WaterWorks Teacher WorkshopInstructors

Michael Dodd: Assistant Professor of CEE

Peiran Zhou: Graduate student

Sponsors:

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 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

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, 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

Regulations

Drinking Water

Systems

Drinking Water from Protected Surface, Ground Water

Drinking Water from

Unprotected Surface, Ground Water Supplies

Clean Water Act (CWA)

Wastewater Systems

Urban Runoff

Agricultural Runoff

Safe 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 PWSs

U.S. EPA; Drinking Water and Ground Water Statistics for 2008

Population

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:

• 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

Overview of Core Treatment Processes

Courtesy of M. Benjamin

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”

Primary Water Treatment ObjectivesRemoval 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)

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 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

Filter media and facilities:

Filtration

Representative 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 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

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)

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 filter their 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

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

Disinfection from the microbial perspective

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

FAC CT Value (mg*min/L)

0 50 100 150 200 250

Lo

g(N

/N0

)

-4

-3

-2

-1

0

pH 8 - Dark with [FAC]0 = 4 mg/L

pH 6 - Dark with [FAC]0 = 2 mg/L

pH 7 - Dark with [FAC]0 = 4 mg/L

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).

Milwaukee (1993) & the advent of the LT2/DDBP rules

**No inactivation of C. parvum within the drinking water distribution system.

Relative effectiveness of common disinfectants

CT values for 99% (2-log) inactivation

from Crittenden et al. (MWH), 2005

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

Figures from Crittenden et al. (MWH), 2005

Required CT

The weaker the disinfectant, the higher the CT needed to inactivate a microorganism.

CT values for 99%

inactivation

IT values for 99%

inactivation

Required IT

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

Some treatment processes are more appropriate for certain pathogens than others

Treatment Process

Microorganisms

Viruses Bacteria Protozoans

Free chlorine Very effective Very effective Less effective

Chlorine dioxide Effective Very effective Effective

Iodine Effective Effective Not effective

UV light Effective Very effective Very effective

Natural sunlight Effective Effective Less effective

Boiling Very effective Very effective Very effective

Membrane Filtration

Variably effective Very effective Very effective

*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