INL Science Feature: INL scientists help harness bacteria power to brew eco-friendly plastic from waste

Three samples of premium wood-plastic composite lumber sit in a stack on a shelf in David Thompson's office at Idaho National Laboratory. The dense, fine-grained boards are uniformly colored in shades that range from light to dark brown.

All three boards match each other in strength and durability. But one of the boards has two special ingredients: plastic made by bacteria, and the same harmless bacteria that made the plastic — by eating wastewater.

Eat more food than you can use, and your body will stockpile the surplus in all sorts of curvaceous and unsightly ways. Many species of bacteria do something similar.

"Plastic, to these bacteria, is like fat," says Thompson, an INL biochemical engineer. Given an abundance of sugars, alcohols or other simple carbon sources, the bacteria will ferment the molecules for energy and string together the leftovers into long chains, or polymers, that they can stash for use in leaner times. Many of these polymers are actually types of plastic called polyhydroxyalkanoates, or PHA for short.

What bacteria make, they can also break down. All three of the sample composite boards in Thompson's office are too dense to absorb much water, which helps them resist rotting and cracking better than natural wood. But if you chipped up Thompson's bacteria-PHA composite board and buried it in an active compost pile, it would biodegrade completely in three to six months. In contrast, the petroleum-based plastics in standard wood-plastic composites could sit in your backyard or in a landfill for hundreds of years or more before breaking down completely.

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