Wastewater Treatment

Question 1

Why is drinking water treated?

Answer 1

to remove insoluble material, microorganisms, organic/inorganic compounds, and to prevent growth of new microorganisms

Question 2

How is drinking water treated?

Answer 2

• 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

Question 3

What are the goals of wastewater treatment?

Answer 3

• 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

Question 4

What is BOD?

Answer 4

• 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

Question 5

What are clarifiers?

Answer 5

• used to remove solid particulates or suspended solids from the water
• water is allowed to settle in tanks
• involved in primary wastewater treatment

Question 6

What is sludge?

Answer 6

• a byproduct of wastewater treatment
• mix of organic matter, microorganisms, trace chemicals, and inorganic solids
• disposed of after each step of treatment

Question 7

What is floc?

Answer 7

• 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

Question 8

What happens in primary wastewater treatment?

Answer 8

• physical processes
• uses grates and screens to remove solid particles
• water is allowed to settle in tanks (clarifiers)
• effluent still has a substantial BOD

Question 9

What happens in secondary wastewater treatment?

Answer 9

• 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

Question 10

What happens in tertiary wastewater treatment (nitrogen removal)?

Answer 10

• 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

Question 11

What happens in tertiary wastewater treatment (phosphorus removal)?

Answer 11

• a group of bacteria called PAOs (phosphorus accumulating organisms) removes phosphorus under the appropriate conditions
• bacteria is cycled between anaerobic and aerobic conditions

Question 12

How are coliforms detected in water?

Answer 12

• 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

Question 13

What is the purpose of anaerobic digestion?

Answer 13

• used for high BOD industrial wastewater
• reduces amount of sludge for disposal
• produces methane