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Posted: 27 February 2006

Training bugs to eat plastic… Scientists team up to convert polystyrene into a biodegradable plastic

Worldwide, more than 14 million metric tons of polystyrene are produced annually and it is so durable that it takes thousands of years to decompose.

With 70% of polystyrene ending up in landfill within a year of manufacture and 99% of all polystyrene ultimately ending up in dumps, the long term problem created by this versatile plastic is causing major anxiety among local and national governments throughout the world.

But a solution may be on the horizon if a new technology, which shows how a combination of chemistry and microbiology can help transform polystyrene into a useful biodegradable plastic, gains widespread recognition and is put into practice.
Scientist Kevin O’Connor and his research team at University College Dublin (UCD Centre for Synthesis and Chemical Biology & UCD School of Biomolecular & Biomedical Science) have teamed up with Professor Walter Kaminsky of the University of Hamburg to work on a solution to the global growth of the styrofoam mountain.

Professor Kaminsky is an expert in chemical degradation of plastics. He uses a technique called Pyrolysis, which uses heat in a vacuum to break down the plastic into a crude pyrolysis oil, composed of 83% styrene.

Dr O’Connor feeds this oil to a bacterium (Pseudomonas putida CA-3) and these tiny microbes transform it into a biodegradable heat-resistant plastic that can be used in a variety of forms ranging from plastic bottles to surgical parts.

“When we first fed the dark black liquid to our bacteria we thought it might be a bit too toxic for them but they grew quite well and formed tiny plastic granules called PHAs (polyhydroxalkanoate).” Dr O’Connor admitted. “The process to extract this biodegradable PHA plastic from the bacteria is as simple as washing with a mild detergent.”

As with any recycling process there are always concerns about energy costs and bi-products. However, Professor Kaminsky believes that redistilling the crude pyrolysis oil could leave a cleaner styrene oil, which could be consumed by the bacteria while the remaining crud could be burned, producing energy for the process. “The burning of the oil residue after distillation produces only carbon dioxide and water.” claimed Professor Kaminsky.

Currently, Kevin O’Connor’s team is concentrating on increasing the yield of the PHA plastic, but they eventually plan to evaluate the costs. “You could imagine a municipal recycling scheme where people are actually putting their polystyrene into a collection system, and so that polystyrene is at low cost,” he says.

Ultimately, the diversion of polystyrene from landfill and its subsequent conversion to a biodegradable plastic is doubly beneficial to the environment as it reduces refuse and produces a plastic that can be added to the compost heap, thereby assisting the carbon cycle.

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