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Solar water disinfection & cleaning: how to disinfect water using solar energy: this article explains using solar heating equipment for correcting unsanitary or unsatisfactory drinking water. Solar water disinfection using solarcatalytic treatment (SODIS) has been under test for some time.
Here we report on recent studies that have improved the efficacy of that approach to using solar power to produce potable water.
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Solar water purifiers use solar energy to produce potable (drinking) water from available water sources. In a typical solar water purifier design, sunlight is converted either to electrical energy typically to operate distillation equipment, pumps, or evaporators, or sunlight is used directly in the form of heat to operate a distillation process. Water is vaporized (evaporated) from a storage container. Water vapor is condensed on the under-side of a glass or plastic surface where it runs down to a clean-water collection container.
The most rudimentary "emergency" solar still has been made using clean black plastic trash bags, a hole in the ground, and plants as a moisture source.
Our placeholder photo at page top is a photovoltaic array in use on a restaurant in San Miguel de Allende, Mexico (not powering solar water purification). [Images of solar water disinfection systems sneeded, CONTACT us].
Comparison of Alternative methods for producing potable water using solar power
Watch out: reviewing popular "solar water purification" articles in our research we observe that some writers are confused about the difference between disinfection and purification. For example, simply using sunlight to heat water in a closed plastic container for some number of hours might reduce the number of bacterial pathogens - those sensitive to high temperatures without having to boil the water. But such water heating may not remove chemical contaminants - though in an open container some volatile chemical components may be driven off or redued.
And without other more effective filtration steps, heating water simply using direct sunlight will not remove fine sediment nor some other pathogens such as giardia cysts, and it may not reliably reduce bacterial contaminants either, depending on the starting level and particular bacteria. At DRINKING WATER - EMERGENCY PURIFICATION we list methods of emergency drinking water purification and give choices that can be matched to the immediate circumstances; also at WATER TREATMENT EQUIPMENT CHOICES we list types of water treatment equipment and methods and the features of each.
Photocatalytic Enhanced Solar Disinfection of Drinking Water
These comments on use of solar powered equipment for water disinfection are based on "Final Report: Enhanced Photocatalytic Solar Disinfection of Water as Effective Intervention Against Waterborne Diarrheal Diseases in Developing Countries", National Center for Environmental Research, U.S. Environmental Protection Agency et als.
Quoting from the above report (http://cfpub.epa.gov/ncer_abstracts/index.cfm/fuseaction/display.abstractDetail/abstract/8841/report/F)
Photocatalytic enhanced solar disinfection using NF-TiO2 was responsible for complete inactivation of E. coli in those reactors exposed to both solar and visible light radiation. The presence of NF-TiO2 enhanced the disinfection rate efficiency of E.coli when compared to those experiments where no photocatalyst was used. Practical application of dye solutions as dosimetric indicator appears as very useful for determining the solar radiation dose necessary for waterborne pathogen deactivation.
Solar water disinfection (SODIS) is a simple, environmentally friendly and low cost point-of-use treatment technology for drinking water purification. However, bacterial re-growth after short storage (24 h) of SODIS treated water has been observed.
Seeking for improvements of SODIS performance, reduction of irradiation time and avoidance of bacteria regrowth, solar based-Advanced Oxidation Technologies (AOTs), such as solar TiO2 photocatalysis, are promising enhancements to SODIS. Unfortunately, one of the main problems with the use of conventional TiO2 for solar applications is its limited capability to absorb only the radiation in the UV range, which is only about 5-8% of the total solar radiation.
In this study, we employed novel nanotechnological procedures to synthesize visible light activated nonmetaldoped TiO2 (i.e., nitrogen-doped TiO2) with high surface area and immobilized on appropriate support materials that were used in novel photocatalytic reactors for water purification in rural zones in Mexico as a case study.
In combination with visible light activated TiO2, we also propose to incorporate in our process the V trough solar collector which has never been applied to solar photocatalytic processes in the past, but has much simpler geometry and demonstrated in preliminary results performance comparable to other types of solar collectors. Because of its simpler geometry, the V trough solar collector is much less expensive and is attractive to applications is developing countries. This overall process for water purification was denominated “Enhanced Photocatalytic Solar Disinfection” (ENPHOSODIS).
A complete inactivation of the bacteria was achieved when using ENPHOSODIS under solar and visible light at three different NF-TiO2 catalyst concentrations. Under dark conditions, no difference in the bacteria count was observed and no inactivation of E. coli was observed when employing visible light only. pH was an important influence on the bacteria resistence to solar radiation. E. coli was able to survive for longer radiation periods at pH 7 and 7.5 than at lower or higher pH values (i.e., 6, 6.5 and 8). An azo dye, acid orange 24 (AO24), was explored for the development of a UV dosimetric indicator for disinfection. Complete color removal was found to be equivalent to that when water submitted to ENPHOSODIS treatment, under the proposed conditions, will get enough energy to deactivate completely the viable helminth eggs present. Different configurations of immobilized TiO2 photocatalytic reactors were tested under real sun conditions. Experiments under full sun and cloudy conditions showed that these photoreactors are capable of disinfection with an optimum configuration of internal and external coationg along with a compound parabolic collector.
Solar Arrays and Solar Evaporation for Demineralization of Water
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How Do I Use Solar Power to Purify Water?