W ater W orks Teacher Workshop

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

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  • WaterWorks Teacher WorkshopInstructorsMichael Dodd: Assistant Professor of CEEPeiran Zhou: Graduate studentSponsors:U.S. National Science FoundationThis 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

  • A Brief History of Water TreatmentImportant 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 gravel1500 BCE: Egyptians use alum to clarify cloudy water1676: van Leeuwenhoek observes microorganisms under microscope1700s: French use filters in homes to treat collected rainwater1804: First municipal WTP (Paisley, Scotland), water distributed by horse and cart1807: WTP connected to distribution piping in Glasgow1829: Slow sand filters constructed in London1830s: Chlorine use recommended for disinfection at individual scale (drinking water, hand-washing by doctors)1854: John Snow; Broad St. well (cholera) see The Ghost Map1864: 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 filtration1897: Rapid sand filtration

  • Drinking Water TreatmentImportant 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, France1908: First continuous chlorination in US (Jersey City, NJ)1914: US PHS sets bacterial standards (coliform) for interstate carriers1942: First comprehensive WQ regulations in US, set by PHS. Apply only to interstate carriers, but most states adopt1972: Chlorinated DBPs discovered in Holland and US1974: SDWA established federal authority to set DW standards (by USEPA)1989: Adoption of Surface Water Treatment Rule (SWTR)1991: Lead and Copper Rule (LCR) adopted1998: Adoption of Stage 1 D-DBP Rule2001: Adoption of arsenic Rule (lowering of arsenic MCL to 10 g/L)2006: Adoption of GWR, LT2ESWR, Stage 2 D-DBP Rule

  • RegulationsDrinking Water SystemsDrinking Water from Protected Surface, Ground WaterDrinking Water from Unprotected Surface, Ground Water SuppliesClean Water Act (CWA)Wastewater SystemsUrban RunoffAgricultural RunoffSafe Drinking Water Act (SDWA)Flagship U.S. Water Quality Regulations

  • 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 PWSsU.S. EPA; Drinking Water and Ground Water Statistics for 2008

  • Water SuppliesPrimary 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

  • Drinking Water ContaminantsPrimary Drinking Water Regulation Categories:MicroorganismsDisinfection by-productsDisinfectantsInorganic ChemicalsOrganic ChemicalsRadionuclides

    Secondary Drinking Water Regulations:Related to aesthetic concernsRecommended, but non-enforceable

    EPA Office of Groundwater and Drinking Wate(OGWDW) web-site http://www.epa.gov/safewater

  • Overview of Core Treatment ProcessesConventional Treatment:

    Complementary and/or Advanced Processes:Membrane filtrationAdsorption (e.g., using powdered or granular activated carbon)Ion exchangeAir stripping, dissolved air flotationChemical oxidation (e.g., ozonation, permanganate oxidation)Process Overview at AWWAs How Water Works

  • Primary Water Treatment ObjectivesRemoval of Particulates:Coagulation/FlocculationSeparation 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 strippingChemical Destruction: Oxidation/Reduction Disinfection:Oxidation with chlorine-based chemicals or ozoneUV IrradiationPhysical processes (filtration)

  • FlocculationFlocculators:

    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

  • SedimentationSedimentation basin:

    Quiescent period following flocculationSedimentation of flocs by gravityIn 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

  • Filter media and facilities:

    FiltrationRepresentative granular filter media (Everett, WA WTP)Filter backwash flowing into launders at start of procedure

  • Membrane FiltrationMembrane types & example full-scale configurations:Microfiltration ~ 0.1 to 100 m Ultrafiltration ~ 0.005 to 10 mNanofiltration ~ 0.5 nm to 1 m Highly effective particle removalReverse osmosis ~ 0.01 nm to 0.1 m Dissolved contaminant removal

    Photos courtesy of M. Benjamin

  • DisinfectionOften 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 HOClChlorine dioxide Applied as ClO2(g)Ozone Applied as O3(g) (no long-term residual)Ultraviolet light Applied via submerged UV lamps (no residual)

  • Disinfection Regulatory RequirementsThe EPAs regulatory framework requires systems using surface water (or groundwater under the direct influence of surface water) to:disinfect their waterand/or filter their water or meet criteria for avoiding filtration so that the following contaminants are controlled at the following levelsCryptosporidium 99 percent (2-log10) removalGiardia lamblia 99.9 percent (3-log10) removal/inactivationViruses 99.99 percent (4-log10) removal/inactivation

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

  • Inactivation of B. subtilis ATCC 6633 spores by FAC:pH 6, 7, 8; 25 CInactivation 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 inactivationAdditional 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).

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

  • Relative effectiveness of common disinfectantsCT values for 99% (2-log) inactivationfrom Crittenden et al. (MWH), 2005

  • Disinfection and the CT conceptDisinfection 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

  • Figures from Crittenden et al. (MWH), 2005Required CTThe weaker the disinfectant, the higher the CT needed to inactivate a microorganism.CT values for 99% inactivationIT values for 99% inactivationRequired ITThe 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 secondsIT therefore has units of mJ/cm2

  • 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

    Treatment ProcessMicroorganismsVirusesBacteriaProtozoansFree chlorineVery effectiveVery effectiveLess effectiveChlorine dioxideEffectiveVery effectiveEffectiveIodineEffectiveEffectiveNot effectiveUV lightEffectiveVery effectiveVery effectiveNatural sunlightEffectiveEffectiveLess effectiveBoilingVery effectiveVery effectiveVery effectiveMembrane FiltrationVariably effectiveVery effectiveVery effective