Compostables and Recycling: Contamination in Both Directions

Compostable plastics and recyclable plastics are chemically distinct families that consumers cannot tell apart by looking - which makes cross-contamination the family's systemic risk. A compostable film in the plastics stream degrades the recyclate's quality (it is screened as a foreign polymer where sorting detects it, and a quality defect where it does not). A conventional plastic in the organics stream survives composting as visible contamination that can fail a compost batch's quality and a facility's acceptance policy for all compostables. The system's defences are labelling (the harmonised mark's routing clarity), detection (near-infrared sorting libraries now identify the main compostable polymers), and design that avoids mimicry.

This guide works the three defences.

The worst compostable products are the ones designed to look like their conventional equivalents - the clear compostable film indistinguishable from PET, the compostable bottle aping the recyclable one. Mimicry guarantees mis-sorting at household speed. The design discipline is differentiation within dignity: compostable items should be visually and tactilely distinguishable (surface, print, the compostable mark prominent and repeated), and their marketing should never trade on 'looks just like plastic' as the virtue. Brands converting a line to compostable should budget the differentiation as part of the conversion, because the stream externality is priced - composters' acceptance bans and recyclers' quality claims both trace back to lookalike products.

Modern sorting identifies the principal compostable polymers spectroscopically and ejects them from the plastic streams - where the ejection target exists and the volumes justify the programming. Recyclers' position is therefore nuanced rather than hostile: identified and ejected, compostables are a manageable stream cost; unidentified (novel blends, black-pigmented items, lookalike laminates) they are a quality risk. Producers of new compostable constructions owe the sorting system a courtesy that is becoming an expectation: notify through the industry channels, supply spectral references, test at sorting facilities where offered. The same logic, mirrored, governs organics: composters' screening removes plastics at cost, and the compostable producer's interest in a clean organics stream is identical to the composter's.

All stream integrity finally depends on a tired person at two bins. The system's aids are the label (the harmonised sorting and compostable marks in their regulated zone, saying the stream in the stream's language), consistency (the same item never changing streams between purchases), and municipal communication that names the local rule for compostables specifically, since national rules differ. Brands can help with radical consistency: do not alternate a line between recyclable and compostable constructions across promotions or regions without changing its face so clearly that the change is the message. The bins forgive many things; ambiguity is not among them.

Each stream's integrity is a commons every producer draws on and every careless product depletes: one brand's lookalike film raises the composter's screening cost for all; one stream's contamination scandal hardens acceptance policy against a whole material family. The disciplines of this guide - differentiation, detection courtesy, household clarity - are commons-keeping, and their return is collective: a compostables family that keeps the streams clean keeps its licence to grow. Article 9's list is short because the legislator was protecting the commons too.

The streams' integrity is decided in the last metre - the hand, the bin, the lid. Every discipline in this station (marks, differentiation, consistency) is design for that metre. Producers should test their compostable items the way the metre experiences them: shown for two seconds to someone who has never seen the pack, in a kitchen, at night - which bin? If the answer hesitates, the design is not finished, whatever the certificate says. The laboratory certifies the material; the kitchen certifies the system.