WaterWorks Teacher Workshop

1
WaterWorks Teacher Workshop

• Instructors
• Michael Dodd Assistant Professor of CEE
• Peiran Zhou Graduate student
• Sponsors
• NSF (CBET Grants 1236303 1254929)
• 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
• 1700s 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
• 1830s 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
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

• Drinking Water Systems

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

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 AWWAs How Water Works

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 EPAs 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

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
B. subtilis spore inactivation

• 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-

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/Lmin.
• Note that disinfection requires higher CTs at
  lower temperature
• Table adapted from the Disinfection Profiling
  and Benchmarking Guidance Manual (1999), USEPA

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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 CT
Required IT
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
Treatment Process Microorganisms Microorganisms Microorganisms
Treatment Process 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/ba
ckcountry_water_treatment.html