Scientists from the University of Edinburgh have recently used a lab-engineered version of the bacteria E. coli to transform terephthalic acid, a molecule derived from PET, into the culinary flavouring vanillin, via a series of chemical reactions.
"Our study is still at a very early stage, and we need to do more to find ways to make the process more efficient and economically viable," says Dr Joanna Sadler, of the university's School of Biological Sciences.
"But it's a really exciting starting point, and there's potential for this to be commercially practical in the future after further improvements to the process have been made."
Meanwhile, a team at the Helmholtz Centre for Environmental Research-UFZ in Leipzig is using a bacterium originally found in a local rubbish dump to break down polyurethane.
Called Pseudomonas sp. TDA1, the bacterium consumes around half the plastic to increase its own biomass, with the rest released as carbon dioxide.
Like other plastic-eating organisms, Pseudomonas breaks down the polyurethane using enzymes; and the team has now carried out a genomic analysis of the bacterium with the aim of identifying the particular genes that code for these enzymes.
But some question whether such techniques will ever be commercially viable.
"Enzyme or microbial conversion of PET to its constituent building blocks is interesting science and needs to be explored. However, the technology will have to compete with proven, commercial conversion technologies using mundane, less exciting water-catalyst systems," says Prof Ramani Narayan of Michigan State University.
"PET bottles can be recycled using this enzyme back to new bottles, but unfortunately PET bottles are very crystalline and very resistant to enzyme degradation, so the company had to introduce an extra pre-treatment where they actually put in a lot of extra energy to melt the material and extrude it to reduce the crystallisation," he says.
"After that, you can degrade it with the enzyme - but economically, and also in terms of carbon footprint, this doesn't make a lot of sense in my opinion."
And while things may improve, enzymatic recycling currently has a very limited range, as Mr Stephan concedes.
"We have developed technologies for the end-of-life of two polyesters only, representing around 75 million tonnes of annual production, compared to a global plastics production of around 350 million tonnes," he says.
"A lot of work is ahead of us."