Water resources managt

Hari Prasad Kafle

Assistant Professor (Public Health)

School of Health and Allied Sciences

Pokhara University.

Inorganic compound made up of 2 part of hydrogen and one part of oxygen.

Essential component for vitality animal and plant life.

Alma Ata Declarations on PHC1978: Water as basic element of Primary Health Care (An adequate supply of safe drinking water and basic sanitation).

Free from pathogenic agents

Free from harmful chemical

substances

Pleasant to taste, i.e. free

from color and order, and

Useable for domestic propose

For drinking purpose: 2 liter/person/day

Domestic purpose: 150-200 liter/person/day

1. Domestic uses;

2. Public purpose: cleaning

streets; fire protection, etc.

3. Industrial purpose;

4. Agricultural purpose;

5. Hydropower production;

6. Other uses: fishing, tourism,

swimming pool, ornamental

ponds, transportation etc.

Rainwater;

Surface water

◦ Impounding reservoir

◦ River and streams

◦ Tanks, Ponds and lakes

Ground water

◦ Sallow well

◦ Deep well

◦ Spring

Prime source of all water

Purest water in the nature

Physically clear, bright and sparkling

Chemically very soft

Corrosive action on pipes due to softness

Bacteriological free from pathogenic organism

Contains atmospheric impurities while raining:

acid rain

Originates from rain water

Main source of water supply

Examples: river, tanks, lake, sea water

Types: 4 types

◦ Impounding reservoir

◦ River and streams

◦ Tanks, Ponds and lakes

◦ Sea water

High chances of contamination

Generally no useable without treatment

Cheapest and more practical means providing water for small communities

Free from pathogenic organism

Usually requires no treatment

Supply even dry seasons

High mineral content e.g. Ca, Mg etc.

Requires pumping

Ground water includes ◦ Sallow well

◦ Deep well

◦ Spring

Particulars Shallow well Deep well

Definition Taps water from above

the first impervious

layer

Taps water from

below the first

impervious layer

Chemical

quality

Moderately hard Much hard

Bacteriologi

cal quality

Often grossly

contaminated

Tapes purer water

Yields Usually goes dry in

summer

Provides a source

of constant

supply

Location 1990 2000 2005 2010 2015*

Drinking

Water

Urban (%) 90 86 93 94 95

Rural (%) 43 71 79 78 72

Total 46 73 81 80 73

*Target MDG

Source: Nepal Millennium Development Goals; Progress Report 2010.

Developmen

t region

Piped

water

Hand

pump

Well Spring

water

Other

FDR 30.7 44 3.5 19.7 1.9

MWR 44.3 28.3 4.1 21.7 1.6

WR 59.8 27. 0.5 10.2 2.2

CR 45.4 39.4 5.4 6.5 3.4

ER 37.7 53.1 3.2 3.1 3

Nepal 45 39.1 3.6 9.6 2.7

Geographic

region

Piped

water

Hand

pump

Well Spring

water

Other

Terai 16.1 78.2 4.3 0.9 0.5

Hill 71 3.3 3.3 17.5 4.9

Mountain 77.3 0.3 0 18.9 3.5

Urban 62.2 28.2 4.3 3.1 2.2

Rural 45.5 41.3 3.4 11 2.8

Nepal 45 39.1 3.6 9.6 2.7

Year Unit Water Supply Leakage (%)

1993/94 Th. l/day 64684 -

1994/95 Th. l/day 62379 -

1995/96 Th. l/day 63447 -

1996/97 Th. l/day 40150 -

1997/98 Th. l/day 32115 -

1998/99 Th. l/day 27011 -

1999/00 Th. l/day 31271 38

2000/01 Th. l/day 26644 37

2001/02 Th. l/day 9876 37

2002/03 Th. l/day 10552 37

2003/04 Th. l/day 11550 36

2004/05 Th. l/day 9580 37

2005/06 Th. l/day 26300 38

2006/07 Th. l/day 33500 37

2007/08 Th. l/day 230450 35

Sewage,

Industrial and

trade pollutants,

Agricultural

pollutants,

Physical pollutants

Radioactive

substances.

Factories, power plants, sewage treatment

plants, latrines that are classified as point

sources, as they discharge pollution from

specific locations.

Non-point sources of water pollution are

scattered or diffuse, having no specific location

for discharge and include runoff from farm

fields and feedlots, construction sites, roads,

streets and parking lots.

Pollutant Main source Effects Possible control

Organic

oxygen

demanding

waste

Human sewage,

animal wastes,

decaying plant life,

industrial waste

Overload depletes

dissolved oxygen in

water: animal life

destroyed or migrates

away: plant life

destroyed

Provide secondary

and tertiary waste

water treatment;

minimize agricultural

runoff

Plant

nutrients

Agricultural

runoff, detergents

industrial wastes

inadequate

waste water

treatment

Algal blooms and

excessive aquatic plant

growth upset

ecological balances:

eutrophication

Agricultural runoff

too

widespread, diffuse

for adequate


Pathogenic

bacteria &

virus

presence of

sewage and animal

wastes in water

Outbreaks of such

diseases

as typhoid infectious

hepatitis

Provide secondary

and tertiary

wastewater

treatment; minimize

agricultural runoff

Inorganic

chemicals

Mining

manufacturing

irrigation, oil fields

Alter acidity, basicity,

or

salinity: also render

water

toxic

Disinfect during

waste-water

treatment; stop

pollutants at source


Synthetic

organic

chemicals

(plastic,

pesticides)

Agricultural

manufacturing, and

consumer uses

Many are not

biodegradable;

chemical interactions

in environment are

poorly understood

many poisonous

Use of biodegradable

materials; prevent

entry into water

supply at source

Sediments Natural erosion,

poor soil

conservation

practices in

agriculture, mining

construction

Fill in waterways,

reduce

fish populations

Put soil conservation

practices to use


Fossil fuels

(oils

particularly)

Machinery,

automobile wastes;

pipeline breaks,

offshore blowout

and seepage,

supertanker

accidents, spills,

and wrecks; heating

transportation,

industry;

agriculture

Vary with location,

duration, and type of

fossil fuel; potential

disruption of

ecosystems; economic,

recreational, and

aesthetic damage to

coasts

Strictly regulate oil

drilling,

transportation,

storage; collect and

reprocess engine oil

and grease; develop

means to contain

spills

A. Biological: water borne

disease

B. Chemical: organic acids,

Detergents, heavy metal

show long term effect.

C. Water associated disease:

Malaria, JE, filaria, dental

carries, CHD, conjunctivitis,

trachoma etc.

Viral: Viral hepatitis A, Hepatitis E, Poliomyelitis,

rotavirus diarrhoea etc.

Bacterial: typhoid & paratyphoid fever, bacillary

dysentery, Cholera, Esch. Diarrhoea etc.

Protozoal: amoebiasis, giardiasis.

Helminthic: round worm, thread worm, hydiatid

disease.

Snail: schistosomiasis.

Cyclops: guinea worm, fish tape worm.

Oh! how big; Could we digest it?

Let’s try!

Hari Prasad Kafle



Pokhara University.

The guideline for drinking water quality

recommended by WHO (1993 and 1996) relate

to following variables:

1. Acceptability aspects

2. Microbiological aspects

3. Chemical aspect

4. Radiological aspects

A. Physical parameters

1.Turbidity: < 5NTU (Nephelometric Turbidity

Unit)

2.Colour: free from colour; upto 15 TCU (True

Colour Unit)

3.Taste and odour: pleasant to taste and no odour

4.Temperature: cool water is more palatable.

Chloride: upto

200mg/liter

Calcium: 100-300mg/liter

Ammonia: <0.2mg/liter

Hydrogen sulphide: 0.05-

0.1mg/liter

Iron: 0.3mg/liter

Sodium: 200mg/liter

Sulphate: <250mg/liter

Zinc: 0.3mg/liter

Manganese: <0.1mg/liter

Cupper: <1mg/liter

Aluminum: 0.2mg/liter

PH value: 6.5-8.5

Dissolved oxygen: no

guideline

Total dissolved solids:

<100mg/liter

B. Inorganic constituents

1. Bacteriological indicator

a. Coliform organism

b. Faecal streptococci

c. Cl. Perfringens

2. Virological aspects

3. Biological aspects

a. Protozoa

b. Helminthes

c. Free living organism

a. Coliform organism: Several region for choosing coliform

indicators of faecal pollution are:

i. Easy to culture; even single E. coli can be culturable

in 100 ml of water.

ii. They are foreign to the water and generally not

present to water.

iii. They are present in greater number (normal human

can excrete 200-400 billion E. coli)

iv. They resist natural purification

v. They live longer than other pathogens

b. Faecal streptococci: It is the confirmatory test for faecal contamination. Some times (very rarely) E. coli doesn't present in water but if present streptococci than there is 100% faecal contamination.

c. Clostridia: the spores of clostridia are highly resistance against the disinfection. If only one spore of clostridia is present in water; it shows faecal contamination taken place in remote time.

Drinking water should be free from any virus

infectious to man. At the level of 0.5% FRC all

pathogenic virus will be destroyed including

hepatitis A. when bleaching powder mix with

2.5 gram mix with 1000ml of water then Free

Residual Chlorine (FRC) will be 0.7%/liter in

water.

a. Protozoa: Entomoba Histolytica, Giardia

Lambia both should not present in drinking

water and both slow and rapid sand filter are

effective In remaining protozoa.

b. Helminthes: Round worm, Flat worm etc.

Even a single egg/larva can produce disease in

man; should not in water. Guinea worm and

schistosomiasis is hazard of unpiped water can

be protect from source protection.

c. Free living organism: free living organism

that occurs in water supply include fungi,

algae etc. which interfere colour, odour, taste,

turbidity etc.

A. Inorganic chemicals

B. Organic constituents

Arsenic: 0.01mg/liter

Cadmium: 0.003mcg/liter

Chromium: 0.05mg/liter

Cyanide: 0.07mg/liter

Fluoride: 1.5mg/liter

Lead: 0.01mg/liter

Mercury: 0.001mg/liter

Nitrate (NO3): 50mg/liter

Nitrite (NO2): 3mg/liter

Selenium: 0.01mg/liter

Organic constituents Upper limit of

concentration

(Mcg/L)

Chlorinated alkanes

Carbon tetrachloride 2

Dichloromethane 20

Chlorinated ethane

Vinyl chloride 55

1.1-dichloroethene 30

1.2-dichloroethene 50


concentration

(Mcg/L)

Aromatic hydrocarbon

Benzene 10

Toluene 700

Xylems 500

Ethyl Benzene 300

Styrene 20

Benzolalpyrene 0.7


concentration(Mcg/L)

Aldrin/dieldrin 0.03

Chloride 0.2

DDT 2

Hepatochlor epoxide 0.03

Hexachlorobenzene 1

Lindane 2

Methoxychlor 20

Pentachlorophenol 9

Gross α activity = 0.1 Bq/L (Becquerel)

Gross β activity = 1.0 Bq/L

Thank you!

Hari Prasad Kafle



Pokhara University.

Don’t be puzzled by problems, what ever

they may be.

Always face them as if they are examinations

you have to pass.

The activities that ideally should be included in

the surveillance function are:

1. Approval of new sources (including private-

owned supplies)

2. Watershed protection

3. Approval of the construction and operating procedures of waterworks, including:

Disinfection of the plant and of the distribution system after repair or interruption of supply.

Periodic flushing programs and cleaning of water storage facilities.

Certification of operators,

regulation of chemical substances used in water treatment

cross connection control, back-flow prevention and leak detection control;

4. Sanitary survey;

5. Monitoring programs, including provision for

central and regional analytical laboratory

services;

6. Development of codes of practice for well

construction, pump installation and plumbing

7. Inspection quality control in bottled-water

and ice manufacturing operations.

1. Sanitary survey:

◦On-the-spot inspection

◦ Evaluation by a qualified person.

◦ Purpose: detection and correction of faults

and deficiencies.

2. Sampling:

◦ Carried out by competent and trained personnel.

◦ Sample for physical and chemical examination:

◦ Clean glass stoppered bottles (known as “Winchester Quart bottles”)

◦ Capacity of bottle: less than 2 liters.

◦ Sample for biological examination:

◦ Collected in clean sterilized bottles made of neutral glass.

◦ Capacity: 200-250 ml

3. Bacteriological Surveillance:

a. Presumptive Coliform Test:

i. Multiple tube method

Tube-Mc Conkey’s Lactose Bile Salt Broth with

bromcresol purple

Incubated for 48 hours.

Most probable number (MPN) is obtained from the

number of tubes showing acid and gas in 100ml water.

ii.Membrane filtration technique

Filtered through a membrane specially made of cellulose

ester.

Obtained result within 20 hours.

3. Bacteriological Surveillance:

a. The detection of faecal streptococci and cl.

perfringens

b. Colony count

Count on nutrient agar (yeast extract agar)

at 37 deg C and 22 deg C.

4. Biological examination

Microscopic organism: algae, fungi, yeast,

protozoa, rotifers, crustacean, minute worms,

etc.

5. Chemical surveillance

Basic Test: PH, colour, turbidity, chlorides,

ammonia, residual chlorine

Include analysis for toxic metal, pesticide,

persistent organic chemical and radioactivity.

55

No matter how handsome

(beautiful) you may be,

you will be judged by your

words and actions.

Always express sweet &

sound words and positive

action & efforts to sustain

your achievements.

Water purification is defined as the process of

removing all those substances, whether

biological, chemical or physical, which are

potentially dangerous or undesirable in water

supply for human and domestic use.

1.To remove pathogenic organisms &

consequently to prevent waterborne disease.

2.To remove substance which impart color, taste or

odor to the water.

3.To remove excess or undesirable chemicals or

minerals from the water.

4.To regulate essential elements or chemicals that

may be in excess or lacking in a certain water

supply.

5.To remove excess/undesirable dissolved gasses.

In order to achieve these objectives, water

treatment procedures may involve a simple

physical process such as sedimentation, or

complex physio-chemical and biological

processes, depending upon the undesirable

elements or substance present in the raw water.

Preliminary planning of water treatment plant work should include a comprehensive study of the catchments area in terms of:

1. Size, topography, population division and surface geology

2. Source of pollution

3. Sewage treatment facilities

4. Raw water characteristics including physical, radiological, chemical, bacteriological and biological characteristics

5. Rainfall and run-off data

6. Evaporation rate

7. Anticipated water supply requirement,

(minimum, maximum and average); and

8. Other items of importance in providing a safe

water supply, adequate in amount for the

community in question.

Purification of water in large scale

◦ Rapid sand filter

◦ Slow sand filter

Purification of water in small scale

◦ Boiling

◦ Chemical disinfection

◦ Filtration

◦Well disinfection

The component of water purification system

comprise one or more of the following

measures:

i. Storage

ii. Filtration

iii.Disinfection

As a result of storage, considerable amount of

purification takes place.

Physical: 90% suspended particles settle

down in 24 hours by gravity.

Chemical: aerobic bacteria oxidize the

organic matter present in the water with aid of

dissolved oxygen.

Biologically: bacterial count drops by 90% by

storage of water for 5-7 days.

Second stage of purification

98-99% of bacteria are removed by filtration.

Two types of filtration procedure are used for

large scale water purification.

Rapid sand filter “Mechanical filter”

Slow sand filter “Biological filter”

The oldest type, this type of filter has been use traditionally and has been effective in the past.

The rate of filtration very low than rapid sand filter.

Some of these filters are still in use in some parts of the Far East, Europe, and North America.

It is very well suited to rural areas, because it

does not require skilled workers to construct or

maintain, and the costs of operation and

maintenance are reasonable.

In this system, the process of filtration is a combination of physical straining, (e.g. sedimentation and biological activities), such as the growth of micro-organisms which takes place in the topmost layer of the sand grains soon after filter is in operation.

This microbial growth in the sand grain forms a sticky gelatinous coat in the top layers of the filter, and is called schmutzdecke, a German term meaning "cover of filth".

a.Raw water

b.A bed of graded sand

c.An under drainage system

d.A system of filter control valve.

The raw water to be filtered should be as clean

as possible, and turbidity should be less than

50 mg/l.

The depth of raw water is about 1-1.5 meter.

The raw water is evenly distributed over the

graded sand to a depth from 90 cm to 1.20

meters (36 inches to 48 inches).

The depth of the filter sand is one of the most

important determinants of the efficiency of

flirtation.

The effective diameter of sand is about 2-

3mm.

The graded sand is laid on the top of the

graded gravel to a minimum depth of 60 cm

(2ft), optimum 90 cm (3ft), and a maximum

depth of 1.20 meters (4ft).

Water percolates through a sand bed very

slowly taking time 2 hours or more to pass

taking number of purification process:

mechanical straining, sedimentation,

absorption, oxidation and bacterial action.

The designated rate of filtration is about 0.1-

0.4m3/m2/hour.

Crushed round gravel of fixed sizes, varying

from about 5 cm to 1.5 mm is laid around and

over the under drains, the largest size at the

bottom and the smallest at the top.

The depth of the graded gravel should be at

least 30 cm (12 inches), and preferably 45 cm

(18 inches).

000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000

oooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo

……………………………......................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

Filter sand

Course sand

Finegravel

Course gravel

Perforated pipes, or drainpipes with open

joints, with side joints (laterals) connected to

the main drain, are laid at the bottom of the

filter bed or tank to collect filtered water.

Equipped with certain valve and devices which

are incorporated in the outlet pipe system.

The purpose is to control the rate of filtration.

An important component is a ‘Venturi meter’

which measure the bed resistance or ‘loss of

head’.

The rate of filtration decreases gradually due

to clogging, it indicates the necessity for

cleaning, filtration is stopped, and the topmost

layer of the sand is removed by careful

scraping.

Each scraping usually removes from 5 cm to

10 cm depth of sand.

The sand that has been scraped off is stored and washed several times.

The cleaned sand is then replaced over the bed of the filter, to maintain the minimum depth.

The cleaning interval varies from about three weeks to several months depending on the quality of the raw mater to be filtered.

First installed in USA in 1885.

Useful for industrialized countries having metro and mega cities.

Supply large amount of water for populations.

Occupies very small space for plant installation.

Mixing

ChamberFlocculation

Chamber

Sedimentation

Tank Filter

Clean

water

storage

Alum

Chlorine

Co

nsu

mp

tion

1. Screening

2. Coagulation

3. Rapid mixing

4. Flocculation

5. Sedimentation

6. Filtration

7. Chlorination

8. Supply

To protect the main units of a treatment plant and

to aid in their efficient operation, it is necessary

to remove any large floating and suspended solids

that are often present in the inflow.

These materials include leaves, twigs, paper, rags

and other debris that could obstruct flow through

a plant or damage equipment in the plant.

The raw water is first treated with a chemical

coagulants such as alum (Aluminum Sulphate)

in the varying dose of 5-40mg/liter depending

up on the colour, turbidity, temperature and PH

value of water.

The treated water is then subjected to violent

agitation in a mixing chamber for a few

minutes.

This allows a quick and through dissemination

of alum through out the bulk of water.

Intense mixing of

coagulant and other

chemicals with the

water.

Generally performed

with mechanical mixers

Chemical Coagulant

Flocculation involves a slow and gentle stirring

of the treated water in a flocculation chamber

for about 30 minutes.

This result in formation of thick, copious, white

flocculent precipitate of aluminum hydroxide.

Water coming from rapid mix.

Water goes to sedimentation

basin.

The coagulated water is now led into

sedimentation tanks where it is detained for

periods varying from 2-6 hours when the settle

down in the tank.

At least 95% of the flocculent precipitate

needs to be removed before the water is

admitted into the rapid sand filter.

Water coming from

flocculation basin.Water goes to

filter.

Floc (sludge) collected

in hopperSludge to solids

treatment

The partly clarified water is then subjected to rapid sand filter.

Filter is a process where the suspended matter is separated or purified by passing it through a minute porous material or medium.

This medium may be sand, diatomaceous earth, or a finely woven fabric.

1.To produce clear sparkling water (reduce turbidity)

2.To reduce number of micro-organisms

3.To minimize the contaminants which cause undesirable taste and odor

4.To remove any suspended solid in water.

Each unit of filter bed has a surface of about 80-90 m sq (about 900 sq feet).

Sand bed: Sand is the filtering medium. The effective size of the sand particles is about 0.4-0.7mm. The depth of the sand bed is usually about 1 meter.

Gravel bed: Below the sand bed is a layer of graded gravel of 30-40 cm. The gravel supports the sand bed and permits the filtrated water to move towards the under drain.

The depth of water on the top of the water is

about 1-1.5 meter.

The rate of filtration is 5-15cubic m3/m2/hour.

Filtration removes “alum-floc” not removed

by sedimentation.

Water coming from

sedimentation basin.

Anthracite

Sand

Gravel (support

media)

Water going to disinfection

It is cleaned by means of its back-washing

system.

In this filter, the sand layer gets clogged

quickly because of the high rate of filtration

and deposition of flocs among the sand grains.

The filter is washed at intervals varying

between 20 hours and 5 days, depending on

the degree of turbidity of the raw water.

Washing of the filter sand is achieved by

forcing clean water up through the sand, by

reversing the flow of water pressure.

The forced upward flow agitates the sand

layers and washes away the clogging materials

to a drain system, which totally gets rid of the

dirt into a final disposal drain.

The washing process is normally

accomplished in five to fifteen minutes.

10

3

Particular Rapid sand filter Slow sand filter

Space Occupies very little

space

Occupies large

space

Rate of

filtration

200 mgad 2-3mgad

Effective

size of sand

0.4-0.7mm 0.2-0.3 mm

Preliminary

treatment

Chemical coagulation

and sedimentation

Plane

sedimentation

Washing By back washing By scraping sand

bed

Particular Rapid sand

filter

Slow sand

filter

Washing By back

washing

By scraping

sand bed

Operation Highly skilled Less skilled

Loss of head allowed 6-8 feet

(2.25m)

4 feet (1.5m)

Removal of turbidity Good Good

Removal of colour Good Fair

Removal of bacterial 89-99% 99.9-99.99%

Simple to construct and operate

The cost of construction is cheaper than rapid

sand filter

physical, chemical and bacteriological quality

is very high.

Reduced total bacterial counts by 99.9-99.99%

and E coli counts by 99-999.9%.

An outdated method

Occupies large space

Very low rate of filtration

Not suitable for mega and metro cities

Deal directly with raw water

No preliminary storage of water is required

Filter beds occupies less space

Rapid filtration rate (40-50 times grater than

slow sand filter)

Flexibility in operation.

Suitable for large populations.

Required highly skilled manpower

High maintenance cost

Required frequent cleaning/washing

A sanitary well is one which is properly

located, well constructed and protected against

contamination with a view to yield a supply of

safe water.

Location

Lining

Parapet

Plate form

Drain

Covering

Hand pump

Consumers responsibility

Quality

At least 50 feet from source of contamination

Appropriate distance from home ( not more

than 100 meter)

Cemented ring or made up of stone or break

lining up to the depth of at least 20 feet.

2-3 feet above the ground level

28 inches above the ground level

Cement concrete plat form at least 1 m (3

feet) in all directions.

Sloping towards the drain

Cemented drain around the platform to drain

waste water

The top of the well should be covered by a

cement concrete cover to protect against

contamination.

The well should be equipped with hand pump

for lifting the water in sanitary manner.

Electronic device can be applied for lifting the

water.

Protection and maintenance

Time to time disinfection

Physical, chemical and bacteriological quality

should be measured in time to time by taking

sample.

Chemical or agent used for water disinfection

meet following criteria:

1. Capable for destroying pathogenic organism

2. Should not leave toxic product after chemical

reaction

3. Reasonable price, simple to use, safe and easy

availability

4. Leaving residual concentration to deal with

possible recontamination.

5. Rapid, practical & simple analytical technique.

Chlorine formula

Ozonization

Ultraviolet radiation

Most commonly used method for large and

small scale purification of water

It is supplement not a substitute of filtration.

Chlorine kills pathogenic bacteria but it has no

effect on spores and certain virus like polio

and hepatitis virus.

Chlorine kills pathogenic bacteria but it has no

effect on spores and certain virus like polio

and hepatitis virus.

It also oxidizes iron, manganese and hydrogen

sulphide.

It also destroys some taste and odour

producing constituents.

It controls algae and slime organisms and aids

coagulation.

When chlorine is added to water, there is

formation of hydrochloric and hypochlorous

acids.

The hydrochloric acid is neutralized by the

alkalinity of water.

The hypochlorous acid ionizes to form

hydrogen ions and hypochlorite ions.

H2O + CL2 HCL + HOCL

HOCL H+ + OCL-

The disinfecting action of chlorine is mainly

due to the hypochlorous acid and to small

extends due to hypochlorite ion.

Chlorine acts best when the PH value of water

is about 7.

1.Water to be chlorinated should be clear and free

from turbidity.

2.Chlorine demand should be estimated exactly.

3.Contact period should be at least one hour to

kill bacteria and viruses.

4.Minimum recommended free residual chlorine

should be 0.5/liter.

5.Chlorine dose should include chlorine demand

and chlorine amount to produce 0.5mg/L FRC.

Chlorine Demand: The amount of chlorine that

is needed to destroy bacteria and to oxidize all

the organic matters and amonical substances

present in the water.

Chlorine Dose: the total amount of chlorine

that is needed to meet the chlorine demand and

to produce 0.5mg/liter free residual chlorine.

Break point: The point at which chlorine

demand of water is meet is known as break point.

If further chlorine is added then free residual

chlorine begins to start in water.

Contact period: The period from a point when

free residual chlorine starts appearing in water to

the period from which can be consumed is known

as contact period. It should be at least hour.

Free Residual Chlorine: the concentration of

free chlorine in water after 1 hour of contact

period is known as free residual chlorine. The

minimum recommended FRC is 0.5mg/L.

Chlorine Demand

Chlorine dose

Contact Period

Break Point FRC

0.5 mg/L

Conce

ntr

atio

n o

f C

hlo

rine

Combined

chlorine

Mono: diachloramine 2:1

NH3+Cl2= NH2Cl (Monochloramine)

NH2Cl+CL2= NHCL2 (Dichloramine)

NH2Cl+NHCL2= N2O (nitrous oxide)

Ozone is relatively unstable gas.

Powerful oxidizing agent

Eliminates undesirable colour, odour, taste and

removal of all chlorine from water.

Strong virucidal effect

> 1000 cities practicing

Appropriate in combination with chlorine

Dose 0.2-1.5mg/Liter.

This method of water disinfection involves the

exposure of a film of water up to about

120mm thick to one or several quartz mercury

vapour arc lamp emitting UV radiation at a

wave length of 200-295 Nanometer.

Documents

Water resources managt