Water purification by sunlight

December 17, 2017

Since its introduction the solar still has remained solely a concept, with its design and structure fully flexible and dependent on its feasibility in the area



The world is currently facing a significant scarcity of clean water and traditional methods of water purification such as nano-filtration and reverse osmosis are extremely expensive and cannot be utilized in remote areas where the problem is most imminent.


Reverse osmosis is a membrane filtration technique which utilizes a semi-permeable membrane to virtually remove all contaminants from water. The solvent is passed through a porous membrane in the direction opposite to that of natural osmosis when subjected to a hydrostatic pressure greater than that of the osmotic pressure. Alongside being extremely expensive, another significant drawback to reverse osmosis is that it removes the mineral content from the water. After analyzing hundreds of scientific studies concerning demineralized or reverse osmosis water, the World Health Organization released a report stating that such water "has a definite adverse influence on the animal and human organism” and showed that the reverse osmosis process actually removes 92-99% of beneficial calcium and magnesium present in water. Therefore, scientists needed to search for more efficient and inexpensive methods of water purification and developed the “solar still”.


About one tenth of the world’s population lacks clean water and the solar still acts a lifeline for the impoverished. Distillation of water with solar energy is quite simple and is quite similar to how nature creates rain: the Sun heats and evaporates water, which at the same time is separated from salt, dirt or any other impurities. Most are simple black-bottomed vessels filled with water, and capped with clear glass or plastic. As black materials are good absorbers of radiation, the heat absorbed by the material speeds up evaporation. The water vapour is trapped by the clear topping and funneled away for drinking water. Most pollutants don’t evaporate, and so are left behind.


Solar still is, by far, the most inexpensive and manageable solution to providing clean water to rural areas


In recent times, scientists have been successful in improving solar stills through two approaches. Firstly, the layer is designed in such a way that only the top layer of water in the vessel is heated and evaporated, which reduces the amount of energy lost. Secondly, nanomaterials are being utilized in order to absorb a greater amount of the Sun’s rays but since these efficient light-absorbing nanomaterials can be extremely expensive, they cannot be used in developing countries where the technology is needed most.


Solar distillers can be used to efficiently remove many impurities ranging from salts to microorganisms and are even used to make drinking water from seawater. The purified water obtained from the solution still does not acquire the "flat" taste of commercially distilled water since the water has not been boiled (which lowers pH). Solar stills use natural evaporation and condensation which retains the natural pH of water that produces excellent taste as compared to steam distillation.

The use of solar stills is not only restricted to rural areas but are an integral asset in urban areas as well. However, their impact is far greater in under-developed and developing areas where other traditional methods cannot be utilized. If they are developed and optimized even further, they can be used to provide pure, clean water all over the globe.






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