44 March 2016
‘More than 16 million tonnes of waste paper are processed each year in Germany,’ said
Philip Klippel of Munich University at the bian-
nual Sensor-Based Sorting congress in Aachen.
The researcher cited a ‘huge variety’ of visual
features in this waste stream and had looked to
near-infrared spectroscopy to ‘break the curse of
dimensionality’. Trials successfully classified 10
different types of paper while managing a 78%
recognition rate by taking 175 scans per second.
‘A realistic view’
Almost 4 million samples of dry paper and card-
board were analysed in the sensor-based sorting
project overseen by Klippel. The material was
sorted at an operational German recycling facil-
ity with a capacity of 130 000 tonnes per year
in order to form ‘a realistic view’ of the results.
The system used 172 near-infrared tracks and
1204 RGB (Red-Green-Blue) tracks at 175 scans
per second and at a conveyor belt speed of 0.5
metres per second, covering a width of around
90 cm.
‘Our classifier implementation system is a
classification and regression tree (CART) that
allows a ranking of features by importance,’ said
Klippel, who tested both coated and uncoated
samples. Overall results were corrected for easy
recognition of the background (conveyor belt)
so that the figures would not be ‘too optimistic’.
Klippel and his team now want to extend the
method to other waste streams, especially plas-
tics.
A matter of purity
‘I’m sure that all recyclers will agree that when
you get 95% purity, you naturally want 96% or
97%, but getting the most out of your materi-
als is tricky and, not least, expensive,’ Dr Aude
Maitrot of resource management specialist Veo-
lia told delegates in Aachen. ‘So Veolia wanted
to investigate how to refine the results without
having anyone touch the material.’
She detailed the success of the I-SORT3R pro-
ject, which centres around a semi-automatic
S E N S O R – B A S E D S O R T I N G By Kirstin Linnenkoper
A human-machine interface
Cutting-edge
technology delivers
recycling success stories
The latest of the biannual Sensor-Based Sorting congresses focused once again on some of
the breakthrough technologies addressing the sorting and separation of various materials.
This article takes a trip through some of the fascinating science described and debated during
the two-day event held in Aachen, Germany, towards the end of February.
