Composting and Biodegradability: A Breakdown
As consumers drive companies towards increased sustainable packaging, companies are investing and innovating to find new sources for raw materials as well as new ways of safely returning them to the environment. Increasingly you will come across words like bio-renewable, bio-based, bio-plastics, biodegradability and compostability. But what do all of these words mean exactly? And what is the best choice for the environment?
The first distinction between these terms has to do with whether it refers to the origin or end of life of the packaging. Bio-renewable and biobased refer to the origin and are not sourced from petroleum. Bioplastic refers to biobased and biodegradable plastics. For example, there are versions of plastic that are made from sugarcane, which can be labeled as bio-based or bioplastic packaging. These plastics can be chemically identical to petroleum plastics; they just come from different sources. Biodegradable and compostable packaging refers to how the packaging behaves during end of life. It’s possible for a product to be both bio-based and biodegradable like paper, PHA (polyhydroxyalkanoate), or PLA (polylactic acid).
Many bio-based polymers are not biodegradable. For example, Polyethylene Terephthalate, or PET plastic made partly from plants in Coca Cola’s plant bottle is not biodegradable or compostable–but it is recyclable. This is because the PET is identical to the PET made from petroleum. The key difference between these two forms of PET is in how they store and release carbon. When carbon dioxide is removed from the atmosphere by plants, it is ultimately released back into the atmosphere when the plant decays. Therefore, plant derived plastics that can be recycled over and over again delay the release of that carbon back into the atmosphere. Plus, using renewable resources like sugarcane and corn to make plastic can be better than using our limited supply of petroleum.
Interestingly enough, all bio-renewable, bio-based and bioplastics can be manufactured using just 1% of the world’s farmable land. This would produce around 300 million tons of bioplastics. (This calculation assumes that all 300 million tons would be made of PLA.) This research, conducted by Dr Ramani Narayan at Michigan State University, concludes that manufacturing “bioplastics will not have any negative impact on food production or land use. On the contrary, it will stabilize rural agrarian economics and food security.”
Now let’s look at biodegradability and compostability. Biodegradable means a material will break down naturally because of microorganisms, fungi or some other biological activity. A specific time or conditions are not usually specified. In fact, most things could be considered biodegradable over a long enough time horizon. Factors that affect the rate of biodegradation are light, water, oxygen and temperature. In general, biodegradability itself is not a useful distinction unless a specific environment and time are included.
The process of biodegradation itself goes through 3 stages: biodeterioration, biofragmentation and assimilation. The biofragmentation stage occurs either through aerobic digestion (when oxygen is present) or anaerobic digestion (when oxygen is absent). Carbon dioxide is produced in both these microorganism digestions. In addition, methane is produced during anaerobic digestion which is worse for the environment. As an example, landfills are the third largest source of man-made methane because of this lack of oxygen. Now, in many modern landfills, these gases are captured and burned for energy which may mitigate some of the environmental harm.
Composting on the other hand is a specific biodegradation process which usually specifies time and the right conditions. The standard for industrial compostability EN13432 specifies following 4 criteria:
- Chemical composition: volatile matter, heavy metals and fluorine should be limited
- Biodegradability: the conversion of >90% of the original matter into CO2, water and minerals by biological processes within six months
- Disintegrability: at least 90% of the original mass should be decomposed into particles that are able to pass through a 2mm x 2 mm sieve
- Quality: Absence of toxic substances and substances that impede composting
A properly tended backyard compost heap or an industrial composting facility should not emit methane. In addition, composting produces natural fertilization that can be used for improving soil carbon health and water retention. In the packaging world, when companies talk about biodegradability, they are usually talking about compostability.
The decision to use biodegradable, and compostable materials is based on the function of the package and the goals of the organization making the decision. If the goal is to reduce methane emissions in the atmosphere, picking certain biodegradable materials that end up in landfills might actually increase methane emissions.
Collection of compostable packaging waste therefore plays a big role — compostable food packaging is extremely convenient because it can be collected with food waste, as opposed to separately like with recyclable packaging.
Similarly, when evaluating biorenewable, biobased or bioplastics, consider whether it will be recycled or compostable. The recycling benefit depends on the average recycling rates for that kind of plastic in the municipal waste stream. Special waste management or take back programs can be considered to increase the effectiveness of the benefit.
Today with the current technology, recyclers are strongly opposed to recycling certain bio-based plastics because of the drop in resultant material quality. PLA is an example of that. However, Polylactic acid, or PLA is a bioplastic that is typically used for foodservice (forks, spoons, coffee lids, etc.) and composting of food waste along with PLA is a good option as long as it makes its way to industrial composting.
Composting is a difficult waste service to scale. Many plastics that are designated “compostable” are not home-compostable. A home-compostable material can be reduced to nutritious loam in the relatively cooler environment of a home compost heap. An industrial compost heap is much larger, and materials deposited in it can be pretreated in order to make them more prone to composting. These heaps reach much higher internal temperatures, and some compostable plastics require those high temperatures to become loam.
Industrial compost heaps provide compost for large farms and other big soil users, and the quality of the compost they sell has to be at a certain level. Some industrial composters don’t accept certain compostable plastics because they don’t compost fast enough or might still leave some residue that affects the quality of the compost for farming.There are many variables to consider when making the decision to use more responsible materials. In order to make the right decision for your company, you need the full story. To start making a difference with your packaging today, whether it be biodegradable, compostable, or recyclable, sign up for a free EcoImpact trial license. Import your company’s product and packaging BOMs into the software, and then create a roll-up dashboard report to view your impacts across your entire portfolio. View your as-designed impact as well as your actual impact based on your production volumes. Generate realistic goals that you can measure progress against. Sign up here.