A microbe that eats polystyrene could provide a solution to the problem of recycling the material.

Polystyrene foam, commonly know as StyrofoamTM, has a new enemy: A hungry bacterium that eats away the indispensable lightweight material and leaves a useful plastic in its place.

Irish researchers developed a method using pyrolysis, the process of degrading a chemical with extreme heat. In this case, they heated Styrofoam to 520° C—in the absence of oxygen— to yield styrene oil.

The microbes, a special strain of the soil bacterium Pseudomonas putida (P. putida for short) then feed on the purified styrene oil and produce polyhydroxyalkanoates, or PHA, which are biodegradable plastics.

“When we saw that it was working, there was a mixture of elation and relief,” said Kevin O’Conner a microbiologist at the University College of Dublin and the lead author of the study.

The study is slated to appear in the April issue of the American Chemical Society journal, Environmental Science & Technology.

The bacterium-produced plastic is grease and oil resistant and durable in hot liquids. But best of all, unlike Styrofoam, it can easily break down in soil, water, septic systems and even be put into backyard composts. Conner estimates its soil decomposition time to be around 12 months.

Besides being biodegradable, PHA is a biocompatible plastic, which means the nontoxic polymer is safe to use inside the body. This makes PHA ideal for medical implants or tissue engineering applications, according to Dr. Conner. The plastic can also be used to make kitchenware, packaging film and other disposable items.

Throughout the world, over 14 million metric tons of polystyrene are produced annually, according to the Environmental Protection Agency. The vast majority ends up in landfills where one polystyrene cup can take several hundred years to decompose. To date, only 1 percent of polystyrene is recycled.

Conner hopes that his new foam-eating bacterium can curb the 2.3 million tons of polystyrene that is dumped in US landfills alone each year.

According to the Polystyrene Packaging Council’s website, recycled polystyrene is not currently economical because the resulting product is a lower grade styrene that is not a reasonable substitute for freshly produced polystyrene.

Conner’s new method of recycling, however, involves “adding value to the product,” he said. “Because now you are taking a non-recyclable product and making it into a recyclable, biodegradable product with alternative uses, like biomedical applications.”
Conner’s study is among the first to research feasible ways of converting a petroleum-based plastic like polystyrene into a biodegradable plastic, closing the loop in the carbon cycle that plastic production mostly ignores.

Originally published March 5, 2006


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