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Water Treatment Plant Operator Test Questions > Disinfection > Flashcards

Disinfection Flashcards

1
Q

At what temperature does a fusible plug melt?

A

between 158 and 165 Fahrenheit

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2
Q

Chlorine is how many times heavier than air?

A

2.5

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3
Q

A quart of liquid chorine will evaporate into how many quart of gaseous chlorine?

A

450

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4
Q

how many fusible plugs are used on a Ton cylinder?

A

6

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5
Q

how many fusible plugs are there on a 100lb and 150lb chlorine cylinder?

A

1

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6
Q

what is the most common cause of a chlorine leak?

A

lead washer failure of failure to change lead washer

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7
Q

what type of respirator is needed when entering a chlorine room?

A

SCBA

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8
Q

what is the IDLH (immediately dangerous to life and health) for chlorine?

A

10

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9
Q

how many ppm of chlorine in a room will bring death in seconds?

A

1000 ppm or 0.10% by volume

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10
Q

what percentage of air is oxygen?

A

20.9%

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11
Q

what chemical is used to oxidize iron from water?

A

Chlorine

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12
Q

How do you open a chlorine cylinder?

A

with a six inch box wrench

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13
Q

The iodometric test is used to test for what parameter?

A

ozone residual

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14
Q

What is the minimum free chlorine residual for the distribution system?

A

0.2 mg/L

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15
Q

What is the minimum combined chlorine residual?

A

0.6 mg/L

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16
Q

What is the maximum residual disinfectant level?

A

4 mg/L

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17
Q

What does the C in CT value mean?

A

concentration of the chlorine residual

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18
Q

What is measured from the chlorine application point to the point where the chlorine residual is taken?

A

time

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19
Q

What does the T mean in CT value?

A

time

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20
Q

How many pounds of chlorine can you withdraw from a ton cylinder in a day?

A

400 pounds

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21
Q

How many pounds of chlorine can you withdraw from a 100 or 150 pound cylinder per day?

A

40 pounds

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22
Q

When chlorine is used to disinfect drinking water, the chlorine cylinder are placed on what device to measure usage?

A

scale

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23
Q

What is the device used to measure the rate of flow of liquid to gasses?

A

rotameter

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24
Q

The chlorine scale reading does not equal the rotameter setting for the past 24 hours. What is the likely cause?

A

Air leak down stream of the chlorinator

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25
Q

Pumping dry air into a container or cylinder to assist with the withdrawal of a liquid or gas is called?

A

Air padding

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26
Q

What is the most common cause of water borne illnesses in the US?

A

cross-connection

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27
Q

What method is considered the most reliable in measuring chlorine residual?

A

Amperometric titration

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28
Q

The addition of chlorine until the demand is satisfied and, thereafter, every drop of chlorine added is free residual is called?

A

Breakpoint chlorination

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29
Q

What is the disadvantage of breakpoint chlorination?

A

THM formation

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30
Q

substances which cause cancer is called?

A

carcinogens

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31
Q

*** What do you call a substance that changes the speed or yield of a chemical reaction without being consumed or chemically changed?

A

A Catalyst

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32
Q

What parameter is the determined by this formula ? C1 2 dosage - residual=?

A

Demand

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33
Q

What is an open or vertical drop or space that separates a potable drinking water supply from an unapproved water or nonportable water called?

A

Air gap

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34
Q

What do you call the indicator organism that is found in the intestines of warm blooded animals, including humans, plants, soil, water, and air?

A

Coliform

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35
Q

What is DPD used for?

A

Measuring chlorine residual

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36
Q

Why is chlorine added to drinking water?

A

To disinfect the water

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37
Q

How many pounds of chlorine can you withdraw for a cylinder within 24 hours?

A

Depend on the temperature ( 8 pounds per degree F*

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38
Q

Disease causing organisms are called?

A

Pathogens

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39
Q

What does HTH mean?

A

High test hypochlorite

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40
Q

What does OC1 mean?

A

Hypochlorite

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41
Q

What does HOC1 mean?

A

Hypochlorous Acid

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42
Q

What is NaOC1?

A

Sodium Hypochlorite (bleach)

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43
Q

An increase in the heterotrophic plate count indicates?

A

Nitrification

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44
Q

What does the initials MPN mean?

A

Most probable number

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45
Q

What bacteria breaks down ammonia nitrogen into nitrites?

A

Nitrosomonas

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46
Q

What bacteria breaks down nitrites to nitrates?

A

Nitrobacter

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47
Q

Which are the ideal conditions for nitrification to take place?

A

A dark environment, with temp between 25-30 Celsius, pH 7.5-8.5, and free ammonia available.

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48
Q

What is used to detect a chlorine leak?

A

ammonia

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49
Q

What is used to detect a sulfur dioxide leak?

A

Ammonia

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50
Q

What is used to detect an ammonia leak?

A

Hydrochloric acid

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51
Q

If your plan is to prechlorinating and you find that you are exceeding the MCL for THMs, what should you do?

A

Stop prechlorinating

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52
Q

Naturally occurring volatile organic compounds react with chlorine and form what cancer-causing compound?

A

THMs

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53
Q

A pure chemical substance that is used to make new products or is used in chemical tests to measure, detect or analyze other substances is called?

A

A. Reagent

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54
Q

The concentration of chlorine present in water after the chlorine demand has been satisfied is called?

A

Residual

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55
Q

What is this formula used to detect (demand + residual =) ?

A

Dosage

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56
Q

The dosage is 5 ppm and the residual is 3 PPM. What is the demand?

A

2 PPM

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57
Q

What do you call the process of adding a chemical reagent in small increments until completion of a reaction, as signaled by the end point?

A

Titration

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58
Q

What do you call the cloudy appearance of water caused by the presence of suspended and colloidal matter?

A

Turbidity

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59
Q

Why are water plant operators concerned with turbidity?

A

Turbidity interferes with disinfection

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60
Q

What is the MCL for turbidity?

A

0.5 nephelometric unit

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61
Q

Name four bacteria found in contaminated water?

A

Typhoid, cholera, dysentery and salmonella

62
Q

Name two parasites that are found in contaminated water?

A

Cryptosporidium and giardia lamblia

63
Q

What determine the number of coliform samples that a water system has to take?

A

Population served

64
Q

What is the MCL for coliform?

A

Presence and absence

65
Q

If a sample test positive for coliform, what actions should be taken?

A

Retest at the site within 24 hours. Notification of the positive test and sample one site upstream and downstream from the positive site

66
Q

If a water system samples 40 or more sites for coliform, how many positive samples are allowed?

A

Two or five percent?

67
Q

If a water system samples 39 or fewer sites for coliform, how many positive samples are allowed?

A

1

68
Q

What are the optimum conditions for disinfection?

A

Hi chlorine, concentration, long contact time, low pH, and low turbidity

69
Q

Why is turbidity of the water important?

A

High turbidity interferes with disinfection and coagulation

70
Q

The surface water treatment rule SWTR requires what minimum level of water treatment

A

Disinfection and filtration

71
Q

Besides chlorination and Ammoniation, what other processes reduce pathogens in the water?

A

Coagulation, filtration, and sedimentation

72
Q

Ultraviolet rays are used to disinfect water. What limits the UV rays efficiency?

A

No Residual, also, if a pathogen is caught between two particles, the light ray have no effect on the pathogen.

73
Q

What color is chlorine gas?

A

Greenish- yellow

74
Q

Chlorine cylinders are filled to what capacity?

A

85% to allow for the expansion of the liquid into the gaseous state

75
Q

How many ppm (parts per million) of chlorine is needed to oxidize 1 ppm of H²S (Hydrogen sulfide) to elemental sulfur?

A

8.32 mg/L

76
Q

If sulfur dioxide comes into contact with a person’s mucous membrane, what can happen?

A

The formation of sulfuric acids (H2so4)

77
Q

In the last four questions, what do you call the oxidation process that took place?

A

Sub- residual chlorination

78
Q

In the normal pH range of drinking water, what is the usual form of chlorine?

A

Monochloramines

79
Q

When you add ammonia to chlorine you form?

A

Chloramines

80
Q

When chlorine is added to water, what is the usual first reaction?

A

Chlorine is used up (destroyed) by reducing compounds ( viruses, bacteria, solids, parasites, etc).

81
Q

⭐ After the reduction of the chlorine dosage, what reaction takes place?

A

Chlororganics and chloramines are formed- residual is present

82
Q

After the reaction in question 85, what takes place?

A

Breakpoint chlorination

83
Q

What causes the swimming pool, taste and odor in water?

A

Low chlorine residual- plant did not use breakpoint chlorination

84
Q

What is the best residual for disinfection?

A

Free available Chlorine

85
Q

A water pH levels of 4.0 or lower, what form will chlorine take?

A

Trichloramine

86
Q

Above pH of 7.5 chlorine is found as?

A

Monochloramines

87
Q

Dichloramines and monochloramines exist together at what pH range?

A

5.5-7.5

88
Q

Dichloramines and trichloramines are associated with what water complaint?

A

Taste and odors

89
Q

If chlorine is used to treat an odor caused by phenols ( Benzene) , what happens ?

A

The taste and odor are intensified

90
Q

Customers are complaining of a sweet, aromatic, medical taste in the water. What is the likely cause?

A

Phenols

91
Q

What is the best method to remove taste and odor caused by ?

A

Phonels

92
Q

What is the best method to remove taste and odor caused by phenols?

A

GAC (granular activated carbon)

93
Q

To avoid THM formation, what options are available to the WTP?

A

Switch disinfectants, remove the precursors, or form THMs and remove them after they are formed.

94
Q

What is the most common alternate disinfectant used to avoid the formation of THMs?

A

Chloramines

95
Q

What is the highest chlorine to ammonia ratio by weight?

A

5 PPM C12 of chlorine as free residual to 1 PPM of NH3 which is ammonia

96
Q

When measuring combine chlorine residual ( chloramines) in the field, what is the process?

A

Analyze for total chlorine ( no free chlorine should be present at chlorine- ammonia ratio of 3:1 and 5:1).

97
Q

What is the MCL for nitrites?

A

1

98
Q

What is the MCL for nitrates?

A

10

99
Q

What is the combined MCL for nitrites and nitrates?

A

10

100
Q

Before moving a chlorine cylinder, what should you do?

A

Replace the protective cap

101
Q

The chlorine cylinders have iced up. What is the likely cause?

A

Too rapid a withdrawal

102
Q

In what direction do you turn a chlorine valve to open the cylinder?

A

Counterclockwise

103
Q

How many turns does it take to open the cylinder valve fully?

A

1 complete turn opens the tank fully

104
Q

If the bottom valve of a cylinder is leaking, what should you do?

A

Rotate the tank so that the leak is at the top

105
Q

A minimum PSI at the injector should be?

A

50 psi

106
Q
    • On a direct mount chlorinator, water is showing in the metering tube. What is the likely cause?
A

Check valve failure

107
Q

If a direct mount chlorinator check valve false, what needs to be done?

A

Clean or replace valve?

108
Q

*** On a direct mount chlorinator, water is venting into the atmosphere. What is the likely cause?

A

Excess water PSI

109
Q

When water is venting into the atmosphere from a direct mount chlorinator, what should you do?

A

Remove vacuum regulator

110
Q

On a direct mount chlorinator, there is no indication of flow on the meter when a vacuum is present. What is the likely cause?

A

Vacuum leak

111
Q

On a direct mount chlorinator, there is an indication on the flow meter, but air is present, no chlorine gas. What is likely cause?

A

Gasket leak

112
Q

If the DPD test is taken on water that has a combined residual, what error can take place?

A

False positive reading- precipitate forms and gives sample appearance of having color

113
Q

Chlorinator will feed okay at maximum outputs, but there is no control at lower feed rates. What’s the problem?

A

Vacuum regulating valve

114
Q

Chlorinator will feed okay at maximum outputs, but there is no control at lower feed rates. What’s the problem?

A

Vacuum regulating valve

115
Q

Chlorinator will not reach maximum point. What’s the problem

A

Faulty injector

116
Q

Variable vacuum control will not go below 30% feed. Signal OK. What is causing problem?

A

CPRV (chlorine pressure-regulating valve)

117
Q

Variable vacuum control reaches full feed, but will not go below 50% feed. CPRV (chlorine pressure-regulating valve) okay. What’s causing the problem?

A

Signal vacuum too high

118
Q

Variable vacuum control won’t go to full feed. Gas pressure okay. CPRV (chlorine pressure-regulating valve) okay. What’s causing the problem?

A

Plugged restrictor

119
Q

Low injector vacuum reading. What is the problem?

A

Flow restricted

120
Q

There is an increase in the coliform level. What is the cause?

A

Low chlorine residual

121
Q

There is a sudden drop in the chlorine residual. What caused this?

A

Increase in chlorine demand or drop in chlorine feed rate

122
Q

What is used to detect a chlorine leak?

A

Soak a rag with ammonia and hold it near connection. Also, polyethylene spray bottle can be used to spray ammonia vapor near connections. A white cloud indicates a leak

123
Q

How do you reduce high chlorine residuals before the water leaves the plant?

A

GAC or sodium bisulfate

124
Q

If there is a leak around the chlorine valve stem, what action is needed?

A

Tighten the nut or stem by turning it clockwise

125
Q

What chemicals can be used to neutralize chlorine?

A

Caustic soda, soda ash, lime

126
Q

What is used to repair a defective ton cylinder?

A

B kit

127
Q

What kit is used to repair a 100 or 150 lb cylinder?

A

A kit

128
Q

What is the maximum temperature that chlorine cylinders should be stored at?

A

100°F

129
Q

ORP probes are used to measure what?

A

Direct measure of the disinfecting power of chlorine

130
Q

Where should the ORP probe be located?

A

6.5 minutes downstream from the injection point

131
Q

In rooms where there is chlorine or carbon dioxide present, what type of respirators should not be used?

A

Gas mask

132
Q

What should you give someone who has inhaled chlorine?

A

Milk or peppermint spirits?

133
Q

What causes UV systems to be ineffective?

A

Scaling or fouling of the quartz sleeve. Also, high flow velocities, turbidity, and decline in lamp output

134
Q

If 30 lb of chlorine are used during an average week at a WTP, how many 150 lb cylinders will be used per month?

A

0.86 cylinder

135
Q

A water system treats 12.8 MGD. It doses the water with 5 ppm of chlorine. How many pounds of chlorine will the WTP use in 30 days?

A

5 ppm x 12.8 mgdx 8.34 = 534 lb day times 30 days= 16,013 lb

136
Q

If the free chlorine residual leaving the plant is less than 0.2 mg/L , what action is needed?

A

WTP/system is allowed up to 4 hours to correct problem

137
Q

A heterotrophic plate count of less than 500 colonies/mL is considered equivalent to?

A

Equivalent to a detectable disinfectant residual

138
Q

Bacteria found in the intestine of warm-blooded animals, including human beings, also, implants, water, soil, and air are called?

A

Coliform

139
Q

Name three disease causing bacteria found in water

A

Salmonella , typhoid , and cholera

140
Q

Which tablet is always found in a coliform sampling twirl bag?

A

Sodium thiosulfate

141
Q

Why is a space left in the twirl bag?

A

To allow for mixing

142
Q

If the sample site is contaminated and you have no other sample site available, what should you do?

A

Swab the spigot with NaOC1 solution?

143
Q

What is the minimum amount needed to test for coliform?

A

100 mL

144
Q

How long can you hold a sample collected for coliform?

A

6 hours

145
Q

What test is also taken when the coliform samples are collected?

A

Chlorine residual

146
Q

What causes blue babies?

A

Nitrites

147
Q

What does heterotrophic organisms use for their growth?

A

Organic matter

148
Q

Which substance in the water increases the chlorine demand?

A

Nitrites

149
Q

An increase in the heterotrophic plate count( HPC) indicates what process is taking place?

A

Nitrification

150
Q

A HPC of less than 500 is an indication that there is a?

A

Chlorine residual

151
Q

When taking samples for analysis by the lab, which of the following protocols must be followed?

A

Must fill out chain of custody report

Water Treatment Plant Operator Test Questions (16 decks)

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