Disinfection-chlorine

Question 1

Exam question

What are the major considerations that affect the bacteriacidal efficiency of chlorine

Answer 1

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.

Question 2

What is disinfection and how it can be achieved?

Answer 2

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.

Question 3

True or false

Very little chlorine will be found in its free form.

Answer 3

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+

Question 4

HCl have no bacterecidal effect (disinfecting material)

Answer 4

True because

it only makes the pH lower.

Question 5

HOCl and OCl- are both disinfecting compounds however HOCl is more active than OCl- (it kills more )

Answer 5

True

q

Question 6

HOCl is more present than OCl- at lower temp

HOCl is more present than OCl- at lower pH

Answer 6

true

Question 7

What are the compounds of chlorine that can be used

instead of chlorine itself

Answer 7

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

Question 8

Why we use ammonia

Answer 8

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.

Question 9

Free residual chlorine

Answer 9

Chlorine available that is present after disinfection

Question 10

Combined residual chlorine

Answer 10

Combined chlorine that is present after disinfection like chloromines

Question 11

Available chlorine

Answer 11

Amount of chlorine available to carry out oxidation process

Question 12

Free residual chlorination

Answer 12

process of chlorination where u end having free residual chlorine

Question 13

Combined residual chlorination

Answer 13

process of chlorination where u end having free residual combined chlorine

Question 14

Chlorine demand

Answer 14

Amount of chlorine needed to oxidize all the oxidizable material present in water

Question 15

Plain chlorination

Answer 15

process where chlorination is the only process needed like for spring water

Question 16

Prechlorination

Answer 16

chlorination is conducted prior to any treatment process.

Question 17

post chlorination

Answer 17

chlorination is conducted at end of treatment process

Question 18

rechlorination

Answer 18

when chlorination is applied again after pre or postchlorination (used when we want to store water for example)

Question 19

Dechlorination

Answer 19

sometimes we overchlorinate we aerate or we add activated calcium to dechlorinate.

Question 20

Discuss briefly how complete disinfection could be achieved

Answer 20

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

Question 21

Break point chlorination Curve

Answer 21

Review curve

Question 22

True or false

Quantity of chlorine to be stored should be equal to the quantity needed for two week operation

Answer 22

True