As single-use plastics fall further out of favour among environmentally-conscious consumers and governments, many companies are turning to newer materials that they say will break down in people’s backyard composting bins. But new research reveals that most of these so-called “home-compostable” plastics don’t live up to their labels.
Sixty percent of plastics that are certified for home composting don’t fully disintegrate, according to a study published in the journal Frontiers in Sustainability. The research urged consumers to exercise caution when evaluating companies’ claims, suggesting they would be better off sending items to an industrial processing facility. “Home composting is not at present a viable, effective, or environmentally beneficial waste processing method for compostable or biodegradable plastics in the U.K.,” the authors wrote.
In response to the plastic waste crisis, countries all round the world have set targets to make plastic packaging 100% recyclable, reusable, or compostable, and to eliminate all unnecessary single-use packaging by 2025. Including compostable plastics in the targets was important for two reasons: firstly, there are some items such as food packaging, wipes, tea bags, sachets, that being small and highly food contaminated are not suited to recycling or reuse; secondly, food waste is of major environmental importance and compostable liners can play an important role in the route out of the home. But there are some fundamental problems.
Although the processing of compostable and biodegradable plastics is regulated under industrial organic waste management processes, the existence of systems of collection and industrial composting for this packaging are rare in the UK. Compostable and biodegradable plastics are currently incompatible with most anaerobic digestion (AD) systems and recycling systems. Hence their fate is either landfill or incineration. Disposal of compostable packaging in landfill is not environmentally beneficial, however under certain instances where incineration processes use energy from waste recovery incinerating compostable packaging may offer some benefit in overall emissions reductions. The typical fate of landfill or incineration is not usually communicated to customers so the environmental claims made for compostable and biodegradable packaging can be misleading.
The research paper was the result of a citizen science project called “The Big Compost Experiment,” which — in addition to evaluating the effectiveness of home composting plastics — asked nearly 10,000 people from across the United Kingdom about their knowledge of and willingness to try the practice. Some 900 of these participants went on to complete a home composting experiment, reporting back to the study authors at University College London over a two-year period.
People are largely enthusiastic about buying compostable and biodegradable plastics, the study found, although there is much confusion over these products’ labelling. Out of a random sample of 50 items that participants put in their composting bins, nearly half showed no identifiable compostable labels and another 14 percent said they were only compostable in a specialized industrial facility.
The rest of the items that were labelled as home-compostable — the bags, cutlery, food packaging, and other products branded by certification bodies like TUV Austria and European Bioplastics — did not break down fully. Out of a sample containing more than 1,300 pieces of plastic, about 60 percent featuring these certifications didn’t disintegrate at all, remained “largely intact,” or simply broke into easily visible pieces.
“We have photos that people have submitted after 12 months where you can still read the home compost certification label on it, which is ironic,” Danielle Purkiss, a research manager at University College London and a co-author of the study, told ABC News.
Why this failure to break down? Although the authors acknowledged a wide range of conditions that can affect composting — from different temperatures and pH levels to micro bacterial diversity — they said the main problem was with the plastics themselves. “It pains me to say this because I want non-plastic alternatives to work,” Judith Enck, a former regional administrator for the U.S. Environmental Protection Agency and founder of the advocacy group Beyond Plastics, told CNN. “But there really is no such thing as biodegradable plastics, and compostable packaging really only gets composted at high-temperature composting facilities.”
Process
The current bioplastics market share is relatively small at 1% of the total 335 million tons of plastics produced globally, the global production capacity for biodegradable plastics is set to increase from around 0.91 million tons in 2018 to around 1.3 million tons in 2023 but it could be much greater if small item formats such as snack packets and chocolate wrappers are switched to compostable plastics. Manufacturers of compostable plastics and the companies using them are aware of the lack of infrastructure for sorting and collecting these plastics but counter them through a number of arguments. Firstly, that the public are in favour of biodegradable packaging; secondly the organic waste collection initiatives in the EU’s Waste Framework Directive and UK Government’s Environment Bill will increase capacity of the organic waste processing systems and closed loop systems that can handle these plastics, and thirdly by designing biodegradable packaging designed to compost at home. In this research a citizen science approach to test these arguments by assessing the public’s attitudes and understanding of compostable and biodegradable materials; and inviting citizens to carry out experiments to test the effectiveness of home composting as a means to biodegrade compostable plastics.
Understanding product performance and user behaviour is vital to the success of circular economy models of material and product use. Several studies have been carried out in the field of user behaviour in relation to biobased and biodegradable packaging, home composting practices and the performance of compostable plastics under home composting conditions. This is the first citizen science study combining large-scale collection of data on home compostable plastic use and behaviour, and disintegration performance of home compostable plastics in the UK.
Biodegradability refers to the capability of being degraded by biological activity. Many materials are biodegradable such as paper, cardboard, wood, and certain types of plastic. The word biodegradable does not describe under what conditions and how long a plastic will take to biodegrade. The term “compostable plastic” is more specific, it describes a material that is capable of undergoing biological degradation in a compost site at a rate consistent with other known compostable materials, leaving no visibly distinguishable or toxic residues.
There are two types of composting environment for which compostable plastics are designed, industrial composting and home composting. Industrial composting is a controlled biotechnological process for transforming biodegradable organic waste into compost, a resource used in agriculture to improve soil. Depending on the process, industrial composting facilities are designed to undertake aerobic composting or anaerobic digestion. In aerobic composting, microorganisms consume oxygen while breaking down organic waste to produce CO2, water, compost, and heat. In anaerobic digestion, bacteria degrade the organic waste in the absence of oxygen, producing biogas (methane and CO2) and digestate. The two different processes are performed in different facilities. Industrial composting (IC) facilities digest garden and green waste under aerobic methods, whilst anaerobic digestors (AD) normally deal with food waste. Typically, AD facilities are not optimized to take compostable plastics which are generally removed even at low volumes.
Home composting is a general term for the process by which biodegradable garden waste or domestic food waste is collected and placed in either a container or heap to allow natural processes to turn it into compost. It is a manual process whereby the composition and process temperatures remain largely unregulated. Both aerobic and anaerobic conditions can occur in home composting, although aerobic conditions are more normal. The time frame for home composting depends on personal preference and the use to which the compost is put, but 3–12 months is typical. The process of microbial biodegradation in soil can vary according to location and season due to variation in uncontrolled parameters influenced by geographical location such as temperature, water content, chemical composition and pH. Little is known about the variation of microbial biodegradation processes in home compost environments.
Industrial composting has a different legal status to home composting. Under Directive 2008/98/EC (2008) and UK Government’s Compost Quality Protocol organic waste segregated at source can obtain legal “end-of-waste” status if the resulting compost complies with specific conditions such as those carried out under authorized industrial composting systems and is considered to be a recycling process. Home composting activities do not comply with these conditions therefore organic waste and compostable packaging processed in this way cannot achieve “end-of-waste” status and is not considered to be a recycling process. However, home composting is encouraged by Article 22 (2b) of Directive 2008/98/EC as it can help minimize the volume of organic waste entering the waste management system. Compostable packaging which complies with relevant European standards or equivalent national standards for packaging recoverable through composting and biodegradation, can be collected separately and processed together with bio-waste under Article 22 of Directive 2008/98/EC.
It’s not the first time compostability claims have come into question. In 2019, other researchers at the University of Plymouth in the U.K. found that a number of ostensibly compostable and biodegradable shopping bags failed to break down fully after three years in the natural environment. In the absence of collection systems to bring compost-friendly materials to a high-temperature industrial facility, these products have been found to more likely be landfilled or incinerated alongside conventional plastics. This creates more pollution and greenhouse gas emissions.
With these concerns in mind, Mark Miodownik, a professor of materials and society at University College London and an author of the study, said there’s a simpler, easier alternative to compostable plastics: Buy less plastic and ditch single-use materials altogether — whether home-compostable or not. “Reduce and reuse are often big money savers for everyone, and yet it seems the strategy that is least intuitive to people”.
Misconception
The idea that a material can be sustainable is a widespread misconception. Only a system of production, collection, and reprocessing of a material can be sustainable. The type and amount of energy used to fuel the process, the water usage, and the by-products also contribute to its environmental footprint. This applies to compostable plastics as much as to normal plastics. Although the bio-sources of compostable plastics make this class of material more renewable, the fact that there is no UK-wide system of collection is problematic.
Most compostable plastics end up in landfill or are burnt. Neither is a good environmental outcome. Some people put compostable plastics in their food waste collection, but this is generally treated as a contaminant and increases the costs of current anaerobic digester systems. Anaerobic digesters are not optimized to degrade biodegradable plastics, which are instead removed and sent to landfill or incinerated. Several studies suggest the persistence of compostable and biodegradable plastics under simulated compost, sea, or soil environment conditions. Further field study evidence is needed to conclude the real-life performance of these plastics in the environment. Evidence reported in this paper shows that citizens don’t understand these complexities of compostable or biodegradable packaging and yet are enthusiastic about buying them (85% reported doing so). Data also shows that citizens are confused about what the labels on compostable and biodegradable packaging mean. For example, 60% of sampled items tested in home composting experiments were not certified home compostable.