2. INTRODUCTION
Brimsu Head Works was constructed in the year 1927 by
Brig Gen. Gordon Guggisberg in the then colonial era
,but the dam was constructed in 1928.The dam has its
source from River Kakum .The main intent of this head
works was to supply potable water to the Cape Coast
community and its environs which has been met till
date.
The dam was built to have enough volume of water to
be impounded for treatment. The dam is maintained by
having a spill way which allows excess amount of water
to flow when the level exceeds 25 ft to prevent the dam
from a breakdown. Also , the dam is designed
periodically to be desilted thus when the sediments
accumulate, it is removed.
5. 1. IMPONDMENT
This is where the Kakum river is dammed to store enough
raw water for abstraction and treatment whiles excess raw
water spilled away downstream. The dam has a maximum
depth of twenty-five feet(25ft).
During impoundment the quality of the upstream water is
improved through ;natural purification, sedimentation and
also stratification. . The dam is stratified into three layers ;
Upper layer / Epilimnium ,Middle layer / Thermokline /
Methalimnium and Hypolimnium.
The upper layer faces the sun thus of a higher temperature
and it is about 3 ft.. The middle layer is a mixture of both
the upper and lower layers that is a mixed temperature
and it is also 9 ft. The lower layer is away from the sun,
highly turbid as a result of the settling of most particles and
also of 13 ft.
Raw water is however mostly tapped from the middle layer.
6. SCREENING
During this stage, any floating debris and other
materials are trapped by macro and micro screens
placed at the entry of the raw water for abstraction.
This is to prevent damage to the pump and other
appurtenances
At the low lift pumps there are five pumps of
which two pumps abstract and transport raw water
to the old head works whilst the remaining three
pumps abstract and transport raw water to the new
works.
7. PRE-CHLORINATION/AERATION
Pre-chlorination is done when the iron II level in the
raw water is high and also to disinfect raw water. This
is done by using oxidizing agents such as potassium
permanganate (KMnO 4 ) and calcium hypochloride(
CaHOCl) . These oxidizing agents oxidize the soluble
Fe2+ to insoluble Fe3+ for removal of the iron
During aeration, raw water flows through cascade
aerator to allow air to dissolve and blow off odour in
the raw water thus improving upon the colour and
taste of the raw water.
The cascade aerator provides a large surface area for
aeration to occur.
9. COAGULATION
Raw water is normally accompanied by impurities
which require treatment before consumption
hence, a coagulant like Aluminium Sulphate (Al2
(SO4)3) is used. Aluminium Sulphate when added
to raw water brings all the impurities (particles)
together, reducing the turbidity of raw water. This
is because the particles are negatively charged thus
repelling each other. However the aluminium is
positively charged hence serving as a central
nucleus to attract the clayey particles to aid in
coagulation
10. FLOCCULATION
After Aluminium Sulphate (Al2 (SO4)3) has been
added to the raw water in the coagulation process,
the pulsator clarifier mixes the Aluminium
Sulphate (Al2 (SO4)3) to form flocs and finally
initiates it into the sedimentation process. The
pulsator clarifier also receives the raw water from
the aerator and has laterals to disperse the water to
different chambers.
12. SEDIMENTATION
This a raw water treatment process where the flocs
formed during flocculation settle at the bottom of
the sedimentation tank as sludge by force of
gravity.
When the sludge accumulates in the
sedimentation tank, it is usually referred to as
sludge blanket. When the sludge blanket level
rises to a particular point, it reduces the volume of
supernatant in the sedimentation tank, hence the
need to disludge.
13. FILTRATION
During sedimentation process, particles with small
densities are not able to settle and are therefore
trapped by the filter bed. The filter bed is
chemically treated to remove bacteria at a
percentage of 99%. As the filtration process
continues, the trapped particles accumulate within
the filter medium, blocking the medium from any
further filtration. As a result of this, backwashing
is done to free the medium from trapped particles
so that the process can continue.
14. PH ADJUSTMENT/DISINFECTION
Here, hydrated lime is added to the filtered water
to neutralize the pH since the initial Aluminium
Sulphate (Al2 (SO4)3) added to the raw water
makes it acidic. Similarly, the addition of hydrated
lime also softens the final water. Calcium
hypochloride is also added alternatively in place
of chlorine gas. Post-chlorination is done to
disinfect or kill any pathogen in the filtered water
and a residual is left to disinfect any pathogen
which may arise during distribution. All these
activities take place in the clear water storage.
15. DISTRIBUTION
At the clear water pump house, there are five high
lift pumps which are used to pump treated water to
distribution areas through trunk mains.
16. LABORATORY ACTIVITIES
At the Brimsu New Head Works, a lot of tests are
carried out on the raw, settled and final water at a
2hour interval to ascertain their parameters. The
various tests include colour, turbidity, pH,
alkalinity, hardness, chloride ions and residual
chlorine and the like. It is always important that
the treated water parameters fall within the World
Health Organization guidelines
17. Test for Alkalinity
Measure 50ml of the water sample into a flask.
Add two to three drops of methyl orange, the solution
now turns orange.
Using a pipette, measure 20ml of hydrochloric acid
(HCl) and add it drop by drop to the solution in the
flask until the solution changes from orange to pink
red indicating the endpoint has been reached. Record
the reading from the pipette
18. Test for Hardness
Measure 50ml of the water sample into a flask.
Add two to three drops of ammonia (NH3) buffer to
the sample.
Add a few portions of Erychrome black T, the solution
now turns violet.
Using a pipette measure 20ml of EDTA, add it to the
solution in the flask drop by drop until the violet
colour changes to blue black indicating the endpoint
has been reached. Record the reading from the
pipette.
19. Test for Chloride ions
Measure 50ml of the water sample into a flask.
Add two to three drops of Potassium
hexaoxodichromate (VI) (K2Cr2O7), the solution now
turns yellow.
Using a pipette measure 20ml of Silver nitrate
(AgNO3), add it to the solution in the flask drop by
drop until the orange colour changes to deep brown
indicating the endpoint has been reached. Record the
reading from the pipette.
20. Test for colour
When testing for the colour of raw water, 10ml of raw water
is measured and diluted to50ml mark on the test tube.In
colour determination for raw water, the comparator with
precision from 10 is used. The test tube containing the
diluted raw water is then placed into the comparator in
which a clear standard solution already exists. Using the
lovibond disc, the colour of the raw water is then
determined by adjusting the disc to match the colour of the
raw water. In
Similarly, settled water and final water colour are
determined by measuring 50ml of each sample into a test
tube and subsequently placing them into the comparator
for onward colour determination using the lovibond disc as
described above.
21. Test for Turbidity
Here few portion of the raw, settled and final water
samples are placed into a standard tube which is
uncalibrated. The tube is then placed into the
microprocessor turbidity meter to read the turbidity of
the water sample
22. Test for pH
When testing for the pH of raw water, it is placed in a
test tube and methyl red indicator of about 3 to 4
drops is added and a comparator matching that
indicator is used to determine the pH Also, for that of
settled water, bromocrycol blue is used to determine
the pH with its comparator as well that of the final
water. Also a pH meter can be used to determine the pH
of the water.
23. Jar Test
Measure 1litre of raw water into six beakers
Pipette 3ml, 4ml, 5ml, 6ml,7ml,8ml of Aluminium
Sulphate solution which is equivalent to 30ppm/g/m3
,40ppm/g/m3,50ppm/g/m3,60ppm/g/m3,70ppm/g/m3,80pp
m/g/m3respectively into each beaker.
Place the beaker in the sedimentation jar test device, lower
the stirrers and increase the stirring speed initially to 80
ms-1 for about three minutes for the Aluminium Sulphate
solution to mix thoroughly with the raw water for flocs to
form. Reduce the speed of the stirrers to 40 ms-1 for about
seventeen minutes so that the flocs will not be destroyed.
After set time, remove the stirrers from the samples and
allow the flocs to settle for thirty minutes. After settling,
fetch portions of each sample and perform the following
test on them: pH, turbidity and colour. From the results
obtained, select one of the samples which meet the
standard parameters with a moderate Aluminium Sulphate
solution and perform alkalinity, hardness and chloride ion
test on the sample.
25. Test for Residual Chlorine
The quantity of chlorine in the final water is tested
using a comparator.10ml of the final water is fetched
into a test tube and one tablet of DPD is placed into it
and allowed to dissolve. After dissolution the colour
formed is then compared to the standard by moving
the chlorine disc to match the colour in the test tube
and the corresponding value is recorded.
26. RECOMMENDATIONS
Workers and Students on attachment should be
provided with protective clothes and they should be
forced to wear them at all times.
students on attachment should be entitled to some
considerable financial emolument.
Students on attachment should be shifted every two
weeks to the various units so they can acquaint
themselves with the activities of the various units.
27. CONCLUSION
One can utter without misgiving that an invaluable
worth of knowledge and skill has been gained from our
attachment at the Brimsu New Head Works and this has
brought to bear an appreciation of theoretical concepts
acquired and as well as practical. We also extend our
immeasurable gratitude to the station manager, his
assistant, the quality control officers and the rest of the
workers.
