i
2010
UNIVERSITY OF NAIROBI
INVESTIGATION ON THE EFFECTIVENESS OF SUNLIGHT IN
DISINFECTION OF DRINKING WATER
MURIITHI FRANKLINE
REG. NO, F16/1335/2010
April 2015
DEPARTMENT OF CIVIL AND CONSTRUCTION ENGINEERING
I
INVESTIGATION ON THE EFFECTIVENESS OF SUNLIGHT IN
DISINFECTION OF DRINKING WATER
BY
MURIITHI FRANKLINE
F16/1335/2010
A Project Report
Submitted to the faculty
Of
CIVIL ENGINEERING
In Partial Fulfillment of the Requirements for the Award
of Degree of Bachelor of Science in Civil Engineering
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ABSTRACT
A safe or reliable year-round supply of drinking water remains a problem for at least one-third of
the population of world, as effective filtration and chlorination are often beyond the financial
means of the community. Boiling water before drinking is not always feasible, especially if fuel
is expensive (financially or environmentally) or labour intensive to collect. Burning carbonbased fuels indoors in poorly ventilated dwellings can also have a significant impact on lung
disease (K.G .McGuigan et al). A water treatment process that requires virtually no initial
expense and absolutely no running cost would be of inestimable value to those most at risk of
water-borne disease. This is the essential appeal of solar disinfection: to use a combination of
irradiation by direct sunlight and solar heating to kill the water- borne pathogens in contaminated
drinking water.
This study was conducted to determine the effectiveness of solar disinfection for the inactivation
of E. coli and coliform bacilli bacteria. The study involved several experiments which included;
test for colour, test for turbidity, test for biochemical oxygen demand, and bacteriological
examination of both E-coli and coliform bacilli count.
Water samples were collected along Nairobi River for the study purpose. Clear bottles of
different sizes of both plastic and glass materials and which had been sterilized were filled with
this water and placed in full, direct sunlight. Samples were taken at predetermined intervals and
the temperatures were recorded during each sampling session. The viable bacteria count was
enumerated using multiple tube method for coliform bacteria and membrane filtration technique
for E-coli bacteria. Curves were obtained on the rate of inactivation on the bacteria and
temperature rise from the results.
Temperatures up to 46.0°C did not significantly inactivate E. coli and coliforms, therefore
radiation or the synergistic effects of radiation accounted for the inactivation in samples exposed
to sunlight.
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DEDICATION
This Project is dedicated to all my teachers from pre-primary school to university level by whom
the mystery of education was unraveled.
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ACKNOWLEDGEMENTS
I would like to sincerely thank the faculty and staff of the Civil Engineering Department at the
University of Nairobi for providing me with the opportunity to carry out my education in a
supportive working environment. I give special recognition of the enduring support and guidance
from my supervisor Eng. Gitonga which forms the backbone of this study.
A special mention goes to the technicians at the PHE laboratory Department of Civil Engineering
and school of Biological Sciences (Chiromo), University of Nairobi for their support and
guidance during the study. I cannot forget to thank the library staffs who assisted in the
acquisition of reference materials.
More so, gratitude to my mother, guardian and my siblings. The constant encouragement and
love given to me were an added energy in my studies.
v
TABLE OF CONTENTS
ABSTRACT .................................................................................................................................................... iii
DEDICATION................................................................................................................................................. iv
ACKNOWLEDGEMENTS ................................................................................................................................ v
LIST OF FIGURES. ........................................................................................................................................ viii
LIST OF TABLES. .......................................................................................................................................... viii
LIST OF GRAPHS ........................................................................................................................................... ix
1.0 CHAPTER ONE ......................................................................................................................................... 1
INTRODUCTION .................................................................................................................................... 1
1.1 General Note .................................................................................................................................. 1
1.2 Research Objective ....................................................................................................................... 4
1.3 Scope and method of study ........................................................................................................... 4
CHAPTER TWO .............................................................................................................................................. 6
2.0 LITERATURE RIVIEW ........................................................................................................................... 6
2.1 Theoretical background information on water disinfection......................................................... 6
2.2 General guidelines to Drinking water Standards .......................................................................... 6
2.3 Roles and responsibilities in drinking-water safety management ............................................. 13
2.4 Surveillance and quality control .................................................................................................. 14
2.5 Guidelines for verification............................................................................................................ 15
2.6 Drinking Water Challenges........................................................................................................... 17
2.7 Disinfection ................................................................................................................................... 18
CHAPTER THREE.......................................................................................................................................... 29
3.0. METHODOLOGY............................................................................................................................... 29
3.1 Introduction .................................................................................................................................. 29
4.0 CHAPTER FOUR ..................................................................................................................................... 33
4.1. RESULTS ........................................................................................................................................... 33
4.1.1 BACTERIA COUNT AND TEMPERATURE CHANGE. .................................................................... 33
4.1.2 BIOCHEMICAL OXYGEN DEMAND OF WATER .......................................................................... 38
4.1.3 TUBIDUTY .................................................................................................................................. 40
4.1.4 COLOUR ..................................................................................................................................... 40
4.2 ANALYSIS AND DISCUSSIONS ........................................................................................................... 41
4.2.1. DESTRUCTION OF BACTERIA .................................................................................................... 41
4.2.2 WATER CONTAINER TYPE.......................................................................................................... 53
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4.2.3. IMPURITIES IN WATER ............................................................................................................. 54
4.2.4. SOLAR RADIATION AND AMBIENT TEMPERATURE................................................................. 55
4.2.5. BIOCHEMICAL OXYGEN DEMAND OF WATER ......................................................................... 56
4.2.6. EFFECTS ON OTHER ORGANISMS............................................................................................. 57
5.0 CHAPTER FIVE ....................................................................................................................................... 58
5.1 CONCLUSIONS .................................................................................................................................. 58
5.2 Recommendations ........................................................................................................................... 60
BIBLIOGRAPHY............................................................................................................................................ 61
APPENDICES ................................................................................................................................................ 63
LABORATORY TESTS ............................................................................................................................... 63
Test for colour .................................................................................................................................... 63
Test for turbidity ................................................................................................................................ 63
Test for biochemical oxygen demand ................................................................................................ 63
Test for coliform and E-coli count ...................................................................................................... 65
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LIST OF FIGURES.
Figure 1: a demonstration of the solar disinfection. .................................................................................... 4
Figure 2: locations of the sampling points .................................................................................................. 31
Figure 3:Testing media before incubation .................................................................................................. 42
Figure 4: results on mackonkey broth media used in analysis of coliform bacilli bacteria ........................ 43
Figure 5: results on EMB plate used in E-coli bacteria count. .................................................................... 43
LIST OF TABLES.
Table 1: Relation between changes in time in hours with change in temperature in 0C .......................... 33
Table 2: Coliforms count (MPN INDEX) in 100ml of water. ........................................................................ 34
Table 3: E-coli count (EMB) plate count in 0.1ml of water ......................................................................... 34
Table 4: Temperature in0C rise with time .................................................................................................. 35
Table 5: Coliforms count (MPN INDEX) in 100ml of water ......................................................................... 35
Table 6: E-coli count (EMB) plate count in 0.1ml of water ........................................................................ 36
Table 7: Temperature in0C rise with time .................................................................................................. 36
Table 8: Coliforms count (MPN INDEX) in 100ml of water ........................................................................ 37
Table 9: E-coli count (EMB) plate count in 0.1ml of water ......................................................................... 37
Table 10: A. biochemical oxygen demand .................................................................................................. 38
Table 11: B. Biochemical oxygen demand .................................................................................................. 39
Table 12: C .Biochemical oxygen demand .................................................................................................. 39
Table 13: TUBIDUTY .................................................................................................................................... 40
Table 14: COLOUR ....................................................................................................................................... 40
viii
LIST OF GRAPHS
Graph 1:graph showing inactivation of coliform bacilli bacteria in 1litre, 2litre, and 3litre plastic bottles;
1litre 500ml glass bottles and control experiment set at room temperature............................................ 44
Graph 2:curves depicting the rate of E-coli survival during the exposure the exposure time in 1litre,
2litre, 3litre plastic bottles; 1litre 500ml glass bottles and the control experiment set at room
temperature. ............................................................................................................................................... 45
Graph 3:curves depicting temperature rise during the exposure time in various volume of water in
different types of bottles used. .................................................................................................................. 46
Graph 4:: graph showing the rate of inactivation of coliform bacilli bacteria during the exposure time in
1litre, 2litre, 3litre plastic bottles and 1litre, 500ml glass bottles and in the control bottle set at room
temperature. ............................................................................................................................................... 47
Graph 5:: a graph showing inactivation of E-coli bacteria with change in exposure time in 1litre, 2litre,
3litre plastic bottles; 1litre, 500ml glass bottle and the control bottle set at room temperature ............. 48
Graph 6:: a graph showing change in temperature as compared to the change in exposure time in 1litre,
2litre, 3litre plastic bottles; 1litre, 500ml glass bottles. ............................................................................. 49
Graph 7:inactivation of coliform bacilli bacteria using 500ml and 1litre glass bottles and 1litre,2litre,3litre
and control bottle at room temperature ................................................................................................... 50
Graph 8:inactivation of E-coli bacteria in 500ml,1litre glass bottles and 1litre 2litres ,3litres plastic bottles
and the control bottle. ................................................................................................................................ 51
Graph 9: a relation between temperature increase during the exposure time in 500ml, 1litre glass
bottles and 1litre, 2litres, 3litres plastic bottles. ........................................................................................ 52
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1
1.0 CHAPTER ONE
INTRODUCTION
1.1 General Note
Contaminated drinking water poses a major health threat to human beings worldwide. Essentially,
surface and ground waters such as rivers, streams, lakes and drilled ponds are used for multiple
activities, including livestock watering, bathing, cooking etc. Apparently this water, which may be
contaminated with pathogenic organisms, is also used for drinking. Many people may have no other
options for drinking water because there is a lack of water distribution infrastructure and lack of funding
for developing water treatment systems. This is experienced mostly in third world countries
Studies have shown that over one billion people each year are exposed to unsafe drinking water
due to poor source water quality and lack of adequate water treatment. This results in 900
million cases of diarrhoea each year. Five out of every 1000 of those exposed to unsafe drinking
water will die from diseases carried by the contaminated water; another 2.5million will die from
dehydration due to diarrhoea. Children are particularly affected. Diarrhoea illness results in
malnutrition, weakness, and an increase in susceptibility to diseases, and can be life threatening.
The estimated number children that die each year due to water related diseases ranges from 2.5
million to 15 million.
The lack of adequate drinking waters is a continually growing problem due to population
increases and increased demands on source waters. Therefore, water disinfection methods that
are easily employed on individual basis and cheaply are needed. There are a few methods
commonly advocated for disinfection of drinking water at the household level. These include;
boiling of water for about 10 minutes or the use of certain chlorine compounds available in the
form of tablets (calcium hypochlorite tablets) or solutions (sodium hypochlorite solutions).Water
purification tablets available have an expiration date and instructions call for the addition of 1 to
2 tablets per litre of water and waiting for 25 minutes before use.
As each of these procedures has its own drawbacks ,their application is extremely limited in the
developing regions of the world where water borne diseases are prevalent and the safety of the
drinking water supplies cannot always be assured availability and costs are only part of the
problem . In the case of boiling water for instance, the need for about one kilogramme of wood
to boil a litre of water is unjustifiable in fuel short regions already suffering from aridity and
desertification.
1
Besides, the disagreeable taste of boiled water often discourages consumers. The addition of 1 to
2 drops of 5% sodium hypochlorite solution per litre of water requires the use of a dropper and a
litre measure, both being uncommon devices in most homes. In view of these difficulties and
constraints, it is deemed necessary to search for an alternative and effective method for the
disinfection of water on an individual basis using simple and inexpensive method that would be
more appropriate for the application in the third world.
Chemical disinfection options such as chlorine and iodine treatment require chemicals that
must be purchased. These chemicals can be expensive and also have a limited shelf life.
Physical treatment options such as boiling, UV treatment, and filtering require materials that may
not be easily acquired or purchased. One alternative drinking water treatment method that has
been proposed is solar disinfection, a process that is simple and easily utilized. It has been
recommended by several researchers for use in countries that receive abundant sunshine,
specifically those areas between latitudes 350N and 350S.
Solar disinfection is a water treatment method where a drinking water sample is exposed to solar
radiation to inactivate pathogenic organisms. Previous studies have found that solar disinfection
is affected by numerous variables. These variables include the wavelengths of solar radiation,
water temperature, turbidity, and container selection.
Although solar disinfection can be a labour-intensive process and may not be universally
appropriate throughout, there are circumstances in which it may be the only alternative to
untreated drinking water. These are identified as:
 The provision of treated water for people in rural villages and in urban shanty
communities, who may have access only to sewage-contaminated surface water.
 The provision of decontaminated water to widely dispersed rural populations,
mountainous locations or semi-nomadic communities, where a piped water supply
may be impractical or where chemical treatment is too costly.
 Emergency water supplies for refugees and in war zones, where conventional water
supplies may be unavailable, disrupted or inoperative.
 Short-term treatment in response to a specific contamination event such as stormwater or flooding.
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 Short-term treatment of a source contaminated with pathogenic bacteria; e.g., during
an outbreak of cholera or bacterial diarrhoea, in the absence of an alternative
treatment or a suitable water source.
 The provision of treated drinking water for babies or infants, as they are most at risk
of death due to diarrhoea disease.
 The preparation of decontaminated water for oral rehydration solution where no
reliable safe water supply exists.
Other advantages can result from solar disinfection. In endemic areas, schistosomiasis (bilharzia)
can be contracted from drinking water containing the cercarial stage of schistosome worms,
although this is not the most common route of infection. Cercariae lose the ability to penetrate
skin or mucosa within 48hours of being shed by their aquatic snail host. Solar disinfection can
therefore remove one transmission route of schistosomiasis if drinking water is allowed to stand
for two full days before being consumed. Another advantage of storing drinking water in
transparent, rather than opaque, containers is that the risk of ingesting leeches is greatly reduced,
as it is immediately apparent if they are present in the water.
No study has found that solar exposure makes water quality worse, even under overcast
conditions in temperate climates. Ultimately, communities with no established water treatment
facility have nothing to fear or lose from using solar disinfection. The basic apparatus can be
obtained from most household refuse. The fuel costs nothing!
3
Figure 1: a demonstration of the solar disinfection.
1.2 Research Objective
The objective of this study was to test the inactivation of indicator organisms (coliforms or Ecoli) in a contaminated water sample. The variables tested included; the bottle size, turbidity,
biochemical oxygen demand, colour and temperatures.
1.3 Scope and method of study
Prompted by an understanding of prevailing conditions and needs to provide a more efficient and
reliable mode of treating water, and the rampant enteric diseases, this study was at assessing the
feasibility of solar disinfection of small quantities of drinking water that would satisfy the daily
needs of individuals or a family.
This was possible by subjecting artificially contaminated water in small, transparent containers
of approximately 1 to 3 litres in capacity to direct sunlight for varying periods of exposure time.
The method of study employed in the project report development include;
I.
II.
Literature survey from text books, internet and lecture notes.
Experimental work
After study it’s the intention of the investigation to come up with vivid and clear cut evaluations
and conclusions relating to the effectiveness of sunlight use in the inactivation of bacteria in
4
contaminated water. The study will also discuss various factors influencing the effectiveness of
solar disinfection such as; type of container i.e. glass or plastic, turbidity etc.
5
CHAPTER TWO
2.0 LITERATURE RIVIEW
Chapter 2 discusses the worldwide problem regarding the shortage of sanitary of drinking water,
general guidelines to drinking water standards, and the impacts of poor water quality on people.
Specific water treatment options are presented, including chemical treatment options and
physical treatment options, followed by research conducted on the process of solar disinfection
2.1 Theoretical background information on water disinfection
The threat of microbiological contaminants in drinking water is eliminated by three
complementary strategies:
i.
Preventing their access to water source
ii.
Employing water treatment to reduce their concentration in the water
iii.
Maximizing the integrity of the distribution system for finished water
Early in the history of public drinking water systems, the emphasis was almost entirely on
gaining access to a protected source.in recent years, greater emphasis has been directed towards
the providing effective water treatment to reduce microbiological contaminants. Today, there is
increasing emphasis on employing both source protection and treatment to ensure that
contamination does not occur during transport from treatment plant to the consumers tap.
In the water treatment process, reducing microbiological contaminants is accomplished by two
basic strategies, removing them from water or inactivating them. Inactivated micro-organisms,
although present in water, are no longer able to cause disease in the consumer. The process that
use inactivation as their strategy are traditionally referred to as disinfection, the focus of this
research. (R.Parker et al, 2008)
2.2 General guidelines to Drinking water Standards
When the objective of water treatment is to provide drinking water, then we need to select
technologies that are not only the best available, but those that will meet local and national
quality standards. The primary goals of a water treatment plant for over century have remained
practically the same; namely to produce water that is biologically and chemically safe, is
appealing to the consumer and is non-corrosive and non-scaling. Today, plant design has become
6
very complex due to discovery of innumerable chemical substances and microorganisms, the
multiplying of regulations and trying to satisfy more discriminating palates.in addition to the
basics, the designers must keep in mind all manner of legal mandates, as well as public concerns
and environmental considerations, to provide an initial prospective of water works engineering
planning, design and operation
Today resource allocation has necessitated the re-assessment of schedules for new rules. Small
systems are the most frequent violators of water regulations with microbiological violations
accounting for the vast majority of cases.
Among others, violations exceeding maximum contaminant levels (MCLs) are quite common.
Thus bringing small water systems into compliance requires applicable technologies, operator
ability, financial resources and institutional arrangements. (R.Parker et al, 2008)
2.2.1 General considerations and principles
The primary purpose of the Guidelines for Drinking-water Quality is the protection of public
health. Water is essential to sustain life, and a satisfactory (adequate, safe and accessible) supply
must be available to all. Improving access to safe drinking-water can result in tangible benefits to
health. Every effort should be made to achieve a drinking-water quality as safe as practicable.
Safe drinking-water, does not represent any significant risk to health over a lifetime of
consumption, including different sensitivities that may occur between life stages. Those at
greatest risk of waterborne disease are infants and young children, people who are debilitated or
living under unsanitary conditions and the elderly. Safe drinking-water is suitable for all usual
domestic purposes, including personal hygiene.
In developing standards and regulations, care should be taken to ensure that scarce resources are
not unnecessarily diverted to the development of standards and the monitoring of substances of
relatively minor importance to public health. The approach followed in these Guidelines is
intended to lead to national standards and regulations that can be readily implemented and
enforced and are protective of public health. The nature and form of drinking-water standards
may vary among countries and regions. There is no single approach that is universally
applicable. It is essential in the development and implementation of standards that the current
7
and planned legislation relating to water, health and local government are taken into account and
that the capacity to develop and implement regulations is assessed. Approaches that may
Work in one country or region will not necessarily transfer to other countries or regions. It is
essential that each country review its needs and capacities in developing a regulatory framework.
The judgment of safety – or what is an acceptable level of risk in particular circumstances– is a
matter in which society as a whole has a role to play. The final judgment as to whether the
benefit resulting from the adoption of any of the guidelines and guideline values as national or
local standards justifies the cost is for each country to decide.
Although the Guidelines describe a quality of water that is acceptable for lifelong consumption,
the establishment of these Guidelines, including guideline values, should not be regarded as
implying that the quality of drinking-water may be degraded to the recommended level. Indeed, a
continuous effort should be made to maintain drinking-water quality at the highest possible level.
An important concept in the allocation of resources to improving drinking-water Safety is that of
incremental improvements towards long-term targets. Priorities set to remedy the most urgent
problems (e.g., protection from pathogens) may be linked to long-term targets of further water
quality improvements (e.g. Improvements in the acceptability of drinking-water)
The basic and essential requirements to ensure the safety of drinking-water are a “Framework”
for safe drinking-water, comprising health-based targets established by a competent health
authority; adequate and properly managed systems (adequate Infrastructure, proper monitoring
and effective planning and management); and a System of independent surveillance. A holistic
approach to drinking-water supply risk assessment and risk management increases confidence in
the safety of drinking-water. This approach entails systematic assessment of risks throughout a
drinking-water supply – from the catchment and its source water through to the consumer – and
identification of the ways in which these risks can be managed, including methods to ensure that
control measures are working effectively. It incorporates strategies to deal with day-to-day
management of water quality, including upsets and failures.
The Guidelines are applicable to large metropolitan and small community piped Drinking-water
systems and to non-piped drinking-water systems in communities and in individual dwellings.
The Guidelines are also applicable to a range of specific circumstances, including large
buildings, travelers and conveyances. The great majority of evident water-related health
problems are the result of microbial (bacteriological, Viral, protozoan or other biological)
8
contamination. Nevertheless, an appreciable number of serious health concerns may occur as a
result of the chemical and microbiological contamination of drinking-water.
2.2.2 Microbial aspects
Securing the microbial safety of drinking-water supplies is based on the use of multiple barriers,
from catchment to consumer, to prevent the contamination of drinking-water or to reduce
contamination to levels not injurious to health. Safety is increased if multiple barriers are in
place, including protection of water resources, proper selection and operation of a series of
treatment steps and management of distribution systems (piped or otherwise) to maintain and
protect treated water quality.
The preferred strategy is a management approach that places the primary emphasis on preventing
or reducing the entry of pathogens into water sources and reducing reliance on treatment
processes for removal of pathogens. In general terms, the greatest microbial risks are associated
with ingestion of water that is contaminated with human or animal (including bird) faeces.
Faeces can be a source of pathogenic bacteria, viruses, protozoa and helminthes. Faecally
derived pathogens are the principal concerns in setting health-based targets for microbial safety.
Microbial water quality often varies rapidly and over a wide range. Short-term peaks in pathogen
concentration may increase disease risks considerably and may trigger outbreaks of waterborne
disease. Furthermore, by the time microbial contamination is detected, many people may have
been exposed.
For these reasons, reliance cannot be placed solely on end-product testing, even when frequent,
to ensure the microbial safety of drinking-water. Particular attention should be directed to a
water safety framework and implementing comprehensive water safety plans (WSPs) to
consistently ensure drinking water safety and thereby protect public health.
Management of microbial drinking-water safety requires a system-wide assessment to determine
potential hazards that can affect the system identification of the control measures needed to
reduce or eliminate the hazards, and operational monitoring to ensure that barriers within the
system are functioning efficiently and the development of management plans to describe actions
taken under both normal and incident conditions. These are the three components of a WSP.
9
Failure to ensure drinking-water safety may expose the community to the risk of outbreaks of
intestinal and other infectious diseases. Drinking-water-borne outbreaks are particularly to be
avoided because of their capacity to result in the simultaneous infection of a large number of
persons and potentially a high proportion of the community. In addition to faecally borne
pathogens, other microbial hazards (e.g., guinea worm [Dracunculus medinensis], toxic
cyanobacteria and Legionella) may be of public health importance under specific circumstances.
The infective stages of many helminths, such as parasitic roundworms and flatworms, can be
transmitted to humans through drinking-water. As a single mature larva or fertilized egg can
cause infection, these should be absent from drinking-water.
However, the water route is relatively unimportant for helminth infection, except in the case of
the guinea worm. Legionella bacteria are ubiquitous in the environment and can proliferate at the
higher temperatures experienced at times in piped drinking-water distribution systems and more
commonly in hot and warm water distribution systems. Exposure to Legionella from drinkingwater is through inhalation and can be controlled through the implementation of basic water
quality management measures in buildings and through the maintenance of disinfection residuals
throughout the piped distribution system.
Public health concern regarding cyanobacteria relates to their potential to produce a variety of
toxins, known as “cyanotoxins.” In contrast to pathogenic bacteria, cyanobacteria do not
proliferate within the human body after uptake; they proliferate only in the aquatic environment
before intake. While the toxic peptides (e.g., microcystins) are usually contained within the cells
and thus may be largely eliminated by filtration, toxic alkaloids such as cylindrospermopsin and
neurotoxins are also released into the water and may break through filtration systems. Some
microorganisms will grow as biofilms on surfaces in contact with water. With few exceptions,
such as Legionella, most of these organisms do not cause illness in healthy persons, but they can
cause nuisance through generation of tastes and odours or discoloration of drinking-water
supplies. Growth following drinking-water treatment is often referred to as “regrowth.” It is
typically reflected in measurement of increasing heterotrophic plate counts (HPC) in water
samples. Elevated HPC occur especially in stagnant parts of piped distribution systems, in
domestic plumbing, in some bottled water and in plumbed-in devices such as softeners, carbon
filters and vending machines.
10
While water can be a very significant source of infectious organisms, many of the diseases that
may be waterborne may also be transmitted by other routes, including person-to-person contact,
droplets and aerosols and food intake. Depending on circumstance and in the absence of
waterborne outbreaks, these routes may be more important than waterborne transmission.
2.2.3 Chemical aspects
The health concerns associated with chemical constituents of drinking-water differ from those
associated with microbial contamination and arise primarily from the ability of chemical
constituents to cause adverse health effects after prolonged periods of exposure. There are few
chemical constituents of water that can lead to health problems resulting from a single exposure,
except through massive accidental contamination of a drinking water supply. Moreover,
experience shows that in many, but not all, such incidents, the water becomes undrinkable owing
to unacceptable taste, odour and appearance.
In situations where short-term exposure is not likely to lead to health impairment, it is often most
effective to concentrate the available resources for remedial action on finding and eliminating the
source of contamination, rather than on installing expensive drinking-water treatment for the
removal of the chemical constituent. There are many chemicals that may occur in drinkingwater; however, only a few are of immediate health concern in any given circumstance. The
priority given to both monitoring and remedial action for chemical contaminants in drinkingwater should be managed to ensure that scarce resources are not unnecessarily directed towards
those of little or no health concern. Exposure to high levels of fluoride, which occurs naturally,
can lead to mottling of teeth and, in severe cases, crippling skeletal fluorosis. Similarly, arsenic
may occur naturally, and excess exposure to arsenic in drinking-water may result in a significant
risk of cancer and skin lesions. Other naturally occurring chemicals, including uranium and
selenium, may also give rise to health concern when they are present in excess. The presence of
nitrate and nitrite in water has been associated with methaemoglobinaemia, especially in bottlefed infants. Nitrate may arise from the excessive application of fertilizers or from leaching of
wastewater or other organic wastes into surface water and groundwater. Particularly in areas with
aggressive or acidic waters, the use of lead pipes and fittings or solder can result in elevated lead
levels in drinking-water, which cause adverse neurological effects.
11
There are few chemicals for which the contribution from drinking-water to overall intake is an
important factor in preventing disease. One example is the effect of fluoride in drinking-water in
increasing prevention against dental caries. The Guidelines do not attempt to define minimum
desirable concentrations for chemicals in drinking-water. Guideline values are derived for many
chemical constituents of drinking-water. A guideline value normally represents the concentration
of a constituent that does not result in any significant risk to health over a lifetime of
consumption. A number of provisional guideline values have been established based on the
practical level of treatment achievability or analytical achievability. In these cases, the guideline
value is higher than the calculated health-based value.
2.2.4 Radiological aspects
The health risk associated with the presence of naturally occurring radionuclides in drinkingwater should also be taken into consideration, although the contribution of drinking-water to total
exposure to radionuclides is very small under normal circumstances.
Formal guideline values are not set for individual radionuclides in drinking-water. Rather, the
approach used is based on screening drinking-water for gross alpha and gross beta radiation
activity. While finding levels of activity above screening values does not indicate any immediate
risk to health, it should trigger further investigation into determining the radionuclides
responsible and the possible risks, taking into account local circumstances.
The guidance values recommended in this volume do not apply to drinking-water supplies
contaminated during emergencies arising from accidental releases of radioactive substances to
the environment.
2.2.5 Acceptability aspects
Water should be free of tastes and odours that would be objectionable to the majority of
Consumers. In assessing the quality of drinking-water, consumers rely principally upon their
senses. Microbial, chemical and physical water constituents may affect the appearance, odour or
taste of the water, and the consumer will evaluate the quality and acceptability of the water on
the basis of these criteria. Although these substances may have no direct health effects, water
12
that is highly turbid, is highly coloured or has an objectionable taste or odour may be regarded by
consumers as unsafe and may be rejected.
In extreme cases, consumers may avoid aesthetically unacceptable but otherwise safe drinkingwater in favour of more pleasant but potentially unsafe sources. It is therefore wise to be aware
of consumer perceptions and to take into account both health related guidelines and aesthetic
criteria when assessing drinking-water supplies and developing regulations and standards.
Changes in the normal appearance, odour or taste of a drinking-water supply may signal changes
in the quality of the raw water source or deficiencies in the treatment process and should be
investigated.
2.3 Roles and responsibilities in drinking-water safety management
Preventive management is the preferred approach to drinking-water safety and should take
account of the characteristics of the drinking-water supply from catchment and source to its use
by consumers. As many aspects of drinking-water quality management are often outside the
direct responsibility of the water supplier, it is essential that a collaborative multiagency
approach be adopted to ensure that agencies with responsibility for specific Areas within the
water cycle are involved in the management of water quality.
One example is where catchments and source waters are beyond the drinking-water supplier’s
jurisdiction. Consultation with other authorities will generally be necessary for other elements of
drinking-water quality management, such as monitoring and reporting requirements, emergency
response plans and communication strategies.
Major stakeholders that could affect or be affected by decisions or activities of the drinkingwater supplier should be encouraged to coordinate their planning and management activities
where appropriate.
These could include, for example, health and resource management agencies, consumers,
industry and plumbers. Appropriate mechanisms and documentation should be established for
stakeholder commitment and involvement.
13
2.4 Surveillance and quality control
In order to protect public health, a dual-role approach, differentiating the roles and
responsibilities of service providers from those of an authority responsible for independent
oversight protective of public health (“drinking-water supply surveillance”), has proven to be
effective.
Organizational arrangements for the maintenance and improvement of drinking water supply
services should take into account the vital and complementary roles of the agency responsible for
surveillance and of the water supplier. The two functions of surveillance and quality control are
best performed by separate and independent entities because of the conflict of interest that arises
when the two are combined. In this:
 national agencies provide a framework of targets, standards and legislation to enable and
require suppliers to meet defined obligations;
 agencies involved in supplying water for consumption by any means should be required
to ensure and verify that the systems they administer are capable of delivering safe water
and that they routinely achieve this; and
 A surveillance agency is responsible for independent (external) surveillance through
periodic audit of all aspects of safety and/or verification testing.
In practice, there may not always be a clear division of responsibilities between the surveillance
and drinking-water supply agencies. In some cases, the range of professional, governmental,
nongovernmental and private institutions may be wider and more complex than that discussed
above. Whatever the existing framework, it is important that clear strategies and structures be
developed for implementing WSPs, quality control and surveillance, collating and summarizing
data, reporting and disseminating the findings and taking remedial action.
Clear lines of accountability and communication are essential. Surveillance is an investigative
activity undertaken to identify and evaluate potential health risks associated with drinking-water.
Surveillance contributes to the protection of public health by promoting improvement of the
quality, quantity, accessibility, coverage (i.e., populations with reliable access), affordability and
continuity of drinking-water supplies. The surveillance authority must have the authority to
determine whether a water supplier is fulfilling its obligations.
14
In most countries, the agency responsible for the surveillance of drinking-water supply services
is the ministry of health (or public health) and its regional or departmental offices.
In some countries, it may be an environmental protection agency; in others, the environmental
health departments of local government may have some responsibility.
Surveillance requires a systematic programme of surveys, which may include auditing, analysis,
sanitary inspection and/or institutional and community aspects. It should cover the whole of the
drinking-water system, including sources and activities in the catchment, transmission
infrastructure, treatment plants, storage reservoirs and distribution systems (whether piped or
unpiped).
Ensuring timely action to prevent problems and ensure the correction of faults should be an aim
of a surveillance programme. There may at times be a need for penalties to encourage and ensure
compliance. The surveillance agency must therefore be supported by strong and enforceable
legislation. However, it is important that the agency develops a positive and supportive
relationship with suppliers, with the application of penalties used as a last resort.
The surveillance agency should be empowered by law to compel water suppliers to recommend
the boiling of water or other measures when microbial contamination that could threaten public
health is detected
2.5 Guidelines for verification
Drinking-water safety is secured by application of a WSP, which includes monitoring the
efficiency of control measures using appropriately selected determinants. In addition to this
operational monitoring, a final verification of quality is required. Verification is the use of
methods, procedures or tests in addition to those used in operational monitoring to determine if
the performance of the drinking-water supply is in compliance with the stated objectives outlined
by the health-based targets and/or whether the WSP needs modification and revalidation.
2.5.1 Microbial water quality
For microbial water quality, verification is likely to include microbiological testing. In most
cases, it will involve the analysis of faecal indicator microorganisms, but in some circumstances
it may also include assessment of specific pathogen densities. Verification of the microbial
15
quality of drinking-water may be undertaken by the supplier, surveillance agencies or a
combination of the two.
Approaches to verification include testing of source water, water immediately after treatment,
water in distribution systems or stored household water. Verification of the microbial quality of
drinking-water includes testing for Escherichia coli as an indicator of faecal pollution. E. coli
provides conclusive evidence of recent faecal pollution and should not be present in drinkingwater. In practice, testing for thermo tolerant coliform bacteria can be an acceptable alternative
in many circumstances. While E. coli is a useful indicator, it has limitations. Enteric viruses and
protozoa are more resistant to disinfection; consequently, the absence of E. coli will not
necessarily indicate freedom from these organisms.
Under certain circumstances, it may be desirable to include more resistant microorganisms, such
as bacteriophages and/or bacterial spores. Such circumstances could include the use of source
water known to be contaminated with enteric viruses and parasites or high levels of viral and
parasitic diseases in the community.
Water quality can vary rapidly, and all systems are subject to occasional failure. For example,
rainfall can greatly increase the levels of microbial contamination in source waters, and
waterborne outbreaks often occur following rainfall. Results of analytical testing must be
interpreted taking this into account.
2.5.2 Chemical water quality
Assessment of the adequacy of the chemical quality of drinking-water relies on comparison
Of the results of water quality analysis with guideline values. For additives (i.e., chemicals
deriving primarily from materials and chemicals used in the production and distribution of
drinking-water), emphasis is placed on the direct control of the quality of these products.
In controlling drinking-water additives, testing procedures typically assess the contribution of the
additive to drinking water and take account of variations over time in deriving a value that can be
compared with the guideline value, most chemicals are of concern only with long-term exposure;
however, some hazardous chemicals that occur in drinking-water are of concern because of
effects arising from sequences of exposures over a short period. Where the concentration of the
16
chemical of interest varies widely, even a series of analytical results may fail to fully identify and
describe the public health risk (e.g., nitrate, which is associated with methaemoglobinaemia in
bottle-fed infants). In controlling such hazards, attention must be given to both knowledge of
causal factors such as fertilizer use in agriculture and trends in detected concentrations, since
these will indicate whether a significant problem may arise in the future. Other hazards may arise
intermittently, often associated with seasonal activity or seasonal conditions. One example is the
occurrence of blooms of toxic cyanobacteria in surface water.
A guideline value represents the concentration of a constituent that does not exceed tolerable risk
to the health of the consumer over a lifetime of consumption. Guidelines for some chemical
contaminants (e.g., lead, nitrate) are set to be protective for susceptible subpopulations. These
guidelines are also protective of the general population over a lifetime.
It is important that recommended guideline values are both practical and feasible to implement as
well as protective of public health. Guideline values are not normally set at concentrations lower
than the detection limits achievable under routine laboratory operating conditions.
Moreover, guideline values are established taking into account available techniques for
controlling, removing or reducing the concentration of the contaminant to the desired level. In
some instances, therefore, provisional guideline values have been set for contaminants for which
there is some uncertainty in available information or calculated guideline values are not
practically achievable.
2.6 Drinking Water Challenges
In much of the world, there are no funds to develop a drinking water system infrastructure.
Where treatment systems do exist, there are several issues that often preclude adequate water
treatment. These include misemployment, under-employment, in operational equipment, lack of
spare parts, unavailability or cost of chemicals, inadequately trained staff, and lack of
supervision. It is estimated that $150 billion is needed to address these issues and establish full
water supply coverage.
Although water disinfection is a crucial step in preventing waterborne diseases, there are several
aspects of the water collection, treatment, and distribution cycle that affect whether drinking
water arrives at a home in potable condition. First, source water should be carefully selected and
protected to ensure it is free of contaminants. Water that receives runoff from land used for
17
agriculture and livestock farming is likely to have pesticides, feacal matter, and other
constituents that were applied to the surrounding grounds. Improving the sanitation practices of
the local population can reduce the potential for water supplies to be polluted. The second factor
in preventing waterborne disease is adequate and reliable water treatment.
This can be addressed by properly training water plant operators and by providing funding to
ensure all necessary chemicals and equipment can be purchased. Third, distribution systems
must be built and improved to prevent recontamination of treated water. Other intervention
measures, such as increasing public awareness, should also be employed.
2.7 Disinfection
Disinfection is of unquestionable importance in the supply of safe drinking-water. The
destruction of microbial pathogens is essential and very commonly involves the use of reactive
chemical agents such as chlorine. Disinfection is an effective barrier to many pathogens
(especially bacteria) during drinking-water treatment and should be used for surface waters and
for groundwater subject to faecal contamination. Residual disinfection is used to provide a partial
safeguard against low-level contamination and growth within the distribution system.
Chemical disinfection of a drinking-water supply that is faecally contaminated will reduce the
overall risk of disease but may not necessarily render the supply safe. For example, chlorine
disinfection of drinking-water has limitations against the protozoan pathogens – in particular
Cryptosporidium– and some viruses. Disinfection efficacy may also be unsatisfactory against
pathogens within flocs or particles, which protect them from disinfectant action. High levels of
turbidity can protect microorganisms from the effects of disinfection, stimulate the growth of
bacteria and give rise to a significant chlorine demand. An effective overall management strategy
incorporates multiple barriers, including source water protection and appropriate treatment
processes, as well as protection during storage and distribution in conjunction with disinfection
to prevent or remove microbial contamination.
The use of chemical disinfectants in water treatment usually results in the formation of chemical
by-products. However, the risks to health from these by-products are extremely small in
comparison with the risks associated with inadequate disinfection, and it is important that
disinfection not be compromised in attempting to control such by-products. Some disinfectants
18
such as chlorine can be easily monitored and controlled as a drinking-water disinfectant, and
frequent monitoring is recommended wherever chlorination is practiced.
2.7.1 Disinfection Options
When large community-wide water treatment and distribution systems are not available, people
may treat water individually or for their families. There are several water disinfection options
available for small-scale use. Water disinfection methods can be divided into two categories.
The first category is chemical disinfection. Chemical disinfection includes methods such as
chlorination and iodine treatment. Chlorine is the most common method of drinking water
treatment due to its effectiveness at inactivating several types of pathogens and its low chemical
cost. Chlorinated water also retains a residual that further protects from recontamination after the
water is treated. Iodine is a second chemical treatment option and one that is commonly used by
hikers and backpackers as an effective and transportable method of water treatment. However,
iodine is not used to treat large amounts of drinking water because, it costs approximately 20
times more than chlorine. Chemical costs may render such options unavailable to low-income
families.
Other reasons chemical treatment is undesirable include the training needed to calculate proper
chemical dosages and the unpleasant odor and taste of the drinking water.
An additional
disadvantage with all chemical treatment methods is that chemicals oxidize over time and
therefore have limited shelf lives.
Physical treatment methods such as boiling water and UV treatment may also be used to treat
drinking water. Boiling water is a simple process, but requires resources that may not be readily
available. This is especially true for areas concerned with the effects of desertification and
deforestation because boiling one liter of water requires approximately one kilogram of wood.
The process is also time consuming and boiling water has been found to impart a disagreeable
taste. UV radiation is the process where water is exposed to a lamp generating light at a
wavelength of approximately 250 nm. This wavelength is in the middle of the germicidal band
and is responsible for damaging the DNA of bacteria and viruses. However, UV treatment is
only effective for low turbidity waters and therefore pretreatment such as filtering is required for
19
poor water quality sources. Also, developing and maintaining UV radiation treatment requires
the initial cost of purchasing equipment, a knowledgeable operator to properly use the
equipment, and sufficient funds for maintenance. For areas that are unable to financially support
such a treatment scheme, UV radiation is not a viable treatment option.
2.7.2 Solar Disinfection
A potential alternative to the common disinfection methods mentioned previously is solar
disinfection. Solar water disinfection is a process that entails filling a transparent bottle with
water and placing it in the sun for several hours. The following sections describe the process, its
potential for use, and the enhancements that can be employed to increase its effectiveness.
Limitations of solar disinfection are also presented.
2.7.2.1 Solar Radiation as a Disinfection Mechanism
For over 4000 years, sunlight has been used as an effective disinfectant. When organisms are
exposed to sunlight, photosensitizers absorb photons of light in the UV-A and early visible
wavelength regions of 320 to 450 nm. The photosensitizers react with oxygen molecules to
produce highly reactive oxygen species. In turn, these species react with DNA; this leads to
strand breakage, which is fatal, and base changes, which result in mutagenic effects such as
blocks to replication.
2.7.3 Solar Disinfection Process Variables
Previous studies have found that solar disinfection is affected by numerous variables. These
variables include solar radiation wavelengths, water temperature, turbidity, and container
selection. Several process enhancements have also been studied.
2.7.3.1 Solar Radiation Wavelengths
Studies have shown that visible violet and blue light have little disinfection capability.
However, the other components of sunlight, UV-A, UV-B, and UV-C radiation, are able to
inactivate organisms. UV-C radiation, at approximately 260 nm, has the greatest potency
because it corresponds to maximum absorption by DNA. Municipal treatment plants use UV-C
(at 254 nm) to disinfect drinking waters and secondary wastewater effluents because of its
20
germicidal ability to initiate changes in nucleic acids and other structures such as enzymes and
immunogenic antigens. However, near ultraviolet (UV-A) light has been found to be the most
significant component of sunlight that is responsible for the inactivation of microorganisms, with
an increase in effectiveness due to the synergistic effects of UV-A and violet light. This is
because the UV-C component of solar radiation does not reach the earth (Wegelin et al., 1994).
Acra et al. (1984) compared the germicidal effects of different wavelengths of light by
measuring the average number of coliforms inactivated upon exposure to the varying
wavelengths. They found that the most significant decrease in viable bacterial organisms
occurred when they were exposed to wavelengths between 260 to 350 nm (compared to
inactivation at wavelengths between 550 to 850 nm). Because wavelengths below 290nm do not
reach the earth, Acra et al. (1984) concluded that the most bactericidal wavelengths were
between 315 to 400 nm, which corresponds to the wavelengths of the near-ultraviolet region that
are not visible to the eye. The findings of Acra et al. (1984) are further supported by the
research of others. Davies and Evison (1991) attributed half of the toxic effects of sunlight to
wavelengths lower than 370 nm. Wegelin et al. (1994) concurred, stating that wavelengths
between 300 and 370 nm have significant effects on inactivating bacteria and viruses.
Natural sunlight has been shown to have germicidal properties. Wegelin et al. (1994) found that
a fluency of natural light of approximately 2000 kJ/m or 555 Wh/min a 3-log inactivation of E.
coli. This is equivalent to 5 hours of midday summer sun as measured at Duebendorf,
Switzerland. Viruses’ required higher fluencies than bacteria for the same inactivation level: F2
coli phage, rotavirus and encephalomyocarditis virus required 9,000, 6,800, and 34,300 kJ/m for
3-log inactivation. Davies and Evison (1991) also found solar disinfection to be effective, with
1- log inactivation of E. coli in 10 hours of exposure to sunlight, and 4 log inactivation of
Salmonella typhimurium in 4 hours of exposure.
2.7.3.2 Heating
Temperatures at or above boiling can be used to effectively pasteurize water. Liquids may also
be pasteurized using lower than boiling temperatures, provided the liquids are kept at such
21
temperatures for an extended period of time. For example, enteric viruses in water can be
pasteurized in approximately 1 hour at 62°C or in 1 day at 50°C (Burch and Thomas, 1998). It is
known that 10 minutes at 56°C will inactivate Giardia lamblia, G. muris and Entamoeba
histolytica. If a temperature of 50°C is attainable, amoebic cysts are inactivated (Acra et al.,
1984). Ciochetti and Metcalf (1984) state that milk pasteurization occurs at 62.8°C for 30
minutes or at 71.7°C for 15 seconds, and Burch and Thomas (1998) state that the typical
pasteurization of any liquid is at 75°C for 10 minutes.
Pasteurization may not be ideal for some drinking water treatment situations. Effective treatment
by heating requires knowledge of the water quality in order to determine the temperature the
water must reach and the duration of heating that is needed. In addition, disinfection by heating
may be impractical for wide scale use because pasteurization is a labor-intensive process and
requires a significant amount of fuel (Burch and Thomas, 1998). However, heating may be
accomplished by using sunlight, thus alleviating the problem of needing wood or other fuels for
boiling.
In 1984, Ciochetti and Metcalf published the results from a study to determine the effectiveness
of using a solar box cooker to pasteurize river water that had an initial E. coli count of 33 to 350
cfu per 100 mL. They were able to attain temperatures of 65°C in two 3.7 L jugs between midMarch to mid-September in California, with no coliforms detected at 60°C and 65°C. In heating
tests, Ciochetti and Metcalf (1984) detected coliforms at 59°C, but none at 61°C or 63°C.
Although the samples had reached pasteurization temperatures at the end of the solar
pasteurization and heating tests, it is likely the samples were not held at a pasteurization
temperature for the recommended period of time. Therefore, it is possible that temperatures
lower than 63°C have disinfection capabilities as well.
Conroy et al. (1996) exposed water samples to full sunlight in Kenya and confirmed that sunlight
has a bactericidal effect on turbid water, with reductions in the initial bacterial count of over
103cfu per mL. The disinfection was attributed to pasteurization effects, rather than ultraviolet
light. This was confirmed with laboratory experiments by Joyce et al. (1996), who heated
22
contaminated water samples to a maximum of 55°C in 7 hours and observed a 5-log inactivation
of E. coli.
Jorgensen et al. (1998) tested a flow-through copper-piped system that used solar
Radiation to pasteurize naturally contaminated water from the Mlalakuva River near Dares
Salaam, Tanzania. They found that while fecal indicator bacteria were inactivated in water that
was heated to 62°C or above, other organisms such as spore-forming bacteria were never
completely inactivated, even when water temperatures of 75°C were attained They found that
temperatures of 65°C or above inactivated coliform bacteria and thermo-tolerant coliform
bacteria, which were present in the naturally contaminated river water. Such temperatures also
inactivated Salmonella typhimurium, Streptococcus faecalis and Escherichia coli that were
cultured and added to the raw river water.
Rijal and Fujioka (2001) observed the effectiveness of heating using a modified Family Solar
Saver System (FSP). The FSP is a high-density, black polyethylene double-walled collector that
was designed for liquid pasteurization. However, by exchanging the original non-UVtransmittable plastic cover for a UV-transmittable cover, Rijal and Fujioka were able to
determine the effectiveness of pasteurization versus pasteurization and solar radiation on
numerous organisms, including fecal coliforms, E. coli, enterococci, C. perfringens, total
heterotrophic bacteria, hydrogen sulphide producing bacteria and FRNA virus. Tests were
carried out using a low turbidity (<2 ntu) water from the Manoa stream in Hawaii, diluted
sewage (2.5 ntu), or seeded tap water. On the experiment conducted on a sunny day, the
pasteurization only sample was able to achieve a temperature of 65°C with a corresponding
inactivation of more than 3-log of E. coli in 3 hours. The solar radiation and pasteurization
sample heated to 56°C, with the same log inactivation in 2 hours. Therefore, solar radiation and
heating acted synergistically to inactivate the bacteria.
Pasteurization is an effective treatment option for liquids. However, a false sense of security
may mislead one to under treat the drinking water. As detailed above, certain organisms cannot
survive temperatures of 55°C while others are still viable at 75°C.
23
Without knowing the exact composition of organisms in the water, the user may not adequately
treat the drinking water before use. There is also a high capital cost associated with purchasing
pasteurization equipment if the process is used for a community. However, pasteurization of
liquids is independent of turbidity and pH. This, coupled with the fact that solar energy is free
and solar disinfection is a simple process to employ, warrants further study for use by individuals
or small families.
2.7.7.3 Impurities
Turbidity is a significant factor in the disinfection process. The effectiveness of solar
disinfection has been tested on samples with turbidities ranging from less than 10 ntu to
approximately 300 ntu. Researchers have found that higher turbidity samples exposed to
sunlight attained consistently higher water temperatures, which was attributed to absorption of
radiation by the particulate matter. More turbid samples, at 300 ntu, also had less inactivation of
E. coli compared to samples with little or no turbidity. This may be in part due to shielding of
organisms by particles (Joyce et al. (1996) reported that less than 1% of the total incident UV
light is able to penetrate beyond a water depth of 2 cm from the surface in samples with
turbidities greater than 200 ntu. Therefore, it may be necessary to filter turbid waters before sun
exposure.
Impurities in a water sample that cause it to be colored also have an effect on the disinfection
potential for a given drinking water sample. In highly colored samples, sunlight may not have a
lethal effect because the colored water may absorb wavelengths in a certain range. In these
cases, it is recommended that the water sample be treated to reduce coloration before sun
exposure (Acra et al., 1984).
2.7.3.4 Container Selection
Container shape and color may have significant impacts on the effectiveness of solar
disinfection. The bottle shape may interfere with the sun’s disinfection capabilities: as the sun
24
moves across the sky, the intensity will change and may be reduced depending on the bottle
shape. Acra et al. (1984) therefore recommend using round, conical bottles as opposed to square
or irregularly shaped containers. However, the major limiting factor is the availability of the
bottles themselves, with variables such as plastic thickness and light transmittance characteristics
being difficult to assess in the field.
Acra et al. (1984) also noted that colorless containers allow the most transmittance of ultra-violet
wavelengths and are therefore the optimal choice for use in solar disinfection. Blue and violet
tinted containers also transmit radiation, yet other colors, such as orange, yellow, red and green,
will absorb wavelengths with the most lethal bactericidal effects and therefore must be avoided.
With regard to pasteurization, a water sample exposed to sunlight increases in temperature due to
the red and infrared components of sunlight. Blue containers would therefore absorb these
components and minimize any temperature increases (Acra et al., 1984). Therefore, to maximize
the effects of both solar radiation and heating, colorless containers are recommended.
Container size may also be an important parameter in the solar disinfection process. Acra et al.
(1984) specify that container size is a variable that affects solar disinfection. However, their
studies do not specifically test the effect of volume size on solar disinfection. Kehoe et al.
(2001) found no significant difference in the population dynamics of 0.5 and 1.5 L samples. In
contrast, Reed et al. (2000) compared the time needed to achieve a 99.9% reduction in the initial
fecal coliform counts of 22 L and 25 L samples and found that exposure times of 150 minutes
and 290 minutes were required, respectively. A more extensive study on volume variations
2.7.3.5 Enhancements
A number of process enhancements have been studied in order to increase the effectiveness of
solar disinfection. Such efforts have included periodic agitation, using foil to increase
reflectivity, and painting half the bottle black to increase achievable temperatures.
In a field experiment, Kehoe et al. (2001) used sterilized reagent grade water samples that they
had spiked with E. coli and exposed to the sun. Some samples were agitated for 1 minute every
15 minutes. They found no significant difference in E. coli inactivation rates of the agitated
versus non-agitated samples that were exposed to sunlight if the dissolved oxygen (DO) levels
25
did not change significantly. Changes in DO levels did not occur when there were only slight
increases in water temperature, such as from 32.5°C to 39°C. However, Kehoe et al. (2001)
discovered that in samples exposed to both thermal and optical effects, increasing levels of DO
did correspond to an increase in inactivation rates. In conclusion, Kehoe et al. (2001)
recommended against agitating samples to prevent decreases in inactivation rates when
significant temperature differences occur.
Reed et al. (2000) also found that water samples with greater oxygenation had increased
inactivation rates. Complete inactivation of fecal coliforms was achieved in 3 hours in an
oxygenated sample, compared to the less than 1-log inactivation after 4 hours for a deoxygenated
sample.
During laboratory thermal-only simulations, where sample temperature was raised from 20°C to
50°C, agitation significantly lowered the DO levels of samples. There was no significant
correlation found between the inactivation of E. coli in agitated versus non-agitated samples
however, which implies that DO levels are not a significant factor when samples are sufficiently
heated (Kehoe et al., 2001).
Using sterilized reagent grade water samples spiked with E. coli, Kehoe et al. (2001) found that
foil-backed samples averaged almost 1°C higher than non-foil-backed samples when exposed to
sunlight for 3.5 hours. Over 6-log inactivation was reached in less than 1 hour of exposure time
when aluminum foil was placed partway around sample bottles, versus more than 3 hours needed
for 6-log inactivation of non-foil-backed samples.
2.7.4 Field Applications
Conroy et al. (1996, 1999, and 2001) established the potential for field use of solar disinfection
by demonstrating that this process reduced the risk of diarrhea in children.
The studies were conducted in the Kajiado county of Kenya using Maasai children between 5
and 16 years of age. In 1996, the first test group consisted of 108 children that drank solar
treated water. These children were given two 1.5 L plastic bottles to be filled with drinking
water and put on the roof of their huts from dawn until midday. The water could then be used
for drinking. The control group consisted of 98 children that were given the same directions, but
26
rather than putting the bottles on the roof, they kept the bottles indoors. The results of this study
showed that the children in the first group averaged 4.1 diarrhoea episodes over a twelve-week
period, versus an average of 4.5 episodes in the control group (Conroy et al., 1996). In 1999, the
test group was expanded to children less than six years of age. The children drinking treated
water had a two-week period diarrhea prevalence of 48.8%, versus 58.1% in the control children
(Conroy et al., 1999). Five years later, the researchers learned of a cholera outbreak in the test
villages. They returned and found that the test families had continued to treat their drinking
water with solar disinfection. However, while there was no statistical difference in the risk of
contracting cholera between families using solar disinfection and those that did not, the
continued use of the process by the villagers was promising as shown by the earlier successes in
reducing diarrhoea incidences.
2.7.5 Limitations to Solar Disinfection
There are several limitations to using solar disinfection to treat drinking water. The process of
solar disinfection is best suited for regions having approximately 300 sunny days with clear skies
each year, with areas between latitudes 35°N and 35°S having the optimum exposure of sunlight
(Acra et al., 1984). However, any amount of cloud coverage reduces the intensity of sunlight
that reaches the earth, thereby decreasing its germicidal effects. Despite this restriction, Acra et
al. (1984) state that a longer exposure time more than compensates for the reduction in solar
intensity.
Another difficulty presented with solar disinfection is that the materials needed for the process
may not be readily available. Clear, cylindrical bottles are most effective at allowing solar
radiation to reach the water, yet these may be difficult to obtain for large-scale use by remote
communities, where plastic containers are not sold. In addition, enhancements used by various
researchers, such as foil (Kehoe et al., 2001), may be difficult to purchase. Devices such as solar
panels, copper piping, and thermostat valves were required to construct the solar panel described
by Jorgensen et al. (1998) to pasteurize drinking water. Because these materials are not readily
available in many less-developed areas, and knowledge of constructing a solar water heater is not
widespread, this method of heating water for large-scale use is impractical in developing
countries.
27
However, small-scale individual use of plastic bottles is a treatment method that can be
implemented with minimal resources and little training.
2.7.6 Conclusion
Solar disinfection is a process that is simple and effective. It could prove valuable for use in
developing countries and in areas that need a small-scale drinking water treatment method.
Studies have shown that it is effective in reducing diarrheal illness in children when implemented
in field trials. However, the process does have limitations and several variables influence the
effectiveness of the process such as solar intensity, temperature, turbidity, container shape, and
sample volume. Therefore, this study was aimed at establishing relationships between these
variables and the effectiveness of solar disinfection.
28
CHAPTER THREE.
3.0. METHODOLOGY
3.1 Introduction
Prompted by an understanding of the prevailing conditions and needs of clean and safe drinking
water in all parts of the country and more so in rural communities and the enteric diseases, study
was carried out on February 2015 involving a series of experiments carried out over a period of
three weeks aimed at assessing the feasibility of solar disinfection of small quantities of drinking
water that would satisfy the daily needs of individuals or family. These experiments essentially
consisted of subjecting artificially contaminated water in small transparent containers half a litre
to three litres in capacity to direct sunlight for a seven hour period of exposure.
Previous studies have found decreases in effectiveness of solar disinfection with increases in
turbidity and sample volume and an increase in effectiveness with increased fluencies and higher
water temperatures. The experiments conducted for this project examined these variables and
their impact on the inactivation of E. coli and coliforms by solar radiation and heating. By using
the same testing, sampling, and enumeration methods for each experiment, the results can be
directly compared. This chapter details the experimental design, including the variables
examined and the methods employed during the experiments.
3.1.1 Test Organisms
The test organisms chosen were the bacteria Escherichia coli and coliform bacteria. E. coli is
currently the most specific indicator for fecal contamination of a water source; its presence in
high numbers also allows for more likely determination of water contamination than if they were
only found in small numbers in water samples (Toranzos and McFeters, 1997). E. coli is
29
more resistant to disinfection than other enteric bacteria and organisms such as P. aerugenosa, S.
flexneri, S. typhi, and S. enteritidis and may also be used to determine the likely response of
other pathogenic organisms to a given disinfection mechanism (Acra et al., 1984). The World
Health Organization has set the worldwide guideline for safe drinking water as no detectable E.
coli or thermo tolerant bacteria in any 100 mL sample
3.1.2 Types of experiments
In order to achieve the objectives of the project, several experiments were conducted, these
included;
 Test for colour
 Test for turbidity
 Test for coliforms count
 Test for E-coli count
 Test for biochemical oxygen demand in drinking water.
3.1.3 Sampling
To give a reflection of the quality of water, water samples were collected along Nairobi River for
the study purpose. Water from Nairobi River being highly polluted as it transverses Nairobi
town and various slums located along it provided better source for samples due high number of
bacteria expected which could give a clear results during testing. Sampling was done at three
points so as to give a variation of turbidity, biochemical oxygen demand and colour. It was also
carried out manually using 20 litre jerry cans as the samplers. These samplers were immersed in
the river about 30cm deep so as to avoid collecting sample from the surface and also to avoid
large proportions of floating matter. The sampling cans were rinsed two to three times with the
sample water to be tested before being filled. The samples were then taken to the laboratory for
testing.
30
3.1.4 Sampling points
To give a reflection of the quality water in Nairobi River as it traverses the built-up areas of the
city, the study identified three sampling points as shown in the figure below.
Point 1
Point 2
Point 3
Figure 2: locations of the sampling points
Source: Google map
1) Sampling point 1-brigde located at museum roundabout
2) Sampling point 2-globe roundabout bridge
3) Sampling point 3-kariakor bridge
31
3.1.5 Laboratory studies
A variety of containers made of transparent, clear glass or plastic and varied in usage and shape
were used for the experimental purpose. They ranged from the laboratory flasks made of Pyrex
glass to an assortment of ordinary bottles like the normal soda bottles.
The experimental water used was collected from Nairobi River which is highly contaminated
with municipal sewage to high levels not normally encountered even with untreated water used
for drinking in rural areas.
In each case the water was initially examined bacteriologically just before sunlight exposure and
at intervals of one hour for seven hours i.e. from 9.00 am to 4 pm when the solar intensity
reaches its highest level, during exposure of the containers to direct sunlight. Some amounts of
the samples collected in each point were preserved for tests on; colour, turbidity, biochemical
oxygen demand (BOD).
All containers were kept in an upright position and left open, removable labels on some of the
commercial bottles were detached prior to exposure
A control experiment was set by placing one litre of the given sample in a dark room at room
temperature with the bacteriological test being carried out at the end of the aforementioned time
to ascertain bacteria elimination to a substantial percentage.
32
4.0 CHAPTER FOUR
4.1. RESULTS
4.1.1 BACTERIA COUNT AND TEMPERATURE CHANGE.
4.1.1.1 Sampling point 3(Kariakor bridge)
Table 1: Relation between changes in time in hours with change in temperature in 0C
BOTTLE
TIME IN HOURS
SIZE
9.00AM 10.00AM 11.00AM 12.00PM 1.00PM 2.00PM 3.00PM 4.00PM
1L-plastic
240C
2L-plastic
240C
3L-plastic
290C
360C
390C
440C
490C
510C
260C
300C
310C
360C
390C
400C
420C
240C
250C
280C
310C
360C
370C
390C
400C
1L-glass
240C
280C
320C
370C
420C
460C
500C
530C
500ml-glass
240C
280C
340C
390C
440C
490C
520C
560C
33
260C
Table 2: Coliforms count (MPN INDEX) in 100ml of water.
BOTTLE SIZE
COLIFORMS COUNT WITH CHANGE IN TIME
9.00AM 10.00M 11.00AM 12.00PM 1.00PM 2.00PM 3.00PM 4.00PM
1L-plastic
1800
1800
920
920
920
425
425
425
2L-plastic
1800
1800
920
920
920
550
550
550
3L-plastic
1800
1800
1800
1800
920
900
900
900
1L-glass
1800
1800
920
920
550
550
550
425
500ml-glass
1800
1800
550
550
350
170
170
170
CONTROL
1800
1800
1800
1800
1800
1800
1800
1800
Table 3: E-coli count (EMB) plate count in 0.1ml of water
BOTTLE SIZE
9.00AM 10.00AM 11.00AM 12.00PM 1.00PM 2.00PM 3.00PM 4.00PM
1L-plastic
63
N/A
N/A
66
N/A
N/A
N/A
58
2L-plastic
63
N/A
N/A
74
N/A
N/A
N/A
69
3L-plastic
63
N/A
N/A
78
N/A
N/A
N/A
68
1L-glass
63
N/A
N/A
67
N/A
N/A
N/A
38
500ml-glass
63
N/A
N/A
69
N/A
N/A
N/A
24
CONTROL
63
N/A
N/A
85
N/A
N/A
N/A
98
34
4.1.1.2 Sampling point 2(globe roundabout)
Table 4: Temperature in0C rise with time
BOTTLE SIZE
9.00AM 10.00AM 11.00AM 12.00PM 1.00PM 2.00PM 3.00PM 4.00PM
1L-plastic
220C
N/A
260C
320C
N/A
430C
N/A
470C
2L-plastic
220C
N/A
250C
320C
N/A
410C
N/A
430C
3L-plastic
220C
N/A
250C
290C
N/A
410C
N/A
410C
1L-glass
220C
N/A
280C
340C
N/A
440C
N/A
470C
500ml-glass
220C
N/A
290C
360C
N/A
460C
N/A
490C
Table 5: Coliforms count (MPN INDEX) in 100ml of water
BOTTLE SIZE
COLIFORMS COUNT WITH CHANGE IN TIME
9.00AM 10.00AM 11.00AM 12.00PM 1.00PM 2.00PM 3.00PM 4.00PM
1L-plastic
1800
N/A
N/A
1800
N/A
550
N/A
425
2L-plastic
1800
N/A
N/A
1800
N/A
900
N/A
550
3L-plastic
1800
N/A
N/A
1800
N/A
1600
N/A
900
1L-glass
1800
N/A
N/A
1800
N/A
425
N/A
225
500ml-glass
1800
N/A
N/A
550
N/A
275
N/A
225
CONTROL
1800
N/A
N/A
1800
N/A
1800
N/A
1800
35
Table 6: E-coli count (EMB) plate count in 0.1ml of water
BOTTLE SIZE
E-COLI COUNT WITH CHANGE IN EXPOSURE TIME
9.00AM 10.00AM 11.00AM 12.00PM 1.00PM 2.00PM 3.00PM 4.00PM
1L-plastic
10
N/A
N/A
13
N/A
N/A
N/A
4
2L-plastic
10
N/A
N/A
13
N/A
N/A
N/A
8
3L-plastic
10
N/A
N/A
16
N/A
N/A
N/A
11
1L-glass
10
N/A
N/A
12
N/A
N/A
N/A
6
500ml-glass
10
N/A
N/A
11
N/A
N/A
N/A
2
CONTROL
10
N/A
N/A
37
N/A
N/A
N/A
32
4.1.1.3 Sampling point 1 ;( Museum Bridge)
Table 7: Temperature in0C rise with time
BOTTLE
TEMPERATURE RISE WITH TIME
SIZE
9.00AM 10.00AM 11.00AM 12.00PM 1.00PM
2.00PM
3.00PM
4.00PM
1L-plastic
240C
N/A
N/A
360C
N/A
520C
N/A
570C
2L-plastic
240C
N/A
N/A
330C
N/A
440C
N/A
470C
3L-plastic
240C
N/A
N/A
330C
N/A
390C
N/A
460C
1L-glass
240C
N/A
N/A
410C
N/A
520C
N/A
560C
500ML-glass
240C
N/A
N/A
420C
N/A
560C
N/A
610C
36
Table 8: Coliforms count (MPN INDEX) in 100ml of water
BOTTLE SIZE
COLIFORMS COUNT WITH CHANGE IN TIME
9.00AM 10.00AM 11.00AM 12.00PM 1.00PM
2.00PM
3.00PM
4.00PM
1L-plastic
1800
N/A
N/A
1800
N/A
250
N/A
130
2L-plastic
1800
N/A
N/A
1800
N/A
550
N/A
425
3L-plastic
1800
N/A
N/A
1800
N/A
550
N/A
550
1L-glass
1800
N/A
N/A
1800
N/A
130
N/A
35
500ml-glass
1800
N/A
N/A
1800
N/A
80
N/A
25
CONTROL
1800
N/A
N/A
1800
N/A
1800
N/A
1800
Table 9: E-coli count (EMB) plate count in 0.1ml of water
BOTTLE SIZE
E-COLI COUNT WITH CHANGE IN EXPOSURE TIME
9.00AM 10.00AM 11.00AM 12.00PM 1.00PM 2.00PM 3.00PM 4.00PM
1L-plastic
64
N/A
N/A
72
N/A
N/A
N/A
28
2L-plastic
64
N/A
N/A
68
N/A
N/A
N/A
33
3L-plastic
64
N/A
N/A
71
N/A
N/A
N/A
29
1L-glass
64
N/A
N/A
58
N/A
N/A
N/A
11
500ml-glass
64
N/A
N/A
59
N/A
N/A
N/A
13
CONTROL
64
N/A
N/A
86
N/A
N/A
N/A
108
NB: N/A-Not Available
37
4.1.2 BIOCHEMICAL OXYGEN DEMAND OF WATER
4.1.2.1 Sampling point 3: Kariakor Bridge
Table 10: A. biochemical oxygen demand
TRIAL NO
DAY
VOLUME OF Burrete reading(ml)
Volume of
SAMPLE(ml)
titrant(ml)
initial
final
Blank
0
280
22.6
29.9
7.3
10
0
280
0.0
8.0
8.0
25
0
280
8.0
15.5
7.5
50
0
280
15.5
22.6
7.1
10
5
280
14.2
14.3
1.1
25
5
280
15.3
17.2
1.9
50
5
280
17.2
19.0
1.8
𝟏
B.O.D={ (𝟖. 𝟎 − 𝟏. 𝟏)𝟏𝟎 + (𝟕. 𝟓 − 𝟏. 𝟗) 𝟐𝟓} 𝟐
=104.5mg/L
38
4.1.2.2 Sampling point 2: globe roundabout bridge
Table 11: B. Biochemical oxygen demand
Trial no
Day
Volume of
Burrete reading(ml)
Volume of
sample(ml)
Initial
final
titrant
Blank
0
280
28.9
36.2
7.3
10
0
280
7.5
14.6
7.1
25
0
280
14.6
21.7
7.1
50
0
280
21.7
28.9
7.2
10
5
280
22.1
28.3
6.2
25
5
280
28.3
35.2
6.9
50
5
280
35.2
40.8
5.6
𝟏
B.O.D= {(7.1-6.2)10+ (7.1-6.9)25+ (7.2-5.6)50}𝟐
=31.33mg/L
4.1.2.3 Sampling point 3: museum roundabout bridge
Table 12: C .Biochemical oxygen demand
Trial no
Day
Volume of
Burrete reading (ml)
Volume of
sample(ml)
Initial
Final
titrant(ml)
Blank
0
280
14.0
21.2
7.0
10
0
280
0.0
6.8
6.8
25
0
280
6.8
14.0
7.2
10
5
280
15.7
20.7
5.0
39
25
5
280
20.7
25.6
𝟏
B.O.D= {(6.8-5.0)10+ (7.2-4.9)25}𝟐
=37.75mg/l
4.1.3 TUBIDUTY
Table 13: TUBIDUTY
SAMPLING POINT
TURBIDITY(NTU)
1
45
2
56
3
68
4.1.4 COLOUR
Table 14: COLOUR
SAMPLING POINT
COLOUR( 0H)
1
10
2
10
3
10
40
4.9
4.2 ANALYSIS AND DISCUSSIONS
4.2.1. DESTRUCTION OF BACTERIA
The results of each set of experiments have consistently confirmed the fact that the bacteria
contaminating water from feacal sources are as general rule, susceptible to destruction on
exposure to sunlight for an adequate period of time. The rate of destruction actually depends
upon a number of influencing factors. The most important ones that became clear in the course
of the study include the following:I.
The intensity of sunlight at the time of exposure, which in turn depends upon the
geographic location i.e. latitude, seasonal variations and cloud cover and the time of the
day.
II.
The nature and composition of the medium and the presence of nutritive elements
,dissolved oxygen capable of supporting growth and multiplication of various
microorganisms
III.
The characteristics of the containers in which the contaminated water is kept during
exposure i.e. size, material
IV.
Clarity of water i.e. degree of turbidity and its depth, both being important factors that
determine the extent of penetration of sunlight as well as the possibility of shielding the
microorganisms from its lethal effects
Progressive decline with exposure time in terms of the probable number of bacteria still
surviving followed an exponential decline curve, a pattern typical of bacteria destruction by
chemical disinfectants like chlorine and iodine.
Production of gas and change in colour after 24 hour incubation indicated the presence of
bacteria while the E-coli bacteria were counted from EMB plates. The figures below shows the
outcome before after incubation with both positive and negative results showing presence and
absence of coliform bacilli bacteria.
41
Figure 3: Testing media before incubation
42
Figure 4: results on mackonkey broth media used in analysis of coliform bacilli bacteria
Figure 5: results on EMB plate used in E-coli bacteria count.
The following gives a clear account on the results obtained from the laboratory and the impact of
various variables tested on the samples from the three sampling points.
4.2.1.1 Sampling point 1; bridge located at museum roundabout
The figures below shows the exponential survival curves for coliform bacilli bacteria and the
probable E-Coli upon exposure of contaminated water to the sunlight at the intervals of one hour
and the control sample of one litre glass bottle placed in dark at room temperature.
43
MPN INDEX COLIFORM COUNT /100ML OF WATER
SURVIVAL RATE OF COLIFORM
BACILLI BACTERIA AGAINST CHANGE
IN EXPOSURE TIME
1litre plastic
2litre plastic
3litre plastic
1litre glass
500ml glass
control
2000
1800
1600
1400
1200
1000
800
600
400
200
0
0
1
2
3
4
5
6
7
8
9
CHANGE IN EXPOSURE TIME
Graph 1: graph showing inactivation of coliform bacilli bacteria in 1litre, 2litre, and 3litre plastic
bottles; 1litre 500ml glass bottles and control experiment set at room temperature.
44
SURVIVAL RATE OF E-COLI BACTERIA
AGAINST CHANGE IN EXPOSURE TIME
1litre plastic
2litre plastic
3litreplastic
1litre glass
500ml glass
control
E-COLI BACTERIA IN 0.1ML OF WATER
120
100
80
60
40
20
0
0
1
2
3
4
5
6
7
8
9
CHANGE IN EXPOISURE TIME INHOURS
Graph 2: curves depicting the rate of E-coli survival during the exposure the exposure time in
1litre, 2litre, 3litre plastic bottles; 1litre 500ml glass bottles and the control experiment set at
room temperature.
45
TEMPERATURE CHANGE AGAINST EXPOSURE
TIME
1litre plastic
2litre plastic
3litre plastic
1litre glasss
500ml glass
70
TEMPERATURE CHANGE IN °C
60
50
40
30
20
10
0
0
1
2
3
4
5
6
7
8
9
CHANGE IN EXPOSURE TIME IN HOURS
Graph 3: curves depicting temperature rise during the exposure time in various volume of water
in different types of bottles used.
The maximum temperature observed during the period of exposure was 610c observed in the
500ml with the one litre bottles recording 520c and560c for plastic and glass bottles respectively.
This was as a result of fine weather coupled with direct sunlight providing both thermal and
optical inactivation
46
4.2.1.2. Sampling point 2; globe roundabout bridge
At this point a similar trend was observed as shown below:-
COLIFORM COUNT AGAINST
EXPOSURE TIME
1 litre plastic
2 litre plastic
1 litre glass
500 ml glass
3litre plastic
control bottle
MPN INDEX COLIFORM COUNT/100ML
2000
1800
1600
1400
1200
1000
800
600
400
200
0
0
1
2
3
4
5
6
7
8
9
CHANGE IN EXPOSURE TIME IN HOURS
Graph 4: graph showing the rate of inactivation of coliform bacilli bacteria during the exposure
time in 1litre, 2litre, 3litre plastic bottles and 1litre, 500ml glass bottles and in the control bottle
set at room temperature.
47
E-COLI COUNT IN RELATION WITH CHANGE IN
TIME
E-COLI COUNT IN 0.1ML OF WATER
120
100
80
1litre plastic
2litre plastic
60
3litre plastic
1litre glass
40
500ml glass
control
20
0
0
1
2
3
4
5
6
7
8
9
Graph 5: a graph showing inactivation of E-coli bacteria with change in exposure time in 1litre,
2litre, 3litre plastic bottles; 1litre, 500ml glass bottle and the control bottle set at room
temperature
48
TEMPERATURE RISE AGAINST CHANGE IN
TIME
1litre plastic
2 litre plastic
3 litre plastic
1 litre glass
500 ml glass
60
TEMPERATURE RISE
50
40
30
20
10
0
0
1
2
3
4
5
6
7
8
9
CHANGE IN TIME
e.
Graph 6: a graph showing change in temperature as compared to the change in exposure time
in 1litre, 2litre, 3litre plastic bottles; 1litre, 500ml glass bottles.
The evolution of spontaneous inactivation of coliform bacilli bacteria and E-coli bacteria in
relation to the temperature profile tested at the different exposure time at the second sampling
point are shown in Graph 4 and 5.
The spontaneous inactivation of the coliform bacilli bacteria followed a declining profile from
the initial MPN count of 1800in 100ml of water to an approximate count of 170 coliforms
although this high inactivation rate was experienced in the lowest volume of the water exposed
to sunlight. Throughout all the assays though, a similar trend was obtained as shown in the above
curves. In the 5-hours exposure test, the temperature increased from 220C to 42°C for 500ml of
water in glass bottle. Until an exposure time of three hours, the spontaneous decrease in coliform
bacilli bacteria remained above 1800in 100ml of water with temperatures recording a small
change.
49
The results obtained in the 4- and 7-hours exposure tests were significantly different. There was
a sharp significance decrease in coliform bacilli count, which coincided with the maximum
temperatures reached in the tests (maximum of 490c).
The E-coli count from the EMB plate per 0.1ml of water also recorded a sharp decline between
12.00pm and4.00pm but before this time an initial test showed an increase in the count. The
control experiment set at room temperature indicated an increase in the number of E-coli bacteria
throughout the experiment.
4.2.1.3: Sampling point 3: Kariakor Bridge.
Graph 7: inactivation of coliform bacilli bacteria using 500ml and 1litre glass bottles and 1litre,
2litre, 3litre and control bottle at room temperature
50
E-COLI COUNT IN RELATION WITH CHANGE IN
TIME
E-COLI COUNT IN 0.1ML OF WATER
120
100
80
1litre plastic
2litre plastic
60
3litre plastic
1litre glass
40
500ml glass
control
20
0
0
1
2
3
4
5
6
7
8
9
Graph 8: inactivation of E-coli bacteria in 500ml, 1litre glass bottles and 1litre 2litres, 3litres
plastic bottles and the control bottle.
51
1L PLASTIC
2L PLASTIC
3L PLASTIC
1L GLASS
500ML GLASS
60
TEMPERATURE IN C
50
40
30
20
10
0
0
1
2
3
4
5
6
7
8
9
TIME IN HOURS
Graph 9: a relation between temperature increase during the exposure time in 500ml, 1litre
glass bottles and 1litre, 2litres, 3litres plastic bottles.
Seven hour duration was used since this is the time when the sun’s intensity is high i.e. from
9.00am to 4.00pm. Temperatures recorded during the exposure time were to a maximum of 560c
and this was recorded in the 500ml glass bottle. The temperatures varied in accordance to the
volume of water used as indicated in graph 9 above. Subsequently the rate of inactivation varied
directly with the increase in temperature. Inactivation of coliform bacilli bacteria was more
pronounced in the 1litre and 500ml glass bottles and 1ltre plastic bottles which had attained a
temperature of 530c, 560c and460c respectively.
52
This is in broad agreement with Wegelin et al. (1994) who reported that water temperatures
between 20 and 40 °C do not affect the inactivation of bacteria by UVA and visible light but
synergistic effects are observed at a threshold water temperature of 45-50 °C. This is seen in the
e-coli inactivation curve in which bacteria were found to increase at temperatures below 400c
with subsequent decrease beyond this temperature.
Furthermore, a complete inactivation of high populations of E. coli can be produced in drinking
water, even of high turbidity (200 ntu), by exposing water of below 2 litres volumes contained in
plastic and glass soft drink containers too strong to medium solar irradiances for periods of at
least 7 h. If a water temperature greater than 55 °C is reached in the sample, thermal stress is
primarily responsible for the observed inactivation. The inactivated bacteria do not recover as the
water cools following solar exposure. Bacteria in samples that achieve intermediate water
temperatures (about 45 °C) can still be fully and permanently inactivated if the water is of low
turbidity and is exposed to high irradiances (70 mW cm) for periods of up to 7h.
4.2.2 WATER CONTAINER TYPE
Composition, size and depth within the water temperature of the container have unequivocal
capacity to determine the rate. There are a few simple criteria that must be applied in selecting
the appropriate type of containers to be used for the proper disinfection of contaminated water
using sunlight. The general rule that needs to be followed is to base the selection not only on
availability and size, but also on the need to use containers that would permit the penetration of
those sun rays that would effectively destroy microorganisms. Therefore the transparency and
colour of the materials from which the containers are made constitute the important
characteristics required of the container.
This is clearly shown from the curves above whereby the rate of disinfection was most effective
in 500ml container as compared with 3litre container with this small quantity of water due to
high temperature rise of 560c, 490c and 610c in the three set of experiments respectively. The
53
main aim of using transparent bottles was not only to ensure better thermal conduction but also
better optical activity of the sun rays on the contaminated water.
The system for treating low volumes of water (less than 3 Litres) is appropriate as shown in the
figures although more water quantity may be exposed but for a longer time, especially If Water
is containing low turbidity (less than NTU30). Although thin glass bottles showed better rate of
absorbing the sunrays, clear plastic bottles are preferred by most users on glass bottles. These
bottles are less likely to break due to being lighter and less expensive.
Bottles made of Polyethylene Terephthalate (PET), bottles made of poly vinyl chloride (PVC),
other plastics and most types of glass are preferable, because less likely to give hazardous
chemicals during the exposure. They also are light weight, do not break, the chemically stable
and have the chance to taste and odour to water.
During solar exposure, water temperatures within the bottles can reach 55°C. Even higher
temperatures can be achieved if the base or back of the bottle is blackened to enhance heat
transfer through infrared absorption.
4.2.3. IMPURITIES IN WATER
Inorganic chemicals present in water as natural constituents or as extraneous contaminants are
not expected to be affected by sunlight. Very little is known about photo-decomposition of
photosensitive organic compounds upon exposure to sunlight. From practical standpoint and
research however, the presence of reasonable concentrations of both inorganic and organic
impurities would not hinder the disinfection by sunlight.in exceptional cases not encountered in
drinking water supplies, high coloured waters may absorb appreciable solar energy in the range
of wavelengths effective against microorganisms. This was difficult to verify in the laboratory
since all the samples produced similar results on colour of 10degrees hazen.
On the other hand, turbidity due to suspended particulate matter would hinder to some extent the
penetration of sunlight, this depends on the degree of turbidity and the volume of water being
exposed, besides, and the suspended particles would protect any microorganisms adhering to the
surfaces of the container reducing the rate of optical inactivation. Results from above samples
gave a clear indication on this with the last sample producing greater turbidity compared to the
54
other two sampling point of 45 N.T.U as compared to 56 N.T.U and 68 N.T.U in sampling
points 2 and 3 respectively.
Although other factors such as weather weigh in, in the rate of inactivation, the effect of turbidity
could be experienced in curves showing the rate of inactivation of E-coli bacteria whereby the
number of E-coli bacteria inactivated in the sampling point 3 could not compare to that of
sampling point 1 and 2.
Although the problem is not likely to be faced by communities supplied with piped drinking
water, communities deprived of such public utilities should be advised to resort to sources that
yield relatively clear water, wherever this is not feasible and turbid surface waters from streams,
ponds or irrigation canals have to be utilized it would be particularly important to clarify the
water by convenient simple methods such as filtration to reduce both the suspended and
settleable solids or decantation to remove settleable solids if proper disinfection is to be
assured.it remains to be pointed out that waters with relatively low microbial populations as seen
in E-coli inactivation curve under sampling point 2 with or without fair weather and with
relatively high turbidity but with fairy high thermal capacity, can be more rapidly and efficiently
decontaminated by sunlight.
4.2.4. SOLAR RADIATION AND AMBIENT TEMPERATURE
The inactivation mechanism depends on the ambient solar conditions, but involves optical and
thermal processes. The effect of sunlight on bacterial pathogens is well documented. UV-A and
early visible wavelength regions (320-450nm) of the sunlight spectrum are absorbed by
photosensitizers that become electronically excited and react with neighboring oxygen
molecules.
This leads to the production of highly reactive oxygen species that cause strand breakage and
base changes in DNA. Strand breakage is usually lethal, while base changes may result in a
block in replication and other mutagenic effects. Sub lethal optical doses may render the bacteria
temporarily inactive or non culturable, and such damage may be corrected by DNA repair
mechanisms that are active in most living cells. Little is known about the pathogenicity of viable
but non-cultivable organisms.
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Practically, as shown in graph 3and graph 9 during solar exposure, water temperatures within the
bottles can reach approximately 60°C. Even higher temperatures can be achieved if the base or
back of the bottle is blackened to enhance heat transfer through infrared absorption. The
pasteurizing effect of such temperatures over a period of hours causes complete and irreversible
inactivation of most bacterial pathogens, except thermo tolerant or spore-forming species. No
thermal inactivation has been reported for water temperatures < 40°C. Highly turbid or unfiltered
water may not support any significant optical inactivation, because the sunlight is completely
absorbed within the first few millimetres of water. However, turbidity usually increases the
maximum water temperature achieved within the bottle. Strong synergy is observed when the
optical and thermal inactivation processes are combined during solar disinfection.
To achieve these temperatures, daily weather and seasonal factors weigh in, since it is difficult to
attain such high temperatures during cloudy and/or rainy days. This is seen in the graph 6,
whereby the highest temperature attained was 490c in which the day was characterized by
episodes of cloudy hours.
4.2.5. BIOCHEMICAL OXYGEN DEMAND OF WATER
Biochemical oxygen demand (BOD) is an empirical test to provide a measure of the level of
degradable organic material in a water body. The presence of high BOD may indicate faecal
contamination or increases in particulate and dissolved organic carbon from non-human and
animal sources that can restrict water use and development, necessitate expensive treatment and
impair ecosystem health.
The BOD capacity obtained for sample 1 was 37,75mg/l as compared to those of samples 2 and
3 which were 31.33mg/l and 104.5mg/l respectively. This indicted a presence of high bacteria
population in sample 3 as compared to the other samples. High bacteria population coupled with
high turbidity reduces the effectiveness of sunlight as shown in the curves from the three samples
.the rate of E-coli inactivation was generally higher in the low BOD capacity at sample 3 as
compared to sample one that had had a higher thermal capacity.
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4.2.6. EFFECTS ON OTHER ORGANISMS
The question that may arise is whether exposure of contaminated water to the sunlight in
accordance with the experimental procedure adopted in this study would also lead to destruction
of microorganisms other than bacteria e.g. enteric viruses and protozoa.it must be admitted at the
outset that no straightforward answer can be offered at the present in view of the fact that this
study was limited to the possibility of bacterial inactivation.
Although this is the case studies have shown that the lethal effect of ultraviolet light (UV) has
been thoroughly investigated and the use of ultraviolet light radiation has been applied for
disinfection of water supplies in lieu to chlorination. Although information about the virucidal
effect of sunlight is rather scanty, there is some evidence that viruses are inactivated by sunlight
in relatively shallow ponds of water or raw sewage. The intensity and exposure time are mostly
the important factors.
Since viruses are generally recognized to be more resistant than bacteria to the influence of
disinfectants, it would be reasonable to assume that their inactivation by sunlight under the stated
experimental conditions would require prolongation of the period of exposure. However this
matter requires further investigations.
Spore forming organisms not associated with disease are expected to survive the effect of
sunlight until they germinate since spores are known to be more resistance to the destructive
effect of chemical disinfectants commonly used in water purification.
Since the thermal death point of amoebic cysts is about 500 C, contaminated water used in this
study (sample 1= 610 C, sample 2 = 490 C, sample 3 = 560C) which had all attained a
temperature close to 500 C on exposure to sunlight would in itself ensure their destruction by this
mechanism.
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5.0 CHAPTER FIVE
5.1 CONCLUSIONS
This project was conducted to study the effects of numerous variables on the disinfection
properties of solar radiation. The variables tested were turbidity, sample volume, color and
biochemical oxygen demand. The samples were exposed to sunlight during the sunny days of
February in clear plastic and glass bottles. Experiments were also conducted in the laboratory to
obtain the bacteria count. In analyzing the results from these experiments, the following
conclusions were drawn:
1. The rate of inactivation in the with exposure time in terms of the probable number of
bacteria still surviving followed an exponential decline curve, a pattern typical of bacteria
destruction by chemical disinfectants like chlorine and iodine.
2. Temperatures up to 46°C have no significant effect on the disinfection of E. coli and
bacteria. The inactivation properties of solar disinfection are therefore due to its solar
radiation component, or the synergistic effects of sunlight
3. The rate of solar inactivation is directly proportional to the rise in temperature during
exposure with an approximate temperature being 550C at which majority of the E-coli
and coliform bacilli bacteria were found to have been disinfected. The water sample used
was highly contaminated compared to the river water used for drinking in rural villages
showing that it is possible to achieve a total bacteria elimination in these waters if proper
methods of exposure to sunlight are adopted and consequently a reduction in cases of
diarrhoea and other enteric diseases.
4. Solar disinfection rate is inversely proportional to the amount of both organic and
inorganic impurities increasing the turbidity of the water. A reduction in turbidity will
thus increase the rate of sunlight effectiveness hence a need to ensure that the water is
free of both suspended and settleable solids by use of simple methods of filtration or
decantation and also ensures that bacteria lack cover from the optical effect of the
sunlight.
5. Solar disinfection is highly dependent on the weather, with days characterized with high
sunlight intensity producing maximum levels of inactivation. This thus shows that areas
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experiencing low sun intensity i.e. parts of the world experiencing season changes e.g.
winter are unsuited for the process which is mainly advantaging mostly tropical areas that
have daily episodes of sunlight throughout the year.
6. Volume of the water exposed, greatly determines the rate of inactivation with large
volumes posing low rates of inactivation as compared to small quantities. Exposure of
large quantities would therefore require more exposure time.
7. Material used in the inactivation process is also of great importance with clear thin glass
bottles being more effective though it is not recommendable to use them as they break
easily posing a health hazard to people.
Thus it is possible to say that the objective of the study which was to investigate the
effectiveness of the sunlight on bacteriological examination of water with results showing the
decrease in both E-coli and coliform bacteria. Solar disinfection can thus be used to successfully
eliminate pathogenic microorganisms and therefore reduce susceptibility to enteric diseases like
diarrhoea or cholera.
Solar disinfection offers a worthwhile reduction in disease risk under 'real life' conditions, but is
not a panacea. A central problem is that people cannot usually be relied on to follow laboratory
protocols. In practice they may not leave the water in the sun for long enough before drinking it,
and they will probably also drink water directly from water holes or other sources. In addition,
contaminated water is only one of the causes of diarrhoea disease, which is often the main public
health problem in areas where solar disinfection offers potential benefits.
Solar disinfection offers no protection against chemical contaminants in drinking water and
concerns have been raised about health risks associated with chemicals leached from the plastic
containers by prolonged photo degradation. Most plastic drink containers are presently made
from polyethylene terephthalate. The compounds that could potentially leach from such bottles
are acetaldehyde, terephthalic acid, dimethyl terephthalate and ethylene glycol. Terephthalic acid
and dimethyl phthalate are genotoxic, but they are insoluble in water, and the chances of them
leaching into the water, even during solar disinfection, are minimal. Ethylene glycol is more
likely to leach into the water, as it is more water-soluble.
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5.2 Recommendations
Due to limited resources and time in conducting the study, the following section details
recommendations for future research.
1. E-coli and coliforms bacteria are the common the common test organisms and the results
are correlated to the effects of solar disinfection on other organisms such as pathogenic
bacteria, enteric viruses, spore-forming organisms and protozoa. However it is
recommended that solar disinfection tests be conducted on these organisms.
2. The bottles used in this study were only transparent. While most plastic bottles are made
of similar, some are coloured and are differently shaped. Before implementing the
procedure of solar disinfection an evaluation need be made regarding the colour and
shape of the bottles and their effectiveness in solar disinfection. This will allow
researchers to test whether the local water is adequately treated with the process.
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BIBLIOGRAPHY
1. Wegelin, M.; Canonica, S.; Mechsner, K.; Fleischmann, T.; Pesaro, F.; Metzler, A. 1994.
Solar water disinfection: scope of the process and analysis of radiation experiments.
2. Rijal, G. and Fujioka, R. 2001. Synergistic effect of solar radiation and solar heating to
disinfect drinking water sources.
3.
McGuigan, K.; Joyce, T.; Conroy, R. 1999. Solar disinfection: use of sunlight to
decontaminate drinking water in developing countries.
4. Kehoe, S.; Joyce, T.; Ibrahim, P.; Gillespie, J.; Shahar, R.; McGuigan, K. 2001. Effect of
agitation, turbidity, aluminum foil reflectors and container volume on the inactivation
efficiency of batch-process solar disinfectors.
5. Joyce, T.; McGuigan, K.; Elmore-Meegan, M.; Conroy, R. 1996. Inactivation of fecal
bacteria in drinking water by solar heating.
6. Fujioka, R. and Siwak, E. 1985. The effect of sunlight on alternative microbial indicators
of water quality.
7. Conroy, R.; Elmore-Meegan, M.; Joyce, T.; McGuigan, K.; Barnes, J. 1996. Solar
disinfection of drinking water and diarrhoea in Maasai children: a controlled field trial.
8. Ciochetti, D. and Metcalf, R. 1984. Pasteurization of naturally contaminated water with
solar energy.
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9. Burch, J. and Thomas, K. 1998. Water disinfection for developing countries and
potential for solar thermal pasteurization.
10. World Health Organization, 2006.Guidelines for drinking water quality, first addendum
to third edition, volume 1
11. Acra, A.; Raffoul, Z.; Karahagopian, Y. 1984. Solar disinfection of drinking water and
oral rehydration solutions: guidelines for household application in developing countries.
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APPENDICES
LABORATORY TESTS
Test for colour
A Nessler cylinder was filled with the water sample up to the mark and transferred to the right
hand compartment of a Lovibond nessleriser used in conjunction with a white light cabinet. The
colour was then matched against the standard Hazen disc no. NSA. The colour was then read off
directly in Hazen.
Test for turbidity
The turbid meter was allowed to warm up for approximately 110 minutes. 30ml of the water
sample was then pipetted into a clean sample cell and the sample compared with the given
standards. The standard with a value of turbidity closest to, but higher than the water sample was
chosen. The standard chosen (NTU) was found to be in the range of 0 – 100 NTU, thus a cell
riser was inserted into the cell holder assembly.
The standard was then inserted into the cell holder and the instrument standardized while taking
care to use the light shield. This was followed by removing the standard and replacing it with the
range
Test for biochemical oxygen demand
1. The BOD bottles to be used had a capacity of 280 ml each. The volume of the sample
to be taken in each bottle, that would result in dilutions of 1:10, 1:25, 1:50 was
calculated
2. Four sets of BOD bottles, each set up containing three bottles were arranged. And
labeled with the dilution factors mentioned above ( one set per dilution)
3. Calculated amounts of sample were transferred to each bottle as appropriate
4. The bottles were then filled with dilution water without overflowing and the stopper
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placed without trapping any air bubbles.
5. Another set of 3 bottles , identifying them as dilution water were filled with dilution
water without any sample
6. Dissolved oxygen concentration in one bottle was determined as follows:
a. Interfaces due to nitrite-nitrogen and ferrous iron up to 1mg/l
i. The stopper was removed and succession 2 ml each of Manganous
sulphate solution and alkali azide- iodide reagent with the tip of the
pipette well below the water level in the bottle were added and the
stopper replaced again taking care not to trap in any air bubbles.
ii. The contents of the bottle were mixed by inverting the bottle several
times and then letting the precipitate settle halfway down the bottle. The
content were mixed again and the precipitate allowed to settle again
iii. 2 ml conc. Sulphuric acid was added to the contents of the bottle using a
bulb, with the tip of the pipette just below the water level. The stopper
was replaced and the contents mixed again till all the precipitate was
dissolved
iv. 203 ml was measured from the bottle and transferred to an Erlenmeyer
flask. It was then titrated against a standard sodium thiosulphate solution
till the color changed to pale yellow. 1ml of starch indicator solution was
then added and the titration continued until the blue color disappeared.
Reappearance of the blue color after the first disappearance was
disregarded
7. The remaining bottles were incubated at 20oc for 5 days in the incubation cabinet
8. The dissolved oxygen concentration in each bottle at the end of the incubation period as
outlined
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Test for coliform and E-coli count
a) Presumptive test and standard plate count
1ml and 0.1ml water sample was pipetted into each T-soy agar deep. This was mixed and poured
onto petri dish.
Five tubes of single strength lactose broth were inoculated with 1ml water, five tubes single
strength lactose broth with 0.1ml water. These were incubated at 350c for 24 hours. The number
of colonies on the plates were counted and recorded.
The lactose broth tubes were observed for evidence of acid and gas production. The presence of
gas within 24 hours in any lactose tube is a positive presumptive test.
The most probable number (MPN) of coliforms per 100ml of the water sample was obtained by
the use of the table provided in the laboratory.
b) Confirmed test
From the tube of lactose broth testing positive with the smallest inoculum of water
eosin-methylene blue (EMB) agar plate was streaked to get isolated colonies. This was incubated
for 24 hours to get typical E-coli colonies.
E-coli colonies appeared bluish black by transmitted light and have a greenish metallic sheen by
reflected light. This confirmed the test has being positive of e-coli presence.
c) Completed test
A tube of lactose broth and a nutrient agar slant from a typical coliform colony of the EMB plate
was inoculated. This was incubated for 24 hours at 350c.
The lactose broth was observed for evidence of acid and gas formation. A gram stain from the
nutrient agar slant was prepared and observed. The formation of gas in the lactose tube and the
demonstration of gram-negative, non-spore-forming rods from the stained smear constitutes a
positive completed test and indicates that the water was polluted.
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