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Scientists Quantify Waste Plastic Systematically to Reach Maximum Recycling Potential

Published on 2022-04-20. Edited By : SpecialChem

TAGS:  Sustainability and Bioplastics   

A recent study done by DTU researchers quantifies the volumes of the different plastics that are discarded, and it determines how great the recycling potential is. Relative to DTU’s other research in this field, it gives a picture of what a municipality can expect to gain from recycling of plastic.

One pile with PP plastic. One with PVC plastic. One with PET plastic. Etcetera Then one pile with toys. One with food packaging. And one with medicinal products packaging. This is how researchers from DTU have proceeded systematically when they have sorted the collected plastics of citizens at recycling stations in Silkeborg, Roskilde, and Copenhagen.

“Specifically, we’ve emptied the contents of the containers onto the ground, and we’ve then started from one end. If we don’t make a systematic division several times and at several different recycling stations, we run the risk of conducting a study that provides an uncertain statistical basis. We need a true and fair view of how much and how well the plastic can be recycled,” says Thomas Fruergaard Astrup—Professor at DTU—who has headed the study.

At the joint municipal waste management company ARGO in Roskilde, this has led them—together with other waste management companies—to make greater and more qualified demands on the sorting plants with which they collaborate.

“We’ve gone from seeing ourselves as passive purchasers of waste handling services to being active operators in a larger circle. Mapping and documenting the potential of plastic as a basis for continuously making greater demands that can promote a development has become an important key for us,” says Ejvind Mortensen, Senior Consultant at ARGO.

Plastic Processing and Recycling


When a waste management company like ARGO sends the citizens’ plastic for processing and recycling, the first stop on the journey is a large sorting plant in Germany. Here, the plastic is placed on a conveyor belt, where it is scanned and divided into smaller fractions of the most common plastic types. Here, some of the plastic can be processed and recycled in the same type of products from which it originates.

But a large part of the plastic received needs special processing. This may be because the plastic is a mixed product and therefore needs to be separated into its constituent parts or that the packaging is filled with soap residues, meat juice, or the like. It may also be because the plastic itself is contaminated with problematic chemicals. All this plastic often ends up in a residual pile of the lowest quality called mixed plastic. And here the vision of a circular circuit is broken.

“Some of the mixed plastic becomes garden benches or fence posts, which are at the bottom of the recycling pyramid for materials because they cannot be recycled again. Other parts become fuel used in cement kilns. Finally, some is sent for waste incineration and utilized for energy. If the plastic isn’t sorted thoroughly enough, the pile of mixed plastic becomes bigger, and our results clearly show that a large part of the plastic that ends up in this pile has a recycling potential that isn’t exploited well enough,” says Thomas Fruergaard Astrup.

Thomas stresses that the technology for better sorting already exists. You can use more machines and more sensors, and you can send the plastic through fine sorting and cleaning several times. The problem is that this can be an expensive affair.

“Such sorting represents a financial cost, and the gain for the plant must be that they can sell the clean fractions of sorted plastic pieces for recycling. How much you want to process the plastic will therefore often depend on the market prices,” Thomas explains.

According to Thomas Fruergaard Astrup, it has been necessary to promote the commitment to better recycling by making demands.

Waste Management


One of the requirements that ARGO makes today—together with the Vestforbrænd waste incineration plant and the City of Copenhagen—in their public procurement procedures for handling their plastic is that maximum 25 per cent must be discarded as waste in the sorting. They also have a requirement that maximum 45 per cent of the sorted plastic must end up in the mixed plastic pile.

“These are requirements we can make based on our basic knowledge from DTU’s studies. We also ask to receive continuous analyses from the sorting plants showing—among other findings—the quality of the plastic in the mixed plastic pile. So if there is something in the mixed plastic pile that has a greater potential, we’re aware of it and can make greater demands next time,” explains Ejvind Mortensen.

A widespread method in the waste management industry is to use a percentage to estimate the recycling in the area of plastics. This percentage states how much plastic is recycled, but not what it is recycled for. In this connection, DTU’s research shows that recycling in percentages says nothing about the actual environmental benefit, and—for Ejvind Mortensen—this has given a new understanding of how we should measure recycling.

"If you only measure in terms of tonnes, you can make a heavy fence post using lots of low-quality plastic. On paper, you will then have recycled a lot of plastic. When the soft drinks bottle and soap container count in the same way, it makes sense to use the plastic in a fence post. And this results in a poor environmental benefit in the overall accounts,” he explains.

Manufacturers to Own Responsibility


Although environmental and quality awareness is slowly gaining ground in the waste management sector, Ejvind Mortensen points out that—as a waste management company—ARGO is only a tiny element of the large circle.

If the visions of a more circular plastics economy are to be realized, Ejvind points out that the companies designing the products must assume responsibility.

“With this knowledge, we’ve become better at making demands on the sorting of plastics, but we cannot demand more from them than the potential of the mixed pile we get. So—in the long term—the joint municipal waste management companies aren’t the players that will make a difference. Greater demands must be made at preceding levels in the system; for the manufacturers making the products,” Ejvind says.

This view is backed up by Thomas Fruergaard Astrup, whose research shows that there are great environmental benefits to be gained if our products are designed for efficient and real recycling.

“We can change the design of the products to make them easier to process, separate, and sort. And we can make sure that the plastic does not contain all sorts of chemical additives which make it difficult to reuse. But there are so many manufacturers globally, and the materials come from all parts of the world. So it’s difficult,” Thomas says.

Denmark does not yet have rules on manufacturer responsibility requirements in the plastics sector, but a new Waste Directive from the EU means that we must introduce such rules before 2025. This means that a Danish manufacturer responsibility organization is on its way, and the expectation is that it will lay down requirements for the manufacturers’ design of products. At Ejvind Mortensen in ARGO, this gives rise to hope.

“I really hope that the holistic view from DTU will be taken into account when considering the demands to be made on the companies. My greatest wish is that the future manufacturer responsibility organization will invite Thomas Fruergaard Astrup to provide the big picture. That’s needed if we’re to raise the level in the circular plastic circuit.” 

Source: DTU

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