The challenges of bioplastics in waste management

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Abstract

Although they still represent less than 0.5% of global plastics pro­ duction (European Bioplastics, 2023), compostable bioplastics are found everywhere, and their amount is constantly growing. They differ from conventional plastics because of their potential to degrade under industrial composting operations, and in addi­ tion they can be made from biogenic feedstocks, even if this is not always the case. Today, in addition to bags, any kind of packaging as well as several products, can be made of compostable bio­ plastics: films wrapping fresh fruit, containers for vegetables or ice­cream, pasta pillow bags, packages for frozen vegetables, coffee capsules and pods, butter packs, soft cheese wrappers, cotton buds sticks, packs for paper towels, napkins or toilet paper. As for their management at the end of the useful life, the 2018/851 European Directive indicates: ‘Member States may allow waste with similar biodegradability and compostability properties which complies with relevant European standards or any equivalent national standards for packaging recoverable through composting and biodegradation, to be collected together with bio-waste’. Accordingly, a continuously growing amount of compostable bioplastics has to be managed together with the organic waste in biological treatment plants that are not originally designed for their handling. Compostable bioplastics are certified according to the techni­ cal standards EN 13432:2002 (for the packaging) and EN 14995: 2007 (for items other than packaging). The fact that an item is certi­ fied as compostable indicates that it technically complies with the standard requirements but not that it can be managed together with the organic waste under any condition. Therefore, the com­ pliance with the EN 13432:2002 or the EN 14995:2007 standards is a necessary but not a sufficient condition for the compostability/ degradability in industrial recycling plants (Utilitalia, 2020). Moreover, the requirements of these standards do not fully cover the assessment of the degradability under anaerobic conditions. There are many criticalities and challenges of the combined treatment of organic waste and compostable bioplastics. The first one is associated with the mechanical pre­treatments that precede the biological recycling process: when the waste is subjected to size­based separation, most of the bioplastic products are dis car ded as residues, similarly to conventional plastics that are still found in appreciable amounts, as, generally, the separation between bioplastics and other non­compostable materials is tech­ nically not feasible (Utilitalia, 2020). This is particularly relevant in anaerobic digestion plants, where pre­treatments are often very intense to avoid further hydraulic and operational problems in the digester, especially when based on wet or semi­dry processes. The problems and costs associated with the management of discarded bioplastic items are amplified by the fact that, when removed, they exhibit a drag effect on a non­negligible amount of food waste that remains adhered to them and is not delivered to the anaerobic digestion (Utilitalia, 2020). This leads to two detri­ mental effects: an increase of the process residues that must be treated or disposed and a lower production of biogas. Further critical issues are associated with the poor degra­ dability of several compostable polymers, especially under anaerobic conditions. Indeed, the literature reports several stud­ ies focused on the behaviour of compostable polymers when subjected to biological treatments, underscoring first of all their general limited and slow degradability. Moreover, the manage­ ment of bioplastics is further complicated by the existence on the market of several types of biopolymers showing different characteristics and by the existence of deeply different biologi­ cal processes (i.e. composting, mesophilic anaerobic digestion and thermophilic anaerobic digestion). In addition to the critical issues in the organic waste manage­ ment system previously described, the mistaken delivery of compostable bioplastics can favour their presence in the flow of source separated conventional plastics sent to recycling, gener­ ating inefficiencies in this process. In fact, currently, bioplastics cannot be easily distinguished and separated from conventional plastics at the sorting plants because these are not designed to implement this separation. The difficulty in distinguishing compostable bioplastic prod­ ucts from traditional plastic ones is confirmed by the analysis of how compostable bioplastics are split into the current waste treatment system. As an example, in Italy, the country with the highest amount of compostable packaging in Europe, about 40% of compostable bioplastics is currently found in waste streams other than the organic waste. Accordingly, there is a clear need to implement actions (e.g. specific labels or colours on bioplastic items placed on the market) aimed at enabling a better recogni­ tion of compostable products, especially in comparison with similar traditional plastic ones. Because of all the previous critical issues, compostable bio­ plastics can lead to economic, technical and environmental chal­ lenges for the waste management system. Accordingly, their current management at the end of their use­ ful life should be improved. The first suggestion is the use, in applications where this is feasible, of items made of materials more compatible with biological (or other) treatment processes. For example, paper can be a valid substitute for bioplastics in the food waste collection bags as well as in several applications such as trays for food delivery. Paper items do not require a prior removal when sent to anaerobic digestion plants since paper is highly compatible with the digestion process and it also quickly breaks down during pre­treatments (Dolci, 2022). This would lead to a greater simplicity in the plant design in terms of a more The challenges of bioplastics in waste management 1181999WMR0010.1177/0734242X231181999Waste Management & ResearchEditorial editorial2023