Understanding Biodegradability and Compostability of Bioplastics
Bioplastics are often touted as a sustainable alternative to conventional plastics. However, the terms 'biodegradable' and 'compostable' are frequently used interchangeably, leading to confusion. This guide aims to clarify these concepts, explain the Australian standards for compostability, and address common misconceptions surrounding bioplastics degradation.
What are Bioplastics?
Before diving into biodegradability and compostability, it’s important to understand what bioplastics are. Bioplastics are a family of plastics that are either bio-based, biodegradable, or both. Bio-based means the plastic is made from renewable resources, such as corn starch, sugarcane, or vegetable oils. Biodegradable means the plastic can be broken down by microorganisms into natural substances like water, carbon dioxide, and biomass. It’s crucial to note that a bioplastic can be bio-based without being biodegradable, and vice versa. Learn more about Bioplastics.
1. Defining Biodegradability and Compostability
It's essential to understand the distinct meanings of biodegradability and compostability to make informed decisions about bioplastics.
Biodegradability
Biodegradability is the ability of a material to decompose into natural substances (water, carbon dioxide, and biomass) through the action of microorganisms like bacteria and fungi. The rate and extent of biodegradation depend on several factors, including:
Material composition: Different materials degrade at different rates.
Environmental conditions: Temperature, humidity, oxygen availability, and the presence of specific microorganisms all play a role.
Timeframe: Biodegradation can take weeks, months, or even years, depending on the factors above. A plastic labelled 'biodegradable' doesn't necessarily mean it will disappear quickly in a landfill.
It's important to note that the term 'biodegradable' without further qualification can be misleading. A plastic might be biodegradable under specific laboratory conditions but not in a typical landfill environment, which often lacks sufficient oxygen and moisture to support microbial activity.
Compostability
Compostability is a specific type of biodegradability. A compostable material not only breaks down into natural substances but also does so within a reasonable timeframe and under specific composting conditions. Critically, it must also produce a final compost product that is of good quality and does not leave harmful residues. Compostable plastics are designed to break down in a composting environment, which provides the optimal conditions for microbial activity.
There are two main types of composting:
Industrial Composting: This involves controlled environments with high temperatures (55-60°C), high humidity, and a balanced carbon-to-nitrogen ratio. These conditions accelerate the degradation process. Industrial composting facilities are designed to handle large volumes of organic waste, including compostable plastics.
Home Composting: This involves composting in a backyard compost bin or pile. Home composting conditions are less controlled than industrial composting, with lower temperatures and less consistent moisture levels. As a result, materials that are compostable in industrial facilities may not break down effectively in a home compost.
2. Australian Standards for Compostability
To ensure that compostable products meet specific requirements, several standards and certifications exist. These standards define the conditions under which a material must break down and the quality of the resulting compost. In Australia, the relevant standards are primarily based on international standards, adapted for the Australian context.
AS 4736 - 2006: Biodegradable Plastics - Biodegradable Plastics Suitable for Composting and Other Microbial Treatment
This standard specifies the requirements for plastics to be considered compostable in industrial composting facilities. It covers aspects such as:
Biodegradation: The plastic must break down to a specified extent within a certain timeframe (typically 180 days) under controlled composting conditions.
Disintegration: The plastic must physically break down into small fragments, so it is no longer visually distinguishable in the compost.
Ecotoxicity: The resulting compost must not be harmful to plants or other organisms.
Heavy metals: The plastic must not contain excessive levels of heavy metals.
AS 5810 - 2010: Biodegradable Plastics - Biodegradable Plastics Suitable for Home Composting
This standard sets the requirements for plastics to be considered compostable in home composting systems. It is more stringent than AS 4736, as home composting conditions are less controlled. Key requirements include:
Biodegradation: The plastic must break down to a specified extent within a longer timeframe (typically 365 days) under less controlled composting conditions.
Disintegration: Similar to AS 4736, the plastic must physically break down into small fragments.
Ecotoxicity: The resulting compost must not be harmful to plants or other organisms.
Heavy metals: The plastic must not contain excessive levels of heavy metals.
Certification Schemes
To demonstrate compliance with these standards, manufacturers can obtain certification from accredited organisations. Common certification schemes include:
Seedling Logo (DIN CERTCO): This logo indicates that a product is certified compostable according to EN 13432 (the European equivalent of AS 4736) and is suitable for industrial composting.
Home Compostable Logo (DIN CERTCO): This logo indicates that a product is certified compostable according to EN 13432 and is suitable for home composting.
When choosing bioplastic products, look for these certifications to ensure they meet recognised compostability standards. Consider what Bioplastics offers in terms of certified compostable products.
3. The Role of Microorganisms in Degradation
Microorganisms are the key players in the biodegradation and composting processes. These tiny organisms, including bacteria, fungi, and actinomycetes, secrete enzymes that break down complex organic molecules into simpler substances.
The degradation process typically involves several steps:
- Attachment: Microorganisms attach to the surface of the plastic material.
- Enzyme secretion: The microorganisms secrete enzymes that break down the polymer chains of the plastic.
- Consumption: The microorganisms consume the smaller molecules produced by the enzymatic breakdown.
- Mineralisation: The microorganisms convert the carbon in the plastic into carbon dioxide (CO2) and biomass.
The type of microorganisms involved and the rate of degradation depend on the composition of the plastic and the environmental conditions. For example, some microorganisms thrive in high-temperature environments, while others prefer cooler temperatures. Similarly, some microorganisms require oxygen to function (aerobic degradation), while others can survive in the absence of oxygen (anaerobic degradation).
4. Home vs. Industrial Composting
As mentioned earlier, there's a significant difference between home and industrial composting. Understanding these differences is crucial for properly disposing of compostable bioplastics.
Home Composting
Home composting typically involves a backyard compost bin or pile. The conditions in a home compost are less controlled than in an industrial facility. Temperatures are generally lower and fluctuate more, and moisture levels can vary depending on the weather. As a result, the degradation process is slower and less efficient.
Only materials certified as home compostable (e.g., with the 'Home Compostable' logo) are likely to break down effectively in a home compost. Even then, it may take longer than stated in the standard, depending on the specific conditions in your compost bin.
Industrial Composting
Industrial composting facilities provide controlled environments that optimise the degradation process. These facilities maintain high temperatures (55-60°C), high humidity, and a balanced carbon-to-nitrogen ratio. These conditions accelerate the breakdown of organic materials, including compostable plastics.
Industrial composting is the preferred disposal method for most compostable bioplastics, especially those certified to AS 4736 or EN 13432. However, access to industrial composting facilities can be limited, depending on your location. Check with your local council to see if they offer kerbside collection of compostable waste or have designated drop-off points.
5. Common Misconceptions About Bioplastics Degradation
Several misconceptions surround the degradation of bioplastics. Addressing these misconceptions is essential for promoting responsible use and disposal of these materials.
Misconception 1: All bioplastics are biodegradable. As mentioned earlier, not all bioplastics are biodegradable. Some are bio-based but not biodegradable, while others are biodegradable but not bio-based. Always check the product label to determine whether a bioplastic is biodegradable or compostable.
Misconception 2: Biodegradable plastics will quickly disappear in a landfill. Landfills are designed to minimise decomposition, so even biodegradable plastics may take a long time to break down in this environment. The lack of oxygen and moisture inhibits microbial activity.
Misconception 3: Compostable plastics can be thrown into any compost bin. Only plastics certified as home compostable should be placed in a home compost bin. Plastics certified for industrial composting require the higher temperatures and controlled conditions of an industrial facility.
- Misconception 4: Bioplastics are a perfect solution to plastic pollution. While bioplastics offer a more sustainable alternative to conventional plastics, they are not a perfect solution. They still require resources to produce, and their degradation depends on specific conditions. Reducing overall plastic consumption and improving waste management practices are also crucial for addressing plastic pollution. You can find frequently asked questions about bioplastics on our website.
By understanding the nuances of biodegradability and compostability, consumers and businesses can make informed choices about bioplastics and contribute to a more sustainable future.