Solar water disinfection
Encyclopedia
Disinfection
Disinfectants are substances that are applied to non-living objects to destroy microorganisms that are living on the objects. Disinfection does not necessarily kill all microorganisms, especially nonresistant bacterial spores; it is less effective than sterilisation, which is an extreme physical...
water using only sunlight
Sunlight
Sunlight, in the broad sense, is the total frequency spectrum of electromagnetic radiation given off by the Sun. On Earth, sunlight is filtered through the Earth's atmosphere, and solar radiation is obvious as daylight when the Sun is above the horizon.When the direct solar radiation is not blocked...
and plastic PET
Polyethylene terephthalate
Polyethylene terephthalate , commonly abbreviated PET, PETE, or the obsolete PETP or PET-P, is a thermoplastic polymer resin of the polyester family and is used in synthetic fibers; beverage, food and other liquid containers; thermoforming applications; and engineering resins often in combination...
bottles. SODIS is a free and effective method for decentralized water treatment
Water treatment
Water treatment describes those processes used to make water more acceptable for a desired end-use. These can include use as drinking water, industrial processes, medical and many other uses. The goal of all water treatment process is to remove existing contaminants in the water, or reduce the...
, usually applied at the household level and is recommended by the World Health Organization
World Health Organization
The World Health Organization is a specialized agency of the United Nations that acts as a coordinating authority on international public health. Established on 7 April 1948, with headquarters in Geneva, Switzerland, the agency inherited the mandate and resources of its predecessor, the Health...
as a viable method for household water treatment and safe storage. SODIS is already applied in numerous developing countries. Educational pamphlets on the method are available in many languages, each equivalent to the English language version.
Principle
Exposure to sunlight has been shown to deactivate diarrheaDiarrhea
Diarrhea , also spelled diarrhoea, is the condition of having three or more loose or liquid bowel movements per day. It is a common cause of death in developing countries and the second most common cause of infant deaths worldwide. The loss of fluids through diarrhea can cause dehydration and...
-causing organisms in polluted drinking water
Drinking water
Drinking water or potable water is water pure enough to be consumed or used with low risk of immediate or long term harm. In most developed countries, the water supplied to households, commerce and industry is all of drinking water standard, even though only a very small proportion is actually...
. Three effects of solar radiation are believed to contribute to the inactivation of pathogenic organisms:
- UV-A interferes directly with the metabolism and destroys cell structures of bacteria.
- UVUltravioletUltraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
-A (wavelength 320-400 nm) reacts with oxygen dissolved in the water and produces highly reactive forms of oxygen (oxygen free radicals and hydrogen peroxideHydrogen peroxideHydrogen peroxide is the simplest peroxide and an oxidizer. Hydrogen peroxide is a clear liquid, slightly more viscous than water. In dilute solution, it appears colorless. With its oxidizing properties, hydrogen peroxide is often used as a bleach or cleaning agent...
s), that are believed to also damage pathogens. - Cumulative solar energy (including the infrared radiation component) heats the water. If the water temperatures rises above 50°C, the disinfection process is three times faster.
At a water temperature of about 30°C (86°F), a threshold solar irradiance of at least 500 W/m2 (all spectral light) is required for about 5 hours for SODIS to be efficient. This dose contains energy of 555 Wh/m2 in the range of UV-A and violet light, 350 nm-450 nm, corresponding to about 6 hours of mid-latitude (European) midday summer sunshine.
At water temperatures higher than 45°C (113°F), synergistic effects of UV radiation and temperature further enhance the disinfection efficiency.
Process for household application
- Colourless, transparent PETPolyethylene terephthalatePolyethylene terephthalate , commonly abbreviated PET, PETE, or the obsolete PETP or PET-P, is a thermoplastic polymer resin of the polyester family and is used in synthetic fibers; beverage, food and other liquid containers; thermoforming applications; and engineering resins often in combination...
water or soda pop bottles (2 litre or smaller size) with few surface scratches are chosen for use. The labels are removed and the bottles are washed before the first use. - Water from contaminated sources are filled into the bottles. To improve oxygen saturation, bottles can be filled three quarters, shaken for 20 seconds (with the cap on), then filled completely and recapped. Very cloudy water with a turbidity higher than 30 NTU must be filtered prior to exposure to the sunlight.
- Filled bottles are then exposed to the sun. Bottles will heat faster and to higher temperatures if they are placed on a sloped sun-facing corrugated metal roof as compared to thatched roofs.
- The treated water can be consumed directly from the bottle or poured into clean drinking cups. The risk of re-contamination is minimized if the water is stored in the bottles. Refilling and storage in other containers increases the risk of contamination.
| Weather Conditions | Minimum Treatment Duration |
|---|---|
| sunny (less than 50% cloud cover) | 6 hours |
| cloudy (50-100% cloudy, little to no rain) | 2 days |
| continuous rainfall | unsatisfactory performance, use rainwater harvesting Rainwater harvesting Rainwater harvesting is the accumulating and storing of rainwater for reuse before it reaches the aquifer. It has been used to provide drinking water, water for livestock, water for irrigation, as well as other typical uses. Rainwater collected from the roofs of houses and local institutions can... |
Applications
SODIS is an effective method for treating water where fuel or cookers are unavailable or prohibitively expensive. Even where fuel is available, SODIS is a more economical and environmentally friendly option. The application of SODIS is limited if enough bottles are not available, or if the water is highly turbid.In fact, if the water is highly turbid, SODIS can not be used alone, additional filtering is then necessary.In theory, the method could be used in disaster relief or refugee camps. However, supplying bottles may be more difficult than providing equivalent disinfecting tablets containing chlorine, bromine, or iodine. Additionally, in some circumstances, it may be difficult to guarantee that the water will be left in the sun for the necessary time.
Other methods for household water treatment and safe storage exist, e.g. chlorination, different filtration procedures or flocculation/disinfection. The selection of the adequate method should be based on the criteria of effectiveness, the co-occurrence of other types of pollution (turbidity, chemical pollutants), treatment costs, labor input and convenience, and the user’s preference.
Cautions
The following issues should also be considered:
- Bottle material: Some glass or PVC materials may prevent ultraviolet light from reaching the water. Commercially available bottles made of PETPolyethylene terephthalatePolyethylene terephthalate , commonly abbreviated PET, PETE, or the obsolete PETP or PET-P, is a thermoplastic polymer resin of the polyester family and is used in synthetic fibers; beverage, food and other liquid containers; thermoforming applications; and engineering resins often in combination...
are recommended. The handling is much more convenient in the case of PET bottles. PolycarbonatePolycarbonatePolycarbonatePhysical PropertiesDensity 1.20–1.22 g/cm3Abbe number 34.0Refractive index 1.584–1.586FlammabilityV0-V2Limiting oxygen index25–27%Water absorption – Equilibrium0.16–0.35%Water absorption – over 24 hours0.1%...
blocks all UVA and UVB rays, and therefore should not be used.
- Aging of plastic bottles: SODIS efficiency depends on the physical condition of the plastic bottles, with scratches and other signs of wear reducing the efficiency of SODIS. Heavily scratched or old, blind bottles should be replaced.
- Shape of containers: the intensity of the UV radiation decreases rapidly with increasing water depth. At a water depth of 10 cm (4 inches) and moderate turbidity of 26 NTU, UV-A radiation is reduced to 50%. PET soft drink bottles are often easily available and thus most practical for the SODIS application.
- Oxygen: Sunlight produces highly reactive forms of oxygen (oxygen free radicals and hydrogen peroxides) in the water. These reactive molecules contribute in the destruction process of the microorganisms. Under normal conditions (rivers, creeks, wells, ponds, tap) water contains sufficient oxygen (more than 3 mg Oxygen per litre) and does not have to be aerated before the application of SODIS.
- Leaching of bottle material: There has been some concern over the question whether plastic drinking containers can release chemicals or toxic components into water, a process possibly accelerated by heat. The Swiss Federal Laboratories for Materials Testing and Research have examined the diffusion of adipateAdipateAdipate is the ionized form of adipic acid.As food additives, adipates are used as acidity regulators. Examples are sodium adipate and potassium adipate .-See also:* Acidity regulator...
s and phthalatesPhthalatesPhthalates , or phthalate esters, are esters of phthalic acid and are mainly used as plasticizers . They are used primarily to soften polyvinyl chloride...
(DEHA and DEHP) from new and reused PET-bottles in the water during solar exposure. The levels of concentrations found in the water after a solar exposure of 17 hours in 60°C water were far below WHOWorld Health OrganizationThe World Health Organization is a specialized agency of the United Nations that acts as a coordinating authority on international public health. Established on 7 April 1948, with headquarters in Geneva, Switzerland, the agency inherited the mandate and resources of its predecessor, the Health...
guidelines for drinking water and in the same magnitude as the concentrations of phthalate and adipate generally found in high quality tap water.
Concerns about the general use of PET-bottles were also expressed after a report published by researchers from the University of Heidelberg on antimony being released from PET-bottles for soft drinks and mineral water stored over several months in supermarkets. However, the antimony concentrations found in the bottles are orders of magnitude below WHO and national guidelines for antimony concentrations in drinking water. Furthermore, SODIS water is not stored over such extended periods in the bottles.
- Regrowth of bacteria: Once removed from sunlight, remaining bacteria may again reproduce in the dark. A 2010 study showed that adding just 10 parts per million of hydrogen peroxide is effective in preventing the regrowth of wild SalmonellaSalmonellaSalmonella is a genus of rod-shaped, Gram-negative, non-spore-forming, predominantly motile enterobacteria with diameters around 0.7 to 1.5 µm, lengths from 2 to 5 µm, and flagella which grade in all directions . They are chemoorganotrophs, obtaining their energy from oxidation and reduction...
.
- Toxic chemicals: Solar water disinfection does not remove toxic chemicals which may be present in the water, such as factory waste.
Health impact, diarrhea reduction
Research and development
The effectiveness of the SODIS was first discovered by Professor Aftim Acra at the American University of BeirutAmerican University of Beirut
The American University of Beirut is a private, independent university in Beirut, Lebanon. It was founded as the Syrian Protestant College by American missionaries in 1866...
in the early 1980s [3]. Substantial follow-up research was conducted by the research groups of Martin Wegelin at the Swiss Federal Institute of Aquatic Science and Technology (Eawag) and Dr Kevin McGuigan at the Royal College of Surgeons in Ireland
Royal College of Surgeons in Ireland
The Royal College of Surgeons in Ireland , is a Dublin-based medical institution, situated on St. Stephen's Green. The college is one of the five Recognised Colleges of the National University of Ireland...
. Clinical control trials were pioneered by Professor Ronan Conroy of the RCSI team in collaboration with Michael Elmore-Meegan
Michael Elmore-Meegan
Michael Elmore-Meegan, also known as Michael Meegan, is the co-founder of the International Community for Relief Of Starvation and Suffering , an aid agency operating in East Africa that describes itself as "a small international organisation working to fight poverty and disease in the poorest...
.
Currently, a joint research project on SODIS is implemented by the following institutions:
- Royal College of Surgeons in Ireland (RCSI), Ireland (coordination)
- University of Ulster (UU), United Kingdom
- CSIR Environmentek, South Africa, Eawag, Switzerland
- The Institute of Water and Sanitation Development (IWSD), Zimbabwe
- Plataforma Solar de Almería (CIEMAT-PSA), Spain
- University of Leicester (UL), United Kingdom
- The International Commission for the Relief of Suffering & Starvation (ICROSS), Kenya
- University of Santiago de Compostela (USC), Spain
- Swiss Federal Institute of Aquatic Science and Technology (Eawag), Switzerland
The project has embarked on a multi-country study including study areas in Zimbabwe
Zimbabwe
Zimbabwe is a landlocked country located in the southern part of the African continent, between the Zambezi and Limpopo rivers. It is bordered by South Africa to the south, Botswana to the southwest, Zambia and a tip of Namibia to the northwest and Mozambique to the east. Zimbabwe has three...
, South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
and Kenya
Kenya
Kenya , officially known as the Republic of Kenya, is a country in East Africa that lies on the equator, with the Indian Ocean to its south-east...
.
Other developments include the development of a continuous flow disinfection unit and solar disinfection with titanium dioxide film over glass cylinders which prevents the bacterial regrowth of coliforms after SODIS. Research has shown that a number of low-cost additives are capable of accelerating SODIS and that additives might make SODIS more rapid and effective in both sunny and cloudy weather, developments that could help make the technology more effective and acceptable to users. A 2008 study showed that natural coagulants (powdered seeds of five natural legumes (peas, beans and lentils) – Vigna unguiculata
Cowpea
The Cowpea is one of several species of the widely cultivated genus Vigna. Four cultivated subspecies are recognised:*Vigna unguiculata subsp. cylindrica Catjang...
(cowpea), Phaseolus mungo
Urad (bean)
Vigna mungo, known as urad, urad dal, udad dal, urd bean, urd, urid, black matpe bean, black gram, black lentil [not to be confused with the much smaller true black lentil ], maas , đậu đen or white lentil, is a bean grown in southern Asia...
(black lentil), Glycine max
Soybean
The soybean or soya bean is a species of legume native to East Asia, widely grown for its edible bean which has numerous uses...
(soybean), Pisum sativum
Pea
A pea is most commonly the small spherical seed or the seed-pod of the pod fruit Pisum sativum. Each pod contains several peas. Peapods are botanically a fruit, since they contain seeds developed from the ovary of a flower. However, peas are considered to be a vegetable in cooking...
(green pea), and Arachis hypogaea (peanut) – were evaluated for the removal of turbidity), were as effective as commercial alum and even superior for clarification in that the optimum dosage was low (1 g/L), flocculation was rapid (7–25 minutes, depending on the seed used) and the water hardness and pH was essentially unaltered. Later studies have used chestnuts, oak
Oak
An oak is a tree or shrub in the genus Quercus , of which about 600 species exist. "Oak" may also appear in the names of species in related genera, notably Lithocarpus...
acorns, and Moringa oleifera
Moringa oleifera
Moringa oleifera, the word Moringa probably came from dravidian language Tamil and commonly referred to as "Shojne" in Bengali, "Munagakaya" in Telugu,"Shenano" in Rajasthani,...
(drumstick tree) for the same purpose.
Other research has examined the use of doped semiconductors to increase the production of oxygen radicals under solar UV-A.
Issues to consider
The following are some of the issues discussed in the literature:- According to the World Health OrganizationWorld Health OrganizationThe World Health Organization is a specialized agency of the United Nations that acts as a coordinating authority on international public health. Established on 7 April 1948, with headquarters in Geneva, Switzerland, the agency inherited the mandate and resources of its predecessor, the Health...
, more than two million people per year die of water-borne diseases, and one billion people lack access to a source of improved drinking water. - Local education in the use of SODIS is important to avoid confusion between PET and other bottle materials.
- Applying SODIS without proper assessment (or with false assessment) of existing hygienic practices & diarrhea incidence may not address other routes of infection. Community trainers need to themselves be trained first.
- When the water is highly turbid, SODIS can not be used alone, additional filtering or flocculation is then necessary to clarify the water prior to SODIS treatment.
Worldwide application
The Swiss Federal Institute of Aquatic Science and Technology (EAWAG), through the Department of Water and Sanitation in Developing Countries (Sandec), coordinates SODIS promotion projects in 33 countries including Bhutan, Bolivia, Burkina Faso, Cambodia, Cameroon, DR Congo, Ecuador, El Salvador, Ethiopia, Ghana, Guatemala, Guinea, Honduras, India, Indonesia, Kenya, Laos, Malawi, Mozambique, Nepal, Nicaragua, Pakistan, Perú, Philippines, Senegal, Sierra Leone, Sri Lanka, Togo, Uganda, Uzbekistan, Vietnam, Zambia, and Zimbabwe. Contact addresses and case studies of the projects coordinated by the Swiss Federal Institute of Aquatic Science and Technology (EAWAG) are available at sodis.ch.SODIS projects are funded by, among others, the SOLAQUA Foundation , several Lions Clubs, Rotary
Rotary International
Rotary International is an organization of service clubs known as Rotary Clubs located all over the world. The stated purpose of the organization is to bring together business and professional leaders to provide humanitarian service, encourage high ethical standards in all vocations, and help...
Clubs, Migros
Migros
Migros is one of Switzerland's largest enterprises, its largest supermarket chain and largest employer. It co-founded Turkey's largest retailer, Migros Türk, which became independent of Migros Switzerland in 1975....
, and the Michel Comte Water Foundation.
SODIS has also been applied in several communities in Brazil, one of them being Prainha do Canto Verde north of Fortaleza. There, the villagers have been purifying their water with the SODIS method. It is quite successful, especially since the temperature during the day can go beyond 40°C (100°F) and there is a limited amount of shade.
External links
- SODIS
- How does it work
- SODIS in Latin America
- covers the concept briefly
- Drinking Water For All (PDF) by Anumakonda Jagadeesh. Test results in Tamil NaduTamil NaduTamil Nadu is one of the 28 states of India. Its capital and largest city is Chennai. Tamil Nadu lies in the southernmost part of the Indian Peninsula and is bordered by the union territory of Pondicherry, and the states of Kerala, Karnataka, and Andhra Pradesh...
, India. - Kenyans Tap Sun to Make Dirty Water Sparkle Multimedia from CLPMag.org
- Pure water for all, The Hindu Business Line, Apr 15, 2005
- Clean water at no cost, the SODIS way, The Hindu, Sep 14, 2006
- A place in the sun physics.org, October 7, 2009
- Glass Bottles and UV Light (PDF) provides data on how much UV light is filtered by various types of glass bottles, August 2008