[gregsq]

This is one of the reasons we have seperate collection bags for recyclable materials in the UK for households. We don't have the benefit of landfill space, and it's economically more efficient to seperate paper, glass, metals and other potentially recyclable materials at source, than at a post process stage. The resident has two bins side by side, and sorts at source.

[ZeroGravitas]

Assuming your talking about the homeowner sorting each type of material seperately, it depends on local facilities. Some have "single-stream" plants that take all recycling mixed together, which seems like it may be the way forward as the sorting machines get more efficient and ingenious.