Compostable Bags: Solution or Pollution?

The compostable bag was first introduced to the retail industry as a way to curb the plastic problem and close the loop on the production of carrier bags. 

With their dual usability, compostable bags can be first used to bring goods and groceries home from the shops, and then used to line compost bins at home. 

Commonly made from vegetable matter, such as potato and corn starch, compostable bags were originally brought in as an alternative to one-use plastic carrier bags.

And with the ability to be decomposed by microorganisms such as bacteria, the compostable bag has often even been favoured to other one-use alternatives such as the ‘Bag For Life’

However, a common misconception about the biodegradable bag is that decomposition will occur in the natural environment.

This could mean that by sending compostable bags to waste, they could end up in the oceans or landfill and naturally begin to decompose.

However, the reality is that the bags need to be treated in optimum conditions in order to decompose effectively; such as those harvested by industrial composting plants. 

And, in order to be considered a ‘compostable bag’, the material must conform to the standards set by their governing body. 

For members of the European Union, this means adhering to the EN 14995 directive, whereby compostable products must have visibly disintegrated within 3 months, and biodegrade by at least 90% in six months when being treated at 60°C in an industrial composting plant. 

The issue with this process is that very often end-users of the compostable bag don’t know where their food waste is sent to.

While some households might have their food waste collected for industrial composting plants, others could be sent for processing in an Anaerobic Digestion plant.

Due to their high water content of up to 54%, compostable bags can often present a problem when they end up in AD plants as they require an extended drying period before their dry matter can be processed. 

It has therefore been suggested that a new biopolymer should be identified for use in compostable bags, along with a new standard for plastics that will biodegrade in biogas plants. 

However, the varying conditions across different biogas plants means that they could operate under varying temperatures, time periods, and using different microorganisms; thereby making developing a standard a more challenging task. 

Another issue with the biodegradable bag is that, in previous years, it has been confused with a recyclable plastic and placed in with plastic recycling by end-users. 

Whilst it is estimated that plastic recycling plants have the capacity to deal with up to 10% contamination from compostable bags, they have been known to present a much wider issue than just causing contamination. 

Due to their high elasticity and lightweight structure, compostable bags have the tendency to get wrapped around the rotors, screw augers and other components within mechanical recycling plant machinery, causing them to get jammed and ultimately resulting in machine downtime.

On the other hand, compostable bags which have survived the mechanical recycling process have been known to end up in recycled goods where, true to form, they have begun to decompose; leaving gaps in recycled products and rendering them useless. 

Equal but opposite, it has also been estimated that around 5% of materials that are collected for bio-waste plants are non-organic; with the majority of contaminants being made up of plastic. 

To a certain extent, the fate of the biodegradable bags, much like that of recyclable plastic, lies in the hands of the end-user. 

By placing biodegradable bags in the brown food compost caddy provided by the local authorities, end-users can set the compostable bag off on the right tracks.

Thereafter, the bag will rely on the optimum conditions of an industrial composting plant in order to be degraded in the way in which it was intended. 

Find out more about one-use plastic bag alternatives in our press release: Has the ‘Bag For Life’ become a thing of the past?

To read more about the UK’s response to the plastic problem, see our press release about Closing the loop on plastics with UK-based recycling infrastructure and The future is circular. 

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