d2: water treatment

describe the steps to water treatment?

1. raw water is pumped into a water processing plant

2. mixed with flocculant

3. water undergoes filtration

4. water is disinfected

5. water is stored before use by consumers (usually at a higher elevation)

what is the purpose of a flocculant? how does it remove small particles from water?

traps very small particles (colloidals) into larger aggregates that will settle to the bottom

what happens during filtration through sand beds?

particulate matter sticks to the sand grains

some use activated charcoal to remove chemicals

some use bacteria to catch particles in biofilms

what are the pros of using sand filtration?

inexpensive, easy to maintain

how are membranes better or worse?

water passed through a membrane with tiny pores

completely removes large organisms like Giardia

relatively expensive, difficult to maintain

what are the 3 common methods of disinfection of filtered water?

chlorine

ozon

ultraviolet light

why is chlorine used?

most common

effective against many organisms (not Giardia), inexpensive

leaves residual taste; some health concerns

why is ozone used?

no residual taste or health concerns

expensive, hard to maintain

why is ultraviolet light used?

no residual taste or health concerns

must pass through special tubes to give good exposure

expensive, hard to maintain

what is an indicator organism? why do we test for it instead of directly testing for pathogens?

test for fecal contamination in water

can’t test for all pathogens, so it helps to know if a pathogen in general is present