Colorado WW Operator D Exam
questions with verified correct
answers
______ = BOD, lbs./day / MLVSS, lbs. - correct answer ✔✔ F/M ratio
In a conventional activated sludge plant, oxygen demand is highest - correct answer ✔✔ At the
head end of the tank
Air requirements in an activated sludge tank are governed by - correct answer ✔✔ BOD and the
desired removal efficiency, Volatile suspended solids concentration in the aerator, Suspended
solids concentrations of the primary effluent
It is not necessary to be a skilled microbiologist or to be able to identify or count individual
species. Rather the operator needs only to recognize major groups of organisms such as: -
correct answer ✔✔ Filamentous bacteria, rotifers, protozoa
In addition to high energy costs, excess DO levels can cause - correct answer ✔✔ Damage to
floc particles due to turbulence
Which of the following are key factors in activated sludge nitrification? Check all that apply. -
correct answer ✔✔ MCRT, Alkalinity and pH, Temperature, DO, TKN loading
An activated sludge that settles poorly and has an SVI > 250 mL/g is described as what? - correct
answer ✔✔ Bulking
Which of the following is a modification of the activated sludge process? - correct answer ✔✔
All of these answers are correct
,Taking samples at different locations along the length and the width of a reactor (aeration tank)
as well as at different depths and analyzing them for solids concentration will verify whether or
not you have....? - correct answer ✔✔ Proper mixing in the tank
CCSS stands for: - correct answer ✔✔ Clarifier core suspended solids
Because nitrifiers grow slower than other bacteria, sludge ages longer than ____ days are often
needed. - correct answer ✔✔ 5 days
During plant rounds, an operator notices that the secondary effluent is cloudy. The operator
should: - correct answer ✔✔ Check the dissolved oxygen level in the aeration tank
Given the following data, determine the excess solids (in lbs) that should be wasted from this
activated sludge system. Target F:M = 0.6 per day, MLVSS = 2500 mg/L, BOD loading= 18,140
lb/day, Volume of aeration basin = 2 million gallons - correct answer ✔✔ 11,467 lb
Conditions in which oxygen is absent but nitrate is present are referred to as what? - correct
answer ✔✔ Anoxic
What characteristics are associated with quality activated sludge? - correct answer ✔✔ Brown
color, some dissolved oxygen content, and good settling
The activated sludge process removes soluble BOD from wastewater by - correct answer ✔✔
Absorption
Why is the sludge returned from the secondary clarifier to the aeration tank in activated sludge
used for nitrification? - correct answer ✔✔ To provide microorganisms
,If fine-bubble diffusers are used to introduce air into a biological reactor, the surface of the tank
will typically have what type of appearance? - correct answer ✔✔ Mildly agitated, partially
covered with light foam
In an anoxic activated sludge process, oxygen for facultative bacteria is provided by...? - correct
answer ✔✔ Nitrate, NO3
A small area of dark gray/black sludge in an aeration tank can be due to aeration equipment
failure or ____. - correct answer ✔✔ The introduction of a septic sidestream
When doing a 30-minute activated sludge settleability test, a 1000ml Imhoff cone should be
used. - correct answer ✔✔ FALSE
In a conventional activated sludge process, how much oxygen is required per lb. of BOD
removed? - correct answer ✔✔ 0.8 to 1.2 lb oxygen /lb BOD
Which of the following conditions would least likely contribute to rising sludge in secondary
clarifiers? - correct answer ✔✔ Clarifier hydraulic loading
In an activated sludge process bacteria release chemicals called ________ that break down the
food particles that are adsorbed to the cell wall so that they can be absorbed by the
microorganism. - correct answer ✔✔ Enzymes
Acids should never be added to chlorine solutions because they - correct answer ✔✔ Cause
chlorine gas to be released
Chloramines are ____? - correct answer ✔✔ Combined chlorine
What are the characteristics for chlorine as used in pollution control? - correct answer ✔✔
Chlorine gas is toxic, corrosive, and heavier than air
, Chlorine applied minus ____ equals chlorine residual - correct answer ✔✔ Chlorine demand
Unlike chlorine, UV does not leave what in treated water? - correct answer ✔✔ A residual
Coliform bacteria are: - correct answer ✔✔ Indicators
A _____ residual is attained after breakpoint chlorination. - correct answer ✔✔ Free
If you need a chlorine residual of 1 mg/l, how many pounds of chlorine must be applied each
day if the flow is 2.5 mgd and the chlorine demand is 15 mg/l? - correct answer ✔✔ 334 lb/d
A total residual is also referred to as a ______ residual. - correct answer ✔✔ Combined
Total and fecal coliform are pathogenic. - correct answer ✔✔ FALSE
_________ = flow, mgd x chlorine dosage, mg/L x 8.34 lb/gal. - correct answer ✔✔ Feed
Rate/Dose (lbs/day)
Sodium hypochlorite is manufactured by the reaction of gaseous or liquid chlorine with a
solution of _________ _________ to produce a liquid containing NaOCl. - correct answer ✔✔
Sodium hypochlorite
At concentrations less than _____, chlorine gas is not detectable by the human sense of smell. -
correct answer ✔✔ 1 ppm
A treatment plant uses sulfur dioxide to dechlorinate effluent. An operator needs to adjust the
sulfonator so that the dosing concentration is 1.5 mg/l more than the chlorine residual. Based
questions with verified correct
answers
______ = BOD, lbs./day / MLVSS, lbs. - correct answer ✔✔ F/M ratio
In a conventional activated sludge plant, oxygen demand is highest - correct answer ✔✔ At the
head end of the tank
Air requirements in an activated sludge tank are governed by - correct answer ✔✔ BOD and the
desired removal efficiency, Volatile suspended solids concentration in the aerator, Suspended
solids concentrations of the primary effluent
It is not necessary to be a skilled microbiologist or to be able to identify or count individual
species. Rather the operator needs only to recognize major groups of organisms such as: -
correct answer ✔✔ Filamentous bacteria, rotifers, protozoa
In addition to high energy costs, excess DO levels can cause - correct answer ✔✔ Damage to
floc particles due to turbulence
Which of the following are key factors in activated sludge nitrification? Check all that apply. -
correct answer ✔✔ MCRT, Alkalinity and pH, Temperature, DO, TKN loading
An activated sludge that settles poorly and has an SVI > 250 mL/g is described as what? - correct
answer ✔✔ Bulking
Which of the following is a modification of the activated sludge process? - correct answer ✔✔
All of these answers are correct
,Taking samples at different locations along the length and the width of a reactor (aeration tank)
as well as at different depths and analyzing them for solids concentration will verify whether or
not you have....? - correct answer ✔✔ Proper mixing in the tank
CCSS stands for: - correct answer ✔✔ Clarifier core suspended solids
Because nitrifiers grow slower than other bacteria, sludge ages longer than ____ days are often
needed. - correct answer ✔✔ 5 days
During plant rounds, an operator notices that the secondary effluent is cloudy. The operator
should: - correct answer ✔✔ Check the dissolved oxygen level in the aeration tank
Given the following data, determine the excess solids (in lbs) that should be wasted from this
activated sludge system. Target F:M = 0.6 per day, MLVSS = 2500 mg/L, BOD loading= 18,140
lb/day, Volume of aeration basin = 2 million gallons - correct answer ✔✔ 11,467 lb
Conditions in which oxygen is absent but nitrate is present are referred to as what? - correct
answer ✔✔ Anoxic
What characteristics are associated with quality activated sludge? - correct answer ✔✔ Brown
color, some dissolved oxygen content, and good settling
The activated sludge process removes soluble BOD from wastewater by - correct answer ✔✔
Absorption
Why is the sludge returned from the secondary clarifier to the aeration tank in activated sludge
used for nitrification? - correct answer ✔✔ To provide microorganisms
,If fine-bubble diffusers are used to introduce air into a biological reactor, the surface of the tank
will typically have what type of appearance? - correct answer ✔✔ Mildly agitated, partially
covered with light foam
In an anoxic activated sludge process, oxygen for facultative bacteria is provided by...? - correct
answer ✔✔ Nitrate, NO3
A small area of dark gray/black sludge in an aeration tank can be due to aeration equipment
failure or ____. - correct answer ✔✔ The introduction of a septic sidestream
When doing a 30-minute activated sludge settleability test, a 1000ml Imhoff cone should be
used. - correct answer ✔✔ FALSE
In a conventional activated sludge process, how much oxygen is required per lb. of BOD
removed? - correct answer ✔✔ 0.8 to 1.2 lb oxygen /lb BOD
Which of the following conditions would least likely contribute to rising sludge in secondary
clarifiers? - correct answer ✔✔ Clarifier hydraulic loading
In an activated sludge process bacteria release chemicals called ________ that break down the
food particles that are adsorbed to the cell wall so that they can be absorbed by the
microorganism. - correct answer ✔✔ Enzymes
Acids should never be added to chlorine solutions because they - correct answer ✔✔ Cause
chlorine gas to be released
Chloramines are ____? - correct answer ✔✔ Combined chlorine
What are the characteristics for chlorine as used in pollution control? - correct answer ✔✔
Chlorine gas is toxic, corrosive, and heavier than air
, Chlorine applied minus ____ equals chlorine residual - correct answer ✔✔ Chlorine demand
Unlike chlorine, UV does not leave what in treated water? - correct answer ✔✔ A residual
Coliform bacteria are: - correct answer ✔✔ Indicators
A _____ residual is attained after breakpoint chlorination. - correct answer ✔✔ Free
If you need a chlorine residual of 1 mg/l, how many pounds of chlorine must be applied each
day if the flow is 2.5 mgd and the chlorine demand is 15 mg/l? - correct answer ✔✔ 334 lb/d
A total residual is also referred to as a ______ residual. - correct answer ✔✔ Combined
Total and fecal coliform are pathogenic. - correct answer ✔✔ FALSE
_________ = flow, mgd x chlorine dosage, mg/L x 8.34 lb/gal. - correct answer ✔✔ Feed
Rate/Dose (lbs/day)
Sodium hypochlorite is manufactured by the reaction of gaseous or liquid chlorine with a
solution of _________ _________ to produce a liquid containing NaOCl. - correct answer ✔✔
Sodium hypochlorite
At concentrations less than _____, chlorine gas is not detectable by the human sense of smell. -
correct answer ✔✔ 1 ppm
A treatment plant uses sulfur dioxide to dechlorinate effluent. An operator needs to adjust the
sulfonator so that the dosing concentration is 1.5 mg/l more than the chlorine residual. Based
