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Biodegradable vs compostable: Addressing the confusion

Biodegradable vs compostable: Biodegradable and compostable materials both break down in the environment by natural processes, however, for compostable materials, specific environmental conditions are set to control the breakdown processes and the end product produced.

To tackle our global waste crisis, leaders in sustainable business are seeking materials that don’t reside in the environment but break down to cause no further harm to nature. Changing attitudes are pushing for greater investment in the development of green materials. For instance, investments in bioplastic manufacturing have increased by 42% between 2021 and 2022, reaching $500 million. These bioplastics are celebrated as compostable, but what does that term really mean?

As the bio-based industry grows, we’re witnessing an increasing number of biodegradable and compostable claims. Yet, there remains confusion around the meaning of these terms, which is a symptom of ineffective communication and corporate greenwash.

As such, this Green Business Bureau article defines biodegradable and compostable. We aim to remove confusion and give clarity over how materials will impact our planet. We explain the importance of discarding materials correctly, and how certification will remove ambiguity around the planetary impact of a given substance. Use the links below to navigate through this article.

Biodegradable vs compostable: What’s the difference?

The terms biodegradable and compostable are mistakenly used interchangeably. But there are vital differences between the two terms, as we explain below.

All compostable materials are biodegradable, but not all biodegradable materials are compostable.

The end product

Compostable materials are designed to break down to produce nutrient-rich biomass. The biodegradation process does not produce harmful pollutants and toxins, meaning materials are intended to return to the environment safely.

Biodegradable materials, on the other hand, will break down via natural processes in the environment but could cause environmental harm. For instance, although leather is biodegradable, most leather produced in the U.S. is chrome-tanned. Chromium waste is considered a hazardous toxin by the Environmental Protection Agency.

Break down setting

Compostable materials require a specific setting to break down as intended, whereas biodegradable materials will break down in the natural environment. The specific settings given within a compost ensure material break down causes minimal harm to the environment, and in fact, gives back to nature through the production of nutrient-rich biomass.

Timeframe

Compostable materials will break down over a short time frame of ~180 days. For biodegradable materials, no time limit is placed on the degradation processes. That is, a material may be biodegradable, but this biodegradation process could take years. For example, coming back to our leather example. Leather takes up to 50 years to biodegrade, littering in the environment until the process is complete.

Biodegradable vs compostable: Which is better?

Compostable materials offer the cleanest form of biodegradation due to the controlled nature of the environment – high oxygen levels, and the large volume of bacteria available. These conditions ensure efficient physical and chemical break down to produce byproducts that cause minimal harm to the planet. Compostable products have undergone strict testing to ensure they break down within a specific time frame and do not release anything harmful into the environment.

Biodegradable vs compostable glossary: Understanding the jargon surrounding these terms

Biodegradable and compostable are often used in conjunction with additional terminology. In this section, we define the jargon that shrouds these terms.

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Biobased definition

Bio-based materials are intentionally made from living organisms. They are carbon-based, found within nature, and derived from renewable sources.

Examples include corn, sugarcane, cellulose fibers, casino, polylactic acid (polymer produced by industrial fermentation), bioplastics, wood, and leather.

Organic definition

Organic means to come from living plants and animals. Non-organic means to be built from non-living, synthetic chemicals.

Petroleum-based definition

Petroleum-based materials are derived from crude oil. Being oil-based these materials are non-biodegradable, meaning they have a lasting presence in aquatic and terrestrial habitats.

Examples include synthetic polymers (plastics) like polyethylenes (#2), polyethylene terephthalate (#1), polyvinyl chloride (#5), and polystyrene (#6).

Decomposition definition

Decomposition (of degradable materials) describes a process of separation whereby a complex material is divided into its constituent parts, elements, or simpler compounds. Decomposition does not have to involve living organisms. For instance, polyethylene plastic bags will decompose over 20 years to produce microplastics that remain in the environment.

Biodegradation definition

Biodegradation is a form of decomposition that involves living things. That is, organic matter is broken down by microorganisms – such as bacteria and fungi – as a natural process. Biodegradtion is composed of three processes:

  • The material undergoes biodeterioration. This is the mechanical weakening of the material’s structure.
  • The material then undergoes biofragmentation. This is the break down of the material by microorganisms.
  • The material is then finally assimilated. This is the incorporation of the old material into new cells by microorganisms.

Biodegradable definition

To be biodegradable means to be consumed by microorganisms. Through natural processes, microorganisms break down materials to produce carbon dioxide, water, and biomass (in the presence of oxygen). In the absence of oxygen, materials are broken down to produce methane, water, and biomass.

Compostable definition

Composting is an accelerated and managed form of biodegradation. Materials biodegrade under controlled conditions and within a specified timeframe of 180 days. These controlled conditions include high humidity, high temperature, and the presence of microorganisms and bacteria. The environmental conditions of the composting facility are carefully monitored, such as the moisture content, temperature, oxygen levels, and acidity. Compostable materials are designed to provide nutrient-rich biomass once they’ve completely broken down, and not to leave visible, distinguishable, or toxic residue.

Why strict conditions must be met to fully realize the benefits of composting

Compostable materials are designed to break down within the specific conditions of a composting facility. Outside of these conditions, the benefits composting brings are limited.

If compostable material ends up as landfill waste, the green credentials of the composting process are hampered. Composting requires oxygen, and for the most part, landfill sites are sealed and therefore oxygen-starved. Under these conditions, materials will break down anaerobically to produce the bi-product methane – a greenhouse gas 30 times more potent than carbon dioxide.

If a compostable item ends up in landfill, it will wind up as trash, and will not be composted“. – Peter Canepa, a life cycle assessment specialist with the Department of Environmental Quality in Oregon, The Science Behind Composting

Hence, the process of biodegradation can be manipulated to benefit our planet. Such manipulation presents a hierarchy of conditions ordered according to the level of control achieved and the environmental benefits reaped. This is explained via the infographic below.

The decomposition hierarchy for biobased materials

Different levels of biodegradability can be achieved based on the system conditions provided. The infographic below gives the decomposition hierarchy of biobased materials.

Biodegradable vs compostable

As you move up each category, it becomes more difficult for the materials to decompose due to less favorable system conditions (such as a lack of bacteria and oxygen). For this reason, it’s vital brands clearly state the proper disposal methods for a given material.

The most environmentally friendly and favorable conditions that support the composting process are provided by industrial composting facilities.

Home composting and industrial composting (defining the difference)

Industrial composting facilities give a more controlled and managed version of the home composting pile. At the simplest level, home composting describes a backyard compost barrel or bin that’s designed to break down organic waste such as food scraps, grass clippings, and leaves. Other biodegradable materials such as meat, dairy products, or biodegradable bioplastics won’t break down under the conditions provided by the home composting facility. These materials need a more closely monitored, multi-step process.

Such a process is given by industrial composting facilities. These facilities measure and manage inputs of water, air, carbon, and nitrogen-rich materials. This close degree of management optimizes each step of the decomposition process, ensuring rapid biodegradation to high-quality, toxic-free compost.

However, industrial composting is plagued by a lack of facilities. In the United States, there are only 185 full-time commercial composting sites, a figure dwarfed by the number of landfill sites and recycling plants. Plus, most of these facilities are only present in built-up areas, meaning small and local communities lack access.

It’s important to consider this lack of infrastructure when purchasing materials based on their sustainability credentials (industrially compostable). That is, opting for home compostable materials – when possible – seems a safer bet, to ensure materials biodegrade in the right conditions.

Biodegradable and compostable certifications

The term biodegradable seems to have been greenwashed to mean good for the planet. Yet, as we know, the biodegradable process has no timeline stated, nor is the toxicity of bi-products specified. Most materials will eventually biodegrade in the environment given enough time and the presence of very specific and specialized microorganisms.

(E.g. Ideonella sakaiensis bacteria will eventually consume the plastic polyethylene terephthalate (PET). Diatoms and cyanobacteria can actively consume glass. Pseudomonas and mycobacterium consume heavy metals such as mercury, silver, and lead.)

There are currently no requirements or standards to term biodegradable. For that reason, the term is used loosely and carries little indication of how a material affects the environment. This ambiguity must be removed through the use of certification. Below we detail credible biodegradable certification and compostable certification providers.

Industrial composting certification

A product that’s labeled as industrially or commercially compostable requires increased temperature and specifically formulated microbial conditions to be converted into useful compost. Hence, a product must pass certain tests to be accurately labeled as such.

In the US, the American Society for Testing and Materials (ASTM) uses D6400 and D6868 protocols and criteria to test products as commercially compostable.

The US ASTM D6400 is a test standard of choice that determines what solid materials can be labeled as compostable in commercial or municipal facilities. The standards are globally recognized, and although they were originally developed for plastics, they can be used to test food packaging, paper products, textiles, and more.

ASTM D6868 is a compostable product test, again developed for plastics, but it can be used for other materials. The standards test whether the material in question is designed to be aerobically composted in municipal or industrial facilities.

These standards provide a time frame within which both disintegration (physical breakdown) and biodegradation/compost production (chemical breakdown) occur – 180 days. The standards also require that no harmful bi-products are produced during this process.

(In Europe, EN 13432 standards are comparable – which require the same timeline and outputs).

Once a product has passed this vigorous testing, the results are then sent to a 3rd-party organization for certification. In the US, the best-known certification provider is the Biodegradable Products Institute (BPI). Certification by BPI is used to ensure the product in question will biodegrade completely and will not leave any harmful substances behind once it’s been composted. BPI certification is based on ASTM D6400 and ASTM D6868 standards.

Home compostable certification

Certifying a material as home compostable is a new concept, and as such, the US lacks a specialized certification scheme. BPR has yet to evolve the scope of its certification to include home composting. In addition, ASTM does not provide a standard test for home compostable materials. As such, tests are conducted mainly using the Australian standard entitled Biodegradable plastics suitable for home composting (AS 5810). AS 5810 requires that the material will disintegrate in 6 months, with complete biodegradation within the year to produce nutrient-rich compost.

Based on this test standard, NF T 51800 from France and prEN 17427-TUV from Austria have given the certification scheme named OK compost HOME certification. Currently, there’s no comparable certification in the US, meaning this is a brand’s best bet to certify materials as home compostable.

Certified biodegradable and beyond: The importance of green business certification

Understanding exactly what is meant by the terms compostable and biodegradable means a business can accurately communicate how to dispose of products and packaging to consumers – avoiding corporate greenwash and minimizing environmental harm.

The conditions provided for biodegradation determine the length of time the process takes, plus what waste bi-products are produced – hence the environmental impact of this waste. Composting provides a controlled environment for biodegradation, such that environmental harm is minimized. Yet, materials need to be sent to the correct composting facility for the full sustainability benefits to be realized.

In addition, to ensure materials are correctly labeled, brands must turn to third-party certification providers such as BPI and OK compost HOME certification. Yet, seeking business certification must go beyond certifying compostable and biodegradable materials as such. Such material use, although commendable, represents just a single green initiative. To achieve true business sustainability, a holistic approach is needed to address the environmental impact of every operation related to a given business. As such, companies must also seek broader-acting certification providers that guide environmentally and socially responsible business. That is, a business must obtain green business certification.

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