Disinfection Flashcards
At what temperature does a fusible plug melt?
between 158 and 165 Fahrenheit
Chlorine is how many times heavier than air?
2.5
A quart of liquid chorine will evaporate into how many quart of gaseous chlorine?
450
how many fusible plugs are used on a Ton cylinder?
6
how many fusible plugs are there on a 100lb and 150lb chlorine cylinder?
1
what is the most common cause of a chlorine leak?
lead washer failure of failure to change lead washer
what type of respirator is needed when entering a chlorine room?
SCBA
what is the IDLH (immediately dangerous to life and health) for chlorine?
10
how many ppm of chlorine in a room will bring death in seconds?
1000 ppm or 0.10% by volume
what percentage of air is oxygen?
20.9%
what chemical is used to oxidize iron from water?
Chlorine
How do you open a chlorine cylinder?
with a six inch box wrench
The iodometric test is used to test for what parameter?
ozone residual
What is the minimum free chlorine residual for the distribution system?
0.2 mg/L
What is the minimum combined chlorine residual?
0.6 mg/L
What is the maximum residual disinfectant level?
4 mg/L
What does the C in CT value mean?
concentration of the chlorine residual
What is measured from the chlorine application point to the point where the chlorine residual is taken?
time
What does the T mean in CT value?
time
How many pounds of chlorine can you withdraw from a ton cylinder in a day?
400 pounds
How many pounds of chlorine can you withdraw from a 100 or 150 pound cylinder per day?
40 pounds
When chlorine is used to disinfect drinking water, the chlorine cylinder are placed on what device to measure usage?
scale
What is the device used to measure the rate of flow of liquid to gasses?
rotameter
The chlorine scale reading does not equal the rotameter setting for the past 24 hours. What is the likely cause?
Air leak down stream of the chlorinator
Pumping dry air into a container or cylinder to assist with the withdrawal of a liquid or gas is called?
Air padding
What is the most common cause of water borne illnesses in the US?
cross-connection
What method is considered the most reliable in measuring chlorine residual?
Amperometric titration
The addition of chlorine until the demand is satisfied and, thereafter, every drop of chlorine added is free residual is called?
Breakpoint chlorination
What is the disadvantage of breakpoint chlorination?
THM formation
substances which cause cancer is called?
carcinogens
*** What do you call a substance that changes the speed or yield of a chemical reaction without being consumed or chemically changed?
A Catalyst
What parameter is the determined by this formula ? C1 2 dosage - residual=?
Demand
What is an open or vertical drop or space that separates a potable drinking water supply from an unapproved water or nonportable water called?
Air gap
What do you call the indicator organism that is found in the intestines of warm blooded animals, including humans, plants, soil, water, and air?
Coliform
What is DPD used for?
Measuring chlorine residual
Why is chlorine added to drinking water?
To disinfect the water
How many pounds of chlorine can you withdraw for a cylinder within 24 hours?
Depend on the temperature ( 8 pounds per degree F*
Disease causing organisms are called?
Pathogens
What does HTH mean?
High test hypochlorite
What does OC1 mean?
Hypochlorite
What does HOC1 mean?
Hypochlorous Acid
What is NaOC1?
Sodium Hypochlorite (bleach)
An increase in the heterotrophic plate count indicates?
Nitrification
What does the initials MPN mean?
Most probable number
What bacteria breaks down ammonia nitrogen into nitrites?
Nitrosomonas
What bacteria breaks down nitrites to nitrates?
Nitrobacter
Which are the ideal conditions for nitrification to take place?
A dark environment, with temp between 25-30 Celsius, pH 7.5-8.5, and free ammonia available.
What is used to detect a chlorine leak?
ammonia
What is used to detect a sulfur dioxide leak?
Ammonia
What is used to detect an ammonia leak?
Hydrochloric acid
If your plan is to prechlorinating and you find that you are exceeding the MCL for THMs, what should you do?
Stop prechlorinating
Naturally occurring volatile organic compounds react with chlorine and form what cancer-causing compound?
THMs
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. Reagent
The concentration of chlorine present in water after the chlorine demand has been satisfied is called?
Residual
What is this formula used to detect (demand + residual =) ?
Dosage
The dosage is 5 ppm and the residual is 3 PPM. What is the demand?
2 PPM
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?
Titration
What do you call the cloudy appearance of water caused by the presence of suspended and colloidal matter?
Turbidity
Why are water plant operators concerned with turbidity?
Turbidity interferes with disinfection
What is the MCL for turbidity?
0.5 nephelometric unit
Name four bacteria found in contaminated water?
Typhoid, cholera, dysentery and salmonella
Name two parasites that are found in contaminated water?
Cryptosporidium and giardia lamblia
What determine the number of coliform samples that a water system has to take?
Population served
What is the MCL for coliform?
Presence and absence
If a sample test positive for coliform, what actions should be taken?
Retest at the site within 24 hours. Notification of the positive test and sample one site upstream and downstream from the positive site
If a water system samples 40 or more sites for coliform, how many positive samples are allowed?
Two or five percent?
If a water system samples 39 or fewer sites for coliform, how many positive samples are allowed?
1
What are the optimum conditions for disinfection?
Hi chlorine, concentration, long contact time, low pH, and low turbidity
Why is turbidity of the water important?
High turbidity interferes with disinfection and coagulation
The surface water treatment rule SWTR requires what minimum level of water treatment
Disinfection and filtration
Besides chlorination and Ammoniation, what other processes reduce pathogens in the water?
Coagulation, filtration, and sedimentation
Ultraviolet rays are used to disinfect water. What limits the UV rays efficiency?
No Residual, also, if a pathogen is caught between two particles, the light ray have no effect on the pathogen.
What color is chlorine gas?
Greenish- yellow
Chlorine cylinders are filled to what capacity?
85% to allow for the expansion of the liquid into the gaseous state
How many ppm (parts per million) of chlorine is needed to oxidize 1 ppm of H²S (Hydrogen sulfide) to elemental sulfur?
8.32 mg/L
If sulfur dioxide comes into contact with a person’s mucous membrane, what can happen?
The formation of sulfuric acids (H2so4)
In the last four questions, what do you call the oxidation process that took place?
Sub- residual chlorination
In the normal pH range of drinking water, what is the usual form of chlorine?
Monochloramines
When you add ammonia to chlorine you form?
Chloramines
When chlorine is added to water, what is the usual first reaction?
Chlorine is used up (destroyed) by reducing compounds ( viruses, bacteria, solids, parasites, etc).
⭐ After the reduction of the chlorine dosage, what reaction takes place?
Chlororganics and chloramines are formed- residual is present
After the reaction in question 85, what takes place?
Breakpoint chlorination
What causes the swimming pool, taste and odor in water?
Low chlorine residual- plant did not use breakpoint chlorination
What is the best residual for disinfection?
Free available Chlorine
A water pH levels of 4.0 or lower, what form will chlorine take?
Trichloramine
Above pH of 7.5 chlorine is found as?
Monochloramines
Dichloramines and monochloramines exist together at what pH range?
5.5-7.5
Dichloramines and trichloramines are associated with what water complaint?
Taste and odors
If chlorine is used to treat an odor caused by phenols ( Benzene) , what happens ?
The taste and odor are intensified
Customers are complaining of a sweet, aromatic, medical taste in the water. What is the likely cause?
Phenols
What is the best method to remove taste and odor caused by ?
Phonels
What is the best method to remove taste and odor caused by phenols?
GAC (granular activated carbon)
To avoid THM formation, what options are available to the WTP?
Switch disinfectants, remove the precursors, or form THMs and remove them after they are formed.
What is the most common alternate disinfectant used to avoid the formation of THMs?
Chloramines
What is the highest chlorine to ammonia ratio by weight?
5 PPM C12 of chlorine as free residual to 1 PPM of NH3 which is ammonia
When measuring combine chlorine residual ( chloramines) in the field, what is the process?
Analyze for total chlorine ( no free chlorine should be present at chlorine- ammonia ratio of 3:1 and 5:1).
What is the MCL for nitrites?
1
What is the MCL for nitrates?
10
What is the combined MCL for nitrites and nitrates?
10
Before moving a chlorine cylinder, what should you do?
Replace the protective cap
The chlorine cylinders have iced up. What is the likely cause?
Too rapid a withdrawal
In what direction do you turn a chlorine valve to open the cylinder?
Counterclockwise
How many turns does it take to open the cylinder valve fully?
1 complete turn opens the tank fully
If the bottom valve of a cylinder is leaking, what should you do?
Rotate the tank so that the leak is at the top
A minimum PSI at the injector should be?
50 psi
- On a direct mount chlorinator, water is showing in the metering tube. What is the likely cause?
Check valve failure
If a direct mount chlorinator check valve false, what needs to be done?
Clean or replace valve?
*** On a direct mount chlorinator, water is venting into the atmosphere. What is the likely cause?
Excess water PSI
When water is venting into the atmosphere from a direct mount chlorinator, what should you do?
Remove vacuum regulator
On a direct mount chlorinator, there is no indication of flow on the meter when a vacuum is present. What is the likely cause?
Vacuum leak
On a direct mount chlorinator, there is an indication on the flow meter, but air is present, no chlorine gas. What is likely cause?
Gasket leak
If the DPD test is taken on water that has a combined residual, what error can take place?
False positive reading- precipitate forms and gives sample appearance of having color
Chlorinator will feed okay at maximum outputs, but there is no control at lower feed rates. What’s the problem?
Vacuum regulating valve
Chlorinator will feed okay at maximum outputs, but there is no control at lower feed rates. What’s the problem?
Vacuum regulating valve
Chlorinator will not reach maximum point. What’s the problem
Faulty injector
Variable vacuum control will not go below 30% feed. Signal OK. What is causing problem?
CPRV (chlorine pressure-regulating valve)
Variable vacuum control reaches full feed, but will not go below 50% feed. CPRV (chlorine pressure-regulating valve) okay. What’s causing the problem?
Signal vacuum too high
Variable vacuum control won’t go to full feed. Gas pressure okay. CPRV (chlorine pressure-regulating valve) okay. What’s causing the problem?
Plugged restrictor
Low injector vacuum reading. What is the problem?
Flow restricted
There is an increase in the coliform level. What is the cause?
Low chlorine residual
There is a sudden drop in the chlorine residual. What caused this?
Increase in chlorine demand or drop in chlorine feed rate
What is used to detect a chlorine leak?
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
How do you reduce high chlorine residuals before the water leaves the plant?
GAC or sodium bisulfate
If there is a leak around the chlorine valve stem, what action is needed?
Tighten the nut or stem by turning it clockwise
What chemicals can be used to neutralize chlorine?
Caustic soda, soda ash, lime
What is used to repair a defective ton cylinder?
B kit
What kit is used to repair a 100 or 150 lb cylinder?
A kit
What is the maximum temperature that chlorine cylinders should be stored at?
100°F
ORP probes are used to measure what?
Direct measure of the disinfecting power of chlorine
Where should the ORP probe be located?
6.5 minutes downstream from the injection point
In rooms where there is chlorine or carbon dioxide present, what type of respirators should not be used?
Gas mask
What should you give someone who has inhaled chlorine?
Milk or peppermint spirits?
What causes UV systems to be ineffective?
Scaling or fouling of the quartz sleeve. Also, high flow velocities, turbidity, and decline in lamp output
If 30 lb of chlorine are used during an average week at a WTP, how many 150 lb cylinders will be used per month?
0.86 cylinder
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?
5 ppm x 12.8 mgdx 8.34 = 534 lb day times 30 days= 16,013 lb
If the free chlorine residual leaving the plant is less than 0.2 mg/L , what action is needed?
WTP/system is allowed up to 4 hours to correct problem
A heterotrophic plate count of less than 500 colonies/mL is considered equivalent to?
Equivalent to a detectable disinfectant residual
Bacteria found in the intestine of warm-blooded animals, including human beings, also, implants, water, soil, and air are called?
Coliform
Name three disease causing bacteria found in water
Salmonella , typhoid , and cholera
Which tablet is always found in a coliform sampling twirl bag?
Sodium thiosulfate
Why is a space left in the twirl bag?
To allow for mixing
If the sample site is contaminated and you have no other sample site available, what should you do?
Swab the spigot with NaOC1 solution?
What is the minimum amount needed to test for coliform?
100 mL
How long can you hold a sample collected for coliform?
6 hours
What test is also taken when the coliform samples are collected?
Chlorine residual
What causes blue babies?
Nitrites
What does heterotrophic organisms use for their growth?
Organic matter
Which substance in the water increases the chlorine demand?
Nitrites
An increase in the heterotrophic plate count( HPC) indicates what process is taking place?
Nitrification
A HPC of less than 500 is an indication that there is a?
Chlorine residual
When taking samples for analysis by the lab, which of the following protocols must be followed?
Must fill out chain of custody report
