How do municipal sanitation departments separate recyclables?

Most cities have recycling services in addition to normal trash pickup—and sometimes yard waste removal as well.

Into the bin go five categories of recyclable waste—paper, glass, plastic, aluminum, and nuclear. I suspect a lot of non-recyclable plastics and waste is often placed in the containers, as well as glass that gets broken and newspapers that get wet.

Ideally, there would be a way to ‘package’ and separate types of recyclables but we are told, in Memphis at least, that it is not necessary to separate categories of recyclables.

Soooo—how can these things be separated at the recycling plant? It would be extremely time consuming and possibly hazardous to have a workforce who does this. And I personally cannot imagine how machines or sifters could do this.