Water-Borne Pathogens

Question 1

Water-borne pathogens

Answer 1

• Transmission is mediated by fecal contamination of water supplies
• Most of these pathogens grow in the intestinal tract

Question 2

Source of infection of water-borne pathogens

Answer 2

• Portable water
• Recreational water

Question 3

Water-borne pathogens and viruses

Answer 3

• Salmonella typhi: typhoid fever in humans
• Vibrio cholerae: cholera
• Shigella spp.: shigellosis
• Salmonella spp.: salmonellosis, gastroenteritis
• Campylobacter spp.: gastroenteritis
• Enterovirus: poliovirus, norovirus, rotavirus
• Hepatitis A virus

Question 4

Water-borne pathogenic protozoa

Answer 4

• Giardia lamblia: Giardiasis
• Cryptosporidium parvum: chronic & accute diarrhea

Both form cysts that are resistant to several disinfectants

Question 5

Water quality control

Answer 5

• Test the water for organisms that are present in large numbers in feces
• use these organisms as indicators of fecal pollution
• if these organisms are present, there is a chance that the water may also contain pathogens

Question 6

2 indicators of water quality

Answer 6

Coliforms:
* facultative aerobic, Gram-negative, non spore-forming, rod-shaped bacteria
* ferment lactose with gas formation within 48 hours at 35°C.
* Includes a variety of bacteria not all of intestinal origin

Fecal coliforms:
* coliforms derived from the intestines of warm-blooded animals
* can grow at 44.5°C

Question 7

Methods of testing water quality

Answer 7

Membrane filtration:
* Tests for coliforms and fecal coliforms
* Faster and easier than MPN

Most probably number (MPN):
* Test for coliforms
* Samples are added to lactose broth
* If gas production is detected, test is positive

Question 8

Water treatment aims

Answer 8

• Remove pathogens
• Improve clarity of water
• Remove compounds that give badsmell or taste
• Soften the water

Question 9

Water treatment steps

Answer 9

1. Sedimentation
2. Flocculation
3. Filtration
4. Disinfection

Question 10

Sedimentation

Answer 10

• Water is left to stand in a reservoir
• Allow large particle (sands) to settle

Question 11

Flocculation

Answer 11

• A flocculating chemical is added
• Water is transferred to a flocculation basin and allowed to settle for ~6h
• As the flocs form, they trap fine particles
• ~80% of bacteria, color & particulates have been removed

Question 12

Filtration

Answer 12

The water is filtered through sand to remove remaining particles (cysts)
* 98-99.5% of the bacteria have been removed

Question 13

Disinfection

Answer 13

Add disinfectant (Cl/O3)
* Kill remaining bacteria
* Neutralize chemicals that give water bad smell/taste

Question 14

Residual chlorine

Answer 14

Amount of chlorine that remains in the water that left thetreatment plant
* Desired/required to protect the distribution system

Question 15

Waste water treatment aims

Answer 15

• Reduce BOD
• Destroy pathogens

Question 16

Wastewater treatment steps

Answer 16

• Primary treatment
• Secondary treatment
• Tertiary treatment

Question 17

Primary treatment

Answer 17

Sedimentation tanks
* 40-70% of suspended solids settle
* Flocculating chemical can be added
* Produces 1° sludge
* Reduces the BOD of wastewater to 25-40% and bacteria by 25-75%

Question 18

Secondary treatment: Liquid

Answer 18

Trickling filter
* liquid is sprayed over a bed of rock, microorganisms form biofilms & oxidize the OM
* BOD reduced by 80-95%, bacteria by 90-95%

Activated sludge
* Air is blown through the liquid
* Slime-forming bacteria grow and clump together to form flocs that oxidize the OM
* Material passes to a settling tank, sludge is removed for disposal or 2° treatment
* BOD reduced by 85-95%, bacteria by 90-98%

Question 19

Secondary treatment: Sludge

Answer 19

1° & 2° sludge is subjected to microbial digestion under anaerobic conditions
* BOD reduced by 90%
* Material that remains is incinerated or buried

Question 20

Tertiary treatment

Answer 20

May involve any or a combination of the following:
* Biological treatment (ponds: algae)
* Flocculation
* Filtration
* Chlorination or ozonation

May be suitable for drinking

Question 21

Septic tank

Answer 21

Minimal treatment of sewage
* Settling of material + minimal sludge digestion
* requires periodic emptying
* BOD reduced by 60%
* Effluent flows to a leaching field where soil act as a filter and organisms decompose organic matter