Wastewater Treatment Operations Exam Questions with Verified Answers (Graded A)
Ideal velocity for sanitary sewer collection systems - Answers 2 ft/sec
Typical distance between manholes - Answers 300-500 ft
Purpose of preliminary treatment processes - Answers Remove course material from wastewater
Purpose of primary treatment processes - Answers Remove settleable and floatable materials
Purpose of secondary treatment processes - Answers Remove suspended and dissolved solids
Sulfur dioxide (SO2) is used for... - Answers Used to neutralize chlorine & detoxify the effluent
Ideal flow-through velocity of a grit channel - Answers 0.7-1.4 ft/sec
1 ft/sec is best
Types of flow measuring devices in an open channel - Answers Parshall Flume & V-notch weir
Types of flow measuring devices in a closed channel - Answers Venturi meter & magnetic flowmeter
Advantages of measuring flow with a Parshall flume - Answers Smooth constriction
no protruding edges
waste will not collect behind the metering device
Ideal detention time in a primary clarifier - Answers 1.5-2 hrs
Humus - Answers Layer of organisms (aka biomass) on trickling filter media that eventually gets thick
enough to slough off and must be removed by settling in the secondary clarifier
Typical BOD & suspended solids removal rate of an activated sludge plant - Answers 90-99% removal
Mixed liquor - Answers Activated sludge + raw wastewater + return sludge in an aeration tank
Types of bacteria present in a digester - Answers Acid formers & gas formers
Typical organic matter removal rate of a digester - Answers 50% removal
If temperature is kept at 95F, what is the typical digestion time in a digester? - Answers 30 days
Byproducts of digestion - Answers Organic acids
carbon dioxide gas
methane
Typical gas ratio in a digester - Answers 70% methane, 30% CO2
,Types of dewatering methods - Answers sludge drying beds
lagoons
centrifuges
vacuum filters
filter presses
Shallow pond - Answers Aerobic
3-6 ft deep
Oxygen throughout their depth
Deep pond - Answers Anaerobic
8-12 ft deep
Treatment depends on fermentation of sludge at the bottom
Odorous
Mainly for industrial waste
Facultative pond - Answers Most common type of pond
Top layer is aerobic
Bottom layer is anaerobic
Algae supplies oxygen to supernatant
Short-circuiting - Answers When flowing water entering a tank or basin flows along a nearly direct
pathway from inlet to outlet, resulting in shorter contact or settling times
Bar Racks - Answers Spacing between bars is 3-4 in
Usually found in bypass channels
Manually cleaned
Bar Screens - Answers Spacing between bars is 3/8-2 in
The more debris that collects on bar screens leads to... - Answers Greater head loss through bar screens
Organic wastes settled out
Dissolved oxygen is depleted
, Septic conditions
Shear pin - Answers A straight pin that will break when a certain load or stress is exceeded
Typical limit of allowable head loss at a bar screen - Answers 3 in of head loss
Benefits of a communitor - Answers Reduction in screenings disposal
Reduction in flies
Reduction in odors
Most grit channels are designed to remove... - Answers 0.2 mm size sand & and all other heavier
materials
Typical settling rate of sand (0.2 mm) - Answers 0.075 ft/sec
Settling time (sec) = - Answers Depth (ft) / Settling Rate (ft/sec)
Grit channel length (ft) = - Answers [Depth of channel (ft) x Flow velocity (ft/sec)] / Settling Rate (ft/sec)
If inspection of grit reveals a high amount of organic material... - Answers Velocity in the grit channel
may be too low
If inspection of grit reveals mainly large or heavy sand... - Answers Velocity in the channel may be too
high
Aerated grit chambers work on the basis of... - Answers Air and water have a lower specific gravity than
water, so grit settles out better
What is a slurry? - Answers A watery mixture or suspension of insoluble matter
How does a cyclone grit separator work? - Answers Water and suspended particles are carried upward in
the secondary vortex while heavy particles move outward and down in the primary vortex.
Typical grit quantities per volume wastewater - Answers 1-4 cubic ft / 1 MG
When disposing of grit by burial, how much soil should cover the grit? - Answers 6 in
What are the benefits of pre-aerating wastewater before grit removal? - Answers Improve grit removal
efficiency
Freshen wastewater
Remove gases
Add oxygen
Promote flotation of grease
Ideal velocity for sanitary sewer collection systems - Answers 2 ft/sec
Typical distance between manholes - Answers 300-500 ft
Purpose of preliminary treatment processes - Answers Remove course material from wastewater
Purpose of primary treatment processes - Answers Remove settleable and floatable materials
Purpose of secondary treatment processes - Answers Remove suspended and dissolved solids
Sulfur dioxide (SO2) is used for... - Answers Used to neutralize chlorine & detoxify the effluent
Ideal flow-through velocity of a grit channel - Answers 0.7-1.4 ft/sec
1 ft/sec is best
Types of flow measuring devices in an open channel - Answers Parshall Flume & V-notch weir
Types of flow measuring devices in a closed channel - Answers Venturi meter & magnetic flowmeter
Advantages of measuring flow with a Parshall flume - Answers Smooth constriction
no protruding edges
waste will not collect behind the metering device
Ideal detention time in a primary clarifier - Answers 1.5-2 hrs
Humus - Answers Layer of organisms (aka biomass) on trickling filter media that eventually gets thick
enough to slough off and must be removed by settling in the secondary clarifier
Typical BOD & suspended solids removal rate of an activated sludge plant - Answers 90-99% removal
Mixed liquor - Answers Activated sludge + raw wastewater + return sludge in an aeration tank
Types of bacteria present in a digester - Answers Acid formers & gas formers
Typical organic matter removal rate of a digester - Answers 50% removal
If temperature is kept at 95F, what is the typical digestion time in a digester? - Answers 30 days
Byproducts of digestion - Answers Organic acids
carbon dioxide gas
methane
Typical gas ratio in a digester - Answers 70% methane, 30% CO2
,Types of dewatering methods - Answers sludge drying beds
lagoons
centrifuges
vacuum filters
filter presses
Shallow pond - Answers Aerobic
3-6 ft deep
Oxygen throughout their depth
Deep pond - Answers Anaerobic
8-12 ft deep
Treatment depends on fermentation of sludge at the bottom
Odorous
Mainly for industrial waste
Facultative pond - Answers Most common type of pond
Top layer is aerobic
Bottom layer is anaerobic
Algae supplies oxygen to supernatant
Short-circuiting - Answers When flowing water entering a tank or basin flows along a nearly direct
pathway from inlet to outlet, resulting in shorter contact or settling times
Bar Racks - Answers Spacing between bars is 3-4 in
Usually found in bypass channels
Manually cleaned
Bar Screens - Answers Spacing between bars is 3/8-2 in
The more debris that collects on bar screens leads to... - Answers Greater head loss through bar screens
Organic wastes settled out
Dissolved oxygen is depleted
, Septic conditions
Shear pin - Answers A straight pin that will break when a certain load or stress is exceeded
Typical limit of allowable head loss at a bar screen - Answers 3 in of head loss
Benefits of a communitor - Answers Reduction in screenings disposal
Reduction in flies
Reduction in odors
Most grit channels are designed to remove... - Answers 0.2 mm size sand & and all other heavier
materials
Typical settling rate of sand (0.2 mm) - Answers 0.075 ft/sec
Settling time (sec) = - Answers Depth (ft) / Settling Rate (ft/sec)
Grit channel length (ft) = - Answers [Depth of channel (ft) x Flow velocity (ft/sec)] / Settling Rate (ft/sec)
If inspection of grit reveals a high amount of organic material... - Answers Velocity in the grit channel
may be too low
If inspection of grit reveals mainly large or heavy sand... - Answers Velocity in the channel may be too
high
Aerated grit chambers work on the basis of... - Answers Air and water have a lower specific gravity than
water, so grit settles out better
What is a slurry? - Answers A watery mixture or suspension of insoluble matter
How does a cyclone grit separator work? - Answers Water and suspended particles are carried upward in
the secondary vortex while heavy particles move outward and down in the primary vortex.
Typical grit quantities per volume wastewater - Answers 1-4 cubic ft / 1 MG
When disposing of grit by burial, how much soil should cover the grit? - Answers 6 in
What are the benefits of pre-aerating wastewater before grit removal? - Answers Improve grit removal
efficiency
Freshen wastewater
Remove gases
Add oxygen
Promote flotation of grease
