Disinfection Flashcards
What are the three typical forms of pathogens?
Bacteria
Viruses
Parasites
What are some examples of diseases caused by bacteria in wastewater?
Salmonellosis Shigellosis Typhoid fever Cholera Paratyphoid Dysentery Anthrax
What is disinfection?
Getting rid of disease causing organisms
What can be used as an indicator of effectiveness of disinfection?
Fecal coliforms. They are only found in the small intestine of warm blooded animals and can show cross-contamination
What is UV disinfection?
Mercury lamps produce UV light that damages the nucleic acids of microorganisms which prevent reproduction
What is UV dose?
A product of UV intensity and residence time
What is UV transmittance?
The ratio of light entering and exiting the water
What are some water considerations for UV?
Hardness can foul quartz sleeves
pH can effect clarity due to soluble metal
Suspended solids negatively effect clarity
What is solarization in UV?
The quartz sleeve will get dimmer over time
Advantages of UV disinfection
Short detention time (5-7 seconds)
No toxic byproducts
No residual
What are disadvantages of UV?
High energy demand
No residual
Use of mercury
What is ozone?
An extremely strong oxidant; triatomic oxygen
How much energy applied goes to the generation of ozone?
About 10%
Advantages of ozone
High oxidation potential and more reactive than chlorine
Less persistent residuals
Fewer byproducts
Disadvantages of ozone
High capital, operation, and maintenance cost
Corrosive
Safety hazard
How does chlorine react with water?
It produces hypochlorous acid and hydrochloric acid
Hypochlorous acid is a strong disinfectant whereas hydrochloric acid is nothing special
How does hypochlorous acid break down?
Into hydrogen and the hypochlorite ion
The amount of breakdown is dependent on pH; higher pH means more hypochlorite
What is calcium hypochlorite?
Granular
Contains 65% chlorine by weight
Added to water gives you hypochlorous acid and lime
What is sodium hypochlorite?
Clear to greenish yellow liquid
10-15% strength
Added to water makes hypochlorous acid and sodium hydroxide
What is a consideration with the breakdown of sodium hypochlorite over time?
The strength is reduced as it is stored, so dosages may need to be adjusted
How does chlorine react with other substancez?
It can be reduced by reducing agents, resulting in the production of chloramines
What is chlorine dose?
Demand + residual
Which chloramines can be used for disinfection?
Mono and dichloramines, and they have a persistent residual
How does pH affect the formation of chloramines?
<4 will be trichloramines
4-5.5 will be dichloramines
6.5-7.5 mono and di will exist together
What is the difference between hypochlorinators and chlorinators?
Hypochlorinators are used to inject in liquid
Chlorinators are used to inject gas
What are safety considerations with chlorine cylinders?
Keep protective hood in place
Store away from heat
Store upright
Store secured to an immovable object
Chlorine leak detection
An ammonia solution will emit white vapor, but this is toxic
How to dechlorinate?
Long detention times Aeration Sunlight Activated carbon Sulfer dioxide (1:1) basis
What is a chlorine residual?
The concentration of chlorine present in water after the demand has been satisfied
What are some examples of diseases caused by viruses in wastewater?
Polio
Infectious hepatitis
What are some examples of diseases cause by parasites in wastewater?
Amoebic dysentery
Ascaris
Giardiasis
Cryptosporidium is
