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 Disinfectants
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 Fe+2, Mn+2, 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 Curve
Free residual
HOCl, OCl-
Combined Residual
Mono and di-
chloramines

9. DBPs (Disinfection By Products)
Reaction of Chlorine with Organics in water and wastewater
HOCl + NOM
Oxidized NOM
Chlorinated Organics
TOX
THM
HAA
Total Organic Halide
Tri Halo Methane
Halo Acetic Acid
Carcinogens

11. Chick’s Law British Microbiologist
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:

12. Chick’s 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:

13. 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 , September 1978.)

14. This data is plotted, along with a least squares regression line
This data is plotted, along with a least squares regression line. The slope of the line is the disinfection constant k = 0.634/s.

15. Example 9.2 cont.
The time required for a reduction of 1/10,000th is then: