Lowering THMs in Your Distribution System Using In-Tank Aeration

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1 Lowering in Your Distribution System Using In-Tank Aeration August 5, 2015 Dr. Peter S. Fiske PAX Water Technologies, Inc. 1

2012 slides on DBPs, their precursors and

2 Some great resources McGuire et al., August page JAWWA article summarizing the history and current best practices for addressing DBPs Marvin Gnagy s 2012 slides on DBPs, their precursors and formation, and treatment options Google Search: Gnagy Formation and Control of 2

3 in the Distribution System (Trihalomethanes) most common regulated DBP (Disinfection By-Product) Formed from the reaction between natural organic matter in your raw water and Cl disinfectant Function of raw water quality (TOC, Bromide) Function of Cl concentration Function of water age Oldest water = highest

4 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?) Change 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

5 What is post-treatment aeration or air stripping? Exposing water to air Volatile chemicals in the water evaporate into the air

6 Advantages of post-treatment aeration Deal with where they are highest Lower cost than systemic changes Much quicker solution [regulatory compliance] Some added water quality benefits (mixing, lowered VOCs, lowered CO 2, lowered H 2 S ) Key Point: Post-treatment aeration can LOWER cost of other system-wide treatment changes 6

7 Key Benefit: In-tank aeration can lower treatment plant operating costs Lowers peak THM levels at highest points in the distribution system Lowers peak capacity requirements at treatment plant Reduces the frequency of GAC media replacement Takes some of the load off treatment plant Can be applied only when are highest Cut energy cost Treatment plant lift Distribution system lift 1 Ton 7

8 Aeration to remove is not new Aeration has been PROVEN to work 8

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

10 There is also Packed Tower Aeration Not an in-tank aeration system Requires it s own tank Few reported applications of PTA for Probably high capital and energy costs 10

11 Aeration - starts with evaporation

12 At equilibrium, a ratio in THM concentration between the air and the water That ratio is the Henry s Law constant

13 Henry s Law constants for THM species Henry's law 20 C Chloroform 0.13 Bromodichloromethane 0.08 Chlorodibromomethane 0.04 Bromoform 0.02 Chloroform is the most volatile (easiest to remove) Bromoform is the least volatile (hardest to remove) 13

14 Some aeration happens all by itself Diffusional barrier Poor mixing prevents below the surface from escaping Evaporation stops

15 Mixing enhances aeration But you need STRONG mixing

16 Bubble aeration How it works Pop! Air injected here

18 Pop! Bubbles pull out of the water and deliver them to the surface

19 Power (hp) Bubbler versus PAX TRS (XX County, VA) Bubbler system Bubble aeration 50 for THM removal is NOT good practice for THM removal steer utilities elsewhere PAX designs (TRS) 20% 25% 30% 35% 40% 45% 50% 55% 60% TTHM removal (%)

20 Surface Aeration 20

21 Advantages of Surface Aeration More energy efficient than bubblers Do not have to drain the tank to install Low profile (works with tight headspace) Good choice when water level is not changing 21

22 Disadvantages of Surface Aerators Less energy efficient than spray aeration Removal efficiency for bromoform is unknown Some systems have ejector nozzle with thousands of small holes Clogging/maintenance concerns Requires guide rails in tanks where water level changes 22

23 Spray aeration Pump

24 Evaporation from droplets

25 Advantages of spray aeration Energy efficient Mechanical equipment outside tank Easy install

26 Bubble aeration = chemical equilibrium Rate of removal is controlled by Henry s Law CHCl 3 Henry s Law constant = 7x CHBr 3 CHCl CHCl 3 CHCl CHBr 3 CHCl CHCl CHCl CHCl CHCl3 CHCl3 CHBr CHCl 3 3 CHCl CHCl 3 3 CHCl 3 CHCl3 CHCl3 CHCl3 CHCl CHCl 3 CHCl 3 3 CHCl 3 CHCl3 CHBr 3 CHBr3 CHBr CHCl 3 3 CHCl 3 CHCl CHCl 3 CHCl 3 CHCl 3 CHCl 3 CHCl3 3 CHCl CHCl 3 3 CHCl CHCl CHCl CHCl3 CHBr CHCl 3 CHBr 3 CHCl 3 CHCl 3 CHCl 3 3 CHCl 3 CHCl CHCl CHBr 3 3 CHCl 3 CHBr CHCl CHBr CHCl 3 3 CHCl 3 CHCl 3 CHCl 3 CHCl 3 CHCl CHCl3 3 CHCl3 CHCl 3 CHCl 3 CHCl 3 CHCl3 CHCl 3 CHBr 3 CHCl 3 CHBr 3 CHCl 3 CHBr 3 CHCl 3 CHCl 3

27 Chloroform is preferentially stripped Bromoform left behind Bubble aeration is very inefficient for bromoform CHCl CHCl 3 CHCl CHBr 3 CHCl CHCl CHCl CHCl CHCl3 CHCl3 CHBr CHCl 3 3 CHCl CHCl CHCl CHCl3 CHCl3 CHCl3 CHCl CHCl 3 CHCl 3 3 CHCl 3 CHCl3 CHBr 3 CHBr3 CHCl 3 CHCl CHCl 3 3 CHCl 3 CHCl3 CHCl 3 CHCl CHCl 3 3 CHCl3 CHBr CHCl 3 CHBr 3 CHCl 3 3 CHCl CHCl 3 3 CHCl 3 CHCl CHCl CHBr 3 3 CHCl 3 CHBr CHCl CHCl 3 CHCl 3 CHCl 3 CHCl 3 CHCl CHCl 3 3 CHCl CHCl 3 3 CHBr 3 CHCl 3 CHBr CHCl 3 3 CHBr 3 CHCl 3 CHCl 3

28 Droplets in air no equilibrium established Only difference in removal rates is due to differences in liquid-side diffusivity CHBr 3 CHCl 3 CHCl 3 CHBr 3 CHBr 3 CHCl 3

29 % reduction by species TRS 120% 78% average 80% average 70% average 54% average 100% 1/2/13 80% 1/7/13 1/13/13 60% 40% 20% 0% Chloroform Bromodichloro- Dibromo- Bromoform 29

30 Disadvantages of spray aeration Very hard to predict results Need quantitative models for spray and splash Need full-scale experiments

5 years spent measuring mass transfer coefficients for specific aeration technologies (lab and field

31 KL / KL_REF 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!) Van't Hoff equation Diffusivity & Viscosity (n=0.5) Temperature [C]

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

33 NEPTUNE Toolbox We can provide analytical support to evaluate and optimize the aeration designs of others, and we can design for new tanks 33

34 Energy comparison between other spray aeration technologies and PAX TRS Case study 1: Technology 1 (Ohio clearwell 0.3 MG) Equipment: Two 15 hp spray aerators + 2 HP fans Daily turnover: 475,000 GPD Energy used: 32 hp THM removal measured: 55% Case study 2: PAX (Maryland storage tank 8.0 MG) Equipment: Two 7.5 hp pumps, PAX nozzles, one PAX mixer, one PAX PowerVent Daily turnover: 775,000 GPD Energy used: 18 hp THM removal measured: 53% Case study 3: PAX (North Carolina clearwell 0.5 MG) Equipment: One 15 hp pump, PAX nozzles, one PAX mixer, one PAX PowerVent Daily turnover: 750,000 GPD Energy used: 17 hp THM removal measured: 50% 34

35 Power used (HP) less energy efficient Technology 1 more energy efficient more energy efficient PAX TRS MGD of Water Treated to 50% TTHM Removal 35

36 20 Year Electrical Cost of Three THM Removal Installations $600,000 $500,000 $526,310 $400,000 $300,000 $308,933 $313,803 $200,000 $100,000 $0 Installation Technology 1 - Ohio PAX TRS - Maryland PAX TRS - NC Medora SN15 North Baltimore, OH PAX 40 Series Rockville MD PAX 40 Series Madison NC Note: Energy cost calculation assumes all motors (surface aeartor and pumps) operate at 90% efficency, and all pumps operate at 85% efficency. Energy costs assumed to be 0.12 per KwH 36

37 How can two different spray aeration systems have such different energy efficiencies? Oriface sprayers Break-up sprayers 37

38 TRS Case Studies 38

39 Ryan Ranch tank (Monterey, CA) Ryan Ranch Tank: 0.5MG, 72 dia., 16 h end of line, low turnover THM levels average 140 mg/l in tank, max 50 mg/l outside Ryan Ranch Three quarters of elevated levels, to avoid violation (RAA < 80 mg/l), sample needs to be just around 50 mg/l in Q Estimate w/o intervention: 140 mg/l Low Cl periodic dosing onsite Proposed sprayer aeration system ($350K) Limited power at tank

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

41 Design for Ryan Ranch TRS

42 TRS installation: Chemical cleaning

43 TRS Installation: Interior coatings repair

44 TRS Installation: PAX PowerVentTM Installation

45 TRS Installation: Mixer Installation

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

47 7/29/10 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 8/10/11 8/23/ No TRS With TRS Turned TRS on: June 22 Switch to Ryan Ranch water

48 Avg = Avg = Avg =

49 Upper Ragsdale (Compliance point)

50 Source Magazine (CA/NV AWWA Magazine) Winter, 2013 (V. 27, no. 1) p

51 How do various TRS components contribute? 1 MG concrete tank Split into two identical cells AMS-100 On-line THM analyzer Collaborators: Ramon Ariño Tarrago Oriol Mas Alcazar 51

52 Chlorine loss? Depends on ph HOCl is volatile: dominant ph < 7 OCl - is an ion and non-volatile: dominant ph > 7 Chlorine loss low(er) at ph > PAX Water Technologies, Inc.

53 ph and Free Chlorine no aeration 2013 PAX Water Technologies, Inc. 53

54 ph and Free Chlorine aeration vs. no aeration ph rises by 0.3 log units Free Cl drops by ~ 10% 2013 PAX Water Technologies, Inc. 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 55

56 PAX Mixer + PAX PowerVent = THM reduction Significant THM reductions observed just with PAX Mixer and Pax PowerVent Smallest package, fully installed <$30K Need a STRONG mixer See our new White Paper on Mixing Power Advantages of this approach: 1. Quick, economical first step 2. Immediate benefits from better mixing 56

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

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

59 (ppb) (ppb) Water enters clearwell Water leaves clearwell Fast rxn >> slow rxn Aerate in clearwell Fast rxn < slow rxn Aerate in tanks 59

60 Madison, NC - Clearwell

61 TRS sprayer manifold mounted in clearwell

62 PAX Mixer in Clearwell

63 Clearwell after TRS installation

64 Parker Hannifin THM Analyzer 30-minute species-specific analysis Portable, easy to use Requires UHP grade helium 64

65 /16/13 T (ppb) versus time 4/17/13 4/18/13 4/19/13 4/20/13 4/21/13 4/22/13 4/23/13 4/24/13 4/25/13 4/26/13 4/27/13 4/28/13 4/29/13 4/30/13 5/1/13 5/2/13 5/3/13 5/4/13 5/5/13 5/6/13 5/7/13 5/8/13 5/9/13 5/10/13 5/11/13 TRS off TRS on Data collected by Madison staff using Parker Hannifin THM Analyzer

66 Periods of equilibration (~ 1-2 days) /16/13 4/17/13 4/18/13 4/19/13 4/20/13 4/21/13 4/22/13 4/23/13 4/24/13 4/25/13 4/26/13 4/27/13 4/28/13 4/29/13 4/30/13 5/1/13 5/2/13 5/3/13 5/4/13 5/5/13 5/6/13 5/7/13 5/8/13 5/9/13 5/10/13 5/11/13

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

68 Secondary systems No treatment options Longer systems, older water Engineers: think *systemically* Regulators: do NOT let primary systems send barely compliant water to their secondaries! 68

69 Madison, NC elevated tank Sold water to two small towns Water was compliant (barely) as it left Madison system

70 Madison 704 tank: THM reduction post-trs Inlet 10 Outlet 0 3/23/13 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 Secondary systems are now safely in compliance 70

71 San Jose, CA: 12 MG Reservoir Purchased water from Santa Clara Valley Rising organics and bromide due to drought

74 74

75 Aqua Metrology AMS %-75% THM reduction 75

76 TRS on THM TRS off TRS on

77 All aerators and air handling ON THM All aerators and air handling OFF THM sensor offline NEPTUNE model

78 All aerators and air handling OFF All aerators and air handling ON THM NEPTUNE model

79 San Jose, CA Closed-loop energy optimization Control data from THM monitor Sequential activation/de-activation of surface aerators Potential energy savings of over $50,000/year 79

80 Relative Power Summarizing energy considerations for in tank aeration systems Bubbler system PAX Mixer + PowerVent Other surface aerators PAX Surface Aerator + PowerVent PAX Sprayer + PowerVent (+/- Mixer) LOW MEDIUM HIGH Relative TTHM removal % 80

81 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 ph can rise, and Cl can decrease somewhat due to aeration The PAX Mixer + active ventilation alone can significantly reduce THM levels 81

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

In-Reservoir TTHM Surface Aeration: A year of results, experience and lessons learned Jeanne M. Jensen, P.E. Steve Acquafredda, P.E. Jacobs Engineering Group, Inc. February 2, 2012 Presentation Outline