Indian scientists have developed a unique low-cost solar water purifier, which is considered cheap from available water filters, which needs electricity to run and reverse osmosis (RO)-based purifiers waste a lot of water. The solar water purifier, developed by scientists at the Nimbkar Agricultural Research Institute at Phaltan in Maharashtra. It is made up of four tubular solar water heaters attached to a manifold.
Since the cotton cloth can be washed daily, it ensures that the fitter is not clogged. Earlier studies by NARI had shown that filtration of raw water through four-layered cotton sari cloth reduces the coliform count. The tubes have a special coating to absorb maximum sunlight. They are like a thermos flask with a vacuum between the outer and inner tubes. Non-potable water is filled in the tubes after filtering with a four-layered cotton cloth. The water gets heated in the stagnation mode by solar energy, making it potable. Tests done in laboratories have shown that filtered water heated either to 60 degrees for 15 minutes or 45 degrees for three hours inactivated all the coliforms, according to research results published in journal Current Science.
Dr. Anil K Rajvanshi, who led the research team, explained, “Dirty water needs to be filtered with a cloth to remove impurities. For instance, most of E Coli is attached with dirt. That’s why muddy water from rivers and canals during rainy season causes diarrhea and typhoid. Basic filtering using a cloth filter, followed by heating through solar energy helps remove E. Coli”.
Two purifiers installed in the institute have been working for the past one year. “Only for three days in the whole year, water temperature was below 45 degrees and on some of the cloudiest days when it was raining the tubular solar collectors heated the water to 45 degrees for three hours to make it potable,” the study said.
Dr. Rajvanshi said, “Such tubes are available in the market for about Rs 150 to Rs 200, but are coming from China. Nobody makes them in India. The frame can easily be fabricated in any rural workshop. For large scale production, a lightweight frame can be shipped with the tubes. So with a single spanner, the whole unit can be assembled. Our present design is based on this ease of assembly and costs about Rs 3000”. He said the next step would be to design systems which can use the waste heat from purified water for refrigeration. “Water in the tubes can go as high as 80 to 90 degrees and it has to be cooled for drinking. Instead of wasting this heat, it can be used for refrigeration to produce ice via an absorption refrigeration system.