Single-stream recycling seems so simple. There is a bin. You put everything that's not trash—whether it's paper, plastic or metal—into that bin. The city comes and takes that bin away. Easy.
The first communities to use this system, in the 1990s, were in California. By 2005, about a fifth of all U.S. communities with recycling programs used it. By the beginning of this decade, that number was more like two-thirds.
Single-stream recycling has two main advantages: Since it's so much easier than sorting out recyclables for individuals, it increases household recycling rates, and since it's easier to dump one can of stuff into a collection truck with one compartment, it saves cities money. But someone, eventually, does have to sort out the paper from the containers and the glass and cans from the plastic and the different types of plastics from one another.
Material recovery facilities (called MRFs, which rhymes with "smurfs") have gotten pretty good at doing that sorting, with combination of machines and human workers: