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Will Digital Watermarks Really Be Europe’s Holy Grail?

Updated: Nov 3, 2021

The European Union has set a laudable goal in using advanced technologies to boost recycling rates.

The problem with packaging

Consumer-grade packaging waste is an ongoing environmental calamity. In both the United States and the European Union, two of the largest and most developed global economies, only ~50-60% of packaging waste is recycled. Despite the extensive infrastructure that has been set up for the explicit purpose of recycling on both sides of the Atlantic, tens of millions of pounds of single-use packaging is shoved into landfills or incinerated each year, polluting our shared Earth for generations to come. This includes the especially pernicious category of single-use plastics, of which about 9% is recycled properly in the United States and perhaps 14-18% is recycled worldwide. Even global ‘bright spots’ are relatively dim. Take China, which reportedly has a relatively impressive (but still objectively unsustainable) plastic recycling rate of 30%.

Globally, more than 300 million tons of plastic are produced every year, about half of which is estimated to be single-use. This is roughly equal to the body weight of all humans on the planet combined. Over 8 billion tons of plastic has been produced historically, and essentially all of that still exists in the biosphere, aside from the 12% that has been incinerated. The rate of plastic production is rapidly increasing, with far more plastic produced in the last two decades than in the entire 20th century. A growing global population, rising living standards, and the normalization of environmentally destructive behavior by developed countries has pushed the demand for plastics into a “J” curve. If growth continues as expected, plastic production in 2050 will be more than four times greater than it is today.

It is absolutely critical that mankind finds a way to dramatically increase recycling rates before that happens. Consumer apathy, widespread misconceptions about how recycling works, insufficient regulatory action, and careless packaging design have all contributed to this sorry status quo, and all of these factors must be improved. However, a systemic under-investment in waste management infrastructure is perhaps the most blame-worthy and most actionable facet of the problem. If recycling centers were able to sort and process a greater fraction of the items they receive, less new plastic would need to be produced. So how can we make that happen?

Searching for the Holy Grail

The European Union thinks it has an answer. In 2017, the transnational bloc launched its HolyGrail program, a public-private partnership with the goal of covertly tagging all recyclables with embedded data. This includes information that machines can use to instantly categorize and sort waste, saving an enormous amount of labor and ensuring that fewer recyclables get left behind. Stakeholders throughout the Eurozone have agreed that this sort of standardization is not only a crucial goal in and of itself, but will also serve as a catalyst for other eco-friendly changes to package design and manufacturing. In a welcome move, the EU has also committed to banning single use plastics entirely by 2030.

Early HolyGrail stakeholders identified two possible tagging methods that could be adopted by the EU: chemical tracers and digital watermarks. The consortium decided to thoroughly evaluate each of these two solutions and ultimately select one of them to become a new industry standard throughout Europe. Let’s briefly explain what chemical tracers and digital watermarks are before exploring their pros and cons:

Chemical tracers are additives that can be mixed into inks and dyes, printed directly onto packaging, or incorporated directly into glass, plastics, and other materials. Tracers have properties that can be detected (and differentiated) using straightforward equipment. For example, some tracers are designed to be ultraviolet (UV) active. In this case, objects sorted for recycling will be exposed to UV light. An object with no tracer will have no reaction to the light, but an object with a tracer will emit a unique signature that can be detected by a reader. By mixing and matching various different UV-active tracer compounds, it is possible to tag different recyclables according to which stream they should be sorted into – food packaging, compostable packaging, multi-material items, etc.

Digital watermarks are extremely small and subtle patterns that covertly cover the surface of an object, usually in repeating postage stamp-sized tiles. The patterns on these tiles can be created either by making slight alterations to the pixels in a printed design, or by using extremely small etchings to make tiny topographical variations in the material of the packaging itself. There are a functionally infinite number of possible patterns to use, many of which are imperceptible to human eyes. These patterns are also read by digitally connected cameras using machine vision.

Chemical Tracers vs. Digital Watermarks

While the outcome of both solution types is theoretically very similar, the routes they take to get to that outcome are different and contain significant pros and cons. In the context of HolyGrail, the main “pro” of chemical tracers is that they can be consistently read under difficult conditions. This method does not require tags to be a certain size or shape and allows for omnidirectional scanning. Identification of chemical tracers is reliant on the presence or absence of a certain combination of chemicals rather than pattern recognition. Because of this, it is possible to infuse these chemicals directly into materials like plastics and glass, regardless of their shape as size, and read them with machines. These features are compelling in the context of recyclables, which are often broken, incomplete, or dirty.

The main “con” of chemical tracers lies in the simple fact that they involve adding a physical medium to the object being scanned. If an economy like the EU were to adopt a solution based on chemical tracers, it would require adding tiny amounts of food-safe tracer to billions of units of packaging each and every year. This would also involve the purchase and installation of large amounts of excitation sources (e.g. ultraviolet lights), although the HolyGrail consortium is of the belief that retrofitting existing recycling centers to accommodate either solution would be less expensive than any realistic alternative.

As you might expect, the major “pro” of digital watermarks is the fact that this solution does not require the addition of custom-made chemical formulations to connect readers with tagged objects. Instead, this system relies on machine vision to detect nearly imperceptible changes made to the design of normal packaging materials. In addition to this, digital watermarks are a more established technology than chemical tracers and are currently used for real-world authentication and track-and trace applications, although this was not the case when the HolyGrail initiative began in 2017.

The most important “con” of digital watermarks is essentially the inverse of the “pro” for chemical tracers – in order to work properly, readers need to have a direct line of site to a clean, unobstructed, postage-stamp sized scanning area. While this wouldn’t be a huge concern for most applications, it’s possible that a significant fraction of consumer packaging waste would not meet these criteria, resulting in items that fail to scan properly. On top of that, digital watermarking is limited to printed or etched tags only. This is distinct from chemical tracers, which can be mixed or extruded directly into plastics, glass, and other common materials.

The European Union deserves plaudits for being the world’s first major economy to make a real, substantial commitment to ending the destructive linear economy of consumer waste. We have only one Earth, and mankind is burning through its resources and polluting its environs at an unsustainable and immensely damaging pace. As you may have guessed from the title of this piece, the EU ultimately selected digital watermarking over chemical tracers. We are now at the beginning of HolyGrail 2.0, which will see large scale pilot trials of this technology at waste processing centers throughout the Union. Time will tell whether they made the right decision, and other polities – including the United States – will be taking notes.


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