Note: Descriptions are shown in the official language in which they were submitted.
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METHOD AND APPARATUS FOR SOLAR WATER PURIFICATION
TECHNICAL FIELD
[0001] This invention relates generally to the field of water
purification,
particularly solar thermal pasteurization and solar ultraviolet (UV) radiation
purification (collectively solar water purification).
BACKGROUND
[0002] Approximately 80% of all illnesses in developing countries are
caused by poor water and sanitation conditions. It is common for women and
girls to have to walk several kilometers every day to fill water containers
and
provide water for their families. Unsafe water, along with low sanitation and
hygiene represent the leading cause of death in developing countries
especially in young children.
[0003] Water-borne pathogens can lead to many various debilitating
and deadly diseases, such as Cholera, Rotavirus and others. Providing clean
safe drinking water will improve quality of life in third world countries.
[0004] Solar water purification uses solar thermal energy and/or solar
ultraviolet (UV) radiation to make biologically contaminated water safer to
drink. Solar-based solutions are particularly useful in developing countries,
many of which are located within 35 latitude of the equator, which can
provide sufficiently strong solar radiation to allow for solar water
purification.
[0005] Moreover, water purification is often a very energy-intensive
process. The use of solar energy in water purification allows for significant
environmental benefits by harnessing renewable energy. This also has the
added benefit of reducing energy costs, which can pose significant
challenges to people located in developing countries.
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[0006] In solar pasteurization, thermal energy from the sun is used to
heat water to its pasteurization point to eliminate disease-causing
pathogens. In solar UV radiation purification, high energy UV radiation from
the sun is used to inactivate pathogens present in contaminated water
through exposure to solar UV radiation.
[0007] Each approach has its advantages and disadvantages. Solar
thermal pasteurization typically works more quickly, but requires direct and
intense solar radiation. UV irradiation is more tolerant to lower light
intensities, but typically takes longer to remove biological contaminants.
[0008] The required time for solar water purification depends on the
intensity of the solar radiation applied to the water, which in turn may
depend on cloud cover, latitude, seasonal variation, and local weather
conditions. The required time may also depend on the pathogens present in
the contaminated water. As a result, one challenge with solar water
purification is the need for a simple and efficient method to identify when
the
purification process is complete.
[0009] One approach is to utilize a wax indicator that melts when the
water reaches a specific temperature. At a predetermined temperature, the
wax in the indicator melts. The melting of the wax provides a visual
indication that the desired temperature has been reached. Existing wax
indicators are suitable for monitoring a single temperature only, thus
limiting
the nature of the information provided by the indicator to the user.
SUMMARY OF THE INVENTION
[0010] The present invention is directed to a solar water purification
system that can operate either as a solar pasteurizer or a solar UV
irradiation unit. The invention includes a single thermal indicator capable of
providing a visual indication of multiple temperatures. For example, the
indicator may include a wax having a first visual indication at a first
temperature and a second visual indication at a second temperature. The
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first visual indication may be set to a temperature indicative of direct
sunlight exposure. The second visual indication may be set to a temperature
indicative of the pasteurization point for the given pathogen. The visual
indications used in the indicator may take several forms, including melting or
a colour change in the wax.
[0011] Users of the invention expose a transparent container of water
to solar radiation and observe the visual indications of the thermal indicator
to determine the appropriate minimum exposure time to the sun. In
preferred embodiments, a reflector is used to focus the solar radiation on the
container. If a sufficiently high temperature is reached to permit solar
pasteurization, the thermal indicator will reach the second visual indication,
which informs the user that solar pasteurization has occurred and the water
is safe to drink. If prevailing conditions only allow for lower temperatures
to
be reached, then the thermal indicator will only reach the first visual
indication, which informs the user that additional time is required to permit
UV irradiation of the water. If neither visual indication has occurred, the
user may wish to reposition the container to ensure exposure to direct
sunlight.
[0012] Thus, the invention provides a simple and cost-effective means
by which users can engage in dual-mode solar purification depending on the
prevailing sun conditions, using a single thermal indicator.
[0013] In one broad aspect, the invention includes a thermal indicator
for detecting a temperature range in a body of water. The indicator further
includes a wax containing a thermochromatic pigment in which the wax
exhibits a first visual indication at a first temperature and a second visual
indication at a second temperature. The first visual indication may be a
change in colour and the second visual indication may be the melting of the
wax. Alternatively, the first visual indication may also be the melting of the
wax and the second visual indication may be a change in colour. As a further
alternative, the first visual indication may be a change in colour while the
second visual indication may be a change to a different colour. The thermal
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indicator further includes a container housing the wax that permits the first
visual indication to be observed at the first temperature and the second
visual indication to be observed at the second temperature.
[0014] In another broad aspect, the invention includes a method of
solar purification of water. The method includes exposing a transparent
container of water to solar radiation for an initial incubation period and
observing an indicator positioned within the transparent container for a first
visual indication of temperature. The method further includes observing the
indicator for a second visual indication of temperature. The exposure of the
container to the solar radiation is maintained until at least the earlier of a
further incubation period after the first visual indication of temperature or
the occurrence of the second visual indication of temperature.
[0015] In yet another broad aspect, the invention includes an
apparatus for solar purification of water, the apparatus comprising a
transparent container for holding the water to be pasteurized and a thermal
indicator as described above positioned in the transparent container.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] Figure 1A is a perspective view of a thermal indicator according
to an embodiment of the present invention.
[0017] Figure 1B is a cross-sectional view of the thermal indicator of
FIG 1A.
[0018] Figure 2 is a perspective view of a transparent container which
includes a thermal indicator according to another embodiment of the present
invention.
[0019] Figure 3 is a perspective view of a solar purification apparatus
according to an embodiment of the present invention.
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[0020] Figure 4 is a perspective view of a solar purification apparatus
according to an embodiment of the present invention.
[0021] Figure 5 is a flow chart outlining a solar purification method
according to one embodiment of the present invention.
DETAILED DESCRIPTION
[0022] Various embodiments will now be disclosed, by way of example
only, which illustrate the invention contemplated herein.
[0023] A thermal indicator 100 in accordance with the present
invention generally comprises a wax 110 that exhibits at least two visual
indications of temperature. The wax 110 is housed within a container 120
that permits these visual indications to be observed.
[0024] Accordingly, the thermal indicator 100 may be used to provide
visual indication of at least three temperature ranges: (a) a temperature
below the first visual indication of temperature, (b) a temperature at or
between the first and second visual indications of temperature, and (c) a
temperature after the second visual indication of temperature. Thus the
thermal indicator 100 according to the present invention provides greater
flexibility than existing wax indicators and may be used in applications where
multiple temperature points are of interest.
[0025] Moreover, by providing a single indicator 100 that can monitor
multiple temperatures, the invention reduces the size, complexity, weight,
and cost of the wax indicator system. These are often key concerns,
particularly for use in solar water purification systems designed to be used
in
remote areas or developing countries.
[0026] When used in conjunction with solar purification, the second
visual indication is set at a higher temperature and informs the user that the
water has reached the pasteurization point, whereas the first visual
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indication is set at a lower temperature and informs the user that the water
is receiving direct solar radiation.
[0027] Figures 1A and 1B depict a thermal indicator 100 according to
one embodiment of the present invention. In this embodiment, the thermal
indicator 100 is an elongate transparent container 120 having chambers
122, 124 joined together by an opening 126 through which melted wax
110 may flow. The wax 110 within the container 120 changes colour at a
first temperature and melts at a second temperature. When the wax 110
melts, it moves from the first chamber 122 to the second chamber 124
within the container 120. In some embodiments, a guide 128 is provided in
the wax 110 which passes through the opening 126, so as to reduce the
surface tension required for the melted wax to move from one chamber 122
to the other 124.
[0028] In the embodiment depicted in Figure 1A, the container 120 is
constructed by joining two plastic vials end to end, with the opening 126
between the chambers 122, 124 formed by a hole bored through the caps
of each vial. The guide 128 in this embodiment is a straightened paper clip.
Thus, the indicator 100 in Figure 1A may be assembled by boring a hole
126 in the lid of a plastic vial 1.22, inserting the guide 128 in to the vial
122, casting the wax 110 in the vial 122, capping the vial 122, and joining
the cap of the vial 122 to a similarly constructed vial 124, by gluing or
melting the plastic. Many other suitable materials and modes of construction
would also be apparent to the person of skill having regard to the present
disclosure, and all such modes are contemplated herein.
[0029] In some embodiments, the indicator 100 may further include a
housing 130, to help maintain the position of the container 120 in the body
of water being purified. In the embodiment shown in Figures 1A and 1B, the
housing 130 includes viewing windows 132, 134 to permit the user to
monitor the chambers 122, 124 of the container 120. In some
embodiments, the buoyancy of the housing 130 is configured so as to
maintain a vertical orientation of the container 120 in the body of water
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being purified. The housing 130 may also include loops 136 to assist in the
removal of the thermal indicator 100 from the body of water being purified.
In the embodiment shown in Figure 1A, the housing 130 was created using
3D-printing (i.e. additive manufacturing). Various other modes of
manufacture would also be apparent to the person of skill having regard to
the present disclosure, and all such modes are contemplated herein.
[0030] The movement of the wax from the first to the second chamber
provides a permanent record that the temperature threshold has been
reached, should the temperature later fall. In this way, the first visual
indication (i.e. colour change) and the second visual indication (i.e. melting
and movement of the wax 110) can be observed by the user.
[0031] In the embodiment shown in Figures 1A and 1B, the thermal
indicator 100 contains a soybean wax 110 that melts at about 55-60 C.
The wax 110 also includes a sapphire blue thermochromatic pigment mixed
with red beet powder, which provides a colour change in the wax 110 from
purple to light pink at about 35-40 C. Thus, the first visual indication is a
colour change at about 35-40 C and the second visual indication is the
melting (and movement, if appropriate) of the soybean wax 110 at about
55-60 C.
[0032] A number of variations on the thermal indicator 100 are
contemplated. For example, the exact temperatures used for each visual
indication may depend on the specific application. In the context of solar
water purification, this includes the species of micro-organisms to be
removed from the water being purified and the mode of operation (i.e. solar
thermal pasteurization versus solar UV irradiation). The composition of the
wax 110 used in the thermal indicator 100 may also be varied. For
example, the wax 110 may be configured to melt before changing colour,
thereby reversing the order of the visual indications. Likewise, the wax 110
may be configured to undergo two colour changes, either before or after
melting, which serve as the first and second visual indications. Non-soybean
waxes 110 may also be used, depending on the temperature at which the
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visual indication is to occur. In some embodiments it may also be preferable
to use a container 120 having only a single chamber 124, particularly where
manufacturing costs are a key concern.
[0033] A solar purification apparatus 200 according to the present
invention combines a thermal indicator 100 with a transparent container
210 filled with water. Figure 2 depicts one such apparatus. In this
embodiment, the thermal indicator is placed within a two litre plastic bottle
filled with water, which is left out in the sun.
[0034] As shown in Figures 3 and 4, the apparatus 200 may also be
modified to include a reflector 220 made of foil or other suitable material
whereby incident solar radiation that contacts the reflector 220 may be
concentrated onto the container 210. This may increase the amount of solar
radiation absorbed by the water, thereby increasing the efficiency of the
apparatus 200.
[0035] A number of variations are contemplated. For example, the
transparent container 210 may be made of any other suitable material,
preferably a material that is transparent to UV light. The size of the
transparent container 210 may also be varied as suitable to the application.
For example, in Figures 2-4, a standard two-litre plastic soda bottle was
chosen on the basis that such bottles are widely available and easily
obtained in developing countries. The size of the container may also be
relevant. For example, containers larger than a standard two litre soda
bottle may in some settings be too large in terms of volume or diameter to
permit an effective solar pasteurization process.
[0036] In some embodiments, the apparatus 200 may also include a
filtration unit (not shown) that filters the water before entering the
transparent container 210. Filtration of the water in this manner may
reduce its turbidity, which can increase the penetration of solar radiation
into
the transparent container 210. Depending on the design of the filter,
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filtration may also help reduce the number of pathogens in the water prior to
solar water purification.
[0037] The indicator 100 and apparatus 200 of the present invention
can be used in a method of solar purification that can be used for both solar
pasteurization and UV solar irradiation, depending on the prevailing sun
conditions.
[0038] Figure 5 provides a flow chart outlining a method according to
the present invention. Generally, the method involves exposing a
transparent container of water to solar radiation. After an initial incubation
period, the indicator is observed to determine if the first or second visual
indications of temperature have occurred. If the first visual indication has
not occurred, then the container 210 may not be receiving direct sunlight
and should therefore be repositioned and re-incubated. If only the first
visual indication has occurred, then the container 210 is left out for a
further
incubation period to permit UV irradiation to occur. If both the first and
second visual indications have occurred, then solar thermal pasteurization
has occurred.
[0039] The initial incubation time may depend on cloud cover, season,
latitude, the strength of the sun's rays and the pathogens present in the
contaminated water. The initial incubation period may also be shorter where
a reflector 220 is used to concentrate sunlight. In some embodiments, the
initial incubation period is at least six hours. In conditions where solar
pasteurization is unlikely to occur within six hours, the initial incubation
period may be adjusted accordingly.
[0040] The first visual indication of temperature establishes a minimum
temperature threshold which can be used to determine whether the
container 210 is receiving direct solar radiation. Thus, failure to reach this
temperature may indicate that the container 210 needs to be repositioned.
In some embodiments the first visual indication of temperature occurs at
about 35-40 C.
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[0041] In some applications, the temperature at which the first visual
indication occurs is also high enough to impose a physiological stress on the
micro-organisms targeted for purification. Such thermal stress may make
some pathogens more susceptible to disinfection by UV irradiation.
[0042] If the first visual indication of temperature is reached, the user
will then look for the second visual indication of temperature.
[0043] The second visual indication of temperature establishes a
minimum temperature threshold for assessing whether solar pasteurization
has occurred. This temperature may depend on the pathogens to be
removed from the water. In some embodiments the second visual indication
of temperature occurs at about 55-60 C. Higher temperatures such as 70 C
may also be used where there is a need for increased margins of safety and
sufficient solar radiation (either direct or reflected) exists. Example
temperatures are provided in the following Table 1:
Table 1: Example Solar Pasteurization Temperatures
Killing Temperature
Species oc oF
Worms 55 131
Rotavirus 60 140
Cholera 60 140
Poliovirus 60 140
Hepatitis A 65 149
E. Coll 60 140
[0044] The duration of the further incubation period is selected based
on prevailing sun conditions, the pathogens to be removed from the water,
the size of the transparent container used, and whether a reflector 220 is
used to concentrate the sunlight. The purpose of this period is to permit
time for UV irradiation to occur. In some embodiments, the further
incubation period is at least 6-24 hours, preferably at least 42 hours.
[0045] Optionally, the user can observe the container 210 during the
further incubation period to see if the second visual indication has occurred.
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If so, then solar pasteurization has occurred and further UV irradiation may
not be necessary.
[0046] As indicated in dashed lines in Figure 5, the method may also
include filtering the water before loading it into the transparent container.
This step may not be required if the water is sufficiently clear at the
outset.
Filtration reduces turbidity, which may increase the penetration of solar
radiation into the water, thereby increasing the efficacy of UV irradiation.
As
a result, pre-filtering the water can be particularly useful when relying on
UV
irradiation as the means for solar water purification.
[0047] Thus, the method provides a cost-effective system for dual-
mode solar water purification. The first visual indication informs the user as
to whether the container 210 is being exposed to direct sunlight. In
conditions where solar radiation is strong, the second visual indication
informs the user that solar pasteurization has occurred. In conditions where
solar radiation is weakened (due to cloud cover, latitude, seasons, et
cetera), the user is informed that solar pasteurization has not occurred and
so the container 210 is left in the sun for a further incubation period so as
to
permit UV irradiation. In some embodiments, this is achieved using the
indicator 100 described above, such that both visual indications can be
provided by a single wax indicator. Thus, the method provides for greater
flexibility in solar water purification, without adding significant complexity
or
cost.
[0048] The embodiments of the present disclosure are intended to be
examples only. Those of skill in the art may affect alterations, modifications
and variations to the particular embodiments without departing from the
intended scope of the present disclosure.
[0049] In particular, features from one or more of the above-described
embodiments may be selected to create alternate embodiments comprised of
a subcombination of features which may not be explicitly described above.
In addition, features from one or more of the above-described embodiments
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may be selected and combined to create alternate embodiments comprised
of a combination of features which may not be explicitly described above.
Features suitable for such combinations and subcombinations would be
apparent to persons skilled in the art upon review of the present application
as a whole.
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Date Recue/Date Received 2022-08-16
