Solar water disinfection ( ' SoDis ' ) is a type of portable water purification that uses solar energy to create biologically - contamination (eg bacteria, viruses, protozoa and worms) safe drinking water. Water contaminated with non-biological agents such as toxic chemicals or heavy metals requires additional steps to make water safe to drink.
Solar water disinfection is usually done using some electric mixtures generated by photovoltaic panels (solar PV), heat (solar heat), and solar ultraviolet light collection.
Solar disinfection using electrical effects generated by photovoltaics typically uses electric current to provide electrolytic processes that disinfect water, for example by generating oxidative free radicals that kill pathogens by damaging their chemical structure. The second approach uses solar electricity stored from the battery, and operates at night or at low light levels to turn on ultraviolet lights to disinfect secondary ultraviolet water.
The disinfection of the hot water of the sun uses heat from the Sun to heat water up to 70-100 ° C for a short time. A number of approaches are here. Solar thermal collectors can have lenses in front of them, or use reflectors. They can also use different levels of insulation or glass. In addition, some disinfection processes of batch-based solar hot water, while others (through-flow solar thermal desinfection) operate almost continuously while the Sun shines. Water that is heated to temperatures below 100 ° C is commonly referred to as water pasteurization.
The sun's ultraviolet part can also kill pathogens in the water. The SODIS method uses a combination of UV rays and an increase in temperature (solar heat) for water disinfection using only sunlight and PET plastic bottles. SODIS is a free and effective method for decentralized water treatment, usually applied at the household level and recommended by the World Health Organization as a viable method for household water treatment and safe storage. SODIS has been implemented in many developing countries. The educational pamphlets on this method are available in many languages, each equivalent to the English version.
Video Solar water disinfection
Principles
Sun exposure has been shown to deactivate causative organisms in contaminated drinking water. Inactivation of pathogenic organisms is associated with: UV-A (wavelength 320-400Ã, nm) part of sunlight, which reacts with oxygen dissolved in water and produces highly reactive oxygen forms (oxygen-free radicals and hydrogen peroxides) that damage pathogens, while it also disrupts metabolism and destroys the structure of bacterial cells; and simultaneously all solar energy (from infrared to UV) heats the water.
At a water temperature of about 30 ° C (86 ° F), a solar radiation threshold of at least 500 W/m 2 (all spectral light) is required for about 5 hours for SODIS to be efficient. This dose contains energy of 555 Wh/m 2 in the range of UV-A and violet rays, 350-450 nm, corresponding to about 6 hours of midday mid-day sunlight (Europe) summer.
At water temperatures higher than 45Ã, Â ° C (113Ã, Â ° F), the synergistic effect of UV radiation and temperature further increases the disinfection efficiency. Above 50 Â ° C (122 Â ° F), the number of bacteria drops three times as fast.
Maps Solar water disinfection
Processes for home appliances
A guide to the SODIS household usage illustrates the process.
Colorless, transparent PET water or 2 liters or smaller bottle pop with a few surface streaks selected for use. Glass bottles are also suitable. Any labels are removed and bottles are washed before first use. Water from contaminated sources may be filled into bottles, using the clearest water possible. Where turbidity is higher than 30 NTU it is necessary to filter or precipitate particles before exposure to sunlight. Filters are made locally from the fabric stretched over the bottle upside down with the bottom cut off. To improve oxygen saturation, the guidance recommends that the bottle be filled three quarters, shaken for 20 seconds (with lid), then fully charged, sealed, and checked for clarity.
The filled bottles are then exposed to the fullest possible sunlight. The bottle will heat faster and warmer if placed on a reflective metal surface facing toward the sun. The corrugated steel roof (compared to thatched roof) or the slightly curved aluminum sheet increases the light inside the bottle. The overhanging structure or the cropping of the bottle should be avoided, as both reduce lighting and heating. After sufficient time, treated water can be consumed directly from the bottle or poured into a clean drinking cup. The risk of re-contamination is minimized if water is stored in a bottle. Refilling and storage in other containers increases the risk of contamination.
The most favorable areas for the application of the SODIS method lie between latitude 15  ° N and 35  ° N, and also 15  ° and 35  °. These areas have high levels of solar radiation, with limited cloud cover and rainfall, and with more than 90% of sunlight reaching the earth's surface as direct radiation. The second most favorable region lies between latitude 15Ã,  ° N and 15Ã, ° S. These areas have high radiation levels scattered, with about 2,500 hours of sunlight each year, due to high humidity and frequent cloud cover.
Local education in the use of SODIS is important to avoid confusion between PET and other bottle materials. Implementing SODIS without proper assessment (or with incorrect judgment) of hygienic & amp; The incidence of diarrhea can not overcome the route of other infections. Community trainers should be trained first.
Apps
SODIS is an effective method for treating water where fuels or stoves are not available or very expensive. Even where fuel is available, SODIS is a more economical and environmentally friendly option. SODIS application is limited if enough bottles are not available, or if the water is very cloudy. In fact, if the water is very cloudy, SODIS can not be used alone; additional filtering is required.
A basic field test to determine if the water is too cloudy for the SODIS method to work correctly is a newspaper test. For newspaper testing, the user should place a fully stocked bottle above the newspaper title and look down through the bottle opening. If the letter of the title is readable, water can be used for the SODIS method. If the letters are not readable then the water turbidity may exceed 30 NTU, and the water should be pre-treated.
In theory, this method can be used in disaster management or refugee camps. However, the provision of a bottle may be more difficult than providing an equivalent disinfectant tablet containing chlorine, bromine, or iodine. In addition, in some circumstances, it may be difficult to guarantee that water will be left in the sun for the time it takes.
Other methods for household water treatment and safe storage exist (eg, chlorination) of different filtration procedures or flocculation/disinfection. Selection of appropriate methods should be based on criteria of effectiveness, occurrence of other types of pollution (turbidity, chemical pollutants), maintenance costs, labor input and convenience, and user preferences.
When the water is very cloudy, SODIS can not be used alone; additional filtration or flocculation is needed to clarify the water prior to SODIS treatment. Recent work has shown that common table salt (NaCl) is an effective flocculation agent for lowering turbidity for SODIS methods in some soil types. This method can be used to improve the geographic area where the SODIS method can be used as areas with very turbid water can be treated at low cost.
SODIS can be implemented alternatively using plastic bags. SODIS bags have been found to yield processing efficiencies of 74% higher than SODIS bottles, which may be due to the bag being able to reach the high temperatures that cause accelerated maintenance. SODIS bags with a layer of water about 1 cm to 6 cm reach higher temperatures easier than SODIS bottles, and treat Vibrio cholerae more effectively. It is assumed this is due to the increased surface area to the volume ratio in the SODIS bag. In remote areas plastic bottles are not available locally and need to be shipped from downtown which may be expensive and inefficient because bottles can not be packed very tight. Bags can be packed denser than bottles, and can be delivered at a lower cost, representing a more economical alternative to SODIS bottles in remote communities. The disadvantage of using a pouch is that they can provide water to the plastic smell, they are more difficult to handle when filled with water, and they usually require that water be transferred to a second container for drinking.
Another important benefit in using SODIS bottles compared to pockets or other methods that require water to be transferred to smaller containers for consumption is that the bottle is a household water treatment method used in the points. Point-of-use means that water treated in the same container is easy to handle it will be served from, thereby reducing the risk of secondary water contamination.
Caution
If water bottles are not left in the Sun for the right period of time, water may not be safe to drink and may cause illness. If the sun is not strong enough, because of cloudy weather or less sunny climate, longer lighting time in the Sun is required.
The following issues should also be considered:
- Bottle material
- Some glass or PVC material can prevent ultraviolet light reaching water. Commercially available PET bottles are recommended. Handling is much more comfortable in the case of PET bottles. Polycarbonate (resin identification code 7) blocks all UVA and UVB rays, and therefore should not be used. Clear bottles are preferred over colored bottles, such as lemon/lime soda pop bottles.
- Aging of plastic bottles
- SODIS efficiency depends on the physical condition of plastic bottles, with scratches and other wear signs reducing SODIS efficiency. Scratched heavy or old, blind bottles must be replaced.
- Form of container
- The intensity of 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 by 50%. Bottles of PET soft drinks are often easily available and thus most practical for SODIS applications.
- Oxygen
- Sunlight produces highly reactive forms of oxygen (oxygen-free radicals and hydrogen peroxides) in water. These reactive molecules contribute to the destruction of microorganisms. Under normal conditions (rivers, creeks, wells, ponds, taps) water contains sufficient oxygen (more than 3 mg/L of oxygen) and should not be aerated before the SODIS application.
- Bottled material release
- There are some concerns over the question of whether the plastic drinking container can release chemicals or toxic components into the water, a process that may be accelerated by heat. The Swiss Federal Laboratory for Materials Testing and Research has examined the diffusion of adipates and phthalates (DEHA and DEHP) from new PET bottles and reused in water during sun exposure. The concentration levels found in water after exposure to the 17-hour sun in water 60 ° C (140 ° F) are far below the WHO guidelines for drinking water and in an amount equal to the concentration of phthalate and adipate commonly found in quality tap water high. Concerns about the general use of PET bottles were also disclosed after a report published by researchers from the University of Heidelberg on antimony releases from PET bottles for soft drinks and mineral water stored for several months at the supermarket. However, the antimony concentrations found in the bottle are the order of magnitude under WHO and the national guidelines for the concentration of antimony in drinking water. Furthermore, SODIS water is not stored for long periods in bottles.
- Growth of bacteria
- After being expelled from the sun, the remaining bacteria can re-reproduce in the dark. A 2010 study showed that adding just 10 parts per million of hydrogen peroxide was effective in preventing the regrowth of wild Salmonella.
- Toxic chemicals
- Solar water disinfection does not remove toxic chemicals that may be present in water, such as factory waste.
Health impact, diarrhea reduction
According to the World Health Organization, more than two million people per year die from water-preventable diseases, and one billion people do not have access to improved drinking water.
It has been shown that the SODIS method (and other household water treatment methods) can very effectively eliminate pathogenic contamination from water. However, infectious diseases are also transmitted through other channels, namely due to lack of sanitation and general hygiene. Studies on reducing diarrhea among SODIS users show a 30-80% reduction rate.
Research
The effectiveness of SODIS was first discovered by Aftim Acra, from the American University of Beirut in the early 1980s. Follow-up was conducted by Martin Wegelin's research group at the Swiss Institute of Water Science and Technology (EAWAG) and Kevin McGuigan at the Royal College of Surgeons in Ireland. Clinical control trials are pioneered by Ronan Conroy of the RCSI team in collaboration with Michael Elmore-Meegan.ICROSS
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
- Institute for Water and Sanitation Development (IWSD), Zimbabwe
- Plataforma Solar de Almera (CIEMAT-PSA), Spain
- University of Leicester (UL), United Kingdom
- International Commission for Relief and Hunger Relief (ICROSS), Kenya
- University of Santiago de Compostela (USC), Spain
- Swiss Institute of Water Science and Technology (Eawag), Switzerland
The project started multi-country research including study areas in Zimbabwe, South Africa and Kenya.
Other developments include the development of continuous flow disinfection units and solar disinfection with titanium dioxide films on top of glass cylinders, which prevent the regrowth of coliform bacteria after SODIS.
Research has shown that a number of low-cost additives are able to accelerate SODIS and that additives may make SODIS faster and more effective in both sunny and cloudy weather, developments that can help make technology more effective and acceptable to users. A 2008 study showed that powdered beans from five natural legumes (peas, peanuts and lentils) - Vigna unguiculata (cowpeas), Phaseolus mungo (black lentils), Glycine max (soy), Pisum sativum (green beans), and Arachis hypogaea (nuts) - when evaluated as a natural flocculant to remove turbidity, as effective as commercial and even superior alum for clarification that the optimal low dose (1 g/L), rapid flocculation (7-25 min, depending on seed used) and water hardness and pH are basically not changed. Subsequent studies used chestnuts, oak seeds, and Moringa oleifera (drumstick trees) for the same purpose.
Other studies have examined the use of doping semiconductors to increase the production of oxygen radicals under UV-A solar. Recently, researchers at the National Center for Sensor Research and Biomedical Diagnostics Institute at Dublin City University have developed a printable UV dosimeter for SODIS applications that can be read using a mobile phone. The phone camera is used to obtain sensor images and special software running on the phone analyzes the color of the sensor to provide quantitative measurements of UV dosage.
In remote areas the effect of wood smoke increases lung disease, because of the constant need to build fire for cooking water and cooking. The research group has found that boiling water is negligible because of the difficulty of collecting wood, which is rare in many areas. When presented with a basic household water treatment option in remote areas of Africa has shown a preference for the SODIS method of boiling or other basic water treatment methods.
Promotions
The Swiss Institute of Water 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 , Kenya, Guatemala, Guinea, Honduras, India, Indonesia, Kenya, Laos, Malawi, Mozambique, Nepal, Nicaragua, Pakistan, PerÃÆ'º, Philippines, Senegal, Sierra Leone, Sri Lanka, Togo, Uganda, Uzbekistan, Vietnam, Zambia, Zimbabwe.
The SODIS project is funded by, among others, SOLAQUA Foundation, several Lions Clubs, Rotary Clubs, Migros, and Michel Comte Water Foundation.
SODIS has also been applied in several communities in Brazil, one of which is Prainha do Canto Verde, Beberibe west of Fortaleza. The villagers there using the SODIS method have been quite successful, since daytime temperatures can exceed 40 ° C (104 ° F) and there is less color.
One of the most important things to consider for public health workers reaching out to communities in need of appropriate, cost-effective, and sustainable water treatment methods is to teach the importance of water quality in the context of health promotion and disease prevention while educating about self-methods. Although skepticism has posed challenges in some communities to adopt SODIS and other household water treatment methods for everyday use, disseminating knowledge about the important health benefits associated with this method is likely to increase adoption rates.
See also
- Appropriate technology
- Ultraviolet Germicidal Irradiation
- Water Pasteurization Indicator
References
External links
- SODIS
- How does it work
- Cheap water purification using: SODIS on YouTube
- WADI - Device for Solar Water Disinfection
- "Plastic versus glass bottle". Ã, (36,0Ã, KB)
- SODIS in Latin America
- includes concepts in brief
- Drinking Water For All (PDF) by Anumakonda Jagadeesh. Test results in Tamil Nadu, India.
- Kenya Tap Sun Makes a Rich Multimedia Water Glow from CLPMag.org
- Pure water for all , The Hindu Business Line, Apr 15, 2005
- Clean Water at no cost, SODIS way , The Hindu, September 14, 2006
- Places under the sun physics.org, October 7, 2009
- Glass Bottles and UV Light (PDF) provide data on how many UV rays are screened by different types of glass bottles, August 2008
Source of the article : Wikipedia
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