Sorting plants are a more or less sophisticated technology response to the recovery of materials from municipal waste, extracting material fractions from collected waste.
There are three overarching collection/sorting configurations that are typically used to recover material:
All three configurations use sorting plants to produce separate material fractions. The three different collection configurations required different sorting technologies and result in different quantities and qualities of output material for recycling.
Generally speaking, quality of output materials increases as the quality of input materials increases. Sorting mixed municipal waste typically results in a metal, plastic and glass fractions for recycling, together with a large amount of RDF. Typically the aim of sorting mixed municipal waste is to reduce the amount of waste going to landfill, rather than achieving high recovery rates for recycling. The quality of the materials removed is therefore typically lower than that from plants sorting mixed dry recyclables or source separated recyclables. The quality can be increased by separately collecting biowaste, removing the main contaminant from mixed municipal waste.
Sorting mixed dry recyclables will result in relatively clean fractions of paper, plastic, metal and glass (or whatever fractions have been collected together) for direct use by industry or for further sorting into specific types (for example, from a gross plastic fraction into PET, HDPE, PE, PP). Source-separated clean fractions can be sent directly to this fine sorting, and results in the highest quality recycled material.
This illustrates the fundamental symbiosis between collection and sorting systems. They are the two complementary components of the system for extracting materials from waste.
Ambitions at the national and international level for material recovery have a strong influence on the type of collection/sorting system employed. Generally speaking, the more stringent the targets for material recovery, the stronger the driver for source separated multi-stream collection and subsequent sorting.