Private households dumping plastic materials into their organic waste bins contributes to environmental pollution. This is because these wastes are usually used by communal facilities to synthesize biogas and the final residue is processed into organic fertilizer.
Often, minute plastic particles stay back in these fertilizers, eventually ending up in water and soil. A research at the University of Bayreuth, currently published in Science Advances journal, has brought this matter forward.
The research was the fruit of a close interdisciplinary collaboration under the leadership of Professor Dr. Ruth Freitag (Process Biotechnology) and Professor Dr. Christian Laforsch (Animal Ecology). They analyzed various biogas plants to discover, apart from other things, the way the plastic content of the synthesized fertilizers is influenced not only by the source of the organic waste but also by the selected machinery and processing technology.
- When private households contribute to a major portion of the organic waste, the number of plastic particles contained in it is exceptionally high. In general, the particles are made of polyethylene or polystyrene. Both of these materials are generally used in grocery packaging as well as other consumer articles. Majority of the particles can be recognized to be fragments of packages, bags, and other containers that reach the organic waste bins because of a “bad throw.” Even after careful sieving of the residue from fermentation, it is not possible to remove plastic particles that have a diameter of less than a few millimeters. Such particles remain in the fertilizers.
- Biogas plants that run on organic waste supplied from trade and industry, on the other hand, evidence a remarkably high proportion of polyesters. In several instances, these plastics are evidently from protective materials and containers used to package and transport fruits and vegetables in huge quantities.
- The scenario is entirely different in the case of facilities that exclusively use energy crops to synthesize biogas. In these plants, the Bayreuth scientists could not find any or could find only very few, plastic particles in the fermentation residue. The scenario is similar in facilities synthesizing biogas predominantly from manure. In these plants, the scientists could hardly find plastic particles, if any.
However, the research also indicates that the plastic content in fertilizers is determined not just by the origin of the organic waste. Several other factors that impact the type and degree of contamination to a greater extent are the processing of the waste before the fermentation process and the further processing of the fermentation residues.
With a bit of effort, it is possible to sort out foreign bodies such as plastics, metals, or glass from the biowaste prior to fermentation. Of course, it would be better not to let them enter into the organic waste to begin with. Organic waste is an important resource in a recycling economy, which deserves to be intensively utilized now and in the future. Our study shows that contamination with microplastic particles is largely preventable, but it requires members of the public and plant operators to act responsibly.
Professor Dr. Ruth Freitag
For many years, the growing levels of environmental pollution due to plastics have been a research priority at the University of Bayreuth. For instance, the research team headed by ecologist Professor Dr. Christian Laforsch has conducted detailed studies of microplastic pollution in lakes and rivers in Germany.
In order to reveal the consequences of this alarming development and to be able to respond with suitable measures, we first need to know how the plastic particles get into the ecosystems. This was also one of the initial questions in our new study on organic fertilizers made from organic waste. The findings clearly show that all members of the public, in their home and communal environments, can make a contribution to conservation and the ecological recycling economy.
Professor Dr. Christian Laforsch
As part of the new research, only microplastic particles with a size of 1–5 mm are considered. Smaller particles were not investigated; however, they might also have a role in the contamination of organic waste. According to the gathered data, one ton of compost from industrial waste and households contains from about 7000 to about 440,000 microplastic particles. Taking into account the fact that, annually, five million tons of compost is generated in Germany, several billion microplastic particles could reach the environment this way.