This article is part of our Sustainable Shelf series, originally published on theguardian.com

‘The holy grail of packaging recycling’: can digital watermarking put an end to sorting woes?

A guest article by Sarah LaBrecque, a freelance journalist, writing for The Guardian with a particular focus on sustainability and B2B topics
(Illustrations: Bee Johnson for The Guardian)

Illustration: Bee Johnson for The Guardian

A new pan-European project is developing technology to ensure that what goes into a consumer’s bin goes on to be correctly recycled

If there’s one thing the British public likes to complain about, it’s recycling. What gets recycled, what doesn’t, where it ends up and who’s paying for it. And if the sorting machines at recycling plants could talk, they would probably be moaning too.

When recycling arrives at material recovery facilities (MRFs), the first step is to sort items into different material streams. But this isn’t always straightforward. “Sometimes it’s really hard to identify what kind of material it is,” says Thorsten Leopold, director of international packaging for home care at the consumer goods company Henkel. “If the sensors cannot fully identify the material or if it’s covered by a sleeve [or label], then this can give the sorting machine some headaches,” he says.

With a target set by the EU Plastics Pact for 100% of plastic packaging to be reusable or recyclable by 2025, it’s vital that action is taken on all sides. This includes addressing packaging design and consumer behaviour and, crucially, the effectiveness of recycling technologies – essentially the lynchpin of the entire system.

Now, a new pan-European project with more than 85 participating companies and organisations could help ensure that what goes into a consumer’s bin actually goes on to be correctly sorted and recycled. Under the HolyGrail 2.0 project, facilitated by AIM, the European Brands Association, digital watermarking technology will be trialled on an industrial scale. “This means that on the packaging there is an embedded, invisible code that cannot be seen by the naked eye but can be seen by cameras,” says Leopold. The watermark, a bit like a QR code and about the size of a postage stamp, is printed across the bottle and contains information about the product. It could identify what the item is made of or whether it’s a food or non-food product. Once the watermark is read, the item is sent off to the correct waste stream. Importantly, the more accurate the sorting function in MRFs, the higher quality the reprocessed material at the end, which is beneficial for companies looking to buy up that recyclate.

Illustration: Bee Johnson for The Guardian


The HolyGrail 2.0 initiative combines the three key ingredients needed for a circular economy: innovation, sustainability and digitalisation.

And why the curious name? Is the technology so promising that it could be, in fact, the answer in regards to efficiently sorting recycling? Well, actually, yes. “It makes reference to the huge potential of digital watermarks to tackle today’s problems in sorting and recycling packaging,” says Eva Schneider, sustainability and communications manager at the European Brands Association. “[Digital watermarking] has the potential to become the holy grail of packaging recycling.”

Henkel is one of the project pioneers, and has already released a product, its bottle for Vernel fabric softener, which contains this technology. It has been released in Germany, and Leopold is excited about its potential. Not just in regards to more sophisticated and efficient recycling, but the other applications that the watermark could be used for. He picks up his smartphone and scans a Vernel bottle. Up pops the product’s website. He explains that the consumer could access info about the product, perhaps related to its sustainability credentials. Within the supply chain and logistics, there are potential benefits too. “Maybe in future, automatic robot systems could scan an entire aisle and directly see what [needs to be restocked],” he says.

One of the main goals of the EU Plastics Pact (and, indeed, the US and UK Plastics Pacts as well) is to create a circular economy for plastics. This means that materials are kept in use for as long as possible, and nothing is wasted. Developing technologies and improving efficiencies around recycling is an important lever in moving towards this goal. Indeed, the precursor to HolyGrail 2.0 was an initial exploration under the New Plastics Economy initiative run by the Ellen MacArthur Foundation to look into chemical tracers and digital watermarking.

Chemical tracing involves embedding a marker in the label or plastic resin that shows up fluorescent under UV light, so it can be detected by specially designed sorting machines. Although an interesting technology, it was decided that digital watermarking was the more promising of the two technologies and, thus, it became the sole focus of HolyGrail 2.0.

Leopold points out, however, that at present there are no recycling plants equipped with the cameras needed to detect the digital watermarks. “We are in a very early pioneering phase,” he says, emphasising that the bottles are being tested and sorted in a lab environment for the time being. He is hopeful that this testing phase will prove the viability of the technology, and pave the way for a larger rollout. And Schneider is cautiously optimistic. “Even with promising results for the basic proof of concept on a test sorting line (under the first iteration, HolyGrail 1.0), and successful cross-value chain engagement, it is important to keep ourselves grounded,” she says. “The results we achieve over the next year will reveal whether we can scale up digital watermarks on packaging and really get this technology to where it needs to be.”

Nevertheless, there is no doubt in Leopold’s mind that it has legs, particularly because it is multipurpose. “It brings big advantages, especially in the retail space,” he says, explaining that at the checkout the entire item could be scanned, instead of the barcode that sometimes takes a while to find. “This means that checkout times could be decreased by 30% or so, which is a very interesting benefit for retailers.”

The team behind HolyGrail 2.0 is actively looking into all these applications, but Schneider is keen to point out that the main focus is to pioneer solutions around smart packaging. “One of the most pressing challenges in achieving a circular economy for packaging is finding a way to accurately sort post-consumer waste. Digital watermarks have the potential to revolutionise this process,” she says. “The HolyGrail 2.0 initiative combines the three key ingredients needed for a circular economy: innovation, sustainability and digitalisation. Initial proof-of-concept demonstrations have already shown what digital watermarks can achieve on a test sorting line. Now, it’s time to take this testing to the next level.”