1. SEAVURIA Seattle + Kenya (2012)
Water Quality Chemistry: Generation of Sodium hypochlorite (NaOCl) disinfectant by electrolysis of NaCl Solution
SEAVURIA
Seattle + Kenya (2012)

2. Sodium hypochlorite (NaOCl)
NaOCl is produced either when:
Chlorine gas is dissolved in sodium hydroxide solution, or
A sodium chloride solution (brine) is treated with electricity (electrolysis)
NaOCl solutions are called liquid bleach or Javelle water
Onsite generation of NaOCl needed due to decomposition over time
(Disinfectant, 1999)

3. Anode: + electrode
Where the oxidation of chloride ions (Cl-), involving the lose of 1 electron (e-) per Cl-, results in the production of chlorine gas (Cl2).
Cathode: - electrode
Where the reduction of water (H20), involving the gain of 2e-, results in the production of hydrogen gas (H2) and hydroxide ions (OH-).
Electrolysis: Production of NaOCl
Image courtesy of Boal ( 2009)

4. NaOCl + H20 → HOCl + Na+ + OH-
Oxidant
Electrolysis:
NaCl H20 → NaOCl + H2
Sodium chloride
(table salt)
Water
Sodium hypochlorite
Hydrogen gas
Oxidized
Reduced
(Boal, 2009)
Water Treatment:
NaOCl + H20 → HOCl + Na+ + OH-
Hypochlorous acid
(Disinfectant, 1999)

5. Typical Chlorine Dosages
(Disinfectant, 1999)

6. Chlorine: Pathogen Inactivation
In bacteria, chlorine found to adversely affect cell respiration, transport and DNA activity.
Decreases oxygen utilization
Damages cell wall membrane
Decreases levels of DNA synthesis
(Haas and Engelbrecht, 1980)
(Disinfectant, 1999)

7. Chlorine: Environmental Effects
Several environmental factors influence the inactivation efficiency of chlorine, including:
Temperature and pH,
Contact time and mixing,
Turbidity and interfering substances, and
Concentration of available chlorine
Temperature and pH have the most impact on pathogen inactivation by chlorine.
(Disinfectant, 1999)

8. Chlorine: Effect of Temperature and pH
Pathogen inactivation increases with temperature.
If temperature is lowered by 10C, contact time should be increased 2-3X (Clarke et. Al, 1962)
pH:
Most impact on pathogen inactivation by chlorine
Germicidal efficiency of hypochlorous acid (HOCl) much higher than that of hypochlorite ion (OCl-)
Note: addition of OCl- to water increases pH
HOCl dominates at low pH = ↑ disinfection
At less effective pH contact time should be increased (Culp and Culp, 1974; Scarpino et al., 1972)
(Disinfectant, 1999)

9. Chlorine: Disinfection Efficacy
Bacteria Inactivation: Chlorine extremely effective as disinfectant for inactivating bacteria
HOCl is 70-80X more effective than OCl- (Culp/Wesner/Culp, 1986)
If temperature is lowered by 10C, contact time should be increased 2-3X (Clarke et. Al, 1962)
Virus Inactivation: Chlorine is highly effective viricide
In 1971 study (0.5 mg/L free chlorine; pH 7.8; 2⁰C):
Reovirus (least resistant): 2.7 min. contact time for 99.99% inactivation (4 log removal)
Poliovirus (most resistant): 60 minute contact time for 99.99% inactivation
99.99% inactivation for all 20 viruses studied was between 1.4 to >30 mg•min/L (CT values)
Protozoa Inactivation: Chlorine has limited success inactivating protozoa, like Giardia (Hoff et al., 1984); see Figures 2-1, 2-2, and 2-3 for more details
Resistance of Giardia two orders of magnitude higher than some viruses
Resistance of Giardia >three orders of magnitude higher than some bacteria
Chlorine has little impact on viability of Cryptosporidium when used at the relatively low doses encountered in water treatment (e.g., 5 mg/L)
(Disinfectant, 1999)

10. Figure 2-1. Free Chlorine Giardia and Virus CT Requirements
Shows that the CT values (mg•min/L) required to achieve recommended disinfection efficiency for conventional filtration systems (i.e., 0.5-log Giardia cyst and 2-log virus inactivation level) are 23 and 3 mg•min/L, respectively.
(Disinfectant, 1999)

11. Figure 2-2. CT Values for Inactivation of Giardia Cysts by Free Chlorine a 10⁰C (at Cl2 dose of 3.0 mg/L)
According to figure, does the inactivation efficacy of free chlorine increase or decrease with increased pH?
(Disinfectant, 1999)

12. Figure 2-3. CT Values for Inactivation of Giardia Cysts by Free Chlorine at pH 7.0 ( at Cl2 dose of 3.0 mg/L)
According to figure, does the inactivation efficacy of free chlorine increase or decrease with increased temperature?
(Disinfectant, 1999)

13. Proposed Experiments
Test the effect of pH on chlorine bacterial inactivation
Test the effect of temperature on chlorine bacterial inactivation
Test the effect of contact time on chlorine bacterial inactivation
Test the effectiveness of coffee filters on removing yeast from solution before plating

14. Additional Information (Disinfectant, 1999)
2.7.6 Operational Considerations
Application Methods (p. 2-41)
Safety and Handling Considerations (p. 2-42)
2.8 Summary
2.8.1 Advantages and Disadvantages of Chlorine Use (p & 2-43)
2.8.2 Summary Table (Table 2-22, p. 2-44)

15. References
Boal, Andrew K. "On-Site Generation of Disinfectants." National Environmental Services Center. Spring Web. 19 Mar <
Clark, N.A., et al Human Enteric Viruses in Water, Source, Survival, and Removability, Internal Conference on Water Pollution Research. Landar.
Culp, G.L., and R.L. Culp New Concepts in Water Purification. Van Nostrand Reinhold Company, New York, NY.
Culp/Wesner/Culp Handbook of Public Water Systems. Van Nostrand Reinhold Company, New York, NY.
"Disinfectant Use in Water Treatment: Chlorine." EPA Guidance Manual Web. 19 Mar <
Haas C.N. and R.S. Engelbrecht “Physiological Alterations of Vegetative Microorganisms Resulting from Aqueous Chlorination.” J. Water Pollution Control Fed. 52(7): 1976.
Hoff, J.C., E.W. Rice, ad F.W. Schaefer “Disinfection and the Control of Waterborne Giardiasis.” Conference proceedings, ASCE Specialty Conference.
Scarpino P.V., et al “A Comparative Study of the Inactivation of Viruses in Water by Chlorine.” Water Research. 6:959.