DISINFECTION

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DISINFECTION

• CE326 PRINCIPLES OF ENVIRONMENTAL ENGINEERING
• Iowa State University
• Department of Civil, Construction, and
  Environmental Engineering
• Tim Ellis, Associate Professor
• March 14, 2008

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HISTORY

• J_____ S____ and the Broad Street pump in 1854
• he was able to show that 59 of the 77 c________
  victims used the pump on Broad Street
• There was a w___________ in the vicinity where
  cholera was endemic but nobody at this workhouse
  got cholera.
• This particular workhouse had its own w_____.
• The cause of contamination turned out to be the
  d________ of an infected person that was within
  three feet of the well.

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Broad Street Pump
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Chlorination

• Disinfection of water supplies by c____________
  began in Chicago and New Jersey in 1908,
• within 2 years chlorination of w_____ s________
  was practiced in N.Y., Montreal, Milwaukee,
  Cleveland, Nashville, Baltimore, and Cincinnati.
  
• By 1918, over 1000 c_____ treating more than __
  bgd were chlorinating their water supplies.
• By 1923 the typhoid death rate had dropped more
  than 90
• By the beginning of WWII, typhoid, cholera,
  dysentery were practically eliminated in U.S.

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Theory

• Chicks Law
• rate, k, is a function of concentration and time
  (i.e., CT) and type of organism
• Typical disinfectants
• Chlorine Cl2 H2O ? HOCl Cl-
• Chloramines
• NH3 HOCl ? NH2Cl H20
• NH2Cl HOCl ? NHCl2 H20
• NHCl2 HOCl ? NCl3 H20

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Chlorinators
Pellet dropper
Tablet feeder
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Chlorinators
Gas 2,000 pound
Courtesy Smith Group Consulting, LLC
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Chlorine Contact Tank
www.wsd.dst.il.us/tour/imgbig/contact_tk_1.jpg
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Ozonation

• strong o_________, but no residual
• no THM f_________ but other (non-chlorinated)
  DBPs possible
• often used as a p__________ disinfectant

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Chlorine Dioxide

• strong oxidant, but not a powerful as o_____
• dose limited to 1.0 mg/L due to health concerns
  of chlorite and c_______
• residual is not long l_______

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Ultraviolet (UV) Light

• uses thin layer of water and mercury vapor arc
  l______ emitting UV in the range of 0.2 to 0.29
  micron
• depth of light p_________ limited to 50 - 80 mm
• powerful, but no residual

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ADSORPTION

• takes advantage of physical/chemical bond of
  pollutant with adsorbent (typically g_________
  activated carbon or p_________ activated carbon)
• one ounce of GAC has a surface area of _____
  acres
• good process for removal of
• THMs
• DBPs
• SOCs
• VOCs

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ADSORPTION

• PAC dose is typically _____ mg/L can be as high
  as _____mg/L
• GAC can be used instead of a________ in dual
  media filters,
• called filter adsorbers
• must replace GAC every ____ years
• separate stage adsorption unit (contactor unit)
• GAC must be replaced or regenerated every __ to
  ___ months

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Particle Size vs. Treatment Alternatives
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Membrane Treatment
Macromolecules Smaller Particles
Large Suspended Particles
Divalent salts
Monovalent salts
Water
MF
UF
NF
RO
Micro filtration (MF) - bacteria, algae, clay,
large MW humic acids Ultra filtration (UF) -
humic acids, viruses, protein Nanofiltration (NF)
viruses, divalent salts Reverse Osmosis (RO)
monovalent salts
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Reverse Osmosis
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4-stage Reverse Osmosis Unit with Tank and Faucet