Reducing THM via Aeration: A Case Study August 28, 2014

Transcription

1 1 Reducing THM via Aeration: A Case Study August 28, 2014 by Gary Williams, P.E. Jones & Henry Engineers WEA-AWWA 2014 Technical Conference & Expo

2 Agenda 2 Location History Pilot Implementation Take Away Information

3 3 Location Map

4 Water Quality Raw Water Total Hardness 285 mg/l as CaCO 3 Total Alkalinity 133 mg/l as CaCO 3 ph 8.2 Turbidity 3.2 Total Organic Carbon 4.5 mg/l Finished Water Total Hardness 150 mg/l as CaCO 3 Total Alkalinity 36 mg/l as CaCO 3 ph 9.2 Total Organic Carbon (average) 2.1 mg/l TOC Removal (average) 51%

5 THM Total Trihalomethane & HAA5 2007/2008 Date of Sample Location Second MR002 HAA5 Sample Quarter 2007 Average RAA LRAA Average RAA 5/24/2007 RD RD MR Thrid Quarter /10/2007 RD RD MR Fourth Quarter /11/2007 RD RD MR First Quarter /16/2008 RD RD MR Second Quarter /2/2008 RD RD MR Third Quarter /8/2008 RD RD MR Fourth Quarter /9/2008 RD RD MR

6 Water History Water Treatment Plant, Low Head Dam, and Reservoir Constructed 1993 Water Treatment Plant Study 1996 Reservoir Study Water Treatment Plant Expansion $3,000, Second Reservoir $2,300, 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

7 THM Reduction via Aeration Opflow Article

8 Research 8 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 700 gpm = 28,000 cfm blower Approximately 200 hp Blower

9 Pilot 9 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 Aeration Cell Effluent Cell 60 minutes 75 minutes 60 minutes Scaled down the flows of air and water to match a 4-inch PVC pipe

10 10 Pilot

11 Test Pipe Arrangement 11 Pilot Air Requirements Air: Water Ratio Required (cfm) Total Air (cf) 2: : : :

12 Pilot Protocol 12 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

13 Pilot Results 13 Air: Water Air Rate Trihalomethane Results (ug/l) Ratio (scfm) October 14 November 11 Control N/A : : : N/A : : : : :

14 Pilot Results 14 Trihalomethanes (ug/l) Air to Water Ratio October 14 November 11

15 Other Pilot Results 15 Temperature October 16 deg C November 12 deg C Control Sample (no aeration) Initial 52.6 ug/l Finish 47.1 ug/l TTHM ph Initial 9.3 Aerated 7.9 Cl 2 Free mg/l Initial 2.13 Aerated 1.19 Cl 2 Total mg/l Initial 2.45 Aerated A:W ratio > 10:1 CHBrCl 2, CHBr 2 Cl, CHB 3 below Detectable Limit

16 Project Costs 16 Aeration System 5:1 A:W ratio 3,500 scfm Blower Stainless Steel Diffusors Caustic Soda Feed System to increase ph to 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

17 Brand X 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 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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19 Second Thoughts 19 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 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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21 Schedule 21 Bid October 2012 Preconstruction Meeting November 2012 Substantial Completion March 2013 Total Completion June 2013

22 TTHM Summary 22 (all values TTHM in ppb, except where noted) Sample Date Water Temp (deg C) Clearwell 1 Effluent Clearwell 2 Effluent DS202 (Max TTHM) % Removal In Clearwell #2 Regrowth in System 4/3/ % /6/ % /20/ % /17/ % /1/ % /13/ % /9/ % 32.1 Note: Baffle wall opening sealed on 4/12/2013

23 23 Maximum Residence Time Running Annual Average TTHM (ppb) HAA5 (ppb) First Second Third Fourth First Second Third Fourth First Second Third Fourth First Second Third

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25 Take Away Information THMs Have to be Formed Aeration Does Not Reduce Formation Potential 2. Chloroform is Typical Target THM 3. Powered Air Supply for Ventilation Probably Required 4. Check ph/stability 5. Check Chlorine Residual 6. Means for Cleaning Nozzles