http://machinedesign.com/article/using-the-sun-to-disinfect-water-1103A team of engineers at Purdue University has built a prototype of a machine that disinfects water using UV radiation from the sun, a potential boon for the world’s 800 million people who lack access to safe drinking water. The UV radiation inactivates waterborne germs by damaging them so they cannot reproduce. The device consists of a parabolic reflector with a transparent pipe running down the middle. Water flowing through the pipe gets exposed to the sun’s radiation during the day.
The trough-shaped reflector was made by lead engineer Ernest R. Blatchely III in his garage. To make the reflector reflective, the team lined it with aluminum foil. The trough itself is made of paulownia wood from a tree that grows rapidly in equatorial regions, an area which often doesn’t have sources of clean water. The wood is light, strong, and stable, so it will not warp, twist, or crack in climates that are either dry or humid, or those that swing back and forth between the two.
In tests at the college’s Indiana campus, the $100 device worked against E. coli bacteria, but not against the germs that cause cholera, typhoid, or cryptosporidiosis. The team plans on testing other, more-reflective materials such as metallized plastics, similar to the materials used to package potato chips. Such materials are said to be twice as reflective as aluminum foil. The team will also automate the process, adding timers and valves so they can control how fast water speeds through the pipe and how long it’s exposed to sunlight. Plans are to determine how much exposure to tropical sunlight is needed to inactivate the target pathogens, and then to program the timers accordingly.
