Webcast Sources, Fate, and Transport of Chromium in Drinking Water Treatment Plants and Distribution Systems

Transcription

1 No part of this presentation may be copied, reproduced, or otherwise utilized without permission. Webcast Sources, Fate, and Transport of Chromium in Drinking Water Treatment Plants and Distribution Systems February 7, 2017

2 Agenda (Mountain Standard Time) Webcast Introduction Mary Smith 1:00-1:05 Project Introduction Phil Brandhuber 1:05-1:10 Behavior of Cr in Presence of Oxidants Laurie McNeill 1:10 1:20 Sources and Sinks of Cr Zia Bukhari 1:20 1:30 Cr in Plants and Distribution Systems Phil Brandhuber 1:30-1:45 Project Conclusion Phil Brandhuber 1:45 1:50 Questions All 1:50 2:00

3 Project Introduction Phil Brandhuber, PhD Senior Professional Associate HDR

4 Cr Regulatory Status National standards are for total chromium (Cr(III) + Cr(VI)) USEPA MCL = 100 µg/l USEPA MCLG = 100 µg/l No national standard for Cr(VI) California unique Cr standards Total Cr = 50 µg/l Cr(VI) = 10 µg/l California Cr(VI) public health goal (PHG) = 0.02 µg/l

5 Research Questions What is the response of Cr in presence of oxidants? Intentional oxidation Unintentional oxidation Are there unaccounted sources (or sinks) of Cr? Infrastructure Chemicals How does Cr behave in treatment plants and distribution systems? Increase/decrease concentration Change speciation

6 Behavior of Cr in Treatment Treatment chemicals Plants Raw water Treatment Plant Infrastructure Treated water Entry point distribution system (EPDS) Recycle Minutes to hours Many chemicals and processes Large changes to equilibrium Waste (Solid/liquid) Does Cr increase or decrease? Does Cr(III) convert to Cr(VI)?

7 Behavior of Cr in Distribution Systems EPDS X X EPDS Treated water EPDS Customer taps X Max Residence Time (MRT) Hours to days Large surface areas Moving to equilibrium Does Cr increase or decrease? Does Cr(III) convert to Cr(VI)?

8 Conceptual Model of Cr(III) in Water (McNeill et al 2013) Fe(OH) 3 Cr(III) fixed Cr(III) sorbed Cr(III) soluble Cr(OH) 3 precipitate Source: McNeill, L., J. McLean, M. Edwards and J. Parks Trace Level Hexavalent Chromium Occurrence and Analysis. Project #4404. Denver, Colo.: Water Research Foundation.

9 Expanded Conceptual Model of Total Cr in Water Fe(OH) 3 Cr(III) fixed Cr(III) sorbed Treatment Oxidants - Cl 2 - O 3 - ClO 2 - MnO 4 Cr(VI) sorbed Fe(OH) 3 ph 5-10 Cr(OH) 3 precipitate Cr(III) soluble Dissolved Oxygen Mn(IV) Oxides Fe(II) Sulfides Organic Matter Microbial Treatment Reductants - Fe(II) - Sn(II) Cr(VI) soluble ph < 7.5 Cr(OH) 3 precipitate ph < 6 ph 6-10 ph < 8 (?) Cr(III) Cr(VI)

10 Behavior of Cr in the Presence of Oxidants Laurie McNeill, PhD Professor Utah State University

11 Bench-Scale Experiments 5 oxidants: Free chlorine Monochloramine Chlorine dioxide Permanganate Ozone ph 5, 7, 9 Temperature 5 and 16C 3 water qualities Initial Cr(III) = 10 µg/l or 100 µg/l

12 Bench-Scale Results: 10 µg/l Cr(III) + 4 mg/l Chloramine Essentially no oxidation by 1 or 4 mg/l chloramine. Maximum Cr(VI) formed = 0.5 µg/l. Plants and Distribution Systems. Project #4497. Denver, Colo.: Water Research Foundation.

13 Bench-Scale Results 10 µg/l Cr(III) + 4 mg/l Free Chlorine (Cl 2 ) 10 µg/l Cr(III) mg/l Chlorine Dioxide (ClO 2 ) 10 µg/l Cr(III) + 1 mg/l Potassium Permanganate (KMnO 4 ) 10 µg/l Cr(III) + 1 mg/l Ozone (O 3 ) Source: Brandhuber, P., L. McNeill, J. McLean, N. Rogers, and Z. Bukhari. Forthcoming. Sources, Chemistry, Fate, and Transport of Chromium in Drinking Water Treatment

14 Bench-Scale Results: 10 µg/l Cr(III) + 1 mg/l free chlorine Free chlorine continues to oxidize Cr(III) Plants and Distribution Systems. Project #4497. Denver, Colo.: Water Research Foundation.

15 Bench-Scale Results: 10 µg/l Cr(III) + 1 mg/l Cl 2 in Delran WTP water Much less oxidation by Cl 2 in real water: precipitation of Cr(III) NOM consumes the Cl 2 and/or complexes Cr(III)

16 Pipe Loop Experiments American Water pipeloop tester, Tri-County Plant, Delran NJ

17 Pipe Loop Results 10 µg/l Cr(III) + 1 mg/l Chloramine Cr(tot) SP1 Cr(tot) SP2 Filtered Cr(tot)-SP1 Filtered Cr(tot)-SP2 Cr(VI) SP1 Cr(VI) SP2 Chromium (ug/l) Elapsed Time (Hr) Essentially no oxidation by 1 or 4 mg/l chloramine. Maximum Cr(VI) formed = 0.2 µg/l.

18 Pipe Loop Results 10 µg/l Cr(III) + 1 mg/l Free Chlorine Cr(tot) SP1 Cr(tot) SP2 Filtered Cr(tot) SP1 Filtered Cr(tot) SP2 Cr(VI) SP1 Cr(VI) SP2 Chromium (ug/l) Elapsed Time (Hr) Maximum Cr(VI) by 1 mg/l chlorine = 0.3 µg/l. Maximum Cr(VI) by 4 mg/l chlorine = 1.4 µg/l.

19 Oxidation Summary Significant oxidation of soluble Cr(III) by O 3, ClO 2, KMnO 4, and Cl 2 in model waters at bench scale Less oxidation by Cl 2 in real waters (bench scale and pipe loop) Particulate Cr(III) is not easily oxidized Essentially no oxidation by chloramine

20 Sources and Sinks of Cr Zia Bukhari, PhD Senior Scientist American Water

21 Pipe Material Pipeloop for Cr sorption and desorption experiments 2x10 ft sections: Two types of new pipe materials examined: Stainless steel (Cl 2 = 4 mg/l & 10 mg/l) Unlined ductile iron (Cl 2 = 4 mg/l) 5 feet sampling port

22 Stainless steel pipe: 4 mg/l Free chlorine 17 µg/l

23 Stainless steel pipe: 10 mg/l Free chlorine

24 Impact of Cr Leaching For Stainless Steel Cr(tot) release rate for chlorination was: 12.7 µg/(m 2 -day) for 4 mg/l Cl µg/(m 2 -day) for 10 mg/l Cl 2 Assume uniform Cr(tot) release rate of 18(µg/(m 2 -day): 2-inch diameter SS pipe with 1 foot per second (fps) flow requires > 85,000 ft to exceed 10 µg/l. Significance?? 10 µg/l of Cr in bulk water likely to be exceeded within 7 days of stagnation Significant for NF/RO system are shut down even temporarily

25 Unlined Ductile Iron: 4 mg/l Free chlorine

26 Treatment Chemicals Approved Max Cr(tot) Concentration at Max Use Chemical type Use (mg/l) Pre-floc (µg/l) Post-floc (µg/l) Polymer blends Ferric Sulfate Ferric Chloride Ferric Chloride Calcium Oxide (lime) N/A

27 Other Treatment Chemicals Chemical type pdadmac Polyacrylamide Polymer blends Blended Phosphates Potassium Permanganate DL= 0.2 µg/l Cr(tot) Detected X X X X Cr(tot) Not Detected X

28 Cr Trends in Treatment Plants and Distribution Systems Phil Brandhuber, PhD Senior Professional Associate HDR

29 Plant Profile Sampling Approach Utility sample location Raw and EPDS Unit process Chemical addition Recycle stream MRT Parameters sampled Triplicate Cr(tot)/Cr(VI) total and dissolved Free and total Cl 2, ph, temperature, others Cr samples analyzed by American Water Belleville lab Cr(tot) per EPA Rev 5.4; MRL = 0.2 µg/l Cr(VI) per EPA 218.7; MRL = 0.03 µg/l Inter-lab comparison with USU Water Research Lab

30 Plant Profile Add then Remove Cr Raw water is almost all Cr(III)

31 Plant Profile Add then Remove Cr Ozone contactor added Cr(!)

32 Plant Profile Add then Remove Cr Chemical addition added more Cr

33 Plant Profile Add then Remove Cr Clarification removed particulate Cr leaving primarily soluble Cr(IV)

34 Plant Profile Add then Remove Cr Almost all Cr(tot) is soluble Cr(VI), filters don t remove much Cr

35 Plant Profile Add then Remove Cr Cr leaves plant as Cr(VI)

36 Plant Profile Add then Remove Cr Backwash contains particulate Cr removed by filters

37 Plant Profile Add then Remove Cr Cr levels decreases as backwash finishes

38 Plant Profile Add then don t Remove Cr

39 Plant Profile Add then don t Remove Cr Raw water is almost all Cr(III)

40 Plant Profile Add then don t Remove Cr Not much change

41 Plant Profile Add then don t Remove Cr Chemical addition added Cr(VI)

42 Plant Profile Add then don t Remove Cr No change to Cr levels in plant all Cr(VI)

43 Plant Profile Add then don t Remove Cr No change in distribution system

44 Summary of Plant Profile Sampling Max Cr(tot) level in plant > raw Conventional Conventional Lime softening Ozone/ biofilter Ozone/ biofilter Ozone/ Biofilter with UV

45 Summary of Plant Profile Sampling Max Cr(tot) level in plant > raw but Cr removed prior to leaving plant Conventional Conventional Lime softening Ozone/ biofilter Ozone/ biofilter Ozone/ Biofilter with UV

46 Summary of Plant Profile Sampling Cr present as Cr(VI) Conventional Conventional Lime softening Ozone/ biofilter Ozone/ biofilter Ozone/ Biofilter with UV

47 Summary of Plant Profile Sampling Percentage of Cr(tot) leaving plant as Cr(VI) > than percentage in raw Conventional Conventional Lime softening Ozone/ biofilter Ozone/ biofilter Ozone/ Biofilter with UV

48 Summary of Plant Profile Sampling UV Plant Conventional Conventional Lime softening Ozone/ biofilter Ozone/ biofilter Ozone/ Biofilter with UV

49 Cr in Distribution Systems Unregulated Contaminants Monitoring Rule 3 (UCMR3) Data Analysis Methodology UCMR3 Extracted data set MRT site uniquely supplied by single EPDS Cr(tot) and Cr(VI) detected at both EPDS and MRT site 16,582 records for 2052 systems Develop histograms MRT > EPDS (Cr increased) MRT = EPDS (No change in Cr) MRT < EPDS (Cr decreased)

50 Change in Distribution System Cr(VI) Between EPDS and MRT Free Chlorine Residual Disinfectant

51 Change in Distribution System Cr(VI) Between EPDS and MRT Chloramine Residual Disinfectant

52 Change in Distribution System Cr(VI) Between EPDS and MRT No Residual Disinfectant

53 Project Findings What is the response of Cr in presence of oxidants? O 3, ClO 2, MnO 4 and Cl 2 will oxidize soluble Cr(III) Speed and/or completeness of Cr(III) oxidation strongly influenced by water quality Completeness of Cr(III) oxidation in real waters much less than in model waters When in particulate form, Cr(III) is difficult to oxidize Presence of particulate Cr(III) plays important role in slowing Cr(III) oxidation Monochloramine exhibits little tendency to oxidize Cr(III)

54 Project Findings Are there unaccounted sources (or sinks) of Cr? Treatment chemicals can be a source of Cr Point of addition of chemical addition in process train is important Addition as Cr(VI) more problematic than Cr(III) Stainless steel may contribute Cr to treatment plants Unlikely to be problematic More research required

55 Project Findings How does Cr behave in treatment plants? In plants sampled by this project Cr tended to increase within plant But Cr was then mostly removed prior to entering distribution system - if present as particulate Cr(III) Cr(VI) was poorly removed once formed Percentage of Cr(tot) speciated as Cr(VI) Greater at EPDS than in raw water Never saw evidence of complete oxidation of Cr(III) to Cr(VI)

56 Project Findings How does Cr behave in distribution systems? Based on UCMR3 data analysis Tendency for Cr(VI) to increase between EPDS and MRT Cl 2 > Chloramine > No residual Increase in Cr(VI) very small Cr(VI) decreased substantial number of time Observed increase in Cr(VI) never moved system from below to above CA Cr(VI) MCL

57 Thanks to City of Grants Pass, OR Iowa American Water Company Missouri American Water Company Philadelphia Water Department Iowa American Water Company City of Phoenix AZ (and others) USU students and staff: Erin Andersen, Tess Guy, Katie Henderson, Josh Hortin, Adam Jones, Kailey Jorgensen, Kaisa Patterson, Nate Rogers, Chelsea Stewardson, and Joe Stewart Mary Smith, Water Research Foundation Project Advisory Committee Richard Sakaji, PhD East Bay Municipal Utility District Sevinc Sengor, PhD Southern Methodist University Philip Singer, PhD University of North Carolina American Water staff: Minhua Xu and Chandan Venkatesh

58 Questions?

59 Thank You Comments or questions, please contact: For more information visit:

60 Backup

61 Cr Oxidation/Reduction Behavior Free chlorine Chloramine Ozone Permanganate Chlorine dioxide How completely does Cr(III) convert to Cr(VI)? How quickly does Cr(III) convert to Cr(VI)? Does water quality influence conversion?

62 Challenges in Cr Quantification UCMR3 Data Set

63 Cr(VI) Treatment Profiles from McNeill and McLean (2013) Utility Type Trend Plant Trend DS A - Plant 1 SW Increase Variable & A - Plant 2 SW Constant related to A - Plant 3 SW Constant source Unfiltered Cr(VI) (µg/l) B SW Increase Constant C Plant 1 SW Increase Increase C Plant 2 SW Increase Increase D SW Decrease NA 0.05 E GW Increase NA F GW NA Decrease G SW NA Increase 0.13 H SW/GW NA Variable Source: McNeill, L., J. McLean, M. Edwards and J. Parks Trace Level Hexavalent Chromium Occurrence and Analysis. Project #4404. Denver, Colo.: Water Research Foundation.

64 Aqueous Chromium Chemistry Eh ph Diagram Cr(III) Solubility Approximate range for drinking water Approximate range for drinking water Baes and Mesmer 1977

65 Under Certain ph Conditions Soluble Cr will Sorb to Iron Surfaces Approximate range for drinking water MINEQL + Two-Layer model for hydrous ferric hydroxide

66 Summary of Plant Profile Sampling Cr(tot) at EPDS > raw Cr(tot) Conventional Conventional Lime softening Ozone/ biofilter Ozone/ biofilter Ozone/ Biofilter with UV