Purposes of Oxidation

1
Purposes of Oxidation

• Removal of iron, manganese, sulfides
• Removal of Taste Odor
• Destruction of color
• Removal of synthetic organics
• chlorinated solvents
• pesticides, etc.
• Partial Degradation of natural organics
• aids subsequent treatment

2
Oxidation Types of Oxidants

• Oxygen (O2)
• Chlorine (Cl2, HOCl or OCl-)
• Chloramines (NH2Cl or NHCl2)
• Ozone (O3)
• Chlorine Dioxide (ClO2)
• Permanganate (MnO4-)
• Others Peroxide, Bromine, UV light

3
Disinfection

• Kill or inactivate pathogens
• Bacteria, viruses protozoa
• Disinfectants
• Chlorine (Cl2, HOCl or OCl-)
• Chloramines (NH2Cl or NHCl2)
• Ozone (O3)
• Chlorine Dioxide (ClO2)
• Others Bromine, UV light
• Primary purpose for drinking water treatment

4
Chlorine
Chlorine or Cl2 gas, has been used since the end
of the last century as a disinfectant in the
United States. It is an effective and
inexpensive disinfectant. A problem with
chlorine is the formation of trihalomethanes
(THMs) -- chemicals formed when organic matter in
the water reacts with the chlorine.
Trichloromethane, a THM, is a carcinogen. The
current limit for THMs is 100 ppb. Some of the
alternative disinfectants discussed later produce
lower amounts of THMs or do not produce
THMs. When chlorine is injected into water it
forms
5
Chlorine Cont.
The hypochlorous acid ionizes to hypochlorite.
Although both hypochlorous acid and hypochlorite
are disinfectants, hypochlorous acid is much more
powerful. Both termed as free chlorine. The
equilibrium reaction is
6
Chlorine Reactions with Fe2, Mn2, S2-

• H2S 4 Cl2 4 H2O H2SO4 8HCL

7
Chlorine Reactions with Ammonia

• NH3 HOCl NH2Cl H2O
• monochloroamine
• NH2Cl HOCl NHCl2 H2O
• dichloroamine
• NHCl2 HOCl NCl3 H2O
• Nitrogen trichloride
• Chloroamines are called combined chlorine
  residuals and have disinfecting power

8
Breakpoint Chlorination
9
Chicks Law
In the early 1900's Dr. Harriet Chick postulated
a method of estimating the destruction of
microorganisms by disinfectants as a function of
time. Dr. Chick postulated that the death of the
microorganisms was a first order process. So,
for a given disinfectant and concentration
This can be separated and integrated (with N No
at t 0) to yield
10
Chicks Law cont.
where, No initial concentration of
microorganisms, no./mL N concentration of
microorganisms at time t, no./mL t time of
disinfection, hr k an empirical constant
descriptive of the particular microorganisms and
disinfectant in use, hr-1
Or
11
Example 9.2
The following is actual data for the
poliomyelitis virus exposed to an experimental
disinfectant. Determine the k value for Chick's
Law. Estimate the time required to obtain a
reduction of 1/10,000th the original number of
viruses. (Source Floyd, Roger, et. al,
"Inactivation of Single Poliovirus Particles in
Water by Hypobromite Ion, Molecular Bromine,
Dibromine, and Tribromine," Environmental Science
and Technology, Vol. 12, No. 9, pp. 1031-1035,
September 1978.)
12
This data is plotted, along with a least squares
regression line. The slope of the line is the
disinfection constant k 0.634/s.
13
Example 9.2 cont.
The time required for a reduction of 1/10,000th
is then
14
DBPs (Disinfection By Products)

• Reaction of Chlorine with Organics in water and
  wastewater
• HOCl NOM

Oxidized NOM
Chlorinated Organics TOX THM HAA
Carcinogens