Tweet Recycling sorting at River Hills Recycling CenterPhoto: Eric England A sound not unlike rain patters incessantly at the back of the open-air building where trucks dump material at Nashville’s River Hills Recycling Center. This is the largest recycling facility in Nashville, and that sound is a thunderstorm of sorts. It’s a steady stream of pill bottles, drink cans, cardboard boxes and other materials hurtling through a large machine called a drum feeder, which sends the items down a conveyor belt to be sorted. Although operations manager Dilan Vince says the drum feeder can handle about 20 tons of material per hour, not everything that ends up at the River Hills facility is recyclable. In fact, Jenn Harrman, the waste reduction program manager for Metro Public Works, says as much as 46 percent of what Nashville puts into residential recycling bins is unusable. She says that’s a high contamination rate compared to other cities, but Metro is working to educate residents with new initiatives like the Waste Wizard app on the Public Works website. The app launched a few weeks ago, and Harrman says her department is constantly adding to the 300 materials residents can quickly search and learn how to recycle — or if they can be recycled at all.