Is it time to switch to biodegradable plastics?

It seems as though the impact plastics have on the environment has gone from a niche concern to mainstream matter quicker than you can say “Blue Planet”. Suddenly, consumers and businesses alike are taking action. But while concern has ramped up, knowledge still lags behind and there is a risk of ineffective or counterproductive changes being adopted.

For a lot of people, concern about single use plastics has been motivated by striking images of littered plastics blighting beauty spots or harming marine wildlife. This blighting effect results from two factors – poor waste management and the long lifespan of plastics when they escape the proper system. If plastics can be made to break down harmlessly in the environment, that would seem like an obvious solution to the problem. Naturally enough, interest in biodegradable and compostable plastics has been growing.

However, solutions that appear to help with one problem can inadvertently lead to others. In this article, we’ll explain the complicated waste management and litter issues that biodegradables currently present. These need to be understood by anyone considering switching over from a single use, fossil fuel-based plastic product to a biodegradable plastic alternative. Fair warning: those looking for simple answers may be disappointed!

Slow going

Despite their name, very few of the biodegradable plastics currently in use will biodegrade in a way that solves the problem of plastic litter. The key European standard that compostable plastics must meet (EN13432 – there is also a similar American standard, ASTM D6400) concerns how materials degrade in enclosed industrial composting. In the conditions found in a hedgerow or the ocean, where temperatures and levels of microbial activity are lower, EN13432-compliant materials will degrade far more slowly. They therefore offer little practical benefit over conventional fossil fuel based plastics as a means of reducing litter impacts.

Nor will they break down quickly if composted at home. There are other certifications for compostability in a home composter and biodegradation on land and in fresh and salt water but these are not internationally recognised – an American standard for marine biodegradation was withdrawn in 2014. Very few mainstream compostables meet the home composting standard.

To add to the confusing picture, there are also ‘oxo-degradable’ plastics. These are made from conventional plastics but include metal salts that cause them to break down into fragments. The aim is to accelerate biodegradation, but how effective this is, especially in the marine environment, is questionable; in the meantime the microplastic fragments can cause more harm to wildlife than an intact plastic container. In fact, neither the EU nor the bioplastics industry considers these materials to be biodegradable.

So, neither biodegradable nor oxo-degradable plastics will just ‘melt’ away if littered. Perhaps there is a need for new terminology – or perhaps new polymers – to reduce the risk of people wrongly thinking degradable plastics can be littered without consequence.

Equipment breakdown

The preferred waste management option for biodegradable plastics would probably be for consumers to include them in their organic/food waste collection, if they have one. Of course, that assumes people can successfully identify biodegradable plastics from others. There are logos that indicate a plastic item is biodegradable, but they aren’t yet widely understood. Some biodegradable plastics can look very similar to regular ones, and so careful reading of the label is necessary to avoid errors.

At a time when moves are afoot to simplify plastic packaging and collection systems to make it easier for consumers, introducing biodegradables could add an undesirable new layer of complexity. If users struggle to distinguish biodegradable from regular plastic packaging, more fossil fuel-based plastics may enter the biowaste streams, which is problematic; and biodegradables may enter the dry recycling stream.

But let’s assume that people successfully identify biodegradables and start putting them into organic/food waste collections. What would happen?

Nervous breakdown? Producers and consumers should be cautious about switching to biodegradable plastics. Photo: Doug Beckers (CC BY-SA 2.0), via Flickr.

Many food waste collections already accept compostable food waste bags. In principle, if additional biodegradable plastics go for in-vessel composting (IVC) or anaerobic digestion (AD), they should break down harmlessly and contribute to the energy and compost generated. Under the current system, though, that may not occur.

In AD, regular plastics in the feedstock can cause problems with the equipment – for example, clogging up pipes and pumps. Many plants in the UK operate de-bagging, de-packaging and screening processes to remove (as far as possible) anything that looks like plastic at the front-end of the process. This equipment will remove compostable and regular plastics alike, to be sent for energy recovery or landfill, which is a cost to the operator and negates much of the benefit of using biodegradable plastics.

Particular difficulties

In IVC facilities, plastics are less of a problem for the equipment and much of the compostable material should pass into the process and be composted. Regular plastics are a problem, though. Any larger pieces of residual plastic (of any kind) should be screened out of the compost product after treatment – but not smaller pieces of plastic, such as fragments of plant pots and plant label, that may be mixed into garden waste.

Concerns about plastic contamination can make it difficult to find a market for the outputs of IVC and AD, with some justification. It is undesirable to have another source of microplastics entering the wider environment.

A further issue is that not all garden waste goes to an IVC; the use of cheaper open air windrows (OAW) is increasingly common. Conditions at an OAW aren’t likely to lead to compostable plastics fully breaking down at the same rate as the rest of the material. If people assume that biodegradable plastics can be mixed with garden waste, regardless of how it is to be treated, then this is likely to create problems for OAWs, and unless removed from the input, undegraded plastic fragments may be left after the compost has been screened.

Close for comfort

Current practice in AD and OAW, and perhaps at some IVCs, would see little biodegradable plastic actually being composted. However, for AD plants and IVCs, if the operator knew that the only plastics in a batch of waste were EN13432 compliant, the situation would be different.

This level of confidence might be achievable in closed environments. The Glastonbury Festival trialled this approach, stipulating that only biodegradable plastics could be used on site; but this proved sufficiently problematic that the festival now bans biodegradables and is focusing on plastic prevention. It appears that Vegware believes it can be achieved by the hospitality and food service companies that use their products, as it is offering its customers commercial food waste collections. This will mean working closely with its clients, and the receiving biowaste sites, to make sure that the waste is acceptable. It is a novel approach and it will be interesting to monitor its effectiveness. But perhaps the most effective way of increasing confidence would be national legislation compelling the use of biodegradable plastics in certain applications, such as carrier bags or fast food containers.

The other potential mistake consumers may make is to put biodegradable packaging in with the dry recycling. Would that have negative impacts?

Once plastics have been separated from any other materials, Near-Infrared (NIR) technology is generally used to positively select polymers such as PET, HDPE and PP. The sorting process is unlikely to be disrupted by bioplastics, but in the current system they will become part of the non-recyclable remnant. Disposing of this is a cost for the sorting plant, and an increase in bioplastics would therefore increase their costs. There are examples of plants in Germany that are positively selecting biodegradable plastics: composting them is cheaper than disposing of them, but compared with the value they receive from recycling regular plastics, the economics of this approach are not especially favourable.

Plant pots?

One further option is the use of ‘bio-based’ materials that are identical to regular plastics in their make-up (e.g. bio PET). Although not biodegradable, they are fully recyclable and it is argued that they have a smaller carbon footprint than the same fossil-derived plastics. The main concern with these materials is their land take – one way to reduce this is to make them from natural by-products or waste materials, but that could limit how much can be produced.

So, current biodegradable plastics don’t solve – and may inadvertently increase – plastic littering. They are unlikely, within the current system, to be composted, and they will not be recycled, even though some of them are recyclable. That system could change, particularly if law or practice develop so that biodegradable (ideally, home compostable) plastics become ubiquitous, at least in some applications – whether as standalone items, or as barrier coatings/linings for paper-based packaging. If clearly labelled, these products could be composted. AD and IVC plants could be assured that almost all of the plastic they receive would be biodegradable, and may make it worthwhile for plastic sorting facilities to separate out biodegradables for composting.

These potential benefits should not be ignored. However, biodegradable plastics are ultimately a means of ameliorating the harm caused by our seeming addiction to the convenience of throwaway packaging.  Changing business models to ‘design out’ single use plastics, and using measures such as deposit refund schemes to reduce littering of those that remain, are still the highest priorities when it comes to tackling problem plastics.