All You Can Eat?

Following the announcement that scientists have engineered an enzyme that can digest plastic, Vanden Recycling’s David Wilson asks what do these “plastic eating enzymes” mean for rPET…

PET, as a material, is not difficult to recycle, especially when it comes in the form of single polymer drinks bottles. This is the type of material that the recycling sector can easily handle.

Furthermore, there is huge global demand for recycled PET (rPET) and that’s only going to grow as packaging designers increasingly incorporate higher quantities of recycled materials into their designs.

Despite this, our oceans are unacceptably polluted with plastic and many, many new solutions are being brought forward to resolve the situation.

We’ve recently been told that enhanced plastic eating enzymes could revolutionise PET recycling. It’s certainly an interesting piece of research, but this technology is at its very early stages of development1.

The fact is that of all the types of plastic under scrutiny, PET is low down on the list. If this enzyme is purely going to focus on PET, it is unlikely to have an impact on the way we recycle or increase the quantities of bottles recycled. If the enzyme could be adapted to work on more difficult to recycle plastics or even mixed plastics, it becomes more exciting.

But we need to be cautious. We need to understand the operating conditions for enzyme recycling. It could be that we are still reliant on existing recycling infrastructure to collect, sort and wash the PET, before adding an additional step to introduce the enzymes.

Electron microscope photos of enzyme/substrate interactions. Bryon Donohoe, Nic Rorrer and Gregg Beckham are co-authors of a paper on plastic (PET) eating enzymes, “Characterization and Engineering of a Plastic-Degrading Aromatic Polyesterase” being published PNAS. (Photo by Dennis Schroeder / NREL)

In effect, we would simply be replacing granulation with enzymes. How practical and economically viable is this? What conditions (and energy levels) are needed to provide the optimum processing environment? And can it cope with a level of contamination that would be typical on an industrial recycling scale? These are all answers that will come from the current trial.

There has been some talk of the enzymes being sprayed onto patches of polluted oceans to clear them of floating plastics. I’m mindful that this could be like a previous suggestion whereby we could use moths to eat plastic bags2, however this was shown to devastating to the already declining bee population. Could these enzymes solve one problem but create another?

Perhaps we need to look more closely at why plastics end up in the ocean in the first place and find solutions to those problems before we start spraying enzymes into them.

The real challenge with PET recycling is not in its processing, but in its collection. With 1m plastic bottles bought around the world every minute, and only half of these recycled, you can see where the problem lies3.

To improve the amount of PET being recycled we need to face up to the issue of collection, particularly when consumers are “on the go” and segregated recycling bins are not available. This is a big part of the littering problem and makes it difficult to capture good material for recycling. This is where the proposed deposit return scheme could really make a difference.

As well as enzymes, we’ve also had the launch of the UK Plastics Pact by WRAP and the Government recently. Under this, the target is that 100 percent of plastic packaging will be reusable, recyclable or compostable by 2025. If we reach that target, and I hope we do, that represents a transformation of the plastic packaging designed and collected in the UK.

When it comes to new solutions, it is essential we consider their full impacts before leaping in. Will plastic eating enzymes improve the process? Does biodegradable or compostable mean that the plastic literally disappears? Or does it break down into microscopic pieces? In which case, do we know that this is a safe option? And how easy will it be for recycling infrastructure to sort biodegradable and compostable plastics from those materials that need granulation?

One thing I am certain of is that right now we have huge demand for rPET, particularly in the bottled drinks market. Would a plastic eating enzyme grow this further?


Darrel Moore

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