By Ethan Brooke and M. Collins

Transcription

1 By Ethan Brooke and M. Collins 1

2 A Solution for Small Systems Particularly useful for concurrent systems Do not have control over water quality Can not control residence time Alternative to precursor removal 2

3 Diffused Aeration Surface Aeration Spray Aeration 3

4 Aeration Kinetics Equilibrium is the driving force for all forms of Aeration! 4

5 Forms of Henry s Constant 5

6 Forms of Henry s Constant 6

7 Henrys Constant Hcc An Intuitive Feel for Henry s Constants Henrys Constant Hcc With Respect to Percent of Constituent in Aqueous Phase Percent of Constituent in Aqueous Phase 7

8 Henrys Constant Hcc Henrys Constant Hcc of Oxygen, Methane, and Carbon Dioxide With Respect to Percent of Constituent in Aqueous Phase oxygen methane carbon dioxide Percent of Constituent in Aqueous Phase 8

9 Factors Affecting Henry s Constant ph Complex Mixtures: Co-solvents and Co-solutes Ionic Strength: Dissolved Salts Suspended Solids Dissolved Organic Matter Surfactants Temperature 9

10 Factors Affecting Henry s Constant 10

11 Temperature Correction Factors 11

12 Temperature Correction Factors A Critical review of Henrys Law Constants for Environmental Applications Jeff Staudinger and Paul Roberts, Critical Reviews in Environmental Science And Technology,

13 Henrys Constants and Temperature Correction Factor for TTHMs at 20⁰ C and 1⁰ C THM Species H cc 20⁰ C H cc 1⁰ C B Chloroform (CF) Bromodichloromethane (BDCM) Chlorodibromomethane (CDBM) Bromoform (BF)

14 Henrys Constants for Halo Acetic Acids at 20⁰ C Haloacetic Acid Species H cc 20⁰ C Monochloroacetic Acid Dichloroacetic Acid Trichloroacetic acid Monobromoacetic Acid Dibromoacetic Acid

15 The Tendency of a system to seek equilibrium is the driving force for all forms of Aeration! Equilibrium is expressed by Henrys constant Temperature has a large effect on Henrys Constant Haloacetic acids are not volatile enough to strip effectivly 15

16 Diffused Aeration 16

17 17

18 Diffused Aeration Apparatus 18

19 Diffused Aeration Apparatus 19

20 Diffused Aeration Apparatus 20

21 Diffused Aeration Apparatus 21

22 Bench Scale Variables Air Temperature Water Temperature Air Flow Rate Number of Diffusers THM Concentration 4º C and 20º C 4º C and 20º C 1L/Min and 3L/Min 1 and ug/l and 400 Ug/L Contact Time 40 Min and 80 Min 22

23 Experimental design and analysis 23

24 Re sponse Pe rce nt TTHM Remove d Parameter Estimates Term Estimate Std Error t Ratio Prob> t Intercept <.0001* Air Tem p[20c] Water Tem p[1c] <.0001* Concentration[100ug/L] Air Flow Rate[1.5 L/m in] * Number of Diffus ers [1] Aeration Time[45 min] * Air Tem p[20c]*water Temp[1C] Air Tem p[20c]*concentration[100ug/l] Air Tem p[20c]*air Flow Rate[1.5 L/m in] Air Tem p[20c]*num ber of Diffusers[1] Air Tem p[20c]*aeration Time[45 min] Water Tem p[1c]*concentration[100ug/l] Water Tem p[1c]*air Flow Rate[1.5 L/min] Water Tem p[1c]*number of Diffus ers [1] Water Tem p[1c]*aeration Tim e[45 m in] Concentration[100ug/L]*Air Flow Rate[1.5 L/min] Concentration[100ug/L]*Number of Diffusers[1] Concentration[100ug/L]*Aeration Tim e[45 m in] Air Flow Rate[1.5 L/m in]*number of Diffusers[1] Air Flow Rate[1.5 L/m in]*aeration Tim e[45 m in] Number of Diffus ers [1]*Aeration Time[45 m in]

25 Re sponse Pe rce nt TTHM Remov ed Parameter Estimate s Term Estimate Std Error t Ratio Prob> t Intercept <.0001* Water Tem p[1c] <.0001* Air Flow Rate[1.5 L/m in] <.0001* Aeration Time[45 min] * Air Flow Rate[1.5 L/m in]*aeration Tim e[45 m in] * 25

26 Bench Scale Conclusions Water temperature and air to water ratio have a significant effect on removals Air Temperature and initial concentration did not have a significant effect on removals Bubble size does not have a significant effect on overall removals 26

27 Diffused Aeration Minimum Air to Water Ratio 27

28 5% 10% 15% 20% 25% 30% 35% 40% 45% 50% 55% 60% 65% 70% 75% 80% 85% 90% 95% Air to water ratio Percent removal vs. air to water ratio for THMs at 25º C 60 Chloroform Bromodichloromethane Chlorodibromomethane Bromoform Percent removed 28

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31 Field Scale Evaluation By Sherant, Yeuell and Xie Penn State Harrisburg 31

32 Receive finished water from wholesale systems No direct control over water quality Minimal ability to manage hydraulic flow and storage Difficult to reduce residence time 32 32

33 33 33

34 Consecutive system in Western PA Violation for TTHMs Running Annual Average 107 µg/l (Sept. 07) Must go 1 year (4 quarters) below MCL Currently working to remove THMs Aeration field study October

35 Nant-Y-Glo Water Treatment Plant Cardiff Tank (1,000,000 gallons ) Vintondale Tank (300,000 gallons) End of Blacklick Distribution System 35 35

36 C onc entration (µg /L ) THM Concentrations Nant-Y -Glo Inlet Twin Rocks Tank Vintondale T ank E nd of S ys tem F a ll Winter S pring S ummer 36 36

37 Concentration (μg/l) Speciation of THMs Nant-Y-Glo Inlet Twin Rocks Tank Vintondale Tank End of System TTHM Cl3CH BrCl2CH 37 37

38 75,000 gal tank 35 days 16 days of aeration Water flows Min -11,000 gpd Max - 109,000 gpd Avg - 63,000 gpd Temp C 38

39 4- FlexAir -7.5 cfm fine bubble 16 -PermaCap5-1.5 cfm-fine bubble PVC piping 39

40 3.5 HP 3-Phase 63 CFM 40 40

41 Capital costs Blower $5600 Electrical $760 Diffuser Setup $140 Other set up costs Varies Operational costs Blower 2.08 Kw hours 4320 hours (June November) 13 cents per Kw hour Total power cost $1170 / 6 months Total capitol cost $6,800 41

42 Concentration (µg/l) Results at the Tank System Inlet Twin Rocks Tank Time (days) 42 42

43 Concentration (µg/l) Distribution System Results µg/l 65 µg/l Time (days) Twin Rocks Vintondale Pump Station 43 43

44 Chloroform ( μg/l ) Aeration Modeling Same Daily Water Flow Smaller Tank Hour Tank Refill Constant Air Flow : 70 cfm MCL Tim e (days) 75,000 gallon 70,000 gpd (total) 44 44

45 Chloroform ( μg/l ) Aeration Modeling Smoothed Water Flow 9 Hour Tank Refill Constant Air Flow : 70 cfm 100 Water Off 2:00 PM 50 MCL 0 Water on 5:00 AM Tim e (days) 175,000 gallon 70,000 gpd (total) 45 45

46 A simple air diffuser can be placed in a storage tank for THM removal Effective for small system THM compliance No removal of HAAs Most effective for Chloroform Dominant species in most chlorinated water Most effective during warm weather months THMs highest 46

47 Surface Aeration 47

48 Spray Aeration 48

49 Spray Aeration Pilot 49

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51 Assessing mass transfer coefficients and interfacial surface area 51

52 Assessing mass transfer coefficients and interfacial surface area 52

53 Pilot Goals Assess the role of pressure in determining K L a Compare K L a of different shower heads at different pressure settings Assess the influence of atmosphere venting on THM removal from a storage facility Evaluate the role of temperature on spray aeration removal rates Create a spreadsheet based model to relate percent removal of THM to flow through shower head 53

54 Percent of THM removed Percent of flow aerated vs percent of THM removed 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% 0% 20% 40% 60% 80% 100% Percent of flow spray aerated 54

55 Conclusion Aeration provides a way to remove DBS after they have formed with a minimal capital investment DBS most amenable to removal are THMS HAAs could be removed by Biodegradation (data not shown) 55

56 Biodegradation of Disinfection By- Products

57 GAC for THM removal (McGuire & Suffet) 57

58 BAC filtration on HAAs Haloacetic Acid Concentration (µg/l) Monochloroacetic acid Dichloroacetic acid Trichloroacetic acid Monobromoacetic acid Dibromoacetic acid 0 Influent Effluent 58

59 BAC filtration on DBPs 60 DBP Concentration (µg/l) Four trihalomethanes Six haloacetic acids Chloral hydrate 0 BAC Influent BAC Effluent 59

60 DBP removal GAC adsorption Low carbon capacity Membranes RO filtration; excellent for HAAs; OK for THMs Biofiltration Biologically active carbon; HAAs not THMs Aeration THMs, especially chloroform 60

61 Questions? 61