WO2021018653A1

WO2021018653A1 - Solar uv water disinfection container

Info

Publication number: WO2021018653A1
Application number: PCT/EP2020/070474
Authority: WO
Inventors: Denis BORDREZ; Jean-François Daviet; Kevin Durand; Alexandra DEVILLENEUVE; Frédéric HARNY
Original assignee: Valsem Industries Sas
Priority date: 2019-08-01
Filing date: 2020-07-20
Publication date: 2021-02-04

Abstract

A solar ultraviolet (UV) water disinfection container (500) with at least one closable opening (503a) to let the water in and out, and primarily made of fluoropolymer membranes (502, 508) with a fair transparency in the UV region of the solar spectrum where germicidal action is achieved by simply exposing said container to direct sunlight, said fluoropolymer letting in a fair dose of ultraviolet light from the natural solar radiation, where fair germicidal UV transparency is defined by a UV transmission of said membrane of at least 10% in the 264nm area.

Description

SOLAR UV WATER DISINFECTION CONTAINER

TECHNICAL FIELD

This invention pertains to a solar water disinfection apparatus and method.

PRIOR ART

According to the World Health Organization (WHO) , more than two million people per year die of preventable water- borne diseases.

And while fresh water is actually fairly abundant on Earth, the WHO estimates that one billion people lack access to a source of drinking water of adequate quality. This problem is especially vivid in developing countries lacking the technology and / or the financial resources for modern water treatment plants, or even for individual systems (micro-filtration, chemical tablets, etc.).

In many places, the most basic treatment consisting of boiling water with locally harvested wood is not even an option, as wood becomes too scarce.

Incidentally, irreversible deforestation is also a major, unsustainable environmental issue.

A simple method using transparent, repurposed, disposable plastic bottles has been tested as a viable option to perform a so-called solar water disinfection, or SODIS.

This research, led by the Swiss Federal Institute of Aquatic Science and Technology (EAWAG) , is now successfully deployed in dozens of developing, subtropical countries.

The SODIS method takes advantage of the abundance of otherwise wasted, disposable, PET (Polyethylene Terephthalate, the most common hydrocarbon polymer used to make disposable bottles) plastic bottles everywhere in the world (most of which originally containing industrial drinking water) , along with the fact that the residual ultraviolet (UV) transparency of said PET, although poor in the most effective area of the UV spectrum (~264nm, Figs. 1-3), allows for known germicidal action by simple exposure of the water to natural sunlight - provided a minimum set of conditions are met, such as low water turbidity and sufficient sunlight intensity.

Fig. 1 shows the transmittance of light in percentage as a function of the wavelength of the light in nm, for a standard sheet of PET film of 20 pm of thickness (A) and for an UV-hardened PET film of 20 pm of thickness (B) .

Fig. 2 shows that efficacy of UV light for microbial disinfection peaks at about 264 nm, with a graph showing germicidal effectiveness in percentage as a function of the wavelength in nm.

Above and below this wavelength, there is a drop in effectiveness, although wavelengths are still absorbed by DNA.

Figure 3 shows solar UV intensity, above the stratosphere and at ground level, with a graph indicating UV absorption by stratospheric ozone, more specifically the TOA (Top Of Atmosphere) solar flux (according to Dobber et al . 2008) indicated by A, surface irradiance indicated by B, ozone absorption indicated by C and erythmal action spectrum (according to McKinley, CIE 1987) indicated by D, as a function of light wavelengthin in nm, with irradiance in W/m²/nm on the left vertical axis and ozone absorption coefficient in cnr¹ on the right vertical axis. This SODIS method is cheap, simple, widely available, and effective when used properly, and thus, constitutes a great progress in this field.

However, it has several drawbacks, in particular those listed below.

SUSTAINABILITY

The environmental burden of the hundreds of millions of PET bottles produced annually is unsustainable.

PET bottles will eventually be banned, and replaced by non-disposable containers, and / or by disposable but bio-sourced, home compostable polymers (such as polyhydroxyalkanoates , or « PHA ») .

The rapid degradation (a few months) of the PET polymer of the plastic bottles, when exposed to direct sunlight, will incidentally accelerate the disposing of old bottles, compounding thus the environmental issues.

EFFECTIVENESS

All hydrocarbon-based polymers rapidly degrade when exposed to direct sunlight due to their interaction with UVs, unless they are « UV-hardened » with some designers additive .

This enhances the polymer's lifetime very significantly; however, said additives will make the material even more opaque to UV, hence defeating the original goal of UV-based disinfection (Fig. 1) .

Even if not UV-hardened, PET shows poor UV transmission in the germicidal region of the solar spectrum at ground level (Figs. 1-3) .

Note that other polymers (such as PE) exhibit intrinsically better UV transmission than PET. However, they will degrade even faster, and their UV hardening will result in similar, counter-productive UV opacity . SAFETY

There is a great deal of uncertainty of effectiveness vs. exposure time, due to the many factors affecting said effectiveness, in particular: quantity of sunlight actually received, and aging of the bottle material.

Subsequently, it is hardly predictable when water will be safely disinfected.

At best, the safest path may be gross overtreatment, which will result in an unnecessarily poor productivity of the process.

For a more comprehensive understanding of the technical field and prior art, one may refer to the following references.

The webpage https://en.wikipedia.org/wiki/Solar_water_disinfection .

Comparative analysis of solar pasteurization versus solar disinfection for the treatment of harvested rainwater Strauss et al . BMC Microbiology (2016) 16:289, DOI

10.1186/s12866-016-0909-y.

German Patent Application DE 10 2007 052 424 Al 2009.05.07, "Wassersack, insbesondere zur

Trinkwasserentkeimung" .

German Patent Application DE 10 2013 014 712 B4

2016.10.20, "Mobile Wasseraufbereitungsanlage" .

European Patent Application EP 1 106 188 Al, "Plastic containers for solar disinfection of water".

UK Patent Application GB 2 040 436 A, "Solar Heater". A method for water disinfection with solar pasteurisation for rural areas of Bangladesh, Erika Lundgren, Thesis, Uppsala University, Jan. 2014.

US Patent 4,520,793, "Foldable, Insulated Solar Water Heater".

US Patent 6,193,894 Bl, "Method and Apparatus for Disinfecting and Sterilizing Water in Water Dispensers Using Ultraviolet Radiation".

US Patent US 7,837,865 B2 "CONTAINER FOR PURIFYING WATER BY UTILIZATION OF SUNLIGHT".

US 9,868,651 B2, "SOLAR DISINFECTION OF FLUID".

US 2011 / 0011808 A1 , "SOLAR WATER PASTEURIZER".

PCT Patent Application WO 2011/154022 Al, "CONTAINER FOR MAKING THE WATER DRINKABLE AND DEVICE FOR THE DISINFECTION OF THE WATER, IN AN AUTONOMOUS WAY".

SUMMARY OF THE INVENTION

This invention pertains to a next-generation solar water disinfection apparatus and method that builds on the knowledgebase of EAWAG' s SODIS, while circumventing its drawbacks and limitations.

The invention provides a solar ultraviolet (UV) water disinfection container with at least one closable opening to let the water in and out, and primarily made of fluoropolymer membranes with a fair transparency in the UV region of the solar spectrum where germicidal action is achieved by simply exposing said container to direct sunlight, said fluoropolymer letting in a fair dose of ultraviolet light from the natural solar radiation, where fair germicidal UV transparency is defined by a UV transmission of said membrane of at least 10% in the 264nm area . The invention may advantageously have the following features :

- the inner surface of the container side opposite to the incident sunlight (hereinafter, « the frontside » for the side incident to the sunlight, and « backside » for the opposite side) , may feature a UV reflective layer arranged so that incident sunlight bounces back, thus traveling essentially twice through the water to be disinfected, hence enhancing essentially the germicidal action of the container by a factor of two;

- the inner reflective layer may be made of aluminum metallization deposited, or of aluminum foil laminated, on a substrate;

- said reflective layer may be protected by an inner layer of fluoropolymer with fair UV transmission comparable to the outer layer, and laminated onto said reflective layer;

the fluoropolymer may be fluorinated ethylene- propylene polymer (FEP), perfluoroalkoxy polymer (FPA), or any combination thereof;

- the reflective backside of the container features darker areas strategically located, so as to trigger natural convection movement by differential heating of the water being disinfected, hence preventing germs to « hide » in areas less exposed to the light such as edges, corners, spouts ;

a resettable UV dose measuring device may be embedded, so as to confirm the time after which the germicidal action is deemed effective, independently of weather and / or sun conditions;

- at least one of the opening for water intake / outlet may feature a supplementary filter, in order to filter out particulates and / or foul tasting compounds; - the container may features at least one water inlet and one water outlet;

- the container may feature at least one handle to make the filling up, the carrying around, and usage of the disinfected water, optimally convenient;

- the container may be made of overall rigid material; the container is made of overall flexible, collapsible material;

- the container may feature means to self-uncollapse it, so as to allow easy self-filling of the container when set loose on a body of water;

- the self-uncollapsing action may be provided by a set of thin, highly flexible rods; and

- the water inlet may be closed off by the means of a water-tight zip.

BRIEF DESCRIPTION OF THE DRAWING

Figure 1 shows UV absorption spectrum of standard and UV-hardened PET, as used in disposable plastic bottles.

Figure 2 shows germicidal effectiveness of UV wavelengths .

Figure 3 shows solar UV intensity, above the stratosphere and at ground level.

Figure 4 shows UV absorption spectrum of a 125 pm Fluoropolymer film used for the invention.

Figure 5 illustrates a cross-section of principle (not to scale) of a preferred embodiment of the invention

« solar UV water disinfection container and method ».

Figure 6 illustrates a cross-section of principle (not to scale) of a Preferred Embodiment of the Invention

« solar UV water disinfection container and method » in action, based on a simplified view of Fig. 5. DESCRIPTION OF AN EMBODIMENT

This invention pertains to a next-generation solar water disinfection apparatus and method that builds on the knowledgebase of EAWAG' s SODIS, while circumventing its drawbacks and limitations as follows (Fig. 5) .

In Fig. 5, the solar UV water disinfection container 500 according to the invention comprises an external, UV transparent, Fluoropolymer TOP membrane 502, at least one closable opening 503a to let the water in and out, an internal, a UV-reflective layer 504, such as aluminum metallization, featuring darker areas 506 to trigger natural convection, a UV transparent Fluoropolymer membrane 508, to protect the UV reflective layer (optional), and a bottom layer 510, acting as a substrate for the metallization and as a support base for the inner Fluoropolymer layer.

In this embodiment, the water inlet 503a is closed off by the means of a water-tight zip 520, the container features at least one water inlet 503a and one water outlet 503b.

The at least one closable opening 503a can features a supplementary filter (505), in order to filter out particulates and / or foul tasting compounds.

The container 500 also comprises a resettable UV dose measuring device 512 embedded, so as to confirm the time after which the germicidal action is deemed effective, independently of weather and / or sun conditions, with regard to water being UV-disinfected 514.

In addition, the container 500 comprises featuring means 518a, 518b, and 518c to self-uncollapse it, so as to allow easy self-filling of the container when set loose on a body of water, such means can be a set of thin, highly flexible rods 518a, 518b, and 518c. The container can features at least one handle 516 to make the filling up, the carrying around, and usage of the disinfected water, optimally convenient.

Fig. 6 illustrates the solar UV water disinfection container 500 in action, with incoming solar (UV) light 610, outgoing (reflected and attenuated) solar (UV) light 612, natural convection movement leading to natural convection rolls 614, and with water-borne germs being killed in the water payload, by solar UV action enhanced by natural convection stirring as indicated by 616.

SUSTAINABILITY

The present invention is based on the use of engineered, transparent fluoropolymers such as FEP (Fluorinated Ethylene Propylene ), PFA ( Perfluoroalkoxy) (instead of PET or other purely hydrocarbon-based polymers, such as PE (Polyethylene ) , PS (Polystyrene ) , PP (Polypropylene) , EVA (Ethylene-Vinyl Acetateflective ) ) , as modern fluoropolymers feature outstanding UV resistance, hence allowing for non-disposable, very long lasting water containers to be manufactured and used for solar UV disinfection by direct sunlight exposure for several years without any degradation.

Said fluoropolymer basic material will be assembled with other long-life materials, to make a complete, viable and convenient treatment and usage container for water disinfection .

EFFECTIVENESS

The careful selection of said fluoropolymer allow for an excellent UV transmission in the core of the germicidal region of the ground-level solar spectrum (Figs. 2-4), several orders of magnitude higher than PET polymer for instance .

Fig. 4 shows UV absorption spectrum of a 125 pm Fluoropolymer film used for the invention, with a graph representing transmittance of the film as a function of the light wavelength expressed in nm, evidencing that the FEP film used for this invention is still highly transmissive in the vicinity of 264 nm, which is the peak of the UV germicidal effectiveness.

We shall consider here as « excellent », a UV transmission by a layer of polymer of at least 10% at the UV germicidal optimum wavelength of 264 nm (Fig. 2) .

The addition of a UV-reflective surface at the « bottom» of the container, so that the incoming solar radiations bounces back, hence proving essentially a double germicidal UV exposure.

With the use of a container material with high germicidal UV transparency, and the addition of a reflective layer, the germicidal efficacy is at least one order of magnitude higher than that of sheer plastic bottle SODIS, providing thus for the highest possible throughput per container.

SAFETY

The bottom of the container, while mostly reflective, will feature specially designed darker areas, so as to trigger natural convection within the water being treated, hence preventing accumulation of germs in stagnant, « shaded » areas of the container (corners, edges, spouts, etc . ) .

The container may be optionally fitted with a resettable UV dose meter, so as to alleviate process uncertainties due to meteorological conditions. The container may be optionally fitted with an inlet filter, so as to alleviate the processing uncertainty due to water turbidity. CONVENIENCE

The container can be either be rigid, or if flexible (such as a pouch or a bag), will preferably feature a set of thin, highly flexible rod, that can provide self-opening (self-uncollapsing) action, so as to facilitate the water filling.

The container can feature handles, spouts, filters attachments, and everything that makes is usage convenient and effective.

Claims

1. A solar ultraviolet (UV) water disinfection container (500) with at least one closable opening (503a) to let the water in and out, and primarily made of fluoropolymer membranes (502, 508) with a fair transparency in the UV region of the solar spectrum where germicidal action is achieved by simply exposing said container to direct sunlight (610), said fluoropolymer letting in a fair dose of ultraviolet light from the natural solar radiation, where fair germicidal UV transparency is defined by a UV transmission of said membrane of at least 10% in the 264nm area .

2. A solar UV water disinfection container as in claim 1, where the inner surface of the container side opposite to the incident sunlight (hereinafter, « the frontside » (F) for the side incident to the sunlight, and « backside » (B) for the opposite side) , features a UV reflective layer (504) arranged so that incident sunlight (610) bounces back, thus traveling essentially twice through the water (514) to be disinfected, hence enhancing essentially the germicidal action of the container by a factor of two.

3. A solar UV water disinfection container as in claim 2, where the inner reflective layer (504) is made of aluminum metallization deposited, or of aluminum foil laminated, on a substrate.

4. A solar UV water disinfection container as in any one of claims 2 to 3, where said reflective layer (504) is protected by an inner layer (508) of fluoropolymer with fair UV transmission comparable to the outer layer (502), and laminated onto said reflective layer (504) .

5. A solar UV water disinfection container as in any one of claims 1 to 4, where the fluoropolymer is fluorinated ethylene-propylene polymer (FEP), perfluoroalkoxy polymer (FPA), or any combination thereof.

6. A solar UV water disinfection container as in any one of claims 1 to 4, where the reflective backside of the container features darker areas (506) strategically located, so as to trigger natural convection movement by differential heating of the water being disinfected, hence preventing germs to « hide » in areas less exposed to the light such as edges, corners, spouts.

7. A solar UV water disinfection container as in any one of claims 1 to 6, where a resettable UV dose measuring device (512) is embedded, so as to confirm the time after which the germicidal action is deemed effective, independently of weather and / or sun conditions.

8. A solar UV water disinfection container as in any one of claims 1 to 7, where at least one of the opening (503a) for water intake / outlet features a supplementary filter (505), in order to filter out particulates and / or foul tasting compounds.

9. A solar UV water disinfection container as in any one of claims 1 to 8, where the container features at least one water inlet (503a) and one water outlet (503b) .

10. A solar UV water disinfection container as in in any one of claims 1 to 9, where the container features at least one handle (516) to make the filling up, the carrying around, and usage of the disinfected water, optimally convenient .

11. A solar UV water disinfection container as in any one of claims 1 to 10, where the container is made of overall rigid material.

12. A solar UV water disinfection , flexible container as in any one of claims 1 to 10, where the container is made of overall flexible, collapsible material.

13. A solar UV water disinfection, flexible container as in claim 12, featuring means (518a, 518b, 518c) to self uncollapse it, so as to allow easy self-filling of the container when set loose on a body of water.

14. A solar UV water disinfection container as in claim 13, where the self-uncollapsing action is provided by a set of thin, highly flexible rods (518a, 518b, 518c) .

15. A solar UV water disinfection container as in claim 14, where the water inlet is closed off by the means of a water tight zip (520) .