Do bin liners for compostable waste decompose too slowly? Does it make more sense to collect compostable waste without bags? No. Because by now there are numerous scientific studies that prove unequivocally that compostable bags are a thoroughly sustainable solution for the environment and contribute to the fact that more kitchen and garden waste is collected in compostables bins. Compostable waste is a valuable raw material that is used in biogas plants to produce electricity and heat and in composting plants to produce high-quality fertilisers and soil improvers. Operators of biogas and composting plants often express concern that the biodegradable bags decompose too slowly. However, numerous studies prove the opposite.
One of the many concerns about biodegradable bags is that it takes too long for them to decompose completely. However, it has been proven that they break down just as quickly as their contents, i.e. household compostable waste, during industrial-scale composting. This also means that they decompose within the composting time parameters of common types of composting plants. The composting process in most plants takes five to ten weeks. Our bags break down much faster than that. A study on the use of biodegradable bags made of Mater-Bi material from Novamont shows that the bags are completely broken down at the maturation stage of the composting process.
Maturation is the final stage of composting. Industrial-scale composting is controlled decomposition. The process is also called rotting or mouldering. Microorganisms, such as bacteria or fungi, break down dead vegetation into humus, leaf litter and mould. The biomass then serves plants as a nutrient. For home composting, we adopt this cycle in order to convert organic materials into garden soil quickly and in a controlled manner. Industrial-scale composting consists of processing the compostable raw materials, intensive composting and maturation over several weeks. Finally, the compost is sieved and packed.
The DIN EN 13432 standard specifies the extent to which compostable bin liners must be broken down. According to this standard, fully biodegraded means that the bags have decomposed only 90 %. This is because the level of biodegradation is measured by the carbon dioxide produced. Fungi and bacteria are mainly involved in the breakdown process. These convert the bags into carbon dioxide, but they also need a part of this CO2 to grow and multiply - this part cannot be measured and makes up the remaining 10%.
Fermentation is the process of decomposition in the absence of oxygen. Different microorganisms are involved in this process compared to composting and they do not cope so well with compostable bin liners.
After fermentation, the fermented material is composted to mature compost. During this composting process the bags are completely broken down.
Certified bin liners for compostable waste that have been tested according to EN 13432 can be recognised by the seedling symbol printed on them. The seedling symbol is legally protected, and any fraudulent misuse will be prosecuted. This symbol also guarantees that no microplastic is left after composting.
Analyses show that many people prefer to collect their wet kitchen waste in plastic bags. The big advantage is that this keeps the kitchen waste bins clean and the bags can be thrown more easily into the compostables bin. Paper bags or newspaper tear quickly when they get wet. By allowing citizens to use special bin liners for compostable waste, the motivation to collect organic kitchen waste separately increases.