The challenge

Many plastics, such as mixed and soft plastics, are hard to recycle, which means they often end up in landfill.

Around the world there is a boom in organisations developing equipment to convert post-use polyolefin plastics to oils using advanced recycling techniques such as pyrolysis.

The oil they produce is planned to substitute for the fossil oil or natural gas traditionally used to create new plastics. The oil produced may also substitute for fossil-fuel derived transportation fuels with 7 per cent lower overall carbon dioxide emissions and lower PM2.5 and acid gas pollution due to very low sulphur levels.

Advanced recycling could transform ‘hard to recycle’ polyolefin plastics (e.g. soft plastics) into useful chemicals that can then be sold back to existing industries making brand-new plastic or petroleum oils.

Our response

We’re fermenting pyrolysis oil derived from polyethylene (PE) and mixed polyethylene-paper to find new and unexpected uses for these materials. We’ve identified that microbes such as the yeast Candida keroseneae (which lives on jet fuel), or the bacteria Acidovorax facilis (a biological soil conditioner), might be able to not only grow on pyrolysis oil but ferment it into valuable materials.

Initially, we’re looking for growth on the material as a sole carbon source. It is hoped that the similarity between plastic derived oils and naturally occurring oils will allow microbes taken from petroleum contaminated environments to grow and thrive on them, producing biomass.

Where growth is observed, further chemical analysis will be undertaken to determine which components are being consumed and if there are any valuable products of fermentation.

Impact

While the biomass might be used as an feedstocks for making bio-plastics, it may also be possible to isolate valuable materials such fatty acids for use in industrial soaps, soil conditioners or nutrients for animal feeds.

Multiple uses for pyrolysis oil also means that small or remote recyclers can have better certainty in their operations. If one market for their products drops in value or volume, an alternate market can be found. As transport increasingly transitions to electrification, this research could provide alternate secondary markets for pyrolysis oil once liquid fuels are no-longer used.