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W ater W orks Teacher Workshop

W ater W orks Teacher Workshop. Instructors Michael Dodd: Assistant Professor of CEE Peiran Zhou: Graduate student Sponsors: U.S. National Science Foundation

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W ater W orks Teacher Workshop

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  1. WaterWorks Teacher Workshop Instructors Michael Dodd: Assistant Professor of CEE Peiran Zhou: Graduate student Sponsors: U.S. National Science Foundation This material is based upon work supported by the National Science Foundation under Grant Numbers CBET 1236303 and 1254929. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation. UW CEE

  2. A Brief History of Water Treatment Important dates in development of modern water treatment (adapted from Water Treatment Principles and Design, 2nd ed., by MWH (Wiley 2005): • 4000 BCE: Sanskrit and Greek writings say impure water should be purified by heating, boiling, or filtration through sand and gravel • 1500 BCE: Egyptians use alum to clarify cloudy water • 1676: van Leeuwenhoek observes microorganisms under microscope • 1700’s: French use filters in homes to treat collected rainwater • 1804: First municipal WTP (Paisley, Scotland), water distributed by horse and cart • 1807: WTP connected to distribution piping in Glasgow • 1829: Slow sand filters constructed in London • 1830’s: Chlorine use recommended for disinfection at individual scale (drinking water, hand-washing by doctors) • 1854: John Snow; Broad St. well (cholera)  see The Ghost Map” • 1864: Germ theory of disease (Pasteur) • 1881: Chlorine disinfection of bacteria (in laboratory; Koch) • 1892: Hamburg cholera epidemic prevented in Altona by means of slow sand filtration • 1897: Rapid sand filtration

  3. Drinking Water Treatment Important dates in development of modern water treatment (adapted from Water Treatment Principles and Design, 2nd ed., by MWH (Wiley 2005): Continued from previous slide . . . • 1902: First continuous chlorination of a central water supply (Belgium) • 1903: Water softening with lime (St. Louis) • 1906: Ozonation in Nice, France • 1908: First continuous chlorination in US (Jersey City, NJ) • 1914: US PHS sets bacterial standards (coliform) for interstate carriers • 1942: First comprehensive WQ regulations in US, set by PHS. Apply only to interstate carriers, but most states adopt • 1972: Chlorinated DBPs discovered in Holland and US • 1974: SDWA established federal authority to set DW standards (by USEPA) • 1989: Adoption of Surface Water Treatment Rule (SWTR) • 1991: Lead and Copper Rule (LCR) adopted • 1998: Adoption of Stage 1 D-DBP Rule • 2001: Adoption of arsenic Rule (lowering of arsenic MCL to 10 μg/L) • 2006: Adoption of GWR, LT2ESWR, Stage 2 D-DBP Rule

  4. Regulations Drinking Water Systems Flagship U.S. Water Quality Regulations Safe Drinking Water Act (SDWA) Clean Water Act (CWA) Wastewater Systems Drinking Water from Protected Surface, Ground Water Drinking Water from Unprotected Surface, Ground Water Supplies Agricultural Runoff Urban Runoff

  5. Water Systems (United States) Regulated Public Water Systems (PWSs) • 15 connections or 25 people, ≥ 60 days per year • ~85% of U.S. population served by PWSs Population U.S. EPA; Drinking Water and Ground Water Statistics for 2008

  6. Water Supplies Primary Sources: Surface Water – Major risks are microbial, organic (e.g., pesticides, wastewater-derived pollutants) Groundwater – Major risks are inorganic (e.g., arsenic), organic (e.g., PCE, MTBE) Alternative Sources: Seawater, Rainwater, Treated Municipal Wastewater

  7. Drinking Water Contaminants Primary Drinking Water Regulation Categories: • Microorganisms • Disinfection by-products • Disinfectants • Inorganic Chemicals • Organic Chemicals • Radionuclides Secondary Drinking Water Regulations: • Related to aesthetic concerns • Recommended, but non-enforceable EPA Office of Groundwater and Drinking Wate(OGWDW) web-site http://www.epa.gov/safewater

  8. Overview of Core Treatment Processes Conventional Treatment: Complementary and/or Advanced Processes: • Membrane filtration • Adsorption (e.g., using powdered or granular activated carbon) • Ion exchange • Air stripping, dissolved air flotation • Chemical oxidation (e.g., ozonation, permanganate oxidation) Process Overview at AWWA’s “How Water Works” Courtesy of M. Benjamin

  9. Primary Water Treatment Objectives Removal of Particulates: • Coagulation/Flocculation • Separation of solids from solution (settling, filtration through granular media or membranes) Removal of Dissolved Constituents: • Precipitation as solids (e.g., calcium carbonate) • Adsorption onto solids (e.g., activated carbon) • Air stripping Chemical Destruction: • Oxidation/Reduction Disinfection: • Oxidation with chlorine-based chemicals or ozone • UV Irradiation • Physical processes (filtration)

  10. Flocculation Flocculators:  Gentle rotation period following rapid coagulation mix  Promotes contact of destabilized particles to yield formation of multi-particulate “flocs”, which are larger, heavier, and much easier to separate by sedimentation or direct filtration Photos courtesy of M. Benjamin

  11. Sedimentation Sedimentation basin:  Quiescent period following flocculation Sedimentation of flocs by gravity In “Type II” sedimentation, progressive enhancement of floc size and settling rate during sedimentation, due to passage of flocs in upper zones through floc-rich lower zones

  12. Filtration Filter media and facilities: Filter backwash flowing into launders at start of procedure Representative granular filter media (Everett, WA WTP)

  13. Membrane Filtration Membrane types & example full-scale configurations: Microfiltration ~ 0.1 to 100 μm Ultrafiltration ~ 0.005 to 10 μm Nanofiltration ~ 0.5 nm to 1 μm  Highly effective particle removal Reverse osmosis ~ 0.01 nm to 0.1 μm  Dissolved contaminant removal Photos courtesy of M. Benjamin

  14. Disinfection Often the most critical step in protection of consumer against pathogenic microorganisms  organisms are killed (or “inactivated”) by reaction with various chemical oxidants Commonly-used disinfectants: “Free” chlorine – Applied as Cl2(g) or NaOCl (HOCl is the active disinfectant in either case) Chloramines, or “Combined” chlorine – Applied either as pre-formed NH2Cl, or by mixing NH3 and HOCl Chlorine dioxide – Applied as ClO2(g) Ozone – Applied as O3(g) (no long-term residual) Ultraviolet light – Applied via submerged UV lamps (no residual)

  15. Disinfection – Regulatory Requirements • The EPA’s regulatory framework requires systems using surface water (or groundwater “under the direct influence” of surface water) to: • disinfect their water • and/or filtertheir water or meet criteria for avoiding filtration so that the following contaminants are controlled at the following levels • Cryptosporidium 99 percent (2-log10) removal • Giardia lamblia 99.9 percent (3-log10) removal/inactivation • Viruses 99.99 percent (4-log10) removal/inactivation

  16. Disinfection from the microbial perspective Using a bacterial cell as an example here, inactivation of microorganisms during disinfection may be due to: • Disruption of cell wall  structural deterioration of cell • Diffusion of oxidant into cell  disruption of vital functions • Absorption of UV light by cellular constituents (e.g., DNA) Oxidant Oxidant

  17. Inactivation of B. subtilis ATCC 6633 spores by FAC: pH 6, 7, 8; 25 C Inactivation rates increase with decreasing pH on account of shift in HOCl/OCl- equilibrium toward HOCl; HOCl  OCl– + H+; HOCl is a much stronger oxidant than OCl- B. subtilis spore inactivation Additional data on inactivation of B. subtilis spores by NH2Cl and ClO2 at 20-25 C is included in the accompanying articles by Larson and Marinas (2003) and Cho et al. (2006).

  18. Milwaukee (1993) & the advent of the LT2/DDBP rules **No inactivation of C. parvum within the drinking water distribution system.

  19. Relative effectiveness of common disinfectants CT values for 99% (2-log) inactivation from Crittenden et al. (MWH), 2005

  20. Disinfection and the CT concept • Disinfection efficiency can be measured as % “inactivation”. For example, at 90%, inactivation, 90 out of 100 microorganisms would be killed, and 10 out of 100 would survive. • For many microorganisms, the same disinfection efficiency can be achieved by treating a water with any combination of C (disinfectant concentration, in mg/L) and T (contact time, in min) that gives the same CT value. • For example, according to the following table (from the USEPA*), Giardia cysts would be 99% inactivated at 20 C, whether C = 5.0 mg/L and T = 2.0 min, or C = 2.0 mg/L and T = 5.0 min, as long as CT = 10.0 mg/L*min. • Note that disinfection requires higher CTs at lower temperature • *Table adapted from the Disinfection Profiling and Benchmarking Guidance Manual (1999), USEPA % Inactivated 90 99 99.9

  21. The weaker the disinfectant, the higher the CT needed to inactivate a microorganism. • The effectiveness of UV Light for disinfection can be similarly described, but using IT instead of CT, where: • ''I '' stands for light intensity (in units of mW/cm2) • T is in seconds • IT therefore has units of mJ/cm2 Required IT Required CT IT values for 99% inactivation CT values for 99% inactivation Figures from Crittenden et al. (MWH), 2005

  22. Some treatment processes are more appropriate for certain pathogens than others *For more details see: http://www.sodis.ch/methode/forschung/mikrobio/index_EN and http://www.cdc.gov/healthywater/drinking/travel/backcountry_water_treatment.html

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