Water – related diseases
Purification of Water
Hardness of water
Dr Madhavi Bhargava
Asst. Prof
Dept of Community Medicine
Water Pollution
• More than 5 million people die each year due
to unsafe drinking water, lack of sanitation
and insufficient water for hygiene
• More than 2 million die from water-related
diarrhea
• Collectively, they are more lethal than HIV and
AIDS
Other consequences
• Loss of working days and school days
• Leads to or aggravated undernutrition
• Draining of individual and national resources
Sources of impurities
NATURAL
- Derived from
atmosphere, catchment
area and soil
- Dissolved gases, clay,
mud, silt, magnesium,
calcium
MAN-MADE
- Due to urbanization and
industrialization
- Sewage
- Industrial waste
- Agricultural pollutants
- Physical pollutants
Leaky pipes, corrosion of supply system, cross connection with
sewage system are other causes
Water-related diseases
Biological:
Water-borne
diseases
Waterassociated
diseases
Diseases due to
Chemicals
Water-washed
diseases
Water-borne diseases
Presence of infective agent
 Viral: hepatitis A/E,
poliomyelitis, rotavirus
 Bacterial: typhoid, cholera,
dysentery, shigellosis (IF
RESISTANT ORGANISMS?)
 Protozoal: amoebiasis,
giardiasis
 Helminthic: roundworm,
threadworm
 Leptospiral: Weil’s disease
Presence of aquatic host
 Snails: schistosomiasis
 Cyclops: guineaworm, fish
tape worm
Diseases due to presence of chemicals
• Industrial and agricultural in origin
• Important pollutants are:
- Detergent solvents
- Cyanides
- Heavy metals
- Minerals and organic acids
- bleaching agents and dyes
- sulphides, ammonia and pigments
Chemical pollutants
• Fertilizers, pesticides, herbicides, etc
• Arsenic
• Fluorides: optimum levels 0.5 – 0.8 ppm. Up to
1mg/Lt protects against caries, and high levels
cause flourosis
• Nitrates: high concentration causes
methaemoglobinemia and cyanosis in infants
• Carcinogenic pesticides such as DDT
• Lead and heavy metals
Water-associated diseases
• Caused by insect vectors breeding in or near
water
• Malaria (anopheles) and Filaria (culex)
• Arboviral diseases: dengue (aedes), Japanese
Encephalitis (culex), Chikungunya fever
(aedes)
• Onchocerciasis: black fly
Water washed diseases
• Scarcity and inaccessibility of water
• Non-washing of hands and poor hygiene
• Typhus and scabies
General guidelines and IEC
• Avoid contact with soil that may be contaminated
with human feces
• Prevent open field defecation
• Disposal of diapers safely
• Wash hands with soap and water before food
handling
• Travel safety
• Wash, peel or cook all raw vegetables and fruits
before consuming
A Simple Rule of Thumb
"Boil it, cook it, peel it, or forget it"
Purification of Water
It is of great importance to the community.
It comprises of:
Storage
Filtration
Disinfection
Storage
Natural purification takes place on storage
Physical:
Chemical:
Biological:
Suspended
impurities settle
down
Aerobic bacteria
oxidize organic
matter
Pathologic bacteria
die (90% in 5-7
days)
Allows penetration
of light and reduces
the work of filters
Optimum duration
is 10-14 days
Longer storage
causes algae to
grow
Filtration is commonly the mechanical or physical
operation which is used for the separation of solids
from fluids (liquids or gases) by interposing a
medium through which only the fluid can pass.
Filters are of two types-
a) Slow sand or biological filters
b) Rapid sand or mechanical filters
Slow sand or biological filters
• First used in Scotland in 1804.
• 19th century – use spread through out the world
• Standard method of water purification
Elements
• Supernatant (raw) water
• A bed of graded sand
• An under drainage system
• A system of filter
control valves
Slow sand filter
Supernatant Water
• It is above the sand bed
• Level of supernatant water should be kept
constant
• Depth- 1 to 1.5 meter
• Serves two important purpose
– Constant head of water
– Waiting period of 3 to 12 hours depending on filtration velocity.
Sand bed
• Most important part of filter
• Depth- 1 to 1.2 meter
• Sand grains should be rounded with diameter of
0.2 to 0.3 mm
• Supported by layer of graded gravel (30 -40cm)
• Vast surface area (1 cubic meter = 15000 square
meters.
• Rate of filtration – 0.1 and 0.4 m3/m2/hour
Contd…
• Water percolates through sand bed,
number of purification processes act– mechanical straining
– Sedimentation
– Adsorption
– Oxidation
– Bacterial action
Vital layer (Important short-note)
• Schmutzdecke layer/biological layer/zoogleal layer
• Slimy & gelatinous
• Consists of algae, planktons, diatoms & bacteria.
• Indicates ripening of filter
• Heart of slow sand filter
– It removes organic matter
– Holds back bacteria
– Oxidizes ammonical nitrogen
Under drainage system
Consist of porous or perforated pipes
• Provides an outlet for filtered water
• Support the filter medium and valves
Filter control
• Purpose of filter control valves is to
maintain constant rate of filtration.
• Venturi meter– Measures the bed resistance or loss of head.
– When resistance builds up it is opened to
maintain the constant rate of filtration.
Filter cleaning
• Bed resistance increases to extent that the
regulating valve has to be kept fully open.
• Cleaning procedure– Supernatant water is drained off
– Sand bed is scraped to a depth of 1 to 2 cm
– Done by unskilled workers using hand tools or
mechanical equipment.
After 20 to 30 scrapings the thickness of sand
bed is reduced to 0.5 to 0.8 meter
The plant is then closed down
Advantages
• Simple to construct & operate.
• Cost of construction is less.
• The physical, chemical and bacteriological
quality of filtered water is very high.
• Reduce the total bacterial count by 99.99 %
Disadvantage
• Due to the low filtration rate, it is not
suitable for use in municipal cities
• Slow sand filters require extensive land
area for a large municipal system.
Rapid sand filter
• Designed and built by George W. Fuller in Little
Falls, New Jersey 1880
• 1902- went into operation, since then widely
used in large municipal water systems.
Two types-
• Gravity type ( Paterson’s filter)
• Pressure type ( Candy’s filter)
Coagulation: raw water mixed with coagulant like alum
Rapid Mixing: violent agitation in mixing chamber for quick and
thorough dissemination
Flocculation: slow and gentle stirring for 30 minutes (2-4 rpm)
Sedimentation: detained for 2-6 hours, flocculent precipitate with
bacteria and impurities settles
Flow diagram of rapid sand filtration
river
Alum
chlorine
Mixing
chamber
Flocculation
chamber
Sedimentation
tank
Filters
Clean
water
Rapid sand filter bed
Filter bed
• Each unit surface is 80-90 meter square(900 sq feet)
• Water on top of sand bed is 1.0 to 1.5 metre deep
• Filtering medium- sand particle
– Size-0.4 to 0.7 mm
– Depth of sand bed is 1 metre
• Graded gravel –
– supports the sand bed
• Under drains collect the filtered water
• Rate of filtration is 5- 15 m3/m2/hour
CLEANING OF FILTER
Loss of head approaches 7-8 feet.
Filters subjected to a washing process called
BACKWASHING
Done by reversing the flow of water through sand bed
Dislodges the impurities.
It takes 15 min.
Stopped when wash water is sufficiently clear
 In some filters compressed air can also be used for backwashing
Advantages
• Much higher flow rate than a slow sand filter; about 150 to
200 million gallons of water per acre per day (40-50 times
slow filters)
• Requires relatively small land area.
• Less sensitive to changes in raw water quality, e.g. turbidity.
• Requires less quantity of sand.
• Cleaning is easy process
Disadvantages
• Large pore size will not, withhold coagulant or
flocculent,
• Requires greater maintenance than a slow sand filter.
• Generally ineffective against taste and odour
problems.
• Produces large volumes of sludge for disposal.
• Treatment of raw water with chemicals is essential.
• Skilled supervision is essential.
• Cost of maintenance is higher.
• It cannot remove all bacteria (98 to 99%).
Comparison Rapid and Slow sand filter
Rapid sand filter
Slow sand filter
Space
Occupies very little space
Occupies large area
Rate of filtration
200 m.g.a.d
2-3 m.g.a.d
Effective size of sand
0.4-0.7 mm
0.2-0.3 mm
Preliminary treatment
Chemical coagulation &
Sedimentation
Sedimentation
Washing
Backwashing
Scraping the sand bed
Operation
Highly skilled
Less skilled
Loss of head allowed
6-8 feet
4 feet
Removal of turbidity
Good
Good
Removal of color
Good
Fair
Removal of bacteria
98-99%
99.9-99.99%
Disinfection
Ideal disinfectant of drinking water:
• Capable of destroying pathogens within
available contact time with usual temp, pH
and minerals
• No toxic by-products of reaction
• Ready and dependable availability at
reasonable cost
• Detectable for monitoring efficiency of control
Chlorination
•
•
•
•
Supplement and not a substitute to filtration
Kills all bacteria
No effect on spores
Higher concentrations required for viruses like
polio and hepatitis
• Also oxidizes iron, manganese and hydrogen
sulphide
• Controls algae and slime forming organisms thus
controlling odour
Chlorine chemistry
Chlorine compounds used in disinfection
•
•
•
•
Chlorine gas Cl2
Calcium Hypochlorite Ca(OCl)2
Sodium hypochlorite NaOCl
Chlorine dioxide ClO2
Cl2 when applied to water  forms
hypochlorous acid and hydrochloric acid
Cl2 + H2O ↔ HOCl + HCl
Ionization :
HOCl ↔ H+ + OClHypochlorous acid is most effective form of
chlorine
70-80 times more than hypochlorite ion
• Chlorine acts best when pH of water is 7
• At this pH, predominance of Hypochlorous
acid
• If above 8.5: 90% of hypochlorous acid is
ionized to hypochlorite ion
Principles of Chlorination (short-note)
1) Water should be free from turbidity
2) Chlorine demand: Difference between the amount
if chlorine added to water and amount of residual
chlorine remaining at the end of contact period (I
hour), at a given temp and pH
Point at which ‘chlorine demand’ of water is met is
called ‘break-point chlorination’
3) Contact period: One hour
4) Minimum concentration of free residual chlorine:
0.5mg/L (as a margin of safety during storage and
distribution)
5) Correct dose of chlorine: Chlorine demand+free
residual chlorine of 0.5mg/L
Break-point chlorination
Addition of chlorine produces chloramines
Initial reduction in residual chlorine initially due to the
destruction by added chlorine
After a particular stage in adding further chlorine,
free residual chlorine starts appearing:
BREAK POINT CHLORINATION
Generalized curve obtained during breakpoint chlorination
METHOD OF CHLORINATION
1) Chlorine gas: cheapest, quicker, efficient and
easy to apply (Paterson’s chloronome)
2) Chloramines: loose compounds of chlorine
and ammonia. Slower in action but give mre
persistent type of residual chlorine
3) Perchloron (High test hypochlorite): Calcium
compound with 60-70% of available chlorine
Other Methods
• Ozonation
• Ultraviolet Radiation
Purification at household
• Boiling: rolling boil for 10-20 minutes
• Chemical disinfection: Bleaching powder
Chlorine solution
High test hypochlorite (perchloron)
Chlorine tablets (0.5gm/20 litres)
Iodine solution
Potassium permanganate
• Filtration with ceramic filters: Pasteur Chamberland,
Berkefeld and Katadyn
• Ultraviolet irradiation
• Reverse osmosis (RO water)
WATER QUALITY: CRITERIA AND
STANDARDS
Water Quality- Criteria and Standards
• Acceptability
• Microbiological aspects
• Chemical aspects
• Radiological aspects
WHO guidelines for drinking water
Acceptability aspects
Physical parameters:
 Turbidity,
 Color,
 Taste and odor,
 Temperature
Inorganic constituents:
 Chlorides,
 hardness,
 ammonia,
 pH,
 Hydrogen sulphide,
 Iron,
 sodium,
 sulphur,
 Zn, Mn,
 Aluminium
MICROBIOLOGICAL CRITERIA OF
DRINKING WATER (short note)
Bacteriological
Indicators
Virologic
Aspects
Biological
aspects
Bacteriological Indicators
• Ideally it should not
contain any microorganisms
• Primary bacterial
indicator: Coliforms
• Supplementary
indicator: fecal
streptococci and
clostridia
COLIFORMS:
• All aerobic and
facultative anaerobic
• Gram -ve
• Non-sporing
• Motile and non-motile
rods that are
• Lactose fermenting
• Eg: E.coli and Klebsiella
Why Coliforms
• Great abundance in human intestines
• Average person excretes 200-400 billion
coliforms every day
• Easily detectable (even one bacteria in 100 ml)
• Survive longer than other pathogens
• Resistant to natural forces of
purification
Other bacteria
• Fecal streptococci:
• Cl. Perfringens:
Indicator of recent fecal
Spores capable of
contamination because
surviving very long;
highly resistant to
indicator of fecal
drying
contamination of
remote time
Virologic aspects
• Drinking water should be free from all virus
• Free residual chlorine, 0.5mg/L with 30
minutes of contact time at pH of 8 is sufficient
to kill all virus
• Including hepatitis
• Other method is ‘OZONE’
Biological Aspects
• Protozoa: Entamoeba histolytica and Giardia
• Human or animal fecal contamination
• Helminths: roundworms, flatworms,
guineaworm
• Free-living organisms: fungi, algae, etc- mainly
cause color, turbidity, alter taste and odour
Hard water
• Hardness: Soap destroying power of water
• Mainly due to 4 compounds:
Calcium carbonate
Magnesium bicarbonate
Calcium sulphate
Magnesium sulphate
• Others: chlorides, nitrates, iron, manganese,
aluminium are in small quantity and less
important
TEMPORARY HARDNESS
• Carbonates of calcium
and magnesium
PERMANENT HARDNESS
• Non-carbonate
hardness
• Calcium and
magnesium sulphates,
chlorides and nitrates
Expressed as milli-equivalents per litre (mEq/L)
One mEq/L of hardness = 50 mg of CaCO3 (50 ppm)
Classification of Hardness
Disadvantages of Hardness
1) Consumes more soap and detergents
2) On heating carbonates are precipitated to
cause furring and scaling which require more
fuel in boilers
3) Food cooked looses its color and texture
4) Fabrics have short life
5) Unsuitable for some industrial purposes
6) Shortens life of pipes and fixtures
Removal of Hardness
Temporary
• Boiling
• Addition of lime
• Addition of sodium
carbonate
• Permutit process
Permanent
• Addition of sodium
carbonate
• Base exchange process
Questions/Topics for self-study
• Disinfection of wells
• Swimming pool sanitation
• Surveillance of drinking water, including
microbiological indicators
• Horrock’s apparatus
• Orthotolidine test and Orthotolidine arsenite
test (OT and OTA test)
• Superchlorination