Transcript Drinking water Water pollution

Drinking water
Water pollution
• Water is H2O
Water
• is a tasteless, odourless, appearing colourless
for naked eye substance that is essential to all
known forms of life.
• is a universal solvent.
• seawater (97%) has salinity of minimum 3.5%
(35grams of sodium chloride mostly per 1 litre of
water).
• freshwater (3%) contains less than 0.5parts
per thousand dissolved salts. It is surface
water (0.3%) in lakes, rivers and underground
as groundwater. Majority of freshwater is frozen
in glaciers and ice caps.
Chemical and physical properties
of water (H2O)
• Water strongly absorbs infrared radiation. This
results in pure water appearing slightly blue.
• Water is a very good solvent for hydrophilic
(‘water loving’) substances.
• Water sticks to itself (cohesion) because it is
polar.
• Water has a high surface tension caused by
strong cohesion between water molecules
Chemical and physical properties
of water (H2O)
• Water is able to move up narrow tube against
the force of gravity (capillary action).
• Water is able to moderate Earth’s climate by
buffering large swings of temperature as it has
high heat capacity and high heat of
vaporization.
• Freezing point. Ice floats on the water. Fresh
water at standard atmospheric pressure is most
dense at 3.98°C. This keeps deep water to
remain warmer than shallow freezing water and
this is how fish can survive freezing
temperatures in the water.
Chemical and physical properties
of water (H2O)
• Triple point is a single combination of
pressure and temperature at which pure
liquid water, ice and water vapour can
coexist in a stable equilibrium = 0.01°C
and 611.73 pascals.
• Any electrical conductivity observable in
water are from ions dissolved in it.
Water purity refers to purity from:
• toxins
• microbes
• pollutants
Drinking water
(potable water)
• Is fit for human consumption.
• Must be pure from toxins, pollutants and
microbes.
• Must be easily available.
Bacterial water analysis
• Is a routine check to make sure that the
concentration of potentially pathogenic bacteria
in drinking water is sufficiently low to say it is
safe for human consumption.
• Three indicator bacteria are chosen: nonspecific coliforms, Escherichia coli and
Pseudomonas aeruginosa.
• Coliforms (esp. E. Coli) could suggest the
possibility of fecal matter contamination of a
water supply.
• Coliform Index is usually given as a measure
of human fecal matter in the water.
Escherichia coli
• Escherichia coli is
an indicator
bacteria. Its presence
in water supply could
suggest the possibility
of faecal matter
contamination of a
water supply. Such
water cannot be used
for drinking
Drinking water purification
• Is removal of contaminants from raw water
to produce drinking water that is pure
enough for human consumption or for
industrial use.
• Substances that are removed are:
parasites
(Giardia,
Cryptosporidium),
bacteria, algae, viruses, fungi, minerals
(lead, copper), man-made chemical
pollutants.
Sources of drinking water
• Deep groundwater-is generally of very high
biological quality, but may be rich in dissolved
solids, especially carbonates, sulphates of
calcium and magnesium.
• Shallow groundwater is usually abstracted
from wells or boreholes. Its’ bacteriological
quality is variable. A variety of soluble material
may be present in it.
• Upland lakes and reservoirs-bacteria and
pathogen levels are usually low.
Sources of drinking water
• Rivers, canals and low land reservoirswill have a significant bacterial load.
• Atmospheric water generation- is a new
technology that can provide high quality
drinking water by extracting water from air
by condensing water vapour.
• Rainwater harvesting or fog collectioncan be used in areas especially with
significantly dry seasons.
Water treatment
• Primary treatment- collecting, screening and
initial storage.
• Secondary treatment- removal of fine solids
and the majority of contaminants using filters,
coagulation, flocculation and membranes.
• Tertiary treatment-polishing, pH adjustment,
carbon treatment to remove taste and smell,
disinfection, and temporary storage.
Water disinfection
• Means destroying any living pathogens
(viruses, bacteria including E. coli,
Campylobacter, Shigella, protozoans
including
Giardia
lamblia
and
Cryptosporidia).
Means used for water disinfection
• Chlorine- the most commonly used. A major
drawback to using chlorine is that it reacts with
organic compounds in the water to form
potentially harmful trihalomethanes (THMs)
and haloacetic acids, both of which are
carcinogenic.
• Chlorine dioxide
• Chloramines
• Ozone
• UV radiation
Water treatment options
• Fluoridation to prevent tooth decay.
• Water conditioning to reduce the effects of hard
water. Water hardness is content of calcium
and magnesium carbonate dissolved in it.
• Plumbo- solvency reduction- in some
locations water is capable of dissolving lead
from any lead pipes that it is carried in. Lead is
toxic.
• Radium removal.
• Fluoride removal.
Other water purification techniques
• Boiling for three minutes to disinfect
water.
• Charcoal filtering allows to remove many
compounds including toxins.
• Distillation -involves boiling to produce
vapour and then condensing it. Distillation
does not completely purify water. The
distillation apparatus may be the ideal
place to harbour Legionella .
Wastewater
• Is any water that has been adversely
affected in quality by antropogenic
influence. It comprises liquid waste
discharged by domestic residences,
commercial properties, industry and
agriculture .
Sewage
• is the subset of wastewater that is
contaminated with faeces or urine.
Wastewater constituents
•
•
•
•
Water >95%.
Pathogens: bacteria, viruses, prions, parasites.
Non- pathogenic bacteria.
Organic particles (faeces, hairs, food, paper,
plant material).
• Soluble organic material (urea, fruit sugars,
protein, drugs).
• Inorganic particles ( sand, metal particles,
ceramics).
Wastewater constituents
• Soluble inorganic material (ammonia, roadsalt, cyanide, hydrogen sulphide).
• Animals (protozoa, insects, arthropods, small
fish).
• Macro-solids
(sanitary
towels,
diapers,
condoms).
• Gases (hydrogen sulphide, carbon dioxide and
methane).
• Emulsions (paint, adhesives, mayonnaise).
• Toxins (pesticides, poisons).
Biochemical Oxygen Demand
(BOD)
• Is a wastewater quality indicator.
• Any oxidizable material present in a natural
waterway or in an industrial wastewater will be
oxidized by both biochemical (bacterial) or
chemical processes. The result is that the
oxygen content of the water will decrease
• Oxidizable material+ bacteria+ nutrient +O2-›
CO2+ H2O+ oxidized inorganics such as NO3
or SO4.
Chemical Oxygen Demand (COD)
• Oxidizable chemicals (such as reducing
chemicals) introduced into a natural water will
initiate chemical reactions. Those chemical
reactions create what is measured as Chemical
Oxygen Demand.
• Both BOD and COD tests are a measure of
relative oxygen-depletion effect of a waste
contaminant. Both have been widely adopted as
a measure of pollution effect.
5-day BOD
• Measures the amount of oxygen
consumed by biochemical oxidation of
waste contaminants in a 5-day period.
• Oxidizable chemicals (such as reducing
chemicals) introduced into a natural water will
initiate chemical reactions. Those chemical
reactions create what is measured as Chemical
Oxygen Demand.
• Both BOD and COD tests are a measure of
relative oxygen-depletion effect of a waste
contaminant. Both have been widely adopted as
a measure of pollution effect.
Wastewater treatment
• Most wastewater is treated in wastewater
treatment plants which include physical,
chemical and biological treatment
processes.
Wastewater reuse
• Treated wastewater can be reused as
drinking water (Singapore),
• in industry (cooling towers),
• in artificial recharge of aquifiers,
• in agriculture (70% of Israel’s irrigated
agriculture is based on highly purified
wastewater),
• in rehabilitation of natural ecosystems
(Florida’s Everglades).