‘Circular bioeconomy’ could transform plastics sector, study finds

The plastics sector’s environmental impacts could be drastically reduced by shifting to a so-called circular bioeconomy, a new study has found.

The study, published Wednesday in Nature, showed how such closed-loop systems — which are fueled by bio-based raw materials — could help transform the industry and allow it to absorb more carbon than it releases.

“If these plastics are kept in use, stored over the long term in landfills, or their carbon content is recycled, they could theoretically act as a medium or long-term carbon sink,” lead author Paul Stegmann wrote in his Utrecht University doctoral thesis, the basis for the Nature article.

Thus far, none of the pathways to achieve global climate targets have considered the potential of carbon storage in products, according to Stegmann, who is now a consultant on circular plastics for the Netherlands Organization for Applied Scientific Research.

Today’s plastics sector is responsible for about 4.5 percent of greenhouse gas emissions, while global plastic production under current policies is expected to triple by 2100, Stegmann and his colleagues warned.

Representatives of the plastics industry have long touted the merits of what’s known as a “circular economy,” a system in which plastic products retain their value through multiple uses and higher-quality design.

Acknowledging that such a system could boost recycling and reduce carbon emissions, the study’s authors argued these efforts would still fail to achieve global climate targets.

That’s because by the year 2050, there would not be enough plastic waste available from recycling to meet the growing demand for the material, according to the researchers.

In addition, plastic’s capacity for carbon storage would also be underutilized — limiting an opportunity for further emissions reductions, they argued.

Creating a circular plastic sector that uses bio-based raw materials, however, would maximize this possibility, through a process the authors described as “biogenic carbon storage.”

Such storage involves sequestering carbon within biological materials — or keeping carbon in plastic products for long-term use, Stegmann explained in his thesis.

“Plastics with a long service life, such as building materials, represent the largest stock of plastic on earth,” the authors said in a statement.

About 75 percent of the weight of conventional plastics is made up of carbon — meaning they already constitute a type of carbon storage, according to the study.

The authors projected that between 2020 and 2100, about 100 gigatons of plastic will have been cumulatively produced. But if these were all bio-based plastics, then 75 gigatons of biogenic carbon could potentially be sequestered.

Because carbon has an atomic weight of 12 and carbon dioxide has a molecular weight of 44, emitted carbon dioxide is 3.67 times heavier than stored carbon.

Storing 75 gigatons of carbon would therefore prevent the release of about 275 gigatons of carbon dioxide — savings equivalent to nine times current annual energy-related emissions, according to the study.

Stegmann told The Hill, however, that this is only “a theoretical ‘back-of-the-envelope’ calculation.”

These 275 gigatons in so-called negative emissions could be achieved “only if from today on until 2100 all plastics produce are bio-based (and have the same carbon content as current plastics) and are not incinerated,” he explained.

Meanwhile, he and his colleagues noted that “full circularity of the sector could be achieved only by reduction in final demand,” as the available waste cannot currently keep up with those needs.

Also critical will be the creation of a sustainable biomass sector, which curtails the consumption of land and water, as well as nitrogen emissions, according to the study.

Moving forward, Stegmann stressed the importance of powering plastic production with renewable resources, combined with high-quality recycling, minimal waste incineration and the widespread adoption of bio-based raw materials. 

Focusing only on recycling and the circular economy would reduce the use of resources and associated emissions but would fail to eliminate fossil fuels from virgin plastic production, he told The Hill.

And while biomass use alone “achieves strong emission reduction,” the resultant bioeconomy “would just follow the old, linear business model of fossil plastics and require high resource input,” according to Stegmann.

The scenario presented in their study, he argued, would be “feasible if we completely change the way we design products,” so that they can be recycled more easily and last longer.

“And more importantly: reducing our material consumption altogether is of course the most impactful solution instead of just changing the way we produce materials,” Stegmann added.