Water Flashcards
Water resources
- only 2.5% of the earths water is freshwater
- of that 2.5%, 30.1% is groundwater and 1.3% is surface water
- of the 1.3% of surface water, 20.1% is lakes / rivers
- 68.6% of water is “locked up” in glaciers and ice caps
Indicator bacteria
Associated with intestinal tract
- signal potential for waterborne diseases
- characteristics of good indicator bacteria : easily measured, not pathogenic, well represented
Drinking water treatment stages
Coagulation Flocculation Sedimentation Filtration Disinfection
Coagulation
Coagulant chemicals (alum) are added to water and rapidly mixed After mixing , small fine particles in water start to stick to one another Coagulant chemicals neutralize the electrical charges , allowing aggregation
Flocculation
Process of gentle mixing that brings the small clumps formed by coagulation into contact with each other forming a floc
-flocculation basin has a number of compartments with decreasing mixing speeds to allow for flocc to become bigger
Sedimentation
Decreases the concentration of suspended particle in the water
Water sits in thanks or a number of hours allow flocs/ heavy materials to settle to the bottom
Removes 90% of suspended particles from the water (including bacteria)
Disinfection
Chlorination, ozonation, and UV radiation
Removes or inactivates disease causing organisms in water
Protozoan pathogens are large and have been removed by other steps, but bacteria and viruses are destroyed by disinfectant
Chlorine
Most frequently used form of disinfectant
Can deactivate most microorganisms and its relatively cheap
HOCL -most important form of free available chlorine is MOST effective chemical to kill microbes
Four forms of chlorine that can produce HOCl in water
- Chlorine gas, hypochlorite, chloramines, chlorine dioxins (most dangerous)
Advantages and Disadvantages of Chlorine
Advantages : RESIDUAL DISINFECTANT protects water during distribution and can provide protection throughout system if chlorine residual is maintained
- effective at LOW concentrations (most of the time)
- reduces nuisance odor from hydrogen sulfide
Disadvantages : creates DBPS (disinfection by products) like THMS (trihalomethanes) which are bad shit (carcinogenic)
- THMS produce lower birth rate, and a small hazard in the grand scheme of things
- Chlorine provides poor cryptosporidium and Giardia control
- more space required because it needs long time to disinfect
- Chloramines produce less DPBS THAN OTHERS , so it is the most safe.
Advantage and disadvantages of Ozonation
Advantages :
- 30,000 times faster than chlorine, more potent
- does not add chemicals into water. Breaks down into H20 + 02
- NO DBPS (disinfectant by products)
Disadvantages
- No residual disinfectant
- high cost for initial set up/ operational costs
- potential fire and toxicity hazards with ozone generation
- corrosive
Advantage and Disadvantages of UV
- UV can damage the DNA of microbes and cause instantaneous microbe inactivation
Advantages :
- no DBPs
- no chemicals
- low maintenance
Disadvantages :
- NO residual disinfectant
- Pre treatment may be necessary for raw water with moderate mineral content
- anything that blocks UV light from reaching the water will result in poor treatment (no turbidity)
Sources of waterborne disease
Portable water :
- generally has very high standards / treatment , but may sometimes have low quality / be improperly treated (example : what happened in Flint)
- may be from non regulated sources (private wells)
- highly preventable
- waterborne disease outbreaks are an on overall downward trend due to increased sanitation , treatments, and technology
- However, there may be some cyclicality influenced by precipitation events and economics
Recreational water :
- ponds, lakes, public swimming pools
- waterborne disease outbreaks treads are more cyclical than those for potable water,and generally increasing over time
- these patterns may also be altered by what organisms are recognized as being associated with disease
Importance of infective dose
Amount of infectious organisms required to cause infection
- E. coli O157:H7 is 10-100 cells
- Virbrio cholera is 10^3 - 10^8 cells
- Cryptosporidium parvum requires 10-200 oocysts
- Giardia requires 1 cyst (that’s why it is such a bastard!)
- a lower infective dose = THREATENING AS HELL
Waterborne disease example : Milwaukee , WI (1993)
Water treatment plants met existing state and federal standards
- rapidly melting snowpack and heavy rains caused sewer overflow
- high winds influenced a southernly flow
- infections associated with over 400,000 people
John Snow
- a British obstetrician doctor who was convinced that cholera was
spread when people drank contaminated water - a mother washed her baby’s diaper in a town well in 1854 and then an epidemic hit and killed 616 people
- Considered the pioneer of public health research for epidemiology
- Broad street pump was contaminated water and spread cholera
