Probably, after learning about the existence of the ” plastic island in the Pacific “, more and more people are trying to find out how we can contribute to a more adequate management of our consumption and generated waste. In this context, the use of renewable resources and energy, as well as the biodegradability capacity of many materials, are considered as new alternatives and allied tools to reduce the catastrophic environmental impacts resulting from the accumulation of synthetic materials that are difficult to degrade.
Biodegradation of plastics, what is it?
The curious and surprising process of biodegradation of plastics consists of the mineralization of the organic structures of these residues through the action of microorganisms. It is a short-term process that guarantees the use of the degradation of certain plastics to obtain energy and nutrients in the form of biomass and other elements. These plastics that are biodegraded by microorganisms are called biodegradable plastics . In them, degradation and decomposition takes place in the form of organic matter and minerals.
But are all plastics suitable for biodegradation by microorganisms? The answer is no, since, in order to be biodegraded, plastics must meet certain requirements, including:
- They are obtained from natural polymers, present in nature for a long time.
- The living beings in charge of producing these natural polymers through enzymatic reactions are the same ones that will later be in charge of the degradation of biodegradable plastics through biological systems.
- Some of the most abundant biodegradable plastics belong to the group of polyhydroxyalkanoates (PHA), biopolyesters with a carbon and energy reserve function synthesized by microorganisms.
- When extracted from the cells in which they are synthesized, PHAs have physical properties that resemble those of conventional petroleum-based plastics.
- The products of the biodegradation of these plastics are water and carbon dioxide (methane is produced in some conditions), without generating any type of unnatural waste.
The main groups of organisms that have the ability to create and degrade these PHAs belong to different families of bacteria and fungi. Next we will see in more detail what the most common biodegradation methods of plastics consist of , as well as the importance and usefulness of said biodegradation.
When analyzing the different methods that allow the biodegradation of plastics, it is necessary to differentiate between the categories of primary biodegradation and secondary biodegradation:
- Primary biodegradation: it produces structural alterations of the original molecules of the plastic material, which lose their physico-chemical properties.
- Secondary or total biodegradation (mineralization): in this case, the chemicals in plastics are metabolized, in order to serve as a source of carbon and energy for the microorganisms that carry out the biodegradation. In this way, the plastic is completely transformed into inorganic compounds.
These biodegradation processes can be carried out both under aerobic conditions (with the presence of oxygen) and anaerobic conditions (in the absence of the same gas). Different factors directly and indirectly influence the biodegradation process of plastics , such as the pH, temperature and humidity of the medium, as well as the chemical characteristics of the polymers that make up the plastic, their dimensions and, on the other hand, the characteristics of the microorganism. which acts as a biodegradation agent.
The biodegradation of plastics is currently a strategic opportunity to manage the dumping of plastic waste in the environment in a more sustainable way . The urgency of reducing the excessive and tremendously polluting accumulation of synthetic materials has led to the evaluation and scientific investigations of the biodegradation of these polymeric materials.
Thus, to evaluate the environmental impact of plastic materials according to their biodegradation capacities, many countries carry out biodegradability tests, whose tests and requirements have been standardized to guarantee the validity and reliability of their results. In addition, numerous standards have been published as a test to determine the degree of biodegradation of polymers used in the manufacture of packaging and other industrial products, such as:
- ISO EN 13432 standard: certifies compostable and biodegradable plastic packaging so that consumers can easily distinguish between them.
- EN ISO 14853-15985: determines the final anaerobic biodegradability of the plastic materials present in the digestion of sludge.
- EN ISO 17556: 2003: characterizes the final aerobic biodegradability of bioplastics according to the oxygen demand or the amount of carbon dioxide in the earth.
- Immediate, intrinsic and soil biodegradability tests byThe Organization for Economic Cooperation and Development (OECD): from which the biodegradability of plastic substances is determined.
In this way, the importance and usefulness of the biodegradation of plastics resides in the action of these standards and in the certification and labeling of bioplastics as biodegradable or compostable materials, to treat the management of these wastes together with the organic fraction (remains of food, pruning, etc.) of urban solid waste in composting plants, without leaving toxic waste. Thus, natural biodegradable plastics are recognized as substitutes for plastics of petrochemical origin.