Composting is generally carried out "in a container" or in some form of "bioreactor" where process parameters such as humidity, temperature, pH, aeration, retention time and compost content are strictly controlled. It provides a more efficient way for waste polymers to be broken down into carbon outputs that can be used as rich soil products in agricultural activities or even just harmlessly returned to nature. Most importantly, it alleviates the escalating need for landfills.

In the composting process, the decomposition of plastic is carried out by microorganisms (moderate and thermophilic), including bacteria, fungi and actinomyces. Microbes break down carbon-based polymers into organic matter as a food source, producing carbon dioxide as a by-product and humus as an end product. This is a natural process that requires nitrogen, water and oxygen. The composting process is divided into two stages: the initial composting stage and the curing stage. During the initial active phase, temperatures rise and oxygen is needed to support strong aerobic microbial processes. During the curing phase, the temperature drops, but decomposition continues, albeit at a slower rate. The compost will slowly decrease until all the carbon has been converted and all the nutrients have been completely consumed by microorganisms.

The degradation rate is optimal under aerobic and high temperature conditions. As a result, composting facilities typically operate under high temperature aerobic conditions of about 58°C, and mature solid compost contains a high water content (about 50%) and thermophilic microorganisms. The biodegradation process can be accelerated by pre-treatment using ultraviolet light or physical methods, which allow microbial enzymes to act subsequently to break down the polymer waste. In addition to aerobic composting, anaerobic digestion or biogasification can also be used as an alternative to solid waste disposal.

Composting plant

The composting process starts with a basic sorting process to identify and remove waste that is not suitable for composting. Separating waste at source is key to the effectiveness of a composting system. Through source separation, kitchen waste and garden waste are separated from other waste to form a perishable compost "biowaste."

Compost is mixed with additives to achieve the desired nitrogen, moisture, and porosity levels. Peeling and grinding can optionally break down bulk organic items (cardboard and newspaper) to aid in decomposition. Regular turning and mixing of the compost bin is very necessary to ensure that the degraded material breaks down evenly in the compost body. After the initial composting period takes 2 weeks, the compost is moved to an open area for a "rot" or "cure" stage at a slower rate of degradation.

Regulations regarding composting

The European Packaging Directive (EPD) 94/62/EC is a Europe-wide standard for the management of packaging materials. The EPD stipulates composting as the standard treatment method for packaging waste, and CEN TC261 SC4 (European Committee for Standardization) as the regulatory body for biodegradation test methods.

According to the International Organization for Standardization (ISO), the European Committee for Standards (CEN), the American Standard Test Method (ASTM) certified packaging materials for fertilizer and Japanese Industrial standards (JIS). "DIN CERTCO" by DIN (German Standards Institute) and "OK Compost" by AIB Vincotte (Belgium) are based on EN 13432 (based on ISO). The "GreenPla" certification obtained by the Biodegradable Plastics Society (Japan) based on JISK6953 is the same as ISO 14855. Finally, the American Composting Council's "compostable" is based on ASTM D6400.

Standards ISO 14855, EN 13432 and ASTM D6400/5338 establish requirements and criteria for determining the degradability of materials. In addition to biodegradation, certified biodegradable materials must demonstrate their ability to break down into visually indistinguishable fragments without negatively toxic effects on the environment. The European certification standard EN 13432 specifically requires that not only plastic components must be degradable, but also all other components in the product, including colorants, labels, adhesives, etc. It is important to note that compost stability and biodegradability are not used interchangeably. Not all biodegradable materials meet compost standards.

Despite progress in composting efforts in the EU, commercial adoption of composting facilities remains low due to the lack of a comprehensive understanding of complex degradation mechanisms and optimal conditions for suitable degradation.

References: Biodegradation of polymers in managing plastic waste — A review. Science of the Total Environment 813 (2022) 151880.

Hubei Loktec is one of the few suppliers in China to provide complete solutions for material biodegradation performance testing equipment and services through completely independent research and development. We provide RTK PBDA plastic biodegradation analyzer, RTK PBD automatic plastic disintegration analyzer, RTK PBDH home compost disintegration analyzer, RTK CRM closed respiration meter, RTK BMP automatic methane potential test system, RTK-BRE microbial degradation respiration meter and other products for customers with different needs. It can be applied to the test of all kinds of plastic biodegradation performance evaluation standard methods.

Hubei Loktec Instrument Co., LTD., founded in 2013, is a national high-tech enterprise (certificate number GR202042003741), with nearly 30 patent certificates (including invention patents) in the field of biodegradation. It is the Joint Laboratory of Anaerobic Fermentation of China Agricultural University and the cooperative base of industry-university-research of Huazhong Agricultural University. As a research manufacturer of scientific test instruments in China, Loktek strives to provide professional scientific test instruments, test methods, training and technical services to customers around the world. Adhering to the mission of "technology promotes scientific progress", Loktec is committed to the goal of "carbon peak, carbon neutrality" in China, providing services for the government, universities, research institutions and enterprises to achieve healthier, safer and more environmentally friendly high-quality development.

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