Pathogens

Treatment of Public Water Supplies

1. Sedimentation basin with Alum as flocculant, slow agitation– removes up to 95% of bacteria via coagulation -> agitation -> flocculation.

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2. Sand filter comprised of anthracite coal, gravel, and sand with a thin film of microorganisms filters colloidal and dissolved organic matter out of the water

Chlorination
CL2+H2O -> HCL+HOCL (the hypochlorous acid is the killing agent). This stuff is great because it A) oxidizes proteins and interferes with respiration and B) it leaves a protective coating in pipes through which public water travels– a safeguard for extra pathogen-killing power. Twice as much CL is required to kill viruses because their nucleoproteins are much more difficult to denature.
Issues with Chlorination
Carcinogenic chlorinated organics are generated, it contributes to the resistance of certain pathogens such as viruses, giardia lamblia, and cryptosporidium parvum.
Alternatives to Chlorination
UV radiation, ozone, and chlorine dioxide. Chlorine Dioxide kills viruses more effectively and produces less chlorinated organic material than chlorine, but it is more expensive. Also, you need residual killing agent from plant to region of consumption.
Drinking Water Treatment Plant

1. Water is pumped from reservoir or stream

2. Alum is added as flocculant; sedimentation of fluc occurs and is pumped out as sludge

3. Sodium carbonate and hydrated lime added to remove hardness (especially Ca and Mg)

4. Water is filtered through rapid sand filters containing anthracite, gravel, and sand.

5. Chlorine is added.

Waterborne Diseases

2.5 billion people lack improved sanitation facilities

nearly 1 billion do not have access to safe drinking water

diarrhea is second only to pneumonia in child deaths– approx. 3 per minute, kills more people than TB or AIDS

 

Water Pathogens
Viruses, bacteria, protozoans, and helminths; carried by humans and animals; spread by contact, entry, and overcoming the body’s natural defenses.
Important Bacteria

Escherichia Coli

Pseudomonas Aeroginosa

Shigella

Salmonella

Important Protozoans

Cryptosporidium Parvum

Giardia Lamblia

Naegleria spp.

Important Viruses

Adenovirus

Hepatitis A

Norwalk

Unidentified Viruses

Important Helminths
Schistosoma
Gross Stuff about Protozoans
Some produce oocysts in lieu of eggs, which are nasty buggers and hard to kill via chlorination, only removed by boiling or filtration. Digestive juices dissolve oocyst wall and release protozoan into intestinal tract. An infected person may release up to 100 million oocysts per day.
Stuff about Viral Pathogens
Can replicate only inside the living cells of an organism, do not have their own metabolism and require a host cell to make new products. Only account for 5% of identified waterborne pathogens but could be much greater. More resistant to chlorination.
How a Virus Works

1. Adsorption to host cell

2. Penetration of genome into host cell

3. Replication of viral genome using host cell’s machinery

4. Assembly of viral components and enzymes

5. Maturation of virus

6. Release of newly produced viruses from host cell

Helminth Pathogens
Enter via mouth or skin, normal water treatment effectively kills them, best known is the beef tapeworm. Up to 1 million eggs per day are found in the feces of an infected person; eggs are viable for hundreds of days in the right conditions.
What Makes an Ideal Indicator Organism?
Should be: proportional in abundance to the number of pathogens in the water, and survive just as long outside the digestive tract, easily detectable and present in greater quanitites than any potential pathogen, and absent from the aquatic environment unless the water has been polluted with sewage or animal excrement.
The Problems with Coliforms
First we used total coliforms as an indicator, but they are not ideal since they are found naturally. In the 70s we began to use fecal coliforms but according to the EPA there is no correlation between either of these measures and GI illness.
What are the new indicator species?
Enteroccocus is found to be correlated with GI illness in marine environments and E Coli is found to be correlated with GI illness is freshwater environments (may have a lower survival rate than enterococcus in seawater).
Indicator species…
… have inherent problems due to different survival rates of different pathogens; basically, they suck. They are a “moving target” and no one species will ever be correlated perfectly with the numerous pathogens we are too lazy to test for individually.