In 2021, a total of 8.6 million tonnes of plastic waste will be produced worldwide. This figure is evidence of how well this material is received by society, but also of its great environmental impact. If this waste is not properly managed and treated, the consequences for the planet could be devastating: reduction of natural resources, increase in Greenhouse Gases (GHG) and pollution, rising temperatures… Faced with this drastic prospect, the plastics industry has taken action and has sought more sustainable ways to recycle and recover waste. One of them? The biological recycling of plastics. Here’s what it’s all about.
The process of bio-recycling
Although plastics are unnatural chemical compounds, these materials can be degraded and metabolised by microorganisms for subsequent reuse. This process is known as biological recycling or biorecycling and is a perfect example of circularity.
Unlike mechanised recycling, this technique allows any plastic material – regardless of its origin, colour or number of layers – to be recycled in an unlimited way and without losing its initial quality. In other words, through biorecycling, plastic could be recycled in an unlimited way and maintain its original properties.
To make it easier to understand, let us give an example: let us imagine that, instead of recycling plastic, we have to make a stew. Biological recycling would be equivalent to a crokpot or low temperature cooker and mechanical recycling would be equivalent to a pressure cooker. With both we can make an excellent dish. However, with the former, the stew will retain all its properties and flavour, and with the latter, it may lose some of its nutrients.
Types of bio-recycling in plastic materials
There are several types of bio-recycling. The most widespread are:
Composting” is the name given to the process of decomposition of organic matter. For this to take place, the participation of different micro-organisms (bacteria, fungi and invertebrates) is necessary, but also the continuous presence of oxygen. It is O2 that prevents waste from rotting, emitting bad odours and turning into compost or natural fertiliser.
For a plastic to be compostable, it must be biodegradable or compostable. Two terms that, although similar, do not mean the same thing. Biodegradable plastic is plastic that can be broken down naturally by the action of micro-organisms. Compostable plastic, on the other hand, biodegrades but only under specific conditions and then produces compost.
Anaerobic digestion or biomethanisation, in contrast to composting, is the process of organic waste decomposition that takes place through the intervention of different groups of micro-organisms, but always in the absence of oxygen. During this process, organic matter is broken down into simpler compounds, which in turn are transformed into volatile fatty acids. These acids are consumed by methanogenic micro-organisms, generating gases such as methane and carbon dioxide, which can be used as a source of heat and energy.
For anaerobic digestion to occur, the temperature of the process must be between 35ºC and 55ºC and must be applied to organic matter. This means that for this type of biological recycling to be successful, it requires biodegradable plastics.
Enzymatic recycling is a process
Although unknown to the average person, enzymatic recycling is a waste recovery technique that stands out for its sustainability and energy efficiency. It breaks down the polymer chains of plastic but, unlike mechanised recycling, it does so by means of enzymes. These are proteins produced by microorganisms such as fungi and bacteria that accelerate the partial degradation of the polymers and make it possible to break down the molecules that make up the plastic into its fundamental components: oligomers and monomers. The latter can be purified and repolymerised, resulting in materials with characteristics and physical properties that are as good as the original ones.
Because they are more chemically selective than synthetic catalysts, enzymes allow a purer product to be obtained.
How does bio-recycling impact on the environment?
If mechanical recycling of plastics has multiple benefits for the environment, biological recycling has even more. As mentioned above, this recovery process is an example of circularity: during biological recycling, the plastic is used in its entirety and can be reused in an unlimited way without losing its properties. The advantages are several:
- Saving energy and natural resources: in terms of energy and natural resources, it is less expensive to recycle plastic than to produce it from scratch.
- Preservation of the environment: plastic waste can take between 100 and 1000 years to degrade and, during this process, pollute seas and oceans. That is why it is so important to manage it properly and recover it through techniques such as bio-recycling.
- Pollution reduction: with biological recycling we reduce energy consumption and, thanks to it, the emission of GHGs that impact on the atmosphere.
- Prevention of solid waste reaching landfills: in addition to responsible consumption, recycling is the best way to reduce waste and prevent it from ending up in landfills, contaminating soil and water.