Characterisation of source-separated, rigid plastic waste and evaluation of recycling initiatives: Effects of product design and source-separation system

Highlights

• More than 90% of the source-separated rigid plastic waste was PET, PE or PP.

• Food- and non-food packaging existed in all three polymers.

• High occurrence of products made of multiple polymers in the waste.

• Products designed for recycling can increase quantities of recycled plastic.

• Separate management of food packaging can lead to closed-loop recycling.

Abstract

Recycling of plastic from household waste (HHW) is crucial in the transition towards a circular plastic economy. Plastic from HHW consists of numerous immiscible polymers, product types and product designs (e.g. colour, polymer separability), which often lead to considerable physical losses during sorting, and low-quality recycled plastic. Consequently, recycling initiatives have been proposed to enhance the quantity and quality of plastic recycling from HHW. To quantify the potential effects of such initiatives, a detailed composition of plastic waste is necessary. The aim was to provide such detailed composition of Danish source-separated rigid plastic waste, including information regarding the polymer of the main product component, product type, polymer design and separability as well as colour. The potential effects on recycled quantity and quality from implementing selected recycling initiatives were quantified and recommendations provided. PET, PE and PP made up >90% of the source-separated plastic and both food- and non-food packaging existed in all three polymers. In total, 10–11% of the plastic was black, and around 44% consisted of multiple polymers, of which one-third was non-separable. Initiatives improving product design for recycling will likely result in increased quantity of recycled plastic. By effectively separating food from non-food packaging, e.g. by introducing two bins in the households or politically aligning polymers and product types (all food packaging in PET and PP, all non-food packaging in PE), 39–63% of the waste could potentially be recycled in a closed loop into food-grade quality packaging. The overall highest benefits were reached by combining initiatives.

Introduction

Recycling is often highlighted as a crucial measure in the transition towards a circular economy and closed material loops. Special focus has been placed on plastic, with a 55% recycling target for plastic packaging by 2030 (EU, 2018a) and a 60% recycling target for municipal solid waste, including plastic, by 2030 (EU, 2018b). Mixed plastic from municipal solid waste, particularly household waste (HHW), is a highly heterogeneous waste stream, as it includes a variety of different immiscible polymers, product types and designs. Moreover, plastic from HHW can contain both chemical and physical contamination from the production, use and waste management phases (Eriksen et al., 2018a, Eriksen et al., 2018b), and consequently it is a highly contaminated resource (Ragaert et al., 2017). As a result, recycling of plastic from HHW often includes considerable material losses (Van Eygen et al., 2018, Haupt et al., 2016) and leads to recycled plastic with poor material properties (Rigamonti et al., 2018). This limits the applicability of the recycled plastic and thereby plastic recycling systems’ ability to close material loops (Eriksen et al., 2018a).

The heterogeneous and contaminated nature of plastic from HHW is a consequence of several issues. First, the use of several immiscible polymers in the production of plastic products makes it a prerequisite to separate plastic waste into individual polymer streams subsequent to collection and before reprocessing. During this process, some degree of material loss and contamination is inevitable, the degree depending on the performance and sorting efficiencies (Eriksen et al., 2018a). Second, the presence of numerous different product types, with different shapes, production methods, chemical content and legal requirements, is important. Especially mixing food packaging, which previously complied with strict chemical legislation, and non-food related products, not having to comply with the same strict legislation, is a challenge for the potential quality of recycled plastic (Hahladakis and Iacovidou, 2018), as mixing in many cases makes the recycled material unsuitable for food contact (Welle, 2011). In fact, 100% of a PE or PP waste stream and 95% of a PET waste stream, representing the input to the final recycling, have to have been approved previously for food contact, in order to be recycled into new food-grade secondary plastic (EC, 2008, EFSA, 2011), which is crucial for a recycling system’s ability to close polymer loops (Eriksen et al., 2018a). Thus, a sorting systems ability to mechanically separate food packaging from non-food plastic items, and thereby produce streams potentially suitable for recycling into food-grade material, is closely related to the distribution of food and non-food packaging within the different polymers in the plastic waste. Third, there are many different product designs, including different colours and an increasing complexity regarding polymer design. Black products cannot be sorted using NIR sorting technologies, which is the predominant spectroscopic technology for household plastic (Turner, 2018, Becker et al., 2017). Consequently, black products are lost in the sorting process and sent to incineration. Moreover, several challenges are related to complex polymer designs. If a product consists of several polymers that can be separated during sorting or recycling (e.g. a PET bottle with a PE cap), the non-targeted polymer (the PE cap) will be separated from the main waste stream intended for recycling and thereby often end up in the residual fraction send to incineration (FCP, 2018). Moreover, products made of multiple non-separable polymers (e.g. a multilayer meat tray) contaminate the waste stream and will always introduce some degree of polymer cross-contamination (FCP, 2018, Hahladakis and Iacovidou, 2018). Third, all products made of multiple polymers have an increased risk of being sorted into the wrong polymer stream during mechanical sorting, as the NIR scanner may detect the polymer of the label or lid and sort it accordingly instead of sorting it according to the polymer of the main product component.

To mitigate these challenges, and thereby increase the quantity and quality of recycled plastic from HHW, initiatives related to changes in product design and configuration of the source-separation systems have been in focus. Recently, several organisations and stakeholders have launched guidelines to design new products suitable for recycling (Rethink Plastic, 2018, FCP, 2018, APR, 2018a). These guidelines include, for example, the stipulation that all components of a product should be of the same mono-polymer, or that they are fully disassembled during use (FCP, 2018). Moreover, Hahladakis and Iacovidou (2018) claim that not all plastic products are suitable for recycling; however, separately collecting the ones that are could improve closed-loop recycling and sustainable management. As an example, such an initiative is planned in Denmark in 2020, when the refund deposit system will be extended to include PET bottles for juice and lemonade, in addition to the current PET bottles for water and carbonated drinks (MEFD, 2018). However, detailed compositions of plastic waste, including information related to the polymer type of the main product component, product types, polymer design and separability, as well as colour, are essential, in order to model and accurately evaluate the effects of such initiatives. Various studies have reported compositions of plastic waste from households (e.g. Edjabou et al., 2015, Enviros Consulting, 2009), some of them including the composition of several polymers and product types (Brouwer et al., 2017, Petersen et al., 2015). However, none of these studies includes specific information regarding polymer design and separability or the colour, and they rarely distinguish between food and non-food packing. Without such information, quantifying the effects of new recycling initiatives is not possible.

The aim of this study was to provide a detailed composition of Danish source-separated plastic waste and on this basis quantify the potential improvements in quantity and quality of recycled plastic associated with a range of new recycling initiatives reflecting both product design and configuration of the source-separation system. The following specific objectives were addressed: (1) Based on a sampling campaign, provide a detailed composition of source-separated plastic waste from the municipality of Copenhagen, Denmark, including information regarding the polymer type of the main product component, product type, polymer design and separability as well as colour, (2) define theoretical scenarios representing key types of recycling initiatives related to product design and configuration of the source-separation system, (3) quantify the potential quantity and quality of the recycled plastic in each scenario through material flow analysis and (4) evaluate the effects of the individual initiatives and provide recommendations supporting the highest increase in recycled quantities and qualities, thereby enhancing the overall circularity of HHW plastic recycling.