GoKawiilWaste sampling
Waste samples were collected in April (PMD) and June (PoSo) 2023 at a Dutch facility located in the northern Netherlands. The facility serves municipalities in the region and processes household packaging waste collected under two parallel collection systems.
Source-separated PMD, comprising plastic packaging, metals and drinking cartons collected separately from residual waste at the household level, is received from municipalities with separate collection implemented, encompassing both urban and rural areas. This PMD waste is subsequently sorted in a mechanical sorting plant. This collection-sorting configuration is implemented in many EU member states under different terminologies (for example, PMD, Leichtverpackung (LVP)), including Austria, Estonia, Germany, Poland, Portugal, Slovakia and Slovenia.
In parallel, mixed residual household waste is collected in a single stream from municipalities without separate PMD collection, including densely populated urban areas, and is subsequently post-sorted to recover recyclable materials and organic fractions. This approach is representative of countries and regions that rely on mixed waste collection combined with downstream material recovery.
Separately collected PMD waste (PMD) and post-sorted PMD fractions (PoSo) recovered from residual household waste were processed at different times but on the same sorting line that includes a drum screen, magnet, eddy current, wind shifter, near-infrared sorters and manual quality control.
Although the precise municipal origin of the individual waste streams cannot be fully resolved, the sampled materials are representative of contemporary European collection and sorting systems that rely on either household-level source separation or mixed waste collection, followed mechanical sorting in an MRF into dedicated recyclable streams (for example, ferrous metals, HDPE rigids, LDPE films).
Bale samples were collected randomly in 60-l waste bags in triplicate by bale and collection system directly from the conveyor belts in the manual quality-control cabin, where operators visually inspect the sorted fractions and remove contaminants to ensure product quality, before baling (PE rigids, PP rigids, mixed plastic). LDPE samples were collected at the plant’s own recycling centre (shredded, before pre-wash bunker), and before baling for PMD and PoSo, respectively (Extended Data Table 1). Target items were selected based on ref. 28, which was adjusted to our observations of the material on the conveyor belt in the manual quality-control cabin. For each target sample, for example, a shampoo bottle, a minimum of ten items were collected, that is, ten shampoo bottles of the same brand, sampled both from PMD as well as from PoSo. Target items were later separated into individual components, for example, an HDPE bottle into bottle, closure and label, and mixed to a composite sample per item component (n = 53; Extended Data Table 2). For PoSo, target items also included ‘non-packaging plastic items’ that potentially appear more frequently or exclusively in this collection scheme, for example, toys, textiles and household plastic items, with the aim to assess whether such non-packaging plastic items would cause additional contamination in recycling. Non-packaging plastic items were observed on both the PP rigid and the mixed plastic belts during post-sorting sampling. At the mixed plastic belt, these were not specifically targeted but included within the general grab samples. In contrast, at the PP rigid belt, non-packaging items were deliberately collected to ensure their representation in the analysis, as their occurrence was less frequent. Non-packaging plastic items were grouped into different categories, for example, ‘PP others’, toys, blisters, and combined to composite samples (n = 5, for example, toys, PP others) or analysed as individual samples (n = 9, for example, textiles) (Extended Data Table 2).
All samples were placed in plastic bags, labelled and stored at 5 °C until further analysis. Items were processed and stabilized within the next 7–10 days.
Waste sample preparation
The sample size of bale samples had to be reduced from 3 × 60 l to approximately 20 l using the quartering method. Target samples were divided into equal fractions. One fraction remained unwashed and the other one fraction was prepared for the measurement of residue content and washing. Non-packaging plastic items were checked for any harmful contents, for example, metal pieces or batteries, and, if present, these were removed. All samples were reduced to flakes by shredding (Shini SH Granulator with sieve size 8 mm). After each cycle, the shredder was cleaned to minimize contamination across samples. Target samples were shredded after washing and drying, as described in the following steps.
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