In Malawi,Lilongwe water Board is a major supply of water to different urban locations. Dirty water abstracted is converted into clean and portable water by physical,biological and chemical processes. Lilongwe water board disinfect the water by chlorination. Different tests are carried out every 3hrs to implement HACCP and ensure safe water to people.

1. shareefngunguni@gmail.com
Class work, unpublished
WATER INTAKE AND TREATMENT PROCESS
AT LILONGWE WATER BOARD.
Authored By:
LUANAR,2018
Shareef Ngunguni,BVM.

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WATER INTAKE AND TREATMENT PROCESS AT LILONGWE WATER
INTRODUCTION
Lilongwe Water Board (LWB)
is a statutory cooperation
which was established in
1947and reconstituted by
the Act of Parliament ‘Water
Works Act No. 17 of 1995.
It supplies good quality of
water to maximal number of
people within Lilongwe city
and the surrounding areas.
Lilongwe water board
extracts raw water from
Lilongwe River. The water
from Lilongwe River is
turbid and much
contaminated, and this is
much worse in rainy
season. Lilongwe water
board plant treats the
turbid and contaminated
water into an acceptable
quality for human
consumption and its
activities such as irrigation,
cleaning, etc. water
treatment involves
reduction or removal of
contaminants and
undesired components in
order to produce pure water
which is fit for human use.
The processes involved
include physical processes
such as settling and
filtration, chemical
processes such as

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WATER INTAKE AND TREATMENT PROCESS AT LILONGWE WATER BOARD.
disinfection and
coagulation and biological
processes such as slow
sand filtration (Mallevialle,
1994).
WATER TREATMENT STEPS
I. Raw Water Abstraction
Raw water is abstracted or
extracted from Lilongwe
River. The water is pumped
from abstraction point to
sedimentation tank/plant
via low lift pumps. Water
treatment begins from the
abstraction/intake point
where the raw water is
screened before into the
water reservoir. The
screening involves removal
of big particles that come
together with raw water
from the river.
II. Pre-sedimentation/
Natural sedimentation
Screened water from the
water intake is pumped into
sedimentation tank worthy
1000cm3 .The tank is
divided into 2 chambers
and the first chamber is
smaller than the second
one. The pumped water is
collected directly into the
first chamber which is
passively transported into
the bigger chamber via
holes. In this step, natural

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WATER INTAKE AND TREATMENT PROCESS AT LILONGWE WATER BOARD.
sedimentation takes place
whereby heavier particles
settle out of standing water.
Chemicals are not used to
settle the heavier particles
in this stage. The bottom of
bigger chamber is taper
shaped in order to collect
the settled colloids which
include some
microorganisms and natural
organic matter.
III. Coagulation and
Flocculation
After pre-sedimentation
phase, the water is
conveyed to a conventional
plant where coagulation
takes place. Coagulation is
a process whereby
chemicals are added to
water to remove impurities
or to cause particles that
are slow to settle or are non
-settling to settle out more
readily (Choksuchart,
2002). Chemicals that carry
out this process are called
anticoagulants which
include flocctan, Aniken,
alluminium sulphate, ferric
chloride and Agafloc. The
anticoagulants are positive
charged as water particles,
while the dirty particles are
negatively charged. Once
the anticoagulants are

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WATER INTAKE AND TREATMENT PROCESS AT LILONGWE WATER BOARD.
added into water,
suspended particles
(negative charged) in water
stick together forming flocs
and also neutralizes the
negative charges on non-
settleable suspended
particles such as clay and
colour producing organic
substances(Choksuchart.,
2002). Coagulation is
important since it separates
dirty from water.
IV. Clarification/
Sedimentation
Flocculated water goes into
sedimentation tanks where
flocs formed through
coagulation settle down by
gravitational force.
Sedimentation helps to
separate the suspended
solids trapped in the floc
from water. Excess
deposition of the flocs at
the bottom flow forms floc
blanket which is slowly
released upward until
reaching the middle of the
tank where it is collected
into sludge cone. This acts
as a critical control point to
prevent the floc blanket
reaching the water troughs
which can contaminate
clean water. The troughs
are perforated into v-
shaped walls to trap sludge

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WATER INTAKE AND TREATMENT PROCESS AT LILONGWE WATER BOARD.
not trapped into sludge
cone, then collected water
from troughs through pipes
are conveyed into filters for
filtration.
V. Filtration
Lilongwe water Board uses
rapid sand gravity filters to
carry out filtration process
which
Uses high rates of water
flow and sophisticated
backwashing of the filter
bed to remove trapped
contaminants. The filter bed
is composed of three layers
of sand namely pebbles,
coarse/grit and fine sand in
ascending order. The water
is simply passed through
the filter with no other pre-
treatment, such as the
addition of a coagulant.
During this process, all flocs
that did not settle in the
sedimentation tanks are
removed and the water is
clear and clean. At the bed
flow, nozzles are connected
to collecting pipes and
water is clear when
reaching the collecting
pipes since no any particles
except water passes
through the nozzle. Over
time the sand particles
become

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WATER INTAKE AND TREATMENT PROCESS AT LILONGWE WATER BOARD.
Covered with a thin surface
layer of microorganisms
called biofilm (Hillis, 2000).
Even very small particles
stick to this biofilm and are
held, while water of greatly
improved quality passes out
through the filter.
Backwashing is carried out
when there is excessive
biofilms/silt to remove
trapped contaminants in
media.
VI. Disinfection
After filtration, disinfection
is carried out to kill harmful
microorganisms that may
be
Present in the water and to
prevent microorganisms
regrowing in the
distribution. Without
disinfection, waterborne
disease becomes a
problem, causing high
infant mortality rates and
low life expectancy.
Disinfection processes
include chlorination,
chloramination, ozonation,
and ultraviolent radiation
(Hillis, 2000). Chlorination
is the one used at Lilongwe
water board. This involves
addition of chlorine to
filtered water. Chlorination
is a safe cheap process

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WATER INTAKE AND TREATMENT PROCESS AT LILONGWE WATER BOARD.
which is used worldwide,
easy to use, and effective at
low dose levels against a
wide range of infectious
microorganisms.
Chloramination involves
addition of ammonia and
chlorine together in the
filtered water which
produces chloramines in
the water. The chloramines
maintain disinfecting
capabilities longer than
chlorine but less effective in
killing microorganisms than
chlorine since they are not
chemically active.
Ozonation is addition of
ozone to water, and ozone
is also a powerful
disinfectant which is used
for water treatment. It is
effective to kill difficult
microorganisms such as
protozoan parasites,
Cryptosporidium and
Giardia. UV irradiation is a
component of sunlight and
appropriate level of UV
irradiation produced by
mercury lamps kill bacteria
and viruses. UV irradiation
does not add chemicals in
water but sometimes
ineffective against protozoa.
All these processes are
monitored in the laboratory

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WATER INTAKE AND TREATMENT PROCESS AT LILONGWE WATER BOARD.
through process control
tests that are carried out
every 3 hours. Process
Control Tests ensures
optimization for chemical
dosages and compliance
with World Health
Organization guidelines for
drinking water quality.
CONCLUSION
All in All, water treatment
process improves the
quality of water fit for
drinking and other uses.
The combination of the first
4 steps primarily removes
colloids and Step 5
(filtration) is a polishing
step that removes much of
the colloidal material
followed by killing
microorganisms in step 6.
REFERENCES
a)Choksuchart, P.,
(2002). “Ultrafiltration
enhanced by
coagulation in an
immersed membrane
system.” Desalination,
145, 265-272.
b)Hillis, P., ed., (2000).
Membrane Technology
in Water and
Wastewater Treatment.
TheRoyal Society of
Chemistry, Cambridge,
UK. 269p.
c) http://www.lwb.mw
Extracted on 23th July
2018

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WATER INTAKE AND TREATMENT PROCESS AT LILONGWE WATER BOARD.
d)Mallevialle,J., eds.
(1994). Water
Treatment Membrane
Processes. McGraw-
Hill, New York, NY.