- How long until they can scale this to be practical? And economical?
- How environmentally harmful is it to manufacture styrofoam? Should we still be looking for an alternative to it?
- I hope the study's publication date is an unfortunate coincidence.
March 27, 2006— Bacteria that converts Styrofoam into Earth-friendly plastic could lead to a new kind of biodegradable plastic that breaks down into the soil.
The method could help reduce the 2.3 million tons of petroleum-based plastic waste that makes its way into U.S. landfills each year, said research leader Kevin O'Connor, who heads the bioplastic research group at University College Dublin in Ireland.
O'Connor and his team's research results will appear in the April 1 issue of Environmental Science & Technology.
Scientists have used microorganisms to break down the kinds of chemical products found in Styrofoam, but no one has been able to create a useful plastic byproduct, commented Mannfred Zinn, a research group leader at EMPA, the materials science and technology lab that is part of the Swiss Federal Institute of Technology.
To convert the plastics, O'Connor's team used a strain of soil bacterium known as Pseudomonas putida.
In nature, this microorganism lives in the ground, where it feeds on the carbon, nitrogen, hydrogen, and oxygen found in organic matter such as dead plants.
Styrofoam — a material made from polystyrene — contains hydrogen and carbon, but not in a form that the bacteria can readily digest.
To make the plastic edible, the scientists had to heat it under a special process called pyrolysis, which melted the polystyrene at very high temperatures in an oxygen-free environment to break the chemical bonds.
No oxygen means no burning and so no emissions. During the process, the polystyrene became liquid styrene, a carbon-based compound that the bacteria can eat.
In the lab, the scientists created a growing environment for the bacteria, feeding them all of their favorite foods, including nitrogen and oxygen.
A steady flow of styrene oil supplied to the bacteria in a fermentor allowed the bacteria to proliferate.
After the colony grew to a healthy size, the scientists stopped feeding the bacteria nitrogen. That stimulated the bacteria to begin storing the carbon for use later.
It turns out that when the bacteria store the carbon, they actually convert it into a plastic known as polyhydroxyalkanoate, or PHA.
PHA is made up of fatty acids that are easily attacked by the enzymes produced by bacteria.
"PHA is a 100 percent biodegradable plastic that can be thrown on your compost heap. Bacteria in the compost heap use the plastic as food to grow, so there is no damage to the environment. You can't get greener than that for a plastic," said O'Connor.
It can also be harvested from the bacteria to make biodegradable plastic goods such as shampoo bottles, credit cards, and medical implants and devices — all of which will fully degrade in the trash, said O'Connor.
"This is a great opportunity to make something better from a recycled material," said Zinn.
O'Connor and team know that worldwide, more than 14 million metric tons of polystyrene are produced annually, but are unsure how much investment it would take to build a plant capable of converting the material into PHA.
But he said the process works on any petrochemical plastic waste and that fact could open up new areas of exploration for the petrochemical industry.