Environmental Engineering Final Exam – Comprehensive Study Guide, Review &
Practice Questions
What are MCLs and MCLGs? - correct answer ✔✔Maximum contaminant levels; Maximum
contaminant level goal: drinking water regulations and limits set by the government
What is the difference between Primary Standards and Secondary Standards for drinking water?
- correct answer ✔✔Primary Standards: based on direct human health issues
Secondary Standards: based on aesthetics
Explain the terms coagulation and flocculation, and how they are accomplished - correct answer
✔✔Coagulation--> Particle Destabilization:
-Charge neutralization (eg. dissolved aluminum ions)
-bridging (polymers)
-sweep floc
Flocculation--> Growing large particle from small ones
-Low shear (gentle mixing) allowing particles to stick together
Be able to explain the concept of Overflow Rate and be able to use it to size a settling tank. -
correct answer ✔✔.....
Explain step by step , using a diagram, how a Rapid Sand Filter is backwashed. - correct answer
✔✔a.) Valves 1 and 4 are closed
b.) Valve 2 is opened until water level on other side of wall drops all the way
c.) Valve 2 is closed and valve 5 is opened to backwash filter
d.) After backwashing, valve 5 is closed and valve 2 is opened again until water level drops again
e.) After this, valve 1 and 3 are opened until turbidity goes back to normal levels
, f.) Finally, valve 3 is closed and valve 4 is opened, resuming normal filtering
What is the purpose of backwashing a filter? - correct answer ✔✔Its purpose is to remove any
particles that are trapped within the filter, because over time the filter becomes too overloaded
with particles
What are the the three factors that determine when a Rapid Sand Filter must be backwashed? -
correct answer ✔✔-Head loss a.k.a. pressure drop -->(indication that the filter is clogging; the
faster the vel. of the water through the sand filter, the greater the friction and the greater the
head loss)
-Time (up to 48 hours)
-Turbidity
What is meant by a "dual-media" filter? What materials are typically used for the dual media
and why? - correct answer ✔✔A dual-media filter has very fine particle size diameters to help
filter out particulates. Sand and gravel are typically used in dual media filters.
What factors contribute to head loss during the operation of a sand filter? - correct answer ✔✔-
viscosity of the water
-weight of the water
-velocity of the water
-particle size of the media
-porosity of the media
What is the purpose of disinfection? - correct answer ✔✔To remove pathogenic microbes that
are present in the water that the filter could not remove.
What is the most commonly used disinfectant? - correct answer ✔✔Chlorine
Practice Questions
What are MCLs and MCLGs? - correct answer ✔✔Maximum contaminant levels; Maximum
contaminant level goal: drinking water regulations and limits set by the government
What is the difference between Primary Standards and Secondary Standards for drinking water?
- correct answer ✔✔Primary Standards: based on direct human health issues
Secondary Standards: based on aesthetics
Explain the terms coagulation and flocculation, and how they are accomplished - correct answer
✔✔Coagulation--> Particle Destabilization:
-Charge neutralization (eg. dissolved aluminum ions)
-bridging (polymers)
-sweep floc
Flocculation--> Growing large particle from small ones
-Low shear (gentle mixing) allowing particles to stick together
Be able to explain the concept of Overflow Rate and be able to use it to size a settling tank. -
correct answer ✔✔.....
Explain step by step , using a diagram, how a Rapid Sand Filter is backwashed. - correct answer
✔✔a.) Valves 1 and 4 are closed
b.) Valve 2 is opened until water level on other side of wall drops all the way
c.) Valve 2 is closed and valve 5 is opened to backwash filter
d.) After backwashing, valve 5 is closed and valve 2 is opened again until water level drops again
e.) After this, valve 1 and 3 are opened until turbidity goes back to normal levels
, f.) Finally, valve 3 is closed and valve 4 is opened, resuming normal filtering
What is the purpose of backwashing a filter? - correct answer ✔✔Its purpose is to remove any
particles that are trapped within the filter, because over time the filter becomes too overloaded
with particles
What are the the three factors that determine when a Rapid Sand Filter must be backwashed? -
correct answer ✔✔-Head loss a.k.a. pressure drop -->(indication that the filter is clogging; the
faster the vel. of the water through the sand filter, the greater the friction and the greater the
head loss)
-Time (up to 48 hours)
-Turbidity
What is meant by a "dual-media" filter? What materials are typically used for the dual media
and why? - correct answer ✔✔A dual-media filter has very fine particle size diameters to help
filter out particulates. Sand and gravel are typically used in dual media filters.
What factors contribute to head loss during the operation of a sand filter? - correct answer ✔✔-
viscosity of the water
-weight of the water
-velocity of the water
-particle size of the media
-porosity of the media
What is the purpose of disinfection? - correct answer ✔✔To remove pathogenic microbes that
are present in the water that the filter could not remove.
What is the most commonly used disinfectant? - correct answer ✔✔Chlorine
