Every year more than 460 million tons of plastic is produced. Globally, this amount is expected to quadruple over the coming 25-30 years.

Today, plastic is typically recycled by collecting, cleaning, sorting, shredding, and remelting it. This mechanical recycling approach works very fine with homogeneous and clean plastics – but as soon as the plastic waste is made of multi-materials or is contaminated by food remains or other materials, it becomes expensive and complicated. In such cases, new technologies, such as chemical recycling, are necessary, however they make use of strong chemicals or high temperatures, which is still a challenge.

This means that large streams of plastic waste are not properly managed yet and less than ten percent of the plastic that is produced actually gets recycled. The rest is either incinerated, accumulated in landfills or ends up in the environment, where it stays for hundreds of years, creating microplastics.

- Plastic materials are very diverse and there is no simple solution to the plastic waste challenge, underlines Associate Professor and PhD Cristiano Varrone from Aalborg University’s Department of Chemistry and Bioscience. Along with his colleagues in the UPLIFT-project he is working on developing a sustainable biotechnological solution to plastic-related problems with the help of bacteria and enzymes.

Plastic eating bacteria

Back in 2016, Japanese researchers made a remarkable discovery. They identified a special bacterial species, isolated from a plastic landfill, that had adapted to grow on plastic bottles. This micro-organism had developed specific enzymes to break down PET into its basic molecules, which were then incorporated into the bacterial metabolism. Since then, intense research allowed to identify many new enzymes with similar abilities and also to improve their performance.

- The benefit of this type of biological degradation is that it doesn’t require high temperatures and hardly any chemicals, explains Cristiano Varrone.

- Thus, it is a much more energy efficient and sustainable way of handling plastic waste. The downside is that it takes a very long time compared to both mechanical and chemical recycling. This means that the process is not yet economically profitable, but the project UPLIFT aims to change that.

Beyond the PET bottles

The research at AAU has a special focus on selecting bacteria that can deal with some of the hardest degradable types of plastics: the polyolefins (such as polyethylene and polypropylene). These types of plastics are very commonly used in food packaging and are extremely hard to break down due to their strong chemical bonds.

Therefore, the researchers have to use different pretreatments and a cocktail of various enzymes and micro-organisms that together can break down the plastic.

- If we are able to identify the right enzymes and microbial synergies, we will be able to break down hard types of plastic without having to previously sort, wash and treat the waste as required today, says Cristiano Varrone.

- In our group, we work on developing and optimizing various processes that can be upscaled in a bio reactor to make the reactions happen faster and more efficiently. The idea is to develop so-called “consolidated bioprocesses”, in which the breaking down of highly persistent plastics and the bioupcycling into new materials takes place in the same reactor, he says.

- The potential is quite large, and even though biotechnology alone will not be able to solve the whole plastic problem, it will give an important contribution.

Bio-plastic in the making

At the same time as the researchers in project UPLIFT are working on making the biological degradation process more efficient, they are also using biological residues to create new building blocks for biologically based plastics.

- We consider this approach as a “Plastic Biorefinery”, as we integrate molecules obtained from enzymatic treatment of plastic waste, together with bio building blocks obtained through fermentation, explains Cristiano Varrone.

- By creating new bioplastics from different residues, we are able to upcycle fossil waste into more carbon neutral materials, he says.

Sustainable and designed for a specific use

At least half of all the plastic that is produced in the world is thrown out within a year and 33 percent is only used once – i.e. as packaging for food. When the researchers in UPLIFT design a new bioplastic, they make sure that it has specific, purpose-built properties and durability. This is obtained through the collaboration of several partners with expertise in biotechnology, polymer chemistry, eco-design, formulation of packaging materials, etc.

- If the material is going to be used to make bottles for fizzy drinks, it has to have good barrier properties and be CO2-tight. If it is used for other packaging applications, it might need to have other specific mechanical properties that we can design for. At the same time, the new material has to be recyclable when it is no longer needed, says Cristiano Varrone.

- This way we can contribute to making the plastic sector more circular: the new materials developed in UPLIFT will make us less dependent on fossil resources and at the same time make it possible to recycle the large amount of plastic waste that is currently threating the environment.