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
