Should you put your food waste in a compostable plastic bag?

Should you put your food waste in a compostable plastic bag?

Across Europe rules about the disposal of organic household rubbish vary. Some waste management companies let people line their food waste caddies with compostable plastic bags, while others ban all plastics from organic waste bins

If you walk into a council office or a recycling centre in Germany today you might see a poster for the #wirfuerbio campaign, which states that no plastics including compostable plastics should be added to organic bins. But if you live across the border in Austria the latest campaign encourages people to use compostable plastic bags to collect their food waste. This pattern is repeated across Europe: different rules on adding plastics to organic trash bins exist between countries and even within countries, creating confusion among the public.

The companies behind the #wirfuerbio campaign say that compostable plastics do not fully breakdown in their waste processing plants. But others claim that allowing plastic bags has benefits.

Stefanie Siebert, executive director of the European Compost Network believes that you get “much higher food capture rates” if you allow people to use bags, because food waste is messy and people don't like cleaning the bins.

Sandra Uschnig, from the Austrian Compost and Biogas Association agrees: letting people line their organic bins with plastic bags (compostable, of course) encourages them to use separate food waste collections. “Every year in Austria 255,000 tonnes of organic waste is thrown out with non-recyclable rubbish”, she says.

Earlier this year, at a European bio-waste conference, composting and biogas associations reported that around five per cent of materials entering bio-waste plants is non-organic: and that most of the contaminants are plastic. In 2017 researchers at the University of Bayreuth in Germany, found that a kilogramme of fertiliser produced from household rubbish can contain almost 150 microplastic particles. They estimated that compost from bio-waste plants in Germany add billions of microplastic particles to the environment every year.

In the European Union, bags described as compostable need to conform to the EN 14995 directive. Bruno De Wilde, Lab Manager at OWS, which carries out compostability testing, explains that a bag is compostable if it biodegrades (at least 90 per cent of it has broken-down to C02 by biological action) within six months in an industrial composting plant operating at 60°C, and has visibly disintegrated within three months. This, it turns out, is key to the different organic waste rules across Europe.

Some composting plants operate on shorter time scales than the six months assumed by the EN 14995 directive, meaning that some compostable plastics do not fully biodegrade.

And in other places food waste is not actually composted. When De Wilde talks about “industrial composting”, he is referring to aerobic composting plants. But in some areas organic waste – plus any compostable bags – is sent to anaerobic digestion plants that produce biogas. “Composting is aerobic, that is with oxygen”, De Wilde says. Anaerobic digestion, however, is without oxygen and is therefore not strictly composting, which means that it doesn’t breakdown compostable plastics. “[Compostable bags] cannot be used for bio-gasification,” De Wilde adds.

Veronika Bátori, a researcher at the Department of Resource Recovery and Building Technology, University of Borås, Sweden, thinks that we need to develop a new standard for plastics that will biodegrade in biogas plants. In a recent review of the anaerobic degradation of bioplastics, Bátori and her colleagues identified some promising biopolymers – such as starch, cellulose and pectin.

De Wilde explains that currently there is no certification for plastics that breakdown in anaerobic conditions, because the biogas plants run on various different systems, using different microorganisms, and operating at different temperatures and for different lengths of time, making developing a standard challenging.

While researchers investigate new solutions, Siebert calls on municipalities to keep people informed. “They must have a good education campaign and advice on what is allowed in the bio-bin,” she concludes.

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