CA2925835C

CA2925835C - Method and apparatus for solar water purification

Info

Publication number: CA2925835C
Application number: CA2925835A
Authority: CA
Inventors: Rachel Brouwer
Original assignee: Individual
Current assignee: Individual
Priority date: 2016-04-05
Filing date: 2016-04-05
Publication date: 2023-01-10
Anticipated expiration: 2036-04-05
Also published as: CA2925835A1

Abstract

A method and apparatus for solar purification using a thermal indicator for detecting temperature thresholds in a body of water and a transparent container for holding the water to be purified, is provided. The thermal indicator consists of a wax exhibiting a first visual indication at one temperature, a second visual indication at a second temperature and a container permitting both visual indications to be observed. Example indications include melting or colour changes. The apparatus consists of a transparent container for holding the water to be pasteurized and the thermal indicator. The method consists of exposing the container to solar radiation while observing the container for visual indications of temperature change. The container may be exposed to solar radiation either for a predetermined amount of time or until a desired temperature threshold is reached. The invention extends to methods of using the thermal indicator in solar water purification and the thermal indicator itself.

Description

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.

[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 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 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.

[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 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 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 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, 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.

[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.

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 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.

Date Recue/Date Received 2022-08-16

Claims

1. A thermal indicator for a body of water, the indicator comprising:
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, wherein:
a) the first visual indication is a change in colour and the second visual indication is the melting of the wax;
b) the first visual indication is the melting of the wax and the second visual indication is a change in colour; or c) the first visual indication is a change in colour and the second visual indication is a change to a different colour;
and 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.

2. The thermal indicator of claim 1, wherein the first visual indication is a change in colour and the second visual indication is the melting of the wax and the container permits the melted wax to move from a first position to a second position.

3. The thermal indicator of claim 1 or claim 2, wherein the first temperature is about 35 to about 40 C.

4. The thermal indicator of any one of claims 1 to 3 wherein the second temperature is about 55 to about 60 C.

5. The thermal indicator of any one of claims 1 to 4, wherein the container comprises a first and second chamber joined by an opening and wherein a guide extends through the opening and is configured to direct melted wax from the first chamber to the second chamber.

Date Recue/Date Received 2022-08-16

6. A method of solar purification of water, the method comprising:
exposing a transparent container of water to solar radiation for an initial incubation period;
observing an indicator positioned within the transparent container for a first visual indication of temperature at a first temperature;
observing the indicator for a second visual indication of temperature at a second temperature;
wherein 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.

7. The method of claim 6 wherein the indicator is the indicator of any one of claims 1 to 5.

8. The method of claim 6 or claim 7, wherein the first temperature is about 35 to about 40 C and the second temperature is about 55 to about 60 C.

9. The method of any one of claims 6 to 8, wherein the initial incubation period is at least six hours.

10. The method of any one of claims 6 to 9, wherein the further incubation period is at least 6 hours.

11. The method of any one of claims 6 to 9, wherein the further incubation period is 12 to 24 hours.

12. The method of any one of claims 6 to 9, wherein the further incubation period is 42 to 48 hours.

Date Recue/Date Received 2022-08-16

13. The method of any one of claims 6 to 12, wherein the duration of the initial incubation period and the further incubation period are selected on the basis of the pathogens to be removed from the water.

14. The method of any one of claims 6 to 13, further comprising reflecting the solar radiation onto the transparent container.

15. The method of any one of claims 6 to 14, further comprising pre-filtering the water before exposing the water to solar radiation, to reduce turbidity.

16. The method of any one of claims 6 to 15, wherein the container is repositioned if the indicator does not provide the first visual indication after the initial incubation period.

17. The method of any one of claims 6 to 16, wherein the indicator is re-observed if the indicator does not provide the second visual indication after the initial incubation period.

18. An apparatus for solar purification of water, the apparatus comprising:

a transparent container for holding the water to be pasteurized; and an indicator according to any one of claims 1 to 5 positioned in the transparent container.

19. The apparatus of claim 18, further comprising a reflector for concentrating solar radiation on the transparent container.

20. The apparatus of claim 18 or 19, further comprising a filtration unit for pre-filtering the water to reduce turbidity before adding the water to the transparent container.
Date Recue/Date Received 2022-08-16