The document discusses water purification on a large scale. It describes various methods used including storage, filtration through slow sand filters and rapid sand filters, and disinfection through chlorination. It also discusses small-scale household purification methods. Various filtration techniques are described in detail including slow sand filtration and rapid sand filtration. Membrane processes for water purification including reverse osmosis and nanofiltration are also summarized.

1. WATER PURIFICATION ON A
LARGE SCALE

2. • WATER RELATED DISEASES
• • Biological (Water-borne diseases)
• • Caused by infective agent
• • Viral, Bacterial, Protozoal, Helminthic, Leptospiral
• • Caused by aquatic host
• • Snail, Cyclops
• • Chemical
• • Dental
• • Cyanosis in infants
• • Cardiovascular
• • Inadequate use of water
• • Insect breeding

3. WATER POLLUTION LAW
• • Water (Prevention and Control of Pollution)
Act , 1974
• • Central and State Water Boards and Joint
Water Boards endowed
• with wide powers for controlling pollution

4. • WATER PURIFICATION
• • Large scale
• 1. Storage
• 2. Filtration
• • Slow sand filter
• • Rapid sand filter
• 3. Disinfection
• • Chlorination
• • Ozonation
• • Other agents
• • Membrane processes
• Small scale
1. Household purification
• Boiling
• Chemical disinfection: Bleaching powder, Chlorine solution , High test
hypochlorite
(HTH), Chlorine tablets, Iodine, Potassium permanganate
• Household filtration
2. Disinfection of well
• By adding bleaching powder
• Double pot method

5. • STORAGE
• • In natural or artificial reservoirs
• • Effects of storage:
• • Physical: gravity – 90% suspended impurities settle down in one
day
• • Chemical: oxidizing action
• • Biological: only 10% bacteria remains at the end of 1 week
• • Optimum period of storage: 2 weeks
FILTRATION
Water passed through porous media
1. Slow sand filter: biological 2. Rapid sand filter: mechanical
SLOW SAND (BIOLOGICAL) FILTERS
• Used first in 19th century in Scotland
• Elements of slow sand filter
1. Filter Box
a) Supernatant water
b) Sand bed
c) Under drainage system
2. Filter control valves

6. SLOW SAND (BIOLOGICAL) FILTERS
Parts in general

7. • ELEMENTS OF SLOW SAND
FILTER
• • Supernatant water
• • Sand bed
• • Under drainage system
• • Filter control valves d
Cross-sectional view of the filter
bed
Supernatant water
• Depth: 1 to 1.5 m • Promotes downward flow of water through the sand bed
• Waiting time of 3-12 hours for raw water to undergo partial purification by
sedimentation and oxidation
Sand bed
• Depth, 1 m (sand of diameter 0.2-0.3 mm), 0.3m (gravel with 0.2 - 1 cm
diameter)
• Sedimentation
• The supernatant water acts as a settling reservoir. Settle-able particles
sink to the sand surface.
• Mechanical straining
• Particles too big to pass through the gap between the sand grains are
retained

8. Vital/ Biological/ Zoogleal/ Schumtzdecke layer
• • Slimy, gelatinous layer over sand bed containing threadlike algae, bacteria
and diatoms
• • ‘Heart’ of the slow sand filter
• • Ripening of filter: Formation of vital layer
• • Suspended particles are retained by adhesion to the biological layer •
Removes organic matter, holds back bacteria and oxidizes ammoniacal
nitrogen in to nitrates
Under drainage system
• Depth: 0.15 m • At the bottom of filter bed
• Porous pipes: Outlet for filtered water as well as support to the filter
media above • Rate of filtration 0.1-0.4 m3/hr/m3
Filter cleaning
• Increased bed resistance -> Necessary to open the regulating
valves fully -> Scrapping top portion of sand bed up to 2 cm
depth -> Time for cleaning the filter
• After 3-4 years new filter bed is constructed

9. ADVANTAGES OF SLOW SAND FILTER
• 1. Simple to construct and operate
• 2. Construction is cheaper than rapid sand filters
• 3. Physical, chemical and bacteriological quality of filtered water is very
high (99.9 to 99.99 per cent and E. Coli by 99 to 99.9 per cent)
RAPID SAND FILTER
• First in1885 in USA
• Gravity type (Open)/ Paterson’s • Pressure type (Closed)/ Candy’s

10. • STEPS OF RAPID SAND FILTER
• 1. Coagulation • Addition of Alum (5-40 mg/litre)
• 2. Rapid mixing • Mixing chamber • Violent mixing of alum (minutes)
3. Flocculation
• Flocculation chamber • Slow stirring of water by paddles (30 minutes)
• Flocculent ppt. of Aluminium Hydroxide entangles all particulate,
suspended matter along with bacteria
4. Sedimentation
• Sedimentation chamber • Flocculent ppt. settle down (removal is done from time to
time) • Clear water above goes for filtration
RAPID SAND FILTER
Cross-sectional view

11. ADVANTAGES OF RAPID SAND FILTER
1. Rapid sand filter can deal with raw water directly. No preliminary storage is
needed
2. The filter beds occupy less space
3. Filtration is rapid, 40-50 times that of a slow sand filter
4. The washing of the filter is easy
5. There is more flexibility in operation

12. • DISINFECTION
• • Criteria for satisfactory disinfectant
• • Not influenced from properties of water within short time
• • Should not be toxic and colour imparting or leave the water impotable
• • Available, cheap, easy to use
• • Residual concentration to deal with recontamination
• • Detectable by rapid, simple techniques in small concentration
ACTION OF CHLORINATION
• Kills pathogenic bacteria (no effect on spores and viruses)
• Oxidize iron, manganese and hydrogen sulphide
• Reduces taste and odours
• Controls algae
• Maintains residual disinfection
1. Water should be clear, free from turbidity
2. Chlorine demand: Chlorine needed to destroy bacteria, to oxidize organic matter
and to neutralize the ammonia in water
3. Free residual chlorine for a contact period of 1 hour is essential
4. Breakpoint: Point when chlorine demand of water is met and free residual
chlorine appears
Minimum recommended concentration of free chlorine is 0.5 mg/L for 1hr

13. • SUPER CHLORINATION
• Method of choice for highly polluted waters • High dose of chlorine is added
• • After 20 minutes of contact, dechlorination is done with sodium sulphate/
sodium thiosulphate to reduce the taste of excess chlorine
OTHER DISINFECTION METHODS
• Ozone Used in Europe and Canada, Strong oxidizing agent, Strong virucidal
• No residual effect but, Should be used with chlorination
UV Rays Used in UK , Water should be clear, No residual effect but Expensive
Chloramine, Chlorine + Ammonia – Chloramine, Less effective than chlorine
MEMBRANE PROCESSES
• High-pressure processes
• Lower-pressure processes
High-pressure processes
• Reverse osmosis
• Rejects monovalent ions and organics of molecular weight >50 daltons
• Pore sizes <0.002 μm
• Desalination of brackish water and seawater
• Nanofiltration
• Allow monovalent ions such as sodium or potassium to pass but reject a high
proportion of divalent ions such as calcium and magnesium Pore sizes are typically
0.001-0.01 μm, Effective for the removal of colour-forming organic compounds

14. • Low-pressure processes
• • Ultrafiltration: Reject organic molecules of molecular weight above
about 800 daltons, Pore sizes 0.002 - 0.03 μm
• • Microfiltration: Pore sizes 0.01-12 μm, capable of sieving out particles
greater than 0.05 μm used for water treatment in combination with
coagulation.

15. • During an emergency, it is desirable to ensure a constant dosage of
chlorine to well water ‘Double pot method’
• There are two cylindrical pots, One pot is placed inside the other
• Outer pot: Inside height is 30 cm , Inside diameter is 25 cm
A hole (1 cm diameter) is made at 4 cm above the bottom
• Inside pot:Fits into the outer pot, Has a hole (1 cm diameter) near the
upper end
• A mixture of 1 Kg bleaching powder and 2 Kg sand is prepared and
moistened with some water
• The inner pot is filled with this mixture up to 3 cm below the hole
• The inner pot is placed into the outer one
• The mouth of the latter is closed with polyethylene foil
• The double pot is lowered into the well by means of a rope attached to
the well
• The pot should be immersed at least 1 m below the water level to
prevent damage by the buckets used for drawing water
• This device works satisfactorily for 2 – 3 weeks in small household wells
containing 4500 L of water and a draw off rate of 360 to 450 L per day

16. AIR POLLUTION
• It is occurs when the air contains gases, dust,
fumes or odor in harmful amounts. In other
words it is when concentrated gases exceed
safe limits
TYPES OF AIR POLLUTION
Outdoor Air Pollution
*Smog *Particulates *Acid Rain *Greenhouse Gases
• Indoor Air Pollution (Smoking , cooking, burning wood stoves, fireplaces, and
furnace )
CAUSES
Natural Sources ( smoke that comes from wildfires, volcanoes, methane, dust)
Human Sources ( power plants and automobiles, fumes, burning wood stoves,
fireplaces, and furnace)
Pollutants
• Carbon Dioxide
• Carbon Monoxide
• Sulfur Dioxide
• Nitrogen Dioxide

17. • Total Suspended particulate:They are present in the form of aerosols (solid particles or liquid
droplets suspended in a gaseous medium) such as dust, pollens, smoke. Sources:
Combustion, industry.
• Hazards: Reduce visibility & cause respiratory problems such as pneumoconiosis (particles
less than 2.5 μm)
• Sulfur Dioxide: It is a colorless & corrosive. It dissolves in water present in the air to form
sulfuric acid. Sources: Volcanic eruption, fuel combustion in industry. Hazards: Damaging to
lungs (aggravation of CLD), plants & animals.
• Nitrogen dioxides: It combines with water to form nitric acid, which is responsible for
atmospheric acidification (Acid rain). Sources: High temperature combustion and action of
bacteria on nitrogen containing compounds in the soil. Hazards: Acute & chronic respiratory
diseases and property destruction.
• Carbon monoxide: It is highly toxic and results from incomplete combustion. It has great
affinity for hemoglobin (Carboxy hemoglobin). Source: Internal combustion engines. Hazard:
Combine irreversibly with hemoglobin leading to asphyxia.
• Carbon Dioxide: It is non-toxic in low concentration. Its increase in concentration contributes
to the problem of global warming. Source: Mainly respiration but it is balanced by
photosynthesis (bad effect of deforestation) and from fossil fuel combustion. Hazards:
Increases earth temperature thus producing undesirable climatic changes.
• Lead: It is responsible for 2/3 of all metallic air pollution. Sources: Leaded gasoline, lead processing,
smelters, paints and burning materials containing lead. Hazards: Neurotoxin that causes mental
retardation especially in children.
• Ozone: It is formed by a 2ry atmospheric reaction driven by solar energy in the form of UV rays
(photochemical reaction). Source: It is formed in the atmosphere. Hazard: Eye irritation and respiratory
impairment.

18. volatile organic compounds

19. Primary Mechanism
• Formation of VOC (Volatile organic compound)
• Biological generation of VOC
• Formation of liquid aerosol droplets
• Anthropomorphic generation of particulate
aerosol
• Biological formation of particulate aerosols
• Particulate aerosol formation
Secondary Mechanism
• Condensation
• Adsorption
• Nucleation
IMPACTS
• Climate System
• Health
• Economy
• Environment
• Ecosystem
• Forestry
• Agriculture

20. • CONCLUSION AND RECOMMENDATIONS
• • Air pollution has long been a serious
problem
• in the world.
• • Without air, Earth would be unable to
sustain
• life.
• • Spread the Word.