There's a good chance it's been a long time since you bought or even used a CD or DVD instead of digital music files or online streaming. With all of the CDs out there destined to become e-waste, a new method of sewage treatment may give them a new life instead of seeing them end up in the landfill.
“Optical disks are cheap, readily available, and very commonly used,” says Din Ping Tsai, a physicist at National Taiwan University where a group of researchers came up with the idea of using the disks to clean wastewater. Close to 20 billion disks are manufactured annually, and we all know how many we have stowed away in our closets, so it's definitely a way to reuse something that would otherwise become waste.
The team grew tiny, upright zinc oxide nanorods, which act as photocatalysts for breaking apart organic molecules when exposed to UV light, on the surface of optical disks. The disks make for a durable and lightweight platform and they can spin quickly so when contaminated water hits the device, the water spreads out into a thin film that light can easily pass through and then the pollutants are quickly broken down.
The device is about one cubic foot in volume, containing the coated optical disk, a UV light source and a system for recirculating the water to make sure all contaminants are taken care of. In testing, the device was able to break down over 95 percent of contaminants in 60 minutes, working with about 150 mL of wastewater a minute.
The device is small, low-power and efficient and it could potentially be used for domestic sewage processing, urban run-off, industrial effluents, and farm waste. The team is working to make it even more efficient by stacking layers of treated disks in the device.