ISEF: Sterilizing Water with Trash!

This is the sixth in our series of projects from ISEF that we will be covering. Many more to come. Thanks to Intel for flying me out and putting me up so I could cover the conference.


Access to clean drinking water has been, and will be, a global concern. Even when water is available, sometimes in abundance, it can be unsuitable for drinking due to microbial contamination. This is often the case with river water in Belo Horizonte, Brazil, ioand Veronica Santos and Julia Parreiras have developed a low cost / no cost disinfectn solution for those who use rivers, or other unpotable sources, to obtain their drinking water.

The system can be created and assembled using 100% recycled materials, in fact, the entire system is made out of waste. The basic principle is to heat water using a solar concentrator, thereby killing bacteria and making the water safe to drink. Of course you don’t just find solar concentrators every day, so they built, and will teach those in need to build, their own using scrap cardboard and a reflective surface.

When I asked if aluminum foil was readily available in rural Brazil, thinking they used that for reflection, they smiled and pointed out that if you turn an empty bag of potato chips inside out, you get a very good reflective device. Their concentrators, made from such crude materials, are very efficient. They have achieved temperatures upwards of 70C, but only need to sustain at least 50C for 4 hours to ensure disinfection.

To hold the water they use PET bottles, half painted black in order to absorb more heat, making the process more effective. They chose PET bottles because, from their spectrophotometerical analysis, they afforded more UV transmittance and were thicker, therby extended their usable life. They also found that with some modifications, allowing adjustable reflectors for the concentrator, the total exposure time could be reduced to 2 hours from the original 4, getting potable water to whoever needs it that much faster.

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