Fields of Research in Optical Sorting of Different Types of Waste

Optical sorting appeared for the first time in 1994 in Germany, France and in the USA. Initially, it was limited to the recognition of the main packaging types, as found in the "yellow bin", using the NIR spectroscopy to differentiate molecular bonds: PET, HDPE, PVC, Tetrapak were the main targets. Colour sorting was later introduced for very fine colour nuances (e.g. clear vs light blue bottles). Today, most MRFs in Europe use Optical Sorting for packaging.

by Dr. Antoine Bourely

A second sorting stage in recycling plants was needed, in order to be able to recycle high quality resins in a true closed loop: bottle to bottle PET recycling required less than 50 ppm final contamination, especially in PVC. This was achieved as early as 2001 in France, and a guaranteed contamination level of 10 ppm was achieved in 2011. However, the difficulty remains, as new types of bottles with specific challenges keep appearing: multilayers, blends, PVC labels, etc. Almost all recycling plants use Optical Sorting, but new problems keep arising every year.

The collection of all dry recyclables (packaging and paper / board) into one single stream is very common, especially in North America. In a Material Recovery Facility (MRF), a mix of mechanical solutions separates this stream into two fractions: flat bodies (paper/board), and hollow bodies (packaging). Optical sorting is then used for clean-up, e.g. removing remaining papers in bottle streams.

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published: TK Verlag - Fachverlag für Kreislaufwirtschaft, Waste Management, Volume 3 (Oktober 2012), 10|2012
Keywords: Collection, Material Recovery, Policy Tax Instruments, Sustainability, Climate, Paper Fiber, Plastics, France, Germany