BROOKLYN, New York—A conveyor belt is keeping material flying past at speeds that require both concentration and rapid eye movement if you wanted to track a single item. Above the constant roar of all the heavy equipment, it's just possible to make out the brief hissing of jets of high-pressure air. Those jets are produced where the conveyor belt ends, and most of the material plunges onto a second belt below. Each hiss, however, causes a carefully chosen item to leap off the end of the belt and soar into a different collection area, where yet another conveyor belt takes it on its way.
The process of carefully choosing which items to sift out is all done without human intervention. It's based on how that object reflects light that's outside the range of human vision.