In the iPod age, many people are wondering what to do with their old CD collections. Here's one possible idea: breaking down sewage.
The video below shows a device built by scientists in Taiwan. At its heart is a CD coated with tiny zinc oxide "nanorods"—a cheap photocatalyst. Using strong UV light, the machine breaks down polluted water as it hits the surface of the fast-spinning disc, letting cleaner liquid fall to the bottom.
Din Ping Tsai, a physicist at National Taiwan University, says his team likes CDs because they spin fast, and are durable and commonly available. Manufacturers still make 20 billion of them every year, he points out. In tests with methyl orange dye, the machine broke down 95% of contaminants.
Clean discs are easier to coat with the agent than dirty ones, Tsai says. But, in theory, there's no reason the machine couldn't use second-hand CDs—even some of your horror choices from the '90s. He hopes to have a full-scale application ready in a few years.