Fruit Waste: How discarded peels could give billions access to clean water

NTU Singapore

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Researchers at the Nanyang Technological University (NTU) in Singapore have successfully demonstrated the conversion of fruit waste into a material that can be used to purify water. The researchers can manufacture the material at a third of the cost since the major component is free.

As per the United Nations report on sustainable development, nearly two billion people on the planet do not have access to safely managed drinking water services. Water purifiers could help in solving this issue, but even the simplest of the purifiers that can be deployed even in remote corners of the planet without access to electricity use products made from coal, which is in conflict with sustainable development.

Conventional solar still is the simplest of water purifiers that consists of a vessel containing undrinkable water and a transparent cover. The cover allows sunlight to pass through and heat the water, which then evaporates and rises inside the setup. The water vapor then hits the inside surface of the transparent cover, where it cools down and trickles down, where it is collected in another clean vessel and is suitable for drinking.

To quicken the process, researchers have used materials that facilitate quicker evaporation of water. However, these materials include ingredients that are sourced from coal either directly or indirectly.

Edison Ang, an assistant professor at NTU, and his research team were looking for something that did not have to be mined and could still be a part of the solar still and found that fruit waste such as orange and banana peels, as well as coconut husks, were the answer they were seeking.

To convert the waste into a usable material, it was first heated to temperatures above 1,500 Fahrenheit (850 degrees Celsius) for a few hours and then mixed with molybdenum. This turned it into molybdenum carbide, a hydrophilic or water-attracting metal that also has a high light-to-heat conversion efficiency.

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During laboratory tests, the material was very effective in converting light into heat and caused seawater to evaporate rapidly. The material is also porous, so water vapor could rise through it as it evaporated before condensing inside the still's cover.

The researchers found that the energy conversion efficiency of coconut husks used in this way was as high as 94 percent. The team is now working on improving the technology further and is hopeful of commercializing it soon.

The method is comparatively cheaper than other approaches to make such material since the input costs are lower. Fruit waste is essentially freely available and only needs to be treated to generate this material.