Disinfection and Microbiology Flashcards
Characteristics of chlorine gas.
- Greenish yellow gas
- Non flammable
- Heavier than air
One volume of liquified gas chlorine will produce this much volume of gas.
Approximately 460 volumes of gas
Turbidity can have these effects on disinfection
- React to produce chlorine demand
- “Hid” bacteria and other micro-organisms from disinfection action
Method used to disinfect tank or reservoir walls
Spray or brush a 200 mg/L chlorine solution on the surfaces, and allow to react for 3 hours.
Steps to insure a proper bacteriological sample.
- Allow the tap to run for 1-5 minutes in order to sample from the main
- Do not rinse the sample bottle
- Do not touch any part of the bottle that will come in contact with the sample
- Do not overfill the sample bottle; fill approximately 80% full
- Transport the sample immediately to the lab; store on ice if longer than one hour
- Properly label the sample
Where to pick sample locations for coliform test.
Representative locations throughout the distribution system
Color reaction of chlorine and DPD
Pink to red
Minimum free residual chlorine to be maintained throughout the distribution system.
0.2 mg/L
Disinfection CT must be met before this.
The first customer tap
Disinfection CT
Disinfection concentration (mg/L) x contact time (minutes)
Characteristics of viruses
- Smallest living organism
- Cause of certain waterborne diseases such as hepatitis A and polio
- May be more resistant to disinfection than coliform bacteria
Manner of reporting coliform bacteria in drinking water samples.
Coliform present of coliform absent
“Rule-of-thumb” for the disinfection of chlorine residuals
- Hypochlorous acid is 100x more effective than hypochlorite ion.
- Hypochlorous acid is 1000x more effective than mono chloramine.
Bacteria shapes
- Bacillus- “rod”
- Coccus- “ sphere”
- Spirillum- “ cork screw”
When using solid chlorine tablets to disinfect water mains, the tablet should be placed here.
At the top of the pipe
This material reacts with chlorine to form THM’s
Organic material, especially humic material from decayed vegetation
Chlorine dose =
Demand + residual
The number of chlorine samples required each month is based on this.
Population size
Chlorine left after the demand has been met.
Chlorine residual
Minimum number of repeat samples required in response to a positive coliform result.
Minimum three repeat samples; one at the original tap, one at a tap “downstream,” and one at a tap “upstream”
Free residual chlorine.
Hypochlorous acid + hypochlorite ion
Indicates a positive fermentation tube during the coliform test.
Gas in the fermentation tube
Sample volume collected and tested for coliform bacteria.
A 100 ml volume is tested for coliform bacteria; therefore at least 100 ml be collected in the sample bottle
The presence of total coliform bacteria in drinking water indicates this:
Bacteria of intestinal or soil/vegetation origin, which may indicate the presence of disease causing microorganism
The presence of fecal coliform bacteria in drinking water indicates this:
Bacteria that originate in the intestinal tract of humans or animals, indicating fecal contamination and may indicate the presence of disease causing microorganisms
Relationship between E. coli and fecal coliform bacteria.
E. coli is a member of the fecal coliform group
Able to live in the presence or absence of oxygen.
Facultative anaerobe
Steps for disinfecting a distribution main before placing it into service.
- Disinfect with chlorine at 50 mg/L for 24 hours. At least 25 mg/L must remain after the 24 hour period
- Flush the main, and collect a bacteriological sample
- When the bacteriological sample comes back “negative” the main can be placed into service
Bacterium associated with the intestinal tract of animals or humans.
Enteric bacteria
Define:
- Disinfection
- Sterilization
- Destruction of harmful or undesirable micro-organisms
- Complete destruction of all life
Pathogenic
Disease causing
Definition of coliform bacteria group.
All gram negative, rod shaped, non-spore forming, facultative anaerobic and aerobic bacteria able to ferment lactose to a gas within 48 hours at 35°C
Types of coliform bacteria.
- Fecal coliform bacteria, that live in the intestines of warm blooded animals and man
- Non-fecal coliform bacteria, that live in soil and decaying vegetation.
EPA approved methods for determining the presence of coliform bacteria in drinking water.
- Multiple tube fermentation
- Membrane filter method
- Presence absence broth
- MMO-MUG, Colilert
Media used in the multiple tube fermentation test for coliform bacteria.
- Presumptive step: Lauryl tryptose broth
- Confirmed step: Brilliant green lactose bile broth
Chlorine and ammonia react to for this.
Chloramines
Approved chemical disinfectants for public water systems.
- Free chlorine
- Mono chloramine
- Ozone
- Chlorine dioxide
Field method for measuring chlorine residual.
DPD color comparitor
Chlorine formulations used in the water industry.
- Molecular chlorine: (gas) Cl2
- Sodium hypochlorite: (liquid solution, bleach) NaOCl
- Calcium hypochlorite: (solid) Ca(OCl)2
Cl2 + H20 =
Hypochlorous acid (†) + hydrochloric acid (†) disinfectant
Used dose chlorine bleach into water.
Hypochlorinator
Action to take if routine bacteriological sample shows the presence of total coliform bacteria.
- Initiate repeat sampling within 24 hours
- Tet positive sample for presence of fecal coliform or E. coli
The pH effect when gas chlorine is added to water.
The pH may drop slightly
Chlorine demand =
Dose - residual
Requirement for bacteriological sample bottle.
- Plastic or glass
- Sterile
- Contain dechlorination agent thiosulfate, also called “thio”
- Protected with kraft paper or mailing tube
Timing for bacteriological sampling.
- Samples should be taken at the same time each month: for instance, on the first Wednesday of the month.
- If multipule samples are required to be taken, they should be collected at different times during the month. For example, if three samples are collected, they could be collected during the first, second, and third week of the month.
reason that a positive presumptive test must be confirmed.
Bacteria other than coliform can cause “false presumptive” results.
These protozoa can produce cysts that are more resistant to disinfection.
- Giardia sp.
- Cryptosporidum sp.
The reaction of chlorine and organic material can have this effect on the taste and odor of the water.
Increase the taste and odor of the water
