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Engineered enzymes can turn plastic waste into carbon

Wednesday 02 Sep 20

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Peter Westh
Professor
DTU Bioengineering
+45 45 25 26 41

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Mette Haagen Marcussen
Head of Communications
DTU Bioengineering
+45 23 71 23 10

Plastics

Plastics have been mass produced since the 1950s. This has resulted in more than 8,300 million tonnes of new plastics. Of these, only 9 per cent has been recycled, 12 per cent has been incinerated, and 79 per cent has ended up in landfills or the natural environment. If these trends continue, there will be an estimated 12,000 million tonnes of plastic waste in landfills or in the natural environment by 2050. Source: Production, use, and fate of all plastics ever made

New methods developed at DTU Bioengineering have the potential to convert plastic waste into a new source of carbon.

Biorefineries, which produce green energy from e.g. residual products from agriculture, are emerging much slower than expected. The reason is that the recent year’s low oil prices make it difficult for the green energy to compete with the fossil energy. This poses the question of what to do when you have spent the last 12 years developing new methods for engineering enzymes to degrade biomass faster and more efficiently.

For Professor Peter Westh from DTU Bioengineering, the answer was obvious: You find another material that can be degraded by enzymes, and in this respect, plastics were ideal because biomass and plastics are both polymers.

This means that they are made up of a lot of repeat units, which are linked together successively. The same group one after another. The enzymes cut these free so they dissolve, and these substances can be used to make new materials such as plastics or as a more general substitute for oil in the petrochemical industry, where extractions from oil and gas are used to produce substances for plastics, synthetic rubber, binders for paint, etc.

“There’s a huge demand for carbon worldwide, which today is extracted from fossil sources. We’re therefore on the hunt for a new source of carbon which exists in vast amounts, which is not fossil, and which can be broken down into the molecules needed in the petrochemical industry. We have a major problem with accumulation of plastics—and plastics contain carbon—so if it’s possible to extract carbon from the large amounts of plastic waste, we can kill two birds with one stone,” says Peter Westh.

Since the mass production of plastics took off in the 1950s, only 9 per cent has been recycled, 12 per cent has been incinerated, and as much as 79 per cent has either been accumulated in landfills or is scattered in nature. If the current trends continue, it is estimated that by 2050 roughly 12,000 million tonnes of plastic waste will be in landfills or in nature.

"The market for biological processing of plastics is promising, and Denmark will be able to play an important role in exporting technology and materials such as plastic-degrading enzymes. In this way, we can help facilitate the transition to a circular plastics economy as a better solution to the world’s carbon consumption."
Professor Peter Westh, DTU Bioengineering

Plastic waste therefore has great potential to become a source of carbon, but the carbon is not readily available, and this is where the enzymes come into play.

“Our method is to find some enzymes in nature, which we then reorganize a little so they get better and faster. An enzyme consists of a few hundred amino acids. We might switch out 2 or 8 or 12, and that’s enough to make them more stable, or make them better at cutting up the polyester,” says Peter Westh.

Since plastics are insoluble, enzymes can only attack on the surface, and the process is therefore generally slow. Peter Westh’s research is therefore focusing on optimizing the enzymes to make them faster and more stable, so each enzyme can cut up as much as possible before it degenerates. If enzymatic degradation of plastics is to become good business, it is absolutely essential that the conversion is quick and that the process is stable.

Peter Westh and his research group have discovered that the enzymes are inhibited by only being able to attack the plastics in a limited number of places, and together with Novozymes, they have now applied for funds from Innovation Fund Denmark to find a solution to this challenge. If they are awarded the funds for this, they expect to be able to solve the problem over the next four years, and this will help put Denmark in a position of strength in the emerging market for biological processing of plastics.

Recently EU has passed legislation requiring that a tax of EUR 0.80 per kilo be imposed on newly produced plastics - i.e. plastics which are not made from recycled plastics - from 2021. This is equivalent to approx. 15 per cent of the costs of the material which the plastics are made of, and is expected to have a positive impact on the recycling of plastics.

“The market for biological processing of plastics is promising, and Denmark will be able to play an important role in exporting technology and materials such as plastic-degrading enzymes. In this way, we can help facilitate the transition to a circular plastics economy as a better solution to the world’s carbon consumption,” says Peter Westh.

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