Armazenamento de compostagem. Crédito: Troy Sankey/Wikimedia Commons/CC 4.0

Study forecasts home recycling that turns plastic into biogas

A paper elaborated by Ireland universities shows that installing home composting systems to transform plastic waste into energy source is possible

Currently, the best destination for most plastic waste is recycling, which requires a complex transformation of such material in order to be reintroduced to the production chain. In a not-very-far future, this process may take place at our homes and convert plastic into an extremely useful substance: biogas.

A project developed by the Irish universities College Dublin and Trinity College Dublin published in the American Chemical Society (ACS) magazine Environmental Science & Technology, found a technology that works as a household composting able to decompose certain types of plastic and, from this chemical reaction, produce biogas.

Researchers selected 15 types of plastic or blends of plastic and assessed their behavior under specific conditions, that could be managed (such as composting and anaerobic digestion) or could not be managed (such as soil and freshwater or saltwater).

Then, they showed that many of these plastics and blends decompose under anaerobic digestion conditions, including when degraded under an industrial composting model. The article points out that the polylactic acid (PLA) case, which requires extremely high temperatures to degrade, but when exposed to a combination of carbon dioxide, biomass and water was suitable for home composting.

Biodegradable plastics: a solution, however, requires caution

The goal of the paper was to observe the behavior of biodegradable plastics mixed in blends with more resistant materials. Currently, most biodegradable polymers do not have flexibility, strength or resistance equivalent to those of conventional plastics, but their performance is improved when combined together or with their synthetic forms.

To the authors, the problem is the behavior of combined bioplastic, from environment perspective, is uncertain. In the article, the researchers assert that all tested types of plastic or plastic blends, only two of them, polyhydroxybutyrate (PHB) and thermoplastic starch (TPS), degraded completely under all soil and water conditions.

The conclusion is that biodegradable plastic deserves attention, but should not be considered a “panacea” for improper plastic disposal problem at global scale. “So, biodegradable plastic blends require a careful post-consumption management and additional project is required to make biodegradation faster at multiple environments [test shows that retention times are six times slower than retention at commercial plants], as its release into the environment may cause plastic pollution,” note the authors.

“If society intends to replace nondegradable plastic by the biodegradable one, we have to ensure that we understand the biodegradability of these materials and, in particular, their compositions, as they tend to be more commercialized. This knowledge can inform us areas of applications for these materials so they can have a positive impact on disposal management options,” concludes the study.