May 5, 2014 in City
The Rock Doc: Plastic bags could become biofuel source
My household accumulates quite a number of plastic shopping bags. Most come home with me from the grocery store. I use them to line the little garbage pail that sits under the kitchen sink and the wastebasket that’s in the bathroom. I also have the joy of using them to pick up poop deposited by Buster Brown, my faithful mutt from the pound.
But if you don’t have uses for the plastic shopping bags you bring home, what do you do with them? Researchers hope that one day – perhaps sooner rather than later – your bags may be turned into alternative fuels such as diesel. That’s right, plastic shopping bags could help power diesel-engine cars and pickup trucks.
It’s not as pie-in-the-sky as it may sound. Converting shopping bags into fuel requires less energy than it produces. The key is the high-temperature breakdown of plastic in the bags – done in the absence of oxygen, or anaerobically.
The lead author of a recent study on this topic is Brajendra Sharma of the Illinois Sustainable Technology Center at the University of Illinois. His research write-up was recently published in the journal Fuel Processing Technology. Sharma’s article points out that about 1 trillion plastic bags were produced in the U.S. in 2009, the last year for which figures are available. Of these, only about 13 percent were recycled.
Some of the rest were doubtless reused for household purposes, like mine are, and after that headed to landfills. But many of the bags aren’t recycled or reused and go either directly to landfills or are released into the environment as litter.
Plastic bags that become litter blow around and cause a number of problems beyond being an eyesore. They can kill animals that ingest them or become tangled with them. In the oceans, they compose part of what’s termed the Great Pacific Garbage Patch of floating trash.
“Over time, this material floating in the oceans breaks into tiny pieces. It’s ingested along with plankton by aquatic animals,” Sharma said in an email.
The material in plastic shopping bags has been detected in the oceans near both the north and south poles. It’s also a problem in the Great Lakes. Because the plastic apparently takes centuries to fully degrade in nature, the issues that the bags pose are long-term.
But Sharma and his colleagues have an alternative use for the bags. Once the plastic is broken down anaerobically in a lab, it yields a variety of useful chemicals including solvents, engine oils, gasoline and natural gas. The bulk of the material produced is an alternative diesel fuel, one that Sharma and his co-workers found to be a good blending component for regular diesel.
“This approach can also be applied to other low-value plastics as well,” Sharma wrote to me.
I’ve often thought that there’s no single solution for pollution problems. And while turning plastic bags into diesel may only work for some bags, it’s an interesting approach to getting rid of what otherwise would be trash while producing a valuable commodity.
E. Kirsten Peters, a native of the rural Northwest, was trained as a geologist at Princeton and Harvard universities. This column is a service of the College of Agricultural, Human, and Natural Resource Sciences at Washington State University.