Aspergillus tubingensis: Fungus able to degrade plastic without leaving residues. Recycling in agriculture
With more than 10.000 million tons of plastic produced by humans, the management of these waste that can take centuries to decompose is today one of the great challenges for the environment. However, a scientific team may have found in nature a sustainable and effective remedy: a fungus species found in a landfill in Pakistan that is able to degrade the plastic in weeks.
This has been confirmed in different scientific laboratory tests of the World Agroforestry Center (ICRAF) and the Kunming Botanical Institute, in China, who, led by Sehroon Khan, have discovered in a species of fungus, scientifically known as Aspergillus tubingensis, which they call "Unexpected solution" to the serious threat posed by plastic waste.
"We wanted to identify solutions in nature itself, although finding microorganisms that could achieve this is not easy" He admits Khan, whose team, despite the difficulties, found this fungus after taking different samples at a landfill in Islamabad, Pakistan. The challenge: find some organism that was feeding on the plastic.
It was complicated, but they did it. Thus, after carrying out various tests in the laboratory, he came across this new ally in the fight against plastic: Aspergillus tubingensis, a fungus that grows on plastic surfaces, on which it secretes enzymes that break the chemical bonds of plastic molecules. In addition, as it was verified during this work, these fungi also decompose polymers. "Even plastics that would otherwise remain in the environment for years can be broken down by these fungi in a matter of weeks", The persons responsible for the finding assure us.
The solution is hopeful since it can offer an alternative to methods that, like the burying of plastic waste in landfills or incineration, are not sustainable enough to face this environmental challenge.
However, the authors of this study - “Biodegradation of Polyester Polyurethane by Aspergillus tubingensis”(Biodegradation of polyurethane polyester by Aspergillus tubingensis) - they admit that there is work to be done. This is so because the performance of these fungi in the decomposition of plastic is influenced by environmental factors, such as pH levels or temperature.
Therefore, before the Aspergillus tubingensis can effectively fight a battle against plastic, this research team will continue working to determine the growth conditions of these fungi and the degradation of plastic. Once these answers are found, on the horizon is the large-scale use of these fungi in waste treatment plants or in land that is already contaminated by plastics that can take hundreds and even thousands of years to disappear.
Recycling of plastics for agricultural use
The great diversity of plastic materials finds a significant share in consumer products and covers all market sectors. According to the trends observed in recent years, the packaging, electrical and electronic, electrical appliances and construction sectors stand out for their greater participation; automotive, and agricultural.
Therefore, considering the high volumes of plastics generated, it is clear from this the importance of analyzing the stage of treatment of the residual plastic materials, contemplating recycling as an alternative measure to minimize the environmental impact.
The use of plastics has grown rapidly in the agricultural sector thanks to the increase in production and reduction of costs. The various items used in agriculture are made of different plastics such as low density polyethylene (LDPE), mainly used in greenhouse and mulch film, structures that provide the crop protection against environmental conditions and insects and pests; high density polyethylene (HDPE), in containers for pesticides and pesticides as well as in containers for nurseries or slips for irrigation; polypropylene (PP) in containers for nurseries or floating covers and polystyrene in trays for nursery etc.
Faced with the large amounts of plastic waste, the common disposition practices carried out by farmers have consisted in burying them, which compromises the quality of the aquifers, or burn them in the open with the consequent emission of high levels of gases pollutants
So the recycling of agricultural plastics is presented as a technique of low environmental impact, as it does not produce toxic substances that can be generated during other disposal methods such as incineration, in addition to presenting advantages from a technical and economic point of view.
In recycling, the quality of recovered plastics is determined, mainly, by the amount of pollutants present, such as soil, grease, vegetation, humidity and other types of plastics that can reach up to 40% by weight, thus for agricultural plastics the Contamination is one of the most important and frequently encountered problems that can reduce the acceptance and condition the re-processing of these materials.
The two types of critical pollutants in agricultural plastics are:
- The presence of residual agrochemicals, both in films and containers, which involves a stage of pre-washing and intensive washing to eliminate or minimize the content of these, also conditioning its final application.
- The degradation by ultraviolet light. Greenhouse films are subjected to a degradation process in two different stages of their life cycle.
The first stage is during its application in the field (at the stage of crop development), where it receives the combined effect of both temperature, oxygen and solar radiation, is affected by considerable damage to the chemical structure and consequently in the optical and mechanical properties of the plastic film.
The second stage is during the reprocessing in melting of previously clean material for obtaining pelleted material, which, as during its application, combines the degrading effects of temperature and the mechanical stresses generated during extrusion. So the technical and economic value of the finished product (pellet, film or pipe) will decrease, since it will have losses in its optical and mechanical properties.
Due to the problems present in this type of plastic waste, the following stages of a recycling process are contemplated:
- Pretreatment and separation stage: The high content of powders and solids (mainly soil) is removed by using a rotating drum screen, and immediately the wood, paper and fibers present are separated by hand. Subsequently, plastics are classified mainly into 4 types LDPE, PP, HDPE and PS, which are the most used in agricultural applications.
- Wet grinding stage: Due to the origin of the previous application of agricultural plastics, the presence of earth and other foreign materials gives special consideration, so during the grinding stage, it is not convenient to cut the material dry, as overheating The blades can melt the plastic and agglomerate the contaminants present. Therefore, it is recommended to perform the size reduction in wet phase, trying to avoid the wear or breakage of the blades of granulating equipment and, in turn, providing a longer duration of the blades and internal meshes.
- Washing and drying stage: Starting from the fact that the films or various plastic items for agricultural use have a high probability of being impregnated or contaminated by agrochemicals, the ground material requires a triple washing cycle with water, followed by a centrifugal drying in each stage. The effluent from the washes, after having been decanted from the solid mud and being properly neutralized and chemically treated, is usually sent to the washing tanks to be reused. Subsequently, the ground material must be passed through a hot air dryer, thereby minimizing the presence of moisture that may hinder the subsequent processing steps.
- Pelletizing stage: The previously washed and dried leaflet is subsequently pelleted by extrusion. This in order to homogenize the pellet size and, mainly, try to minimize the viscosity variability of the different batches of mixed materials. Thus, the molten plastic is filtered in a section prior to the head of the extruder to eliminate any foreign material that was not removed in the previous stages of separation and washing, thus allowing the obtaining of pellets as a finished product.
Due to the application characteristics to which agricultural plastics are subjected, ie a high solar exposure and a high content of foreign materials or contaminants, the expected quality of the pelleted material generally fails to meet the requirements demanded for processes such as extrusion. blown film or container, thermoforming or injection molding. So it is recommended the previous preparation of mixtures with virgin resin or the use of additives such as anti-oxidants, uv stabilizers, etc., through the extrusion process, to improve some of the properties of the final product recycled.
Due to the aforementioned, the recycling of agricultural plastics presents a degree of complexity attributed mainly to the degree of degradation, mainly dependent on the period of sun exposure, during the application of the film in the mulch or greenhouse structures, or on the degree of contamination. residual of agrochemicals or solid residues in recovered containers, flowerpots or trays; Therefore, the efficient use of these recovered materials will depend on the previous stages of separation, washing and pelletizing; as well as the preparation or reformulation of mixtures of recycled material with virgin material or the addition of additives to improve the properties of the recovered materials.
Source: Ecoinventos - Pt-México - Portal Frutícola
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