Disinfection-chlorine Flashcards
Exam question
What are the major considerations that affect the bacteriacidal efficiency of chlorine
1-Kind and concentration of disinfectant
2-Contact time provided and temperature
3-Chemical characteristics of water (whether it contains reducing agents)
4-Kind and concentration of organisms to be destroyed.
What is disinfection and how it can be achieved?
Disinfection is the destruction or inactivation of disease producing (pathogenic) organisms.
Disinfection can be achieved by:
1-) Physical treatment such storage or application of heat or other physical agents.
2-) Irradiation such as ultraviolet radiation.
3-) Metalic ions such as copper and silver
4-) Oxidants such as chlorine (Mostly used disinfectant) ,halogens, ozone, and other organic and inorganic materials.
True or false
Very little chlorine will be found in its free form.
True because
When chlorine is added to water it forms hypochlorous acid (HOCl) and hydrochloric acid (HCl) where hypochlorous acid dissociates(ionizes) instantly into hydrogen ion (H+) and hypochlorite ion (OCl-) to a degree depending on the pH and temperature.
Cl2 + H20 giveandgiveback HOCl +HCl
HOCl giveandgiveback OCl- + H+
HCl have no bacterecidal effect (disinfecting material)
True because
it only makes the pH lower.
HOCl and OCl- are both disinfecting compounds however HOCl is more active than OCl- (it kills more )
True
q
HOCl is more present than OCl- at lower temp
HOCl is more present than OCl- at lower pH
true
What are the compounds of chlorine that can be used
instead of chlorine itself
Calcium hypochlorite (Ca(OCl)2) Sodium hypochlorite (NaOCl) Ca(OCl0)2 is better at storage and contains more chlorine than NaOCl Ca(OCl0)2 givesandgiveback Ca2+ + 2OCl- H+ + OCl- givesandgiveback HOCl
Why we use ammonia
We use ammonia in order to form chloramines which is a more stable disinfectinng agent , it is disinfecting strength is lower than HOCl and OCl- =, however it is more stable meaning it stays for longer time. Also see slides there are reaction s that u must study.
Free residual chlorine
Chlorine available that is present after disinfection
Combined residual chlorine
Combined chlorine that is present after disinfection like chloromines
Available chlorine
Amount of chlorine available to carry out oxidation process
Free residual chlorination
process of chlorination where u end having free residual chlorine
Combined residual chlorination
process of chlorination where u end having free residual combined chlorine
Chlorine demand
Amount of chlorine needed to oxidize all the oxidizable material present in water
Plain chlorination
process where chlorination is the only process needed like for spring water
Prechlorination
chlorination is conducted prior to any treatment process.
post chlorination
chlorination is conducted at end of treatment process
rechlorination
when chlorination is applied again after pre or postchlorination (used when we want to store water for example)
Dechlorination
sometimes we overchlorinate we aerate or we add activated calcium to dechlorinate.
Discuss briefly how complete disinfection could be achieved
To achieve complete disinfection we use breakpoint chlorination, which will determine the dose needed to oxidize all the oxidizable material and achieve a complete kill of all bacteria and leave a residual chlorine which could be needed at later stages of the distribution
Break point chlorination Curve
Review curve
True or false
Quantity of chlorine to be stored should be equal to the quantity needed for two week operation
True
