Lecture 9 AW WOW WOW WOW

Question 1

what is log removal?

Answer 1

This term does not mean that the removal of physical
parameters is a logarithmic process, but rather that the percent removal found at a point in time can be mathematically represented by a log removal function.

Question 2

how is log removal expressed as?

Answer 2

90% of the microorganisms inactivated—1-log inactivation
99% of the microorganisms inactivated — 2-log inactivation
99.9% of the microorganisms inactivated — 3-log inactivation
99.99% of the microorganisms inactivated — 4-log inactivation

Question 3

what log removal objective is used in BC?

Answer 3

• 4 log reduction in viruses;
• 3 log reduction in cryptosporidium and giardia lamblia;
• 2 treatment barriers minimum (i.e. Seymour-Capilano filtration plant: filtration +UV);
• ≤ 1 NTU turbidity;
• 0 total coliforms & fecal coliforms (bacteria)

Question 4

what is disinfection?

Answer 4

• Disinfection is the process of selective destruction of disease causing organisms (pathogens).

Question 5

how does disinfection differ from sterilization?

Answer 5

Disinfection is not same as sterilization which implies the destruction of all living organisms. Water and wastewater contain a wide range of pathogens including bacteria, virus, and protozoa. So the basic strategy is to keep these contaminants out of drinking water or treated wastewater.

Question 6

what are the two types of disinfection?

Answer 6

primary disinfection: (happens at the plant level)
secondary disinfection: (happens after water has left the plant, happens @ pipe level, need to maintain some disinfectant properties)

Question 7

what are the 3 processes commonly used for disinfection?

Answer 7

chlorination (secondary disinfection)
ozonation, UV radiation (primary disinfection)

Question 8

true/false, chlorine is not most common disinfectant?

Answer 8

false, term is also synonymous with disinfection

Question 9

what are the benefits of using chlorine?

Answer 9

The benefit of using chlorine is the ‘residual chlorine’ that remains in the water long after its application that provides secondary disinfection.

Question 10

what are some disadvantages of using chlorine?

Answer 10

• The disadvantage of using free chlorine is the formation of halogenated disinfection by products (DBPs) which occurs when chlorine combines with NOM in water.
  o DBP formed: trihalomethanes (THMs) chloroform and haloacetic acids (HAA). These cause adverse health effects.
• Additional secondary reactions of chlorine with phenols forms chlorophenols which that produces strong taste and odor (aesthetics).
• The balance between adequate inactivation of pathogenic microorganisms and limited production of by-products (DBPs) that have adverse health effects (suspected carcinogens) is a major challenge in water and wastewater treatment.

Question 11

what are some common forms of chlorine used in chlorination?

Answer 11

Question 12

what is the actual disinfectant when chlorine reacts with water?

Answer 12

Question 13

what is free residual chlorine?

Answer 13

Defined as sum of
A measure of chlorination effectiveness
Maintaining a specified free residual chlorine value (0.5 to 1 ppm) in water supply system isa standard objective.
HOCl is more effective disinfectant than OCl -

Question 14

what is combined available chlorine?

Answer 14

Question 15

what are the reactions for combined available chlorine dependent on?

Answer 15

pH, temperature, contact time and initial ratio of chlorine to ammonia

Question 16

what are the 3 products known as chloromines?

Answer 16

monochloramine, dichloramine, trichloramine - they are also disinfectants

Question 17

true/false chloramines/combined available chlorine is not ahs effective as free chlorine?

Answer 17

true

Question 18

true/false: chloramines (specifically di and tri-chloramines can cause taste and odor problems?

Answer 18

true

Question 19

what is chlorine demand?

Answer 19

Defined as the difference between chlorine added, and the sum of free + combined chlorine remaining at the end of contact period.
Ammonia in water + chlorine

Question 20

how do we overcome chlorine demand?

Answer 20

breakpoint chlorination

Question 21

what is breakpoint chlorination?

Answer 21

Breakpoint chlorination involves the addition of sufficient chlorine to result in free chlorine residual.

Question 22

what is chloramination?

Answer 22

Excessive chloramines can cause taste and odour issues. However, sometimes chloramination (intentional addition of ammonia into water to combine with chlorine) is practiced.

Question 23

why is chloramination used?

Answer 23

Chloramines are more persistent and have longer half-life than free chlorine – therefore last longer in water distribution systems to inactivate pathogens

Question 24

what is chicks law?

Answer 24

explanation of disinfection kinetics stating The number of organisms destroyed in a unit time is proportional to the number of organisms remaining

Question 25

what are the implications of combined available chlorine?

Answer 25

- good for secondary disinfection as they last longer compared to free chlorine - negative: tastes and has smell issues