ABSTRACT
Public water supply is distributed through water pipe
network, which affects the quality of water that gets to the consumers when the
integrity of the pipe distribution network is compromised. Hence, this study
aimed at investigating and modelling water quality deterioration in the
distribution network of Kaduna Metropolis. In order to achieve this water
samples were obtained from selected points along the distribution network of
Kaduna metropolis for water quality analysis. The parameters analyzed were
residual chlorine concentration, pH, turbidity and dissolved oxygen. Linear
regression equations obtained from the relationship between pairs of parameters
were used in a MATLAB/SIMULINK environment to model the change in the various
water quality parameters along the network. The results clearly showed that the
quality of water produced at the treatment plant is below standard water
specifications (Nigerian Standard for Drinking Water Quality, 2007) with
turbidity and pH having average values of 9.5 NTU and 5.7 respectively; this
quality deteriorates significantly along the network. Residual chlorine
concentration was below 0.35mg/l at all points in the network and ranged from 0
to 0.3 mg/l; turbidity levels varied between 2.6 to 10.6 NTU were observed at
the treatment plant and reservoirs/booster stations; pH and dissolved oxygen
levels varied slightly between 5.4 to 7.4 and 0.4 to 0.7 mg/l along the
network. Leakages were also observed along the network. On an average, the
model was 77% accurate in predicting values of water quality parameters along
the network. Also significant differences observed between the water quality
values at Kaduna North Water Works and the selected sampling points. This
indicates that the quality of water deteriorates along the network and is not
safe for human consumption. Improvement of treatment processes and
rehabilitation of the water distribution network were suggested to improve
quality of water produced and distributed to the consumers in Kaduna
metropolis.
CHAPTER ONE
INTRODUCTION
1.1 Preamble
Safe drinking water and basic sanitation are extremely
important to the preservation of human health, especially among children.
Water-related diseases are the most common cause of illness and death among the
poor of developing countries (World Water Council, 2005). The World Health
Organization (WHO) has observed that about 80 percent of diseases in the world
are water related. Currently, about 20% of the world‟s population lacks access
to safe drinking water and more than 5 million people die annually from illness
associated with safe drinking water or inadequate sanitation. If everyone had
safe drinking water and adequate sanitation services, there would be 200
million fewer cases of diarrhoea and 2.1 million fewer deaths caused by
diarrhoea illness each year (Hunt et al., 2001). In addition to these „direct
health‟ effects of inadequate water supply provision, there is an additional
cost in time and energy expended in carrying water from the supply to the
family dwelling.
Improving water supplies has been a high priority activity
for most developing country governments, donor agencies and communities for
many years now so as to achieve the Millennium Development Goal 7 target 10
(halving by 2015, the proportion of people without sustainable access to safe
water and basic sanitation), with the reference year of 1990. In order to
achieve this goal, the federal and the state governments of Nigeria have step
up efforts in expanding
the various water corporations‟ distribution networks, which
are charged with the responsibilities of delivery potable water to the
populace. In spite of these recent efforts, water and sanitation coverage rates
in Nigeria are among the lowest in the world. According to WHO/UNICEF (2006)
drinking water coverage in Nigeria fell from 49 percent in 1990 to 48 percent
in 2004 as against the expected 65 percent coverage.
A large number of those with access to the public water
systems in Nigeria are not completely free from water borne diseases, because
the quality of the water that eventually get to the consumers may not be
guaranteed. Although protected water sources and modern, well-maintained
drinking water treatment plants can provide water adequate for human
consumption; ageing, stressed or poorly maintained distribution systems can
cause the quality of piped drinking water to deteriorate below acceptable
levels and pose serious health risks to its consumers (Lee and Schwab, 2005).
Biofilms, which are coatings of organic and inorganic
materials in water pipe distribution systems, has generated health concerns
because they harbour, protect and allow the proliferation of several bacteria
pathogens, including Legionella and Mycobacterium avium complex (MAC). Bacteria
growth in biofilms is affected by several factors, including water temperature,
type of disinfectant and residual concentration, biodegradable organic carbon
level, degree of pipe corrosion and treatment/distribution system
characteristics. Hence, Lahlou (2002) noted that the water quality of a
drinking water system might be acceptable when the water leaves a treatment
plant. However, a variety
of physical, chemical, and biological transformations can
happen once the water enters and travels through a distribution system, which
can result to objectionable taste and odour and the risk of gastrointestinal
illnesses. This situation was confirmed by Frederick (2007) who reported that
microorganisms in municipal drinking water supplies have led to several
outbreaks of water-borne diseases in the United States. For instance,
cryptosporidium in Milwaukee‟s water supply resulted in some 400, 000 serious illnesses
and 50 deaths in the spring of 1993. In 1983, contaminated drinking water in
Luzerne County, Pennsylvania caused an outbreak of giardiasis-a common
diarrhoea that left 6, 000 people ill and forced 75, 000 others to obtain more
expensive alternative sources of drinking water.
The integrity of water distribution networks in Nigeria and
in particular in Kaduna State is highly questionable, as it is characterized
with leaky pipe joints, pipe breaks, corrosive pipes, intermittent supply etc.
which may impact negatively on water quality through contamination before it
gets to the consumer. But unfortunately, most people used to assume that if
water entering into a distribution system were of high quality, its quality
would still be good at the tap (AWWA, 2013). Therefore, people consume tap
water without any doubt of its quality. This situation can be very dangerous if
actually the quality of water that gets to the consumer has been compromised.
Although water is a scarce commodity, its quality should be
assured no matter how small the quantity may be. Thus, the goal of a water
treatment and
distribution network is to deliver water in sufficient
quantities and of good quality where and when it is needed at the required
pressure.
First, this quality can be expressed in terms of the water
being physically and chemically free from carcinogens and contaminants that
impart colour, taste and odour. Secondly, water quality can be expressed as
water devoid of pathogenic microorganisms. This suggests that ideally,
treatment processes at water treatment plants as well as pipes and storage
facilities of a good drinking water distribution network should constitute a
network of uncontrolled chemical and biological reactors capable of withstanding
significant variations to maintain water quality. But unfortunately, even
before these pipes are networked to form a distribution system, their sterility
may not be guaranteed during storage and transportation to construction sites
and they may have been left outdoors for months or years leading to
contamination potentially caused by a variety of animals, plants and
microbiological life entering it (Kofi, 2012).
Consequently, after installation, if such mains are not
properly “purified” and flushed, then although treated water may meet the
required quality criteria when it leaves the treatment head-works and travels
through such a distribution network, the quality will deteriorate. In cases
where these distribution mains are properly disinfected and flushed after
installation, as water continues to run through for some number of years, there
may be sediment build up (which may lead to encrustation), corrosion and subsequent
leaching of pipe materials, formation of biofilms etc. These occurrences
normally compromise the quality
of the distributed water. Generally, some indicators of water
quality deterioration in distribution networks include (Kofi, 2012);
1. Loss of disinfectant residual
2. Corrosion of iron pipes
3. Dissolution of Pb and Cu from pipe walls
4. Biofilm formation
5. Occurrence of compounds that confer poor taste and odour
6. Formation of disinfection by-products (some of which are carcinogens).
These compounds are normally products of reactions between organic and/or
inorganic soluble compounds and disinfectants.
7. Increased turbidity caused by particulate re-suspension.
To attain microbiological safety, potable water should be free
of pathogenic microorganisms, and this is achieved through purification by a
specific treatment step called disinfection (Kofi, 2012).
Generally, disinfection can be defined as the inactivation of
pathogenic microorganisms and is purposed to eliminate any microbiological
risks of water-related diseases. The use of Ultra Violet (U.V) light, ozonation
and chlorination are all forms of disinfection, but chlorination is usually
preferred and employed in most drinking water systems because of its efficiency
and durability (leaves adequate residuals) and it is relatively cheap (Mays,
2000).
Thus, to reduce the microbiological risk of potable water, it
should have adequate residual chlorine to ensure the bacteriological safety of
the water. In
view of this, the World Health Organization (W.H.O)
recommends a chlorine residual concentration of 0.5mg/l in final water whereas
the Nigerian Standard for Drinking Water Quality (NSDWQ) recommends a
concentration not less than 0.35mg/l at the point of consumption. To ensure
that potable water is bacteriologically safe at the taps, a chlorine residual
concentration between 0.20 to 0.5 mg/l should be maintained in the treated
water (WHO, 1997).
However, the physical, chemical and microbiological
transformations (existing pipe material/age, water age, biofilm formation,
encrustation etc.) occurring within and along a distribution network may defeat
this purpose by “using up” the chlorine thereby enhancing its decay. This decay
may occur within the bulk of the water (bulk decay) or as a result of the
interaction between the water and pipe walls (wall decay). Therefore, to ensure
that adequate chlorine residuals persist in distribution lines till
consumption, studies must be done to find out how these transformations
occurring along a particular distribution network contribute to the bulk and
wall reactions.
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