3. THEORY OF DISINFECTION
• What is Disinfection & why it is done ? ?
• Disinfection is the process of the removal, deactivation or killing of
pathogenic microorganisms.
• Microorganisms are destroyed or deactivated, resulting in
termination of growth and reproduction such that they
represent no significant risk of infection. When
microorganisms are not removed from drinking
water, drinking water usage will cause people to fall ill.
• When water leaves the filter plant, it is till
found to contain some of the impurities. These impurities can
be grouped as:
-Bacteria, Viruses, Protozoa
-dissolved inorganic salts,
-colour, odour and taste,
-iron and manganese.
• The substances or materials which are to be used
for disinfection are called the DISINFECTANTS.
4. Water Disinfection Procedure
Personal
· Crews shall maintain personal
hygiene during working on water
network
· Crews shall maintain personal
health, safety and protection
during working
RiskSituation
Recommended
Procedure
GeneralHygiene
Vehicle
· Interior must be kept clean &
tidy
· Fittings carried must be
boxed/covered/wrapped
Tools and Equipment
· Hand tools and
equipment(saws, tapping
machines etc) should be
thoroughly cleaned and
disinfected before use
Storing and Handling of Materials
· Pipes, fittings, gaskets, sealings
stored under hygiene conditions
(e.g., wrappings) until the time of
use.
· Fittings shall not be placed directly
on the ground
· All fittings, gaskets and pipe ends
to be cleaned and disinfected
before installation
Site visit
Job Assessment &
Risk Classification
Low Risk Situation (no shutdown)
When positive pressure is
maintained while carrying out the
repair works
· Split mains
· Installing service or branch
connection under pressure
tapping (UPT)
· Minor repairs (V & H)
· Excavate trench 300mm
below pipe invert to provide
sump and prevent dirty
water from contacting pipe
· Spray the fitting with 1%
chlorine solution before
installation
Medium Risk Situation (full shutdown)
When the pressure in the main depressurized
through hydrant/isolation valve/turning the
main shut
· Broken mains/ Blown saddles
· Minor / major repair works
· Replacement works
· Service line repairs
· New meter and main connections
· Temporary supplies
· Dis-connecting of abandoned mains
· Excavate trench while maintaining positive pressure to
prevent backflow into pipe
· Excavate trench 300mm below pipe invert to provide sump
and prevent dirty water from contacting pipe
· Disinfect the trench with 1% chlorine solution
· If pipe has been cut, ensure the ends are examined inside
of the remaining pipe ends and remove scale debris
· Provide temporary end caps/plugs to pipe ends while
preparing the fittings/when not being worked on / risk of
flooding
· Spray the fittings and pipe ends with 1% chlorine solution
before installation
· Thoroughly flush the main (down stream) immediately after
the repair
· Collect sample for bacteriological testing downstream and/
or upstream
High Risk Situation (full shutdown)
When suspected contaminant liquid/solid
material (e.g., Sewer, chemiclas, hydrocarbon)
or leaks in the contaminated ground has made
contact with the leaky area
· Leaky main / Brokenmain/blown saddles
· Replacement works
· Drainage works currently taking place
within the vicinity of the watermain
· Ingress of ground water or material into
pipe
· Escalate the incident to EW Engineer / Management
· Isolate the section
· Isolate service connections and advise customers
· Flush the isolated section to remove contaminants
· REPEAT MEDIUM RISK PROCEDURE
· Thoroughly clean the area and spray with chlorine solution
· Collect two to three samples for bacteriological testing
downstream and/or upstream of the repair work
· Record the incident on forms for future reference and
action
Yes
NoNo
YesYes
Repeat
WATER DISINFECTION PROCEDURE
5. DISINFECTION MECHANISM
• Disinfection commonly takes place because of
cell wall corrosion in the cells of microorganisms,
or changes in cell permeability, protoplasm or
enzyme activity (because of a structural change in
enzymes).
• These disturbances in cell activity cause
microorganisms to no longer be able to multiply.
This will cause the microorganisms to die out.
• Oxidizing disinfectants also demolish organic
matter in the water, causing a lack of nutrients.
• Chemical inactivation of microbiological contamination in
natural or untreated water is usually one of the final steps to
reduce pathogenic microorganisms in drinking water.
Combinations of water purification steps (Oxidation,
Coagulation, settling, disinfection, filtration) cause (drinking)
water to be safe after production.
6. ROLES OF DISINFECTANTS
. Disinfection achieve inactivation which is achieved by
altering or destroying essential structures or functions
within the microbe.
Disinfectants are used for more than just disinfection in drinking water
treatment. While inactivation of pathogenic organisms is a primary function,
disinfectants are also used oxidants in drinking water treatment for several
other functions:
· Minimization of DBP (Disinfection By-Products) formation(strong oxidants,
including potassium permanganate and ozone, may be used to control DBP);
· Oxidation of iron and manganese;
· Prevention of regrowth in the distribution system and maintenance of biological
stability;
· Removal of taste and odors through chemical oxidation;
· Improvement of coagulation and filtration efficiency;
· Prevention of algal growth in sedimentation basins and filters;
· Removal of color;
7. PRIME TARGETS FOR DISINFECTANTS
• Bacteria such as E.coli, leptospira species,
salmonella species, shigella and vibrio chollrae.
Protozoa such as Balantidium coli,
Cryptospiridium parvum, Entamoeba histolytica and
Giardia lambia.
• Viruses such as Entero viruses, Hepatitis A virus and Rota virus.
COMMON MICRO ORGANISMS PRESENT IN WATER
• Helminths such as Ascaris lumbricoides, T. solium and
Trichuris trichuria
8. DISINFECTANTS USED FOR WATER
• For Chemical Disinfection of water the following disinfectants can be used:
• - Chlorine (Cl2)
- Chlorine dioxide (ClO2)
- Hypo chlorite (OCl-)
- Ozone (O3)
- Halogens: bromine (Br2), iodene (I)
- Bromine chloride (BrCl)
- Metals: copper (Cu2+), silver (Ag+)
- Potassium Permanganate (KMnO4)
- Fenols
- Alcohols
- Soaps and detergents
- Hydrogen peroxide
- Several acids and bases
• For Physical Disinfection of water the following disinfectants can be used:
- Ultraviolet light (UV)
- Electronic radiation
- Gamma rays
- Sounds
- Heat
9. SCENARIO OF DISINFECTION
WORLDWIDE
• As an extra measure many countries apply
a second disinfection step at the end of the
water purification process, in order to
protect the water from microbiological
contamination in the water distribution
system.
• Bacteria can remain in the water after the
first disinfection step or can end up in the
water during backflushing of
contaminated water (which can contain
groundwater bacteria as a result of cracks in
the plumbing).
10. TYPES OF DISINFECTION
• Disinfection can be done by two methods:
• Physical Methods
Heating to Boiling
Incineration
Irradiation with X-rays or UV rays
• Chemical Methods
Chlorination
Ozonation
