In Salt Lake County, we use a process called “single-stream” recycling, where residents can put all their approved recyclables into one bin. These materials are collected and taken to a materials recovery facility (MRF) where they are sorted, baled, and sold to manufacturers, who turn them into new products. The sorting process is mostly automated, using various screens, magnets, and optical sorters to identify materials. MRFs are built to only sort certain items, so any additional materials are contaminants.
For some materials, like newsprint, plastics bags and Styrofoam, these materials can be recycled, but must be separated and taken to an approved drop-off location. Do not place these materials in your recycling bin, as the MRF cannot separate them and they may be contaminants, which are discarded as trash.