Reduction of THMs Within Storage Tanks Using Aeration

Transcription

1 Reduction of THMs Within Storage Tanks Using Aeration May 9, 2014 Elizabeth A. Hirschhorn, P.E. PAX Water Technologies, Inc. Randy Moore Utility Service Group

2 Goals for today: Review DBPs, THMs and conventional approaches Explain the science of in tank aeration Review latest case studies Explain when in tank aeration is best at the clearwell versus in the distribution system Q&A

3 Typical Approach to DBP reduction Lower the organic matter in raw water GAC, Miex, Filtration, RO (get the organics OUT!) Improve raw water source (new source?) Reduce the chemistry of disinfection Change primary disinfection (ozone, UV, etc.) Change secondary disinfection (chloramines) Problem: All these options are VERY expensive! (big changes to your water system)

4 Have you heard of In-tank Aeration?

5 Aeration to remove THMs is not new Aeration has been PROVEN to work

6 Post-treatment Aeration can reduce THMs Deal with THMs where they are highest in your system

7 Different In-tank Aeration Technologies for different applications Bubble aeration Surface aeration Spray aeration Any of these technologies can be made to work but capital and energy costs vary greatly

8 What is the TRS? TRS = Trihalomethane Removal System Partnership between PAX and Utility Service Group A portfolio of technologies: Spray nozzles, Mixers, Surface Aerators, Ventilation and future tools (Hardware) Design software, Computer models (Software) Experience, databases, engineering (Know how) An integrated approach to THM reduction TRS factors in operational choices and their effects on THM levels TRS is a fully engineered, fully installed solution customized to EACH tank, with a performance guarantee

9 How did we develop the TRS? 2 years spent analyzing published and unpublished case studies on aeration for THM reduction 1.5 years spent measuring mass transfer coefficients for specific aeration technologies (lab and field studies) Optimized spray nozzle designs Trials (and tribulations!) KL / KL_REF Van't Hoff equation Diffusivity & Viscosity (n=0.5) Temperature [C]

10 Spray Aeration: Droplet Size Dependent Spraying efficiency (X)

11 Tank Hydraulics and Fill Cycles Tank remained stratified Time

12 NEPTUNE Toolbox We can provide analytical support to evaluate and optimize the aeration designs of others, and we can design for new and existing tanks

13 TRS Case Studies

14 Ryan Ranch tank (Monterey, CA) 0.5MG, 72 dia., 16 h end of line, low turnover Max 50 µg/l THM levels outside Ryan Ranch Ryan Ranch THM levels average 140 µg/l in tank Estimate w/o intervention: 140 µg/l To avoid violation (RAA < 80 µg/l), sample needs to be around 50 µg/l in Q Low Cl periodic dosing onsite Others proposed sprayer aeration system ($350K) Limited power at tank site

15 Historic TTHMs Ryan Ranch Tank TTHMs Jul 10 5 Aug Aug 10

16 The TRS goals and design Goals Lower Cl demand Eliminate stratification Clean tank Remove THMs Aeration Goal: 60% reduction Use as little power as possible Design Wash out Chemical clean 1 PWM 400 mixer 1 PAX PowerVent fan

17 Design for Ryan Ranch TRS

18 TRS installation: Chemical cleaning

19 TRS Installation: Interior coatings repair

20 TRS Installation: PAX PowerVent TM Installation

21 TRS Installation: Mixer Installation

22 Initial results of Q3 compliance test Post-TRS Q3 Sample result = 49.2 µg/l RAA = 79.3 µg/l

23 /29/10 8/10/11 8/5/10 8/30/10 12/9/10 6/28/11 6/29/11 7/1/11 7/6/11 7/14/11 7/15/11 8/2/11 8/3/11 8/23/11 No TRS With TRS Turned TRS on: June 22 Switch to Ryan Ranch water

24 Avg = Avg = Avg =

25 Upper Ragsdale (Compliance point)

26 Quarterly TTHMs Harris Court (dead end)

27 Case Study: Ryan Ranch tank Source Magazine (CA/NV AWWA Magazine) Winter, 2014 (V. 27, no. 1) p

28 Is it better to address THMs in clearwell or in distribution system tanks? Depends: Rate of THM formation potential Physical limitations (available headspace in tank)

29 THMs grow with time but not steadily Cl introduced here Clearwell Filters Dist. system THMs (ppb) Fast formation 90 ppb 130 ppb Slow formation time

30 Water enters clearwell Water leaves clearwell w/o TRS THMs (ppb) 60 ppb 90 ppb 130 ppb w/ TRS THMs (ppb) 60 ppb 50 ppb 90 ppb

31 Water enters clearwell THMs (ppb) Water leaves clearwell Fast rxn >> slow rxn Aerate in clearwell THMs (ppb) Fast rxn < slow rxn Aerate in tanks

32 Case Study: Madison, NC - Clearwell

33 TRS sprayer manifold mounted in clearwell

34 PAX Mixer in Clearwell

35 Clearwell after TRS installation

36 Parker Hannifin THM Analyzer 30-minute species-specific analysis Portable, easy to use Requires UHP grade helium

37 Madison, NC Clearwell: TTHMs (ppb) versus time /11/13 5/10/13 5/9/13 5/8/13 5/7/13 5/6/13 5/5/13 5/4/13 5/3/13 5/2/13 5/1/13 4/30/13 4/29/13 4/28/13 4/27/13 4/26/13 4/25/13 4/24/13 4/23/13 4/22/13 4/21/13 4/20/13 4/19/13 4/18/13 4/17/13 4/16/13 Data collected by Madison staff using Parker Hannifin THM Analyzer TRS off TRS on

38 Madison, NC Clearwell: Recorded TTHM Data Periods of equilibration (~ 1 2 days) /11/13 5/10/13 5/9/13 5/8/13 5/7/13 5/6/13 5/5/13 5/4/13 5/3/13 5/2/13 5/1/13 4/30/13 4/29/13 4/28/13 4/27/13 4/26/13 4/25/13 4/24/13 4/23/13 4/22/13 4/21/13 4/20/13 4/19/13 4/18/13 4/17/13 4/16/13

39 Madison, NC Clearwell TRS: Roughly 50% THM removal TRS off 50 ppb TRS on 25 ppb 5/11/13 5/10/13 5/9/13 5/8/13 5/7/13 5/6/13 5/5/13 5/4/13 5/3/13 5/2/13 5/1/13 4/30/13 4/29/13 4/28/13 4/27/13 4/26/13 4/25/13 4/24/13 4/23/13 4/22/13 4/21/13 4/20/13 4/19/13 4/18/13 4/17/13 4/16/13

40 Madison, NC elevated tank

41 Inlet Outlet THM reduction post-trs /23/13 3/18/13 2/27/13 2/20/13 2/14/13 2/11/13 2/3/13 1/28/13 1/22/13 1/13/13 1/7/13 1/2/13 Average = 55% reduction

42 Unlike bubble aeration systems (and surface aeration?) spray aeration removes ALL THM species at nearly the same rate 120% 100% 80% 60% 40% 20% 0% 56% average 63% average 50% average 40% average Chloroform Bromodichloro Dibromo Bromoform 1/2/13 1/7/13 1/13/13 1/22/2013 1/29/2013 2/4/2013 2/12/2013 2/15/2013 2/21/2013 2/28/2013 3/19/2013 3/23/2013

43 How do we assure TRS remains on and functional? Wireless, remote monitoring system Inlet and Outlet pressure Flow Current to all subsystems Alerts sent to PAX and customer

44 Other Technology vs. Spray Aeration (XX County, VA) Power (hp) Bubbler system Bubble aeration is NOT good practice for THM removal PAX designs (TRS) 20% 25% 30% 35% 40% 45% 50% 55% 60% TTHM removal (%)

45 Evaluate Aeration Technologies on Energy Efficiency per MGD Treated 35 less energy efficient more energy efficient Power used (HP) more energy efficient MGD of Water Treated to 50% TTHM Removal

46 Effects of aeration on water chemistry What would you expect? Aeration removes Cl (?) Residual Cl should drop Aeration removes CO 2 ph should rise

47 Chlorine loss? Depends on ph HOCl is volatile: dominant ph < 7 OCl - is an ion and non-volatile: dominant ph > 7 Chlorine loss low at ph > 7

48 Aeration, THMs and water chemistry 1 MG concrete tank Split into two identical cells AMS-100 On-line THM analyzer Collaborators: Ramon Ariño Tarrago Oriol Mas Alcazar

49 Inlet THMs 49

50 Outlet THMs: no aeration 50

51 Outlet THMs: aeration vs. no aeration 50% removal 51

52 Results from AMS 100 from Aqua Metrology

53 ph and Free Chlorine no aeration 53

54 ph and Free Chlorine aeration vs. no aeration ph rises by 0.3 log units Free Cl drops by ~ 10% 54

55 How do the sub-components of the TRS contribute to overall THM reduction? 70% 60% 50% 40% 30% % removal 20% 10% 0% Sprayer + Powervent + Mixer Sprayer + Powervent + Mixer Mixer + PowerVent Aigües de Barcelona Department of Water Quality

56 Summary of today s presentation In tank aeration (TRS) is a safe and effective means of lowering THM levels in finished water But NOT a silver bullet!!! Different aeration technologies vary in their effectiveness and energy usage Calculate energy consumption per MGD treated The PAX Mixer + active ventilation alone can significantly reduce THM levels

57 Some final thoughts: Stage 2 D/DBP Rule is a burden and an opportunity Opportunity to look holistically at your distribution system Opportunity to fix some things for the LONG TERM Everything matters Quality of your source water Condition of your pipes Condition of your tanks Mixing, water age, etc. etc. Optimization is the key Use Stage 2 Rule compliance as an opportunity to step up your game in overall water quality and water consistency

58 Questions? Want to learn more? Visit us at AWWA Annual Conference Boston, June 9 12 Upcoming PAX webinars: Mixing, Aeration, Active Residual Control in the Distribution System Questions/comments contact one of us: Peter Fiske: pfiske@paxwater.com or Liz Hirschhorn: lhirschhorn@paxwater.com or Randy Moore: rmoore@utilityservice.com Interest in examining whether TRS is suitable for your system? contact Ethan Brooke: ebrooke@paxwater.com Review our case studies and articles and other references at: or Thank You!