John’s WEF/ABC Exam
1
The threshold limit value (TLV) concentration for chlorine
vapor is _________.
a. 0.1 ppm
b. 0.3 ppm
c. 0.5 ppm
d. 1.0 ppm
John’s WEF/ABC Exam
2
Answer: c.
The American Conference of Government Industrial Hygienists
(ACGIH) recommends the threshold limit value (TLV) concentration for
a specific chemical. TLVs are guidelines to recommended maximum
safe levels of workplace exposure to various chemical and physical
agents. It is important to note that chlorine is not detectable by the
human sense of smell at the TLV concentration of 0.5 ppm.
National Institute for Occupational Safety and Health (NIOSH)
Recommended Exposure Limit (REL): 0.5 ppm TWA; 1 ppm STEL
STEL = Short Term
Exposure Limit. TLV
= Threshold Limit
Value.
https://www.mathesongas.com/pdfs/products/threshold-limit-values-(tlv).pdf
Reference: Water Environment Federation (1994) Safety and Health in
Wastewater Systems. Manual of Practice No. 1, Alexandria, VA, pg. 26
John’s WEF/ABC Exam
3
When working in confined spaces where flammable gases
may be present, use only tools made of ______________.
a. stainless steel
b. lead
c. iron
d. a non-sparking alloy
John’s WEF/ABC Exam
4
Answer: d.
Non-sparking tools must be used in confined spaces where
flammable gases may be present. Beryllium-copper alloy based tools
are almost as durable as steel, and are preferred in certain situations
because they will not cause a spark that could ignite flammable
gases.
Reference: Water Environment Federation (1994) Safety and Health in
Wastewater Systems. Manual of Practice No. 1, Alexandria, VA, pg. 104
John’s WEF/ABC Exam
5
In addition to the worker entering a confined space, what is
the minimum number of people required to be present
during a confined space entry?
a. 0
b. 1
c. 2
d. 3
e. 4
John’s WEF/ABC Exam
6
Answer: b.
A qualified entry supervisor and an attendant must be present during
any confined space entry, in addition to the entrant however it is
possible to have a single person approved to fulfill the requirements of
both the supervisor and the attendant.
Reference: Water Environment Federation (1998) Confined Space Entry.
Special Publication, Alexandria, VA, pg. 9
John’s WEF/ABC Exam
7
Hearing protection must be made available to all employees exposed
to noise levels above _____________.
a. 85 decibels (db) averaged over 8 working hours
b. 850 decibels (db) averaged over 8 working hours
c. 85 decibels (db) continuously for 8 working hours
d. 85 decibels (db) at any point in the 8-hour workday
John’s WEF/ABC Exam
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Answer: a.
OSHA hearing conservation programs require hearing testing, hearing
protection and other measures for employees exposed to noise levels
that exceed an eight-hour time-weighted average of 85 decibels (db).
NOTE: OSHA sets legal limits on noise
exposure in the workplace. These limits
are based on a worker's time weighted
average over an 8 hour day. With noise,
OSHA's permissible exposure limit (PEL) is
90 dBA for all workers for an 8 hour day.
The OSHA standard uses a 5 dBA
exchange rate. This means that when the
noise level is increased by 5 dBA, the
amount of time a person can be exposed
to a certain noise level to receive the same
dose is cut in half.
Reference: Water Environment Federation (1994) Safety and Health in
Wastewater Systems. Manual of Practice No. 1, Alexandria, VA, pg. 24
John’s WEF/ABC Exam
9
How loud is too loud?
Noise is measured in units of sound
pressure levels called decibels, named
after Alexander Graham Bell, using Aweighted sound levels (dBA). The Aweighted sound levels closely match the
perception of loudness by the human ear.
Decibels are measured on a logarithmic
scale which means that a small change in
the number of decibels results in a huge
change in the amount of noise and the
potential damage to a person's hearing.
It is convenient to express the sound pressure as a
logarithmic decibel scale related to this lowest
human hearable sound = 20 micro Pa, 0 dB.
John’s WEF/ABC Exam
10
Recommended personal hygiene practices to minimize
the risk of being infected by wastewater pathogens
include _____________.
a. only rubbing your eyes while working if you are
wearing impervious gloves
b. washing your hands before the beginning of your
shift
c. changing out of your work clothes and showering
before leaving work
d. reading the material safety data sheets for all
chemicals used at the plant.
John’s WEF/ABC Exam
11
Answer: c.
Wastewater may contain pathogens that can cause serious
illness and disease. Therefore, never touch your eyes, nose
or mouth while you are around wastewater even if you are
wearing gloves. Remember to practice good hygiene while
working. For example, always wash your hands when
finished handling or working with anything that might be
contaminated with wastewater. Also, shower and change
your clothes at the end of your shift to reduce the likelihood
that you will carry any pathogens on yourself or your
clothing when you leave the wastewater treatment plant.
You should be familiar with the information contained within
the material safety data sheets for all of the chemicals with
which you may come into contact. This is not, however, a
personal hygiene practice, and these data sheets do not
provide information on the biological hazards potentially
associated with wastewater.
Reference: Water Environment Federation (1994) Safety and Health in
Wastewater Systems. Manual of Practice No. 1, Alexandria, VA, pg. 81
John’s WEF/ABC Exam
12
The BOD loading rate divided by the quantity of
microorganisms present in the biological reactors
(aeration tanks) is known as ______________.
a. organic loading
b. toxicity
c. hydraulic loading
d. food-to-microorganism ratio
e. sludge age
John’s WEF/ABC Exam
13
Answer: d.
The
food-to-microorganism
ratio (F:M) is the ratio of the
mass of organic loading to the
mass of microorganisms in
the biological reactors.
F=
M
Reference: Water Environment Federation (1994) Basic Activated Sludge Process
Control. Problem-Related Operations-Based Education, Alexandria, VA, pg. 94
John’s WEF/ABC Exam
14
White, fluffy foam on the biological reactors in an activated
sludge process is usually caused by ___________.
a. insufficient biomass to treat the incoming waste
b. low BOD
c. high DO
d. too little sludge being wasted from process
e. too much soap entering the reactors
John’s WEF/ABC Exam
15
Answer: a.
Stiff white foam typically indicates there are too few microorganisms in
the system to treat the incoming waste. This shortage can be caused
by start-up conditions, excessive wasting, toxic material in the influent,
low DO, or other conditions harmful to the microorganism population.
Reference: Water Environment Federation (2001) Operations Training Activated
Sludge 40 Process Control Training Manual, Alexandria, VA, pgs. 6-4 and 6-5
John’s WEF/ABC Exam
16
Typical components of grit removal systems include ____.
a. belt presses
b. comminutors
c. chain-and-flight scrapers
d. bar racks
e. parshall flume
John’s WEF/ABC Exam
17
Answer: c.
The components of a grit removal system will depend on the type used
at your facility. The components of commonly used equipment include:
chain-and-flight scrapers, bucket elevators, grit screws, air
compressors, and pumps/air lifts. Bar racks are typically used at the
headworks of the facility to remove larger foreign objects like sticks,
stones and miscellaneous material. Comminutors reduce the size of
larger debris by chopping, shredding, or pulverization. They are typically
located downstream of grit removal systems. Belt presses are used to
thicken sludge not grit.
Reference: Water Environment Federation (1994) Preliminary Treatment for
Wastewater Facilities, Manual of Practice No. OM-2, Alexandria, VA, pgs.
63 and 82
John’s WEF/ABC Exam
18
Daily maintenance procedures for a rectangular secondary
clarifier include ____________.
a. inspecting the drive unit and the chain-and-flight
system
b. lubricating the drive unit
c. inspecting the stilling well
d. inspecting all oil baths
John’s WEF/ABC Exam
19
Answer: a.
The drive unit, flights, effluent, overall appearance, and the scum
skimmer of a rectangular secondary clarifier should be examined on a
daily basis. Oil baths should be inspected weekly. Daily lubrication of
drive unit components should not be necessary. A stilling well is a
typical component of a flume.
Reference: Water Environment Federation (1993) Basic Maintenance of
Rectangular Secondary Clarifiers, Problem-Related Operations-Based
Education, Alexandria, VA, pgs. 17 and 18
John’s WEF/ABC Exam
20
The mechanism used to remove dewatered sludge from
the belt of a belt filter press is commonly referred to as
a(n) _________________.
a. pressure belt
b. edge sensor
c. doctor blade
d. scum collector
John’s WEF/ABC Exam
21
Answer: c.
Doctor blades are typically plastic or metal edges located near the cake
discharge section of a belt filter press. They are used to remove
remaining dewatered sludge from the belt before the belt is washed.
Reference: Water Environment Federation (1997) Basic Maintenance of Belt
Filter Presses. Problem-Related Operations-Based Education, Alexandria, VA,
pg. 5
John’s WEF/ABC Exam
22
Healthy mixed liquor in an activated sludge process should
have what appearance?
a. black with a gray foam
b. dark brown, covered with a greasy tan foam
c. light brown and frothy
d. gray with no foam of any kind
John’s WEF/ABC Exam
23
Answer: c.
Healthy mixed liquor should have a uniform light brown color, should
be slightly frothy, and should have a mild musty smell. Close
examination of a mixed liquor sample should reveal floc formations,
which are clusters of microorganisms and other suspended solids that
are loosely bound together.
Reference: Water Environment Federation (2001) Operations Training
Activated Sludge Process Control Training Manual, Alexandria, VA, pg. 1-2
John’s WEF/ABC Exam
24
Which of the following is a typical piece of flow measuring
equipment?
a. parshall flume
b. nephelometer
c. downward looking acoustic sensor
d. counterweighted float-level indicator
e. stilling well
John’s WEF/ABC Exam
25
Answer: a.
Devices used for flow measurement are typically divided into two
categories, openchannel and closed-pipe. Devices typically used are
flumes, weirs, mechanical meters, magnetic meters, and ultrasonic
meters. A counterweighted float-level indicator and downward looking
acoustic sensors are used to measure the level in a well, tank, or
chamber. A nephelometer is used to measure turbidity in liquids. A
stilling well can be adjacent (adjunct ) to a flume or a weir and is used
for determining the height of the water passing through.
Stilling well
Parshall
flume
Reference: Water Environment Federation (1996) Operation of Municipal
Wastewater Treatment Plants. 5th Ed., Manual of Practice No. 11, Alexandria,
VA, pgs. 150-159
John’s WEF/ABC Exam
26
A “dead” spot in an activated sludge biological reactor is
typically identified visually as ____________.
a. an area where conditions are very calm and no
mixing is taking place
b. an area where the sludge seems lighter than the rest
of the reactor contents
c. an area with only a small amount of foam on the
surface
d. an area with no foam on the surface
John’s WEF/ABC Exam
27
Answer: a.
The best visual indication of a dead spot in a biological reactor is the
existence of an area where conditions are very calm and no mixing is
taking place. These areas may also collect a lot of foam since there is
no turbulence to disperse the foam. Dark colored sludge in a
particular area may also be a sign of a dead spot. However, a dark
area may be attributed to a septic recycle stream or an industrial dye
rather than a dead spot. Measurement of the DO level in that area will
determine its status.
No Visual
Dead Spots
Noted Here
Reference: Water Environment Federation (2001) Operations Training/
Activated Sludge Process Control Training Manual, Alexandria, VA, pg. 5-5
John’s WEF/ABC Exam
28
Healthy activated sludge has what type of smell?
a. rotten egg
b. sharp, acidic
c. mild, musty
d. antiseptic
John’s WEF/ABC Exam
29
Answer: c.
Healthy mixed liquor should have a uniform light brown color, should
be slightly frothy, and should have a mild musty smell.
Mildew
Mushrooms
Reference: Water Environment Federation (2001) Operations Training/Activated
Sludge Process Control Training Manual, Alexandria, VA, pg. 1-2
John’s WEF/ABC Exam
30
The mixed liquor total suspended solids (MLTSS)
concentration range (in mg/L) for a typical conventional
activated sludge process is ____________ mg/L.
a. 500 – 1 000
b. 1 500 – 3 000
c. 5 000 – 7 500
d. 8 000 – 10 000
John’s WEF/ABC Exam
31
Answer: b.
The typical range for MLTSS in a conventional activated sludge plant is
1 500 to 3 000 mg/L. Some alternate activated sludge process modes,
such as high-rate or contact stabilization, could have MLTSS
concentrations as low as 500 or as high as 10 000 mg/L.
Reference: Water Environment Federation (1998) Design of Municipal
Wastewater Treatment Plants. 4th Ed., Manual of Practice No. 8, Alexandria,
VA, pg. 11-14
John’s WEF/ABC Exam
32
The surface of a healthy activated sludge reactor (aeration
tank) should have what type of foam?
a. a thin layer of light tan foam
b. very dark or black foam
c. stiff, white foam
d. thick, greasy, dark tan foam
John’s WEF/ABC Exam
33
Answer: a.
In a well-operated activated sludge process, 10 to 25% of the
biological reactor surface may be covered with a thin layer of light tan
foam. Other types or excessive amounts of foam can indicate problem
conditions in the reactor.
Reference: Water Environment Federation (2001) Operations Training/
Activated Sludge Process Control Training Manual, Alexandria, VA, pg. 6-3
John’s WEF/ABC Exam
34
Which of the following terms refers to a hydraulic condition,
typically indicated by billowing solids flowing over the
effluent weir, where a portion of the flow through a clarifier
experiences a much shorter detention time than the rest of
the wastewater in the tank?
a. surging
b. short-circuiting
c. overload
d. dispersion
John’s WEF/ABC Exam
35
Answer: b.
Short-circuiting is a hydraulic condition usually occurring in clarifiers
where a portion of the influent wastewater flows directly to the effluent
weir rather than being held in the clarifier long enough to allow
flocculation and settling to occur. Adding baffles to properly direct the
flow can usually minimize short-circuiting.
Reference: Water Environment Federation (2001) Operations Training/
Activated Sludge Process Control Training Manual, Alexandria, VA pg. 1-7
John’s WEF/ABC Exam
36
The typical concentration range of total suspended solids
(TSS) in domestic influent wastewater is ________ mg/L.
a. 100 – 300
b. 400 – 600
c. 700 – 900
d. 1 000 – 1 200
John’s WEF/ABC Exam
37
Answer: a.
Suspended solids removal is one of the primary process goals for
activated sludge treatment. Typically, raw domestic wastewater contains
approximately 100 - 300 mg/L of total suspended solids (TSS).
Raw Wastewater
Treated Wastewater
Reference: Water Environment Federation (2001) Operations Training/
Activated Sludge Process Control Training Manual, Alexandria, VA pg. 1-7
John’s WEF/ABC Exam
38
The temperature of a drying oven used for TSS analysis
must be kept at _______.
a. 104 ± 1 °F
b. 104 ± 1 °C
c. 180 ± 2 °C
d. 550 ± 50 °C
John’s WEF/ABC Exam
39
Answer: b.
For TSS analysis, samples must be dried to a constant weight at 104 ±
1 °C. That means that the drying oven must operate between 103 and
105 °C. Remember that water boils at 100 °C.
Reference: American Public Health Association, American Water Works
Association, Water Environment Federation (1992) Standard Methods for the
Examination of Water and Wastewater, 18th Ed., Washington, D.C., p. 2-54
John’s WEF/ABC Exam
40
Coliform bacteria and the procedures used to test for them
are divided into the two categories of _______________.
a. MF and MTF
b. LTB and BGB
c. total and fecal coliforms
d. M-Endo and M-FC
John’s WEF/ABC Exam
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Answer: c.
For coliform bacteria, the two categories of interest are total and fecal
coliforms. There are a number of ways to test for these bacteria.
Total Coliform with
Shiffs reagent
Fecal Coliform
with Analine dye
Reference: American Public Health Association, American Water Works
Association, Water Environment Federation (1992) Standard Methods for the
Examination of Water and Wastewater, 18th Ed., Washington, D.C., pgs. 954 to 9-61
John’s WEF/ABC Exam
42
Simultaneously detects both total
coliforms and Escherichia coli in
water, or fecal coliforms in
wastewater. Results in 18 hours.
Colilert®-18 / Quanti-Tray® has
become the new International
Organization for Standardization (ISO)
standard 9308-2:2012. Colilert-18 is
also U.S. EPA-approved and included
in Standard Methods for the
Examination of Water and
Wastewater.
John’s WEF/ABC Exam
43
Assume that the typical pH of the influent at your treatment
plant is about 7.2. As you are reviewing new laboratory
data, you notice that the pH in the influent this morning was
measured and found to be 6.1. This decrease is most likely
be caused by __________.
a. a caustic substance in the influent
b. a corrosive (acidic) substance in the influent
c. a change in outside temperature
d. too much alkalinity in the influent
e. an error in laboratory methodology
John’s WEF/ABC Exam
44
Answer: b.
A corrosive/acidic substance is typically the cause of such a large pH
drop in the influent. An excess of alkalinity in the influent would serve
to buffer the pH and prevent such a sudden drop.
RECALL:
6.1
Reference: Water Environment Federation (1996) Operation of Municipal
Wastewater Treatment Plants. 5th Ed., Manual of Practice No. 11, Alexandria,
VA, pg. 482
John’s WEF/ABC Exam
45
The temperature of wastewater that is being treated has
the following effect on reaction rates of the microorganisms
used in the treatment process.
a. reaction rates stay constant until they stop when
temperatures exceed 20°C (70°F)
b. reaction rates double with every 10°C (18°F) increase
in temperature up to a level where high temperature
inhibits biological activity
c. reaction rates exponentially decrease for every 10°C
(18°F) increase in temperature
d. temperature has no effect on reaction rates when it is
in the range of 5°C (41°F) to 30°C (86°F); outside of
this range, all reaction rates go to zero
John’s WEF/ABC Exam
46
Microorganism Growth Rate
Answer: b.
Within the temperature range typical for most domestic wastewater,
increases in temperature have the positive effect of speeding up the
treatment process. Within the mesophilic range the reaction rates of
microorganisms does double for every 10oC.
Any of various
single-celled
prokaryotes
genetically
distinct from
bacteria, often
thriving in
extreme
environmental
conditions
Temperature, in oC
Reference: Water Environment Federation (1996) Operation of Municipal
Wastewater Treatment Plants. 5th Ed., Manual of Practice No. 11,
Alexandria, VA, pg. 47
John’s WEF/ABC Exam
47
John’s WEF/ABC Exam
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