Wastewater Treatment Flashcards
1
Q
Why is drinking water treated?
A
to remove insoluble material, microorganisms, organic/inorganic compounds, and to prevent growth of new microorganisms
2
Q
How is drinking water treated?
A
- coagulation: form and remove floc containing insoluble material and microorganisms
- filtration: removing remaining particulates and most organic and inorganic compounds
- chlorination: kills remaining microorganisms and prevents growth of new inocula
3
Q
What are the goals of wastewater treatment?
A
- preventing waterborne disease (typhoid fever, cholera, protozoan infections)
- preventing pollution and dead zones
- keeping water clean and safe to swim in (tourism)
- keeping water clean for downstream users
4
Q
What is BOD?
A
- stands for biological oxygen demand
- measures how much oxygen it takes for the bacteria to break down organic compounds
- an indirect measure of the amount of organic matter in the water
5
Q
What are clarifiers?
A
- used to remove solid particulates or suspended solids from the water
- water is allowed to settle in tanks
- involved in primary wastewater treatment
6
Q
What is sludge?
A
- a byproduct of wastewater treatment
- mix of organic matter, microorganisms, trace chemicals, and inorganic solids
- disposed of after each step of treatment
7
Q
What is floc?
A
- flakes of material in the water
- forms globs to that it can be more easily removed
- normal floc settles well
- bulking sludge does not settle properly
8
Q
What happens in primary wastewater treatment?
A
- physical processes
- uses grates and screens to remove solid particles
- water is allowed to settle in tanks (clarifiers)
- effluent still has a substantial BOD
9
Q
What happens in secondary wastewater treatment?
A
- water from primary clarifier moves into an aeration basin
- mixers are used to aerate the water
- organic matter in the water is processed by suspended biomass
- the final clarifier removes the bacteria and sludge
- activated sludge and biomass is returned to the aeration basin
- waste sludge is disposed of
10
Q
What happens in tertiary wastewater treatment (nitrogen removal)?
A
- nitrogen is present in sewage as ammonia (NH3)
- nitrosomonas and nitrobacter convert ammonia (NH3) to nitrate (NO3) in an aeration basin (nitrification, step 1)
- nitrification consumes a great deal of oxygen
- bacteria convert nitrate (NO3) to N2 gas in an anoxic basin (denitrification, step 2)
- nitrate (NO3) from the aeration basin is recycled back to the anoxic basin
11
Q
What happens in tertiary wastewater treatment (phosphorus removal)?
A
- a group of bacteria called PAOs (phosphorus accumulating organisms) removes phosphorus under the appropriate conditions
- bacteria is cycled between anaerobic and aerobic conditions
12
Q
How are coliforms detected in water?
A
- coliforms are indicators of microorganisms in water
- standard method: add water to MacConkey broth and gas tube, plate on EMB agar, plate on nutrient agar slant, Gram stain
- membrane filter: see if colonies form on the plate through the filter, takes about 1 day to get the results
13
Q
What is the purpose of anaerobic digestion?
A
- used for high BOD industrial wastewater
- reduces amount of sludge for disposal
- produces methane