Digital watermarks: sort post-consumer waste more intelligently

How can plastic packaging become intelligent? By providing them with digital watermarks that can be read by sorting systems and thus simplify the sorting process. The fact that this technology works was proven in the pioneering HolyGrail 1.0 project with a proof of concept.

Now the project is going into the second round: Under the auspices of AIM, the branded goods industry became active in order to test the technology of digital watermarks on an industrial scale and to evaluate it with regard to its economic viability. Eva Schneider explains in this interview what advantages watermarks offer the industry and how they can be applied in the future.

What is the HolyGrail 2.0 project about and what results do you expect?

Eva Schneider: One of the most pressing challenges in achieving a circular economy for packaging is finding a way to accurately sort post-consumer waste, consequently resulting in more efficient and higher-quality recycling. Digital watermarks for packaging have the potential to revolutionise this process, opening up new possibilities that are currently not feasible with existing technologies.

Digital watermarks are imperceptible codes, the size of a postage stamp, covering the surface of a consumer goods packaging and carrying a wide range of attributes. The aim is that once the packaging has entered into a waste sorting facility, the digital watermark can be detected and decoded by a high resolution camera on the sorting line, which then is able to sort the packaging in corresponding streams. This would result in better and more accurate sorting streams, thus consequently in higher-quality recyclates benefiting the complete packaging value chain.

How does the project proceed?

Schneider: The project includes 3 different phases: (1) the development of the prototype sorting and detection unit combining NIR and digital watermarks detection, (2) the semi-industrial test phase, and (3) the industrial test phase. In this way, HolyGrail 2.0 looks into scaling up the technology from current Technical Readiness Level TRL 6 – technology demonstrated in relevant environment to TRL9 – actual system proven in operational environment as well as proving the business case of the technology at large scale, with the objective to make it an automatic choice (high ROI) for the waste industry to invest in after the initiative. The results that will be achieved within the (semi-)industrial trials and published in a final techno-economic analysis report will reveal whether the packaging value chain can scale up digital watermarks on packaging for improved sorting and really get this technology to where it needs to be. A successful demonstration of the technical and economic viability of the technology would inspire more countries and waste management operators to implement this new sorting technology.

 What successes have you been achieving so far?

Schneider: To date, the first prototype, which was developed by Pellenc ST and Digimarc and which combines the digital watermarks technology and NIR/VIS infrared for sorting of packaging waste, achieved a >95 percent ejection rate. This prototype was installed in the Amager Resource Centre (ARC) in Copenhagen for the semi-industrial test phase. For four months, trials and demonstrations with around 125.000 pieces of packaging representing up to 260 different stock-keeping units (SKUs), all prepared by HolyGrail 2.0 members, were held in Copenhagen. Engineers tested for several parameters including the speed and accuracy of the system, to ensure its ability to withstand the pressures of full-scale industrial operations. Beginning of February 2022, the prototype was shipped back to the headquarters of Pellenc ST in France for the final tests.

How are the digital watermarks applied to the products?

Schneider: Digital watermarks can either be printed on the packaging or embossed in molds. Digital watermarks for print consist of repeated tiles, whose pieces can be combined together to recover a barcode and which are applied by the encoder in a mosaic manner. For enhancing the artwork with digital watermarks, existing pixels are used, hence, this process does not require special inks or printing processes. On the other hand, digital watermarks for molds are the result of micro-topological variations in the substrate of the mold, creating signal tiles.

How does the technology for reading them work and what technical requirements do the recycling companies have to bring along?

Schneider: Digital watermarks on packaging would be detected through an add-on module that would be mounted onto existing detection sorting units at sorting and recycling facilities, and would be used in combination with existing NIR detection. The aim is that once the coded packaging has entered into a waste sorting or recycling facility, the digital watermark can be detected and decoded by a high resolution camera of this add-on module on the sorting line, which then – based on the transferred attributes (for example food versus non-food) – is able to sort the packaging in corresponding streams.

What advantage do the recycling companies gain from the information contained in the watermarks?

Schneider: Waste sorting and recycling facilities will have the possibility to sort packaging waste into more accurate streams that are currently not feasible with existing technologies. Operators could expect a general increase of product quality, by for example identification of PET trays suitable for recycling. In general, all kinds of recycling (mechanical, dissolution and chemical like pyrolysis) would benefit from a controlled feedstock to further optimise the recycling process. The digital watermark codes are removed during the shredding step at the recycler, so they can be used for the first sorting steps at sorting and recycling plants without problems. Furthermore the recycled material can be used again in any new application and a new digital watermark code could be tailored to the new packaging application.

How do you think such watermarks will be used in the future?

Schneider: HolyGrail 2.0 holds the potential to be a game-changer for the sorting and recycling industry in Europe, achieving a truly Circular Economy for packaging. In addition, next to encoding a "digital recycling passport", digital watermarks also have the potential to be used in other areas such as consumer engagement, supply chain visibility and retail operations.

HolyGrail 2.0 aims at proving the business case of the technology at large scale, with the objective to make it an automatic choice (high ROI) for the waste industry to invest in in the future. The results that will be achieved within the (semi-)industrial trials and published in a final techno-economic analysis report will reveal whether the packaging value chain can scale up digital watermarks on packaging for improved sorting and really get this technology to where it needs to be. A successful demonstration of the technical and economic viability of the technology would inspire more countries and waste management operators to implement this new sorting technology, in the EU and possibly beyond.