For every retail item you buy, chances are you bring it home in a plastic bag. Cheap to produce, lightweight yet strong, plastic bags are among the unsung heroes of convenience in our society. Yet this convenience is short-lived. The average plastic bag has a duty cycle on the order of minutes to hours from its initial use to being discarded, although some of the lucky ones might be stored temporarily by consumers for later use.
Once discarded, roughly 13 percent of plastic bags are actually recycled. The rest are landfilled or wind up as litter. One reason plastic bags wind up as litter is not that people fail to throw them into a waste receptacle, but that they easily blow away. Once in the environment, plastic bags are problematic. They can clog up stormwater drainage systems and contribute to man-made debris in rivers, lakes and oceans. Plastic bags comprise a significant portion of the Great Pacific Garbage Patch, and now have been found as far as the North and South poles.
Although plastic bags are recyclable, a large number of recycling programs do not accept them. The larger philosophical reason for this is that plastic bags have been designed and manufactured with little regard as to their recyclability and end-of-life management. However, this is a larger discussion for a different time. From a practical standpoint, the reasons for limited recycling of plastic bags are that they can clog recycling equipment and are difficult to separate from other materials; plus, if they are contaminated or dirty, plastic bags can detrimentally affect the quality of the recycled end-product. The plastic bag that has stuff in it (like food scraps or dirty disposable diapers) and gets thrown into a recycling bin is much more common than you might think.
To minimize the challenges with collection and at the materials recovery facility, one strategy is to manage plastic bags separately from other recyclables. For example, many grocery and retail stores have drop-off locations for this purpose. Similarly, many policymakers have recognized plastic bags’ potential environmental issues and have begun enacting legislation to require recycling. Yet the larger challenge of what to do with these bags after collection remains.
Researchers at the University of Illinois (Urbana-Champaign) are evaluating the ability to convert plastic bags to a diesel fuel alternative using a waste conversion technology called pyrolysis. The development of large-scale technologies using mixed municipal solid waste has been slow to materialize; such technologies have a better track record at smaller scale and using one material as a feedstock.
Results thus far have shown that pyrolysis of plastic bags produces a fuel that consists of 74 percent crude oil, 17 percent solid residue and 9 percent gases. The quality of the product is comparable to conventional petroleum diesel fuel and the research team has thus far demonstrated that the product from the pyrolysis of plastic bags can be satisfactorily blended with petroleum-based fuels. While some questions remain—such as what levels of contamination can be accepted while still creating a high-quality fuel—this represents a first step towards a potential next-generation technology to deal with problem materials like plastic bags.
Of course, the larger challenges for a technology like this rely more on taking it from lab scale to field scale and implementing it in a way that works within the existing societal and waste management infrastructure, yet this cannot be done without first demonstrating a viable technology. A full description of this research can be found in the journal Fuel Processing Technology (2014, Issue 122, p. 79-90).