Water-Borne Pathogens Flashcards
Water-borne pathogens
- Transmission is mediated by fecal contamination of water supplies
- Most of these pathogens grow in the intestinal tract
Source of infection of water-borne pathogens
- Portable water
- Recreational water
Water-borne pathogens and viruses
- 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
Water-borne pathogenic protozoa
- Giardia lamblia: Giardiasis
- Cryptosporidium parvum: chronic & accute diarrhea
Both form cysts that are resistant to several disinfectants
Water quality control
- 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
2 indicators of water quality
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
Methods of testing water quality
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
Water treatment aims
- Remove pathogens
- Improve clarity of water
- Remove compounds that give badsmell or taste
- Soften the water
Water treatment steps
- Sedimentation
- Flocculation
- Filtration
- Disinfection
Sedimentation
- Water is left to stand in a reservoir
- Allow large particle (sands) to settle
Flocculation
- 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
Filtration
The water is filtered through sand to remove remaining particles (cysts)
* 98-99.5% of the bacteria have been removed
Disinfection
Add disinfectant (Cl/O3)
* Kill remaining bacteria
* Neutralize chemicals that give water bad smell/taste
Residual chlorine
Amount of chlorine that remains in the water that left thetreatment plant
* Desired/required to protect the distribution system
Waste water treatment aims
- Reduce BOD
- Destroy pathogens
Wastewater treatment steps
- Primary treatment
- Secondary treatment
- Tertiary treatment
Primary treatment
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%
Secondary treatment: Liquid
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%
Secondary treatment: Sludge
1° & 2° sludge is subjected to microbial digestion under anaerobic conditions
* BOD reduced by 90%
* Material that remains is incinerated or buried
Tertiary treatment
May involve any or a combination of the following:
* Biological treatment (ponds: algae)
* Flocculation
* Filtration
* Chlorination or ozonation
May be suitable for drinking
Septic tank
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
