Development and evaluation of waste collection and sorting systems for biodegradable plastics

Plastic is one of the most used materials in the human world and about 353 million tonnes of plastic waste was produced worldwide in 2019. However, only 9% of this generated waste was recycled. With respect to Europe, of the total 25.2 million tonnes of plastic waste generated in 2020, only 14% was recycled. Thus, numerous targets are set for the future, to improve the circularity of plastics. As a part of the Plastics Transition report (Plastics Europe, 2024), by 2050, 65% of the plastic packaging demand should be met by circular plastics. One example of these circular plastics is biobased plastics, and they should meet 18% of the total plastics demand by 2050. In other words, biobased plastics, which form one of the three types of bioplastics, are envisaged to contribute to increasing the circularity of plastics.

Bioplastics are defined as plastics which are either biobased, biodegradable, or both. They represent 0.5% of the total global plastic production, of which ~ 52% are biodegradable plastics. Moreover, their quantity is expected to grow in the future. Biobased non-biodegradable plastics have the same molecular structures as their fossil-fuel counter type; hence, their waste can be handled effectively in the existing waste management system of fossil-based plastics. However, the challenge lies in managing biodegradable plastics (both biobased and fossil-based), as additional investment will be needed to facilitate their waste management. Furthermore, with their expected rise in production and frequent applications in packaging, the future targets related to plastic packaging recycled will also apply to biodegradable plastics.

As of now, there is no functioning waste management system established for biodegradable plastics. Moreover, the existing literature presents numerous challenges related to their waste management; for example, their presence contaminating the fossil-based plastic recyclates and the unacceptance of the biowaste treatment facilities. For waste material to be recycled, it should be first collected and properly sorted. However, there is hardly any scientific literature available discussing the collection stage of these plastics. Furthermore, even if the near-infrared sortability of polylactic acid was effectively studied, the literature on the other commercially available biodegradable plastics is sparse.

The objective of this thesis was to investigate the product-oriented collection and sorting systems for biodegradable plastics.

A systematic literature review was conducted which gave a holistic overview of the biodegradable plastic waste management-related challenges as well as pointed to the discrepancies between the information about the best disposal method for these plastics in the legislation and source separation guidelines (Section 2).

Moreover, the existing qualitative studies and the waste characterisation study (conducted as a part of this thesis, Section 3.2) suggested that consumers are confused about the proper disposal option for biodegradable plastics. Thus, clear source separation instructions and labels are crucial. To assist in the awareness creation of consumers, 24 drivers influencing the source separation behaviour of the consumers were ranked based on the relative importance as perceived by the three groups (Section 4). The knowledge of these drivers will help the decision-makers in developing source separation-related policies. These results were interpreted for biodegradable plastics.

Near-infrared (NIR) sortability of the commonly available biodegradable plastics was successfully tested (Section 5). Additionally, the effect of surface contamination on their NIR spectra was studied (Section 6), which showed that the contaminations could result in an overlap with some conventional plastics; hence, it is important to optimise the NIR database with clean as well as contaminated samples.

Lastly, a life cycle assessment was conducted to evaluate the environmental performance of collecting biodegradable plastics in one of the three waste streams with the respective treatment methods (Section 7). The results showed that collecting these plastics with packaging for mechanical recycling yielded maximum environmental benefits; however, for realising these results certain technical and regulatory prerequisites ought to be fulfilled.

Based on these results, certain recommendations for improving the collection and sorting of these plastics were provided. These can support in developing practical actions in reducing the confusion surrounding biodegradable plastics, which in turn will facilitate their correct disposal and ultimately, their recycling.