With the successful validation of its advanced sortation capability in an industrial environment, the digital watermarks initiative HolyGrail 2.0 has moved another step forward. The technology performed especially well in relation to the separation of food and non-food waste streams.
The industrial trials took place at the Wellman/Indorama recycling plant in Verdun, France, using a prototype detection module developed by machine vendor Pellenc ST and digital watermarks technology provider Digimarc, as part of the HolyGrail 2.0 Initiative.
This assessment focused on a PET waste stream, with two primary objectives – to remove watermarked non-food PET bottles from the stream to meet EFSA guidelines i.e to reduce non-food PET content in a food PET stream to less than 5%, and to create a non-food PET output stream.
Carried out in January and February 2023 under the supervision of the HolyGrail 2.0 technical team, this most recent assessment built on the success of the previous semi-industrial trials performed in 2021 and 2022. First, 5.6 tons of watermarked non-food PET bottles were produced, which were then mixed with post-consumer waste at material recovery facility Suez in Epinal, France, to mimic typical waste workflows. Multiple fractions of mixed waste containing around 200,000 watermarked bottles were created, baled, and shipped to the Wellman/Indorama recycling facility for sorting tests.
The trials were carried out on a fully operational line – equipped with the digital watermark detection module – working in standard operating conditions with nominal throughput of 3 tonnes/hour and belt speed of 3 metres/second. An NIR unit was also used in combination to assist with blowout.
Detection efficiency was 92.1%, while sorting efficiency was 88.3%, on average. For two-pass sorting, the detection and sorting efficiencies were 95.9% and 95.1% respectively.
These results yet again validate the efficacy of digital watermarks in separating with high granularity – in this case food versus non-food separation. The high efficiencies indicate that use of digital watermarks can reduce impurities in food-grade PET output streams in recycling plants.
