample (no aeration) TTHM
Initial – 52.6 ug/L Finish – 47.1 ug/L
pH Initial – 9.3 Aerated – 7.9Cl2 Free mg/L Initial – 2.13 Aerated – 1.19Cl2 Total mg/L Initial – 2.45 Aerated – 1.96@ A:W ratio > 10:1 CHBrCl2, CHBr2Cl, CHB3 below Detectable Limit
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Project Costs
Aeration System 5:1 A:W ratio 3,500 scfm Blower Stainless Steel Diffusors Caustic Soda Feed System to increase pH to 8.9 12-inch Air Piping to Clearwell Diffusors Electric and Controls
Project Cost - $401,700 Annual O&M - $73,000
GAC System Project Cost - $1,225,600 Annual O&M - $145,000
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Brand X 2011 SolarBee Aeration System Proposal
Two 15 HP Blowers 580 scfm Each Three Submersible Mixers 86 Diffusor Assemblies Caustic Soda Feed System to increase pH to 8.9 8-inch Air Piping to Clearwell Diffusors Electric and Controls
Project Cost - $571,700 Annual O&M - $21,000
SolarBee Offer Install Clearwell Equipment Provide Temporary Blower and Piping 6-month Trial If Satisfied, Purchase Price $360,000
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Second Thoughts April 1, 2012 SolarBee Oops
Further Testing Showed Spray Aeration Preferable Highly Recommended Spray System
One GS-12 Submersible Mixer in Clearwell 1 Two SN-15 Floating 15 HP Pump/Mixer/Spray Systems Two Ventilation 2HP Blowers 750 scfm Each Caustic Soda Feed System to increase pH to 8.9 12-inch Air Piping to Clearwell Electric and Controls
Project Cost - $369,900 Annual O&M - $22,000
SolarBee Offer Provide In-Clearwell Equipment and Two Blowers Install Clearwell Equipment 6-month Trial If Satisfied, Purchase Price $168,000
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Schedule
Bid – October 2012 Preconstruction Meeting – November 2012 Substantial Completion – March 2013 Total Completion – June 2013
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TTHM Summary22
Sample Date
Water Temp (deg C)
Clearwell 1 Effluent
Clearwell 2 Effluent
DS202 (Max TTHM)
% Removal In Clearwell #2
Regrowth in System
4/3/2013 7 29.6 18.4 31.8 38% 13.4
5/6/2013 15 47.2 20.4 43.4 57% 23.0
5/20/2013 18 56.2 24.8 64.7 56% 39.9
6/17/2013 22 62.7 21.2 62.3 66% 41.1
7/1/2013 24 63.2 30.7 64.7 51% 34.0
8/13/2013 23 53.3 20.3 52.1 62% 31.8
9/9/2013 20 56.0 20.5 52.6 63% 32.1
Note: Baffle wall opening sealed on 4/12/2013
(all values TTHM in ppb, except where noted)
Maximum Residence Time Running Annual Average
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0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0
90.0
100.0
First Second Third Fourth First Second Third Fourth First Second Third Fourth First Second Third
2011 2012 2013 2014
TTHM (ppb)
HAA5 (ppb)
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Take Away Information
1. THMs Have to be Formed Aeration Does Not Reduce Formation Potential
2. Chloroform is Typical Target THM3. Powered Air Supply for Ventilation Probably
Required4. Check pH/Stability5. Check Chlorine Residual6. Means for Cleaning Nozzles
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