Do Compostable & Biodegradable Plastics Break Down in Landfills?
Short Answer
No. Compostable plastics are not designed to break down in landfills.
Biodegradable plastics are also unlikely to fully degrade under landfill conditions.
Landfills lack the heat, oxygen, and controlled microbial activity required for proper biological breakdown.
Why This Question Matters
Many buyers assume that materials labeled “compostable” or “biodegradable” will naturally decompose anywhere.
This is incorrect.
Landfills are engineered to slow decomposition, not accelerate it.
Understanding this boundary is critical for:
Preventing contamination
Avoiding greenwashing risk
Making compliant packaging decisions
For a definition of compostable materials, see: What Is Compostable? https://orizonbags.com/knowledge/compostable-definition/
For biodegradable meaning in packaging systems, see: What Is Biodegradable? https://orizonbags.com/knowledge/biodegradable-definition/
Compostable vs Biodegradable Plastics in Landfills
Although both terms sound environmentally friendly, neither material is designed for landfill disposal.
Key Differences in Landfill Conditions
| Condition | Compostable Plastic | Biodegradable Plastic |
|---|---|---|
| Designed for landfill? | No | No |
| Requires oxygen? | Yes | Often |
| Certified standard? | Yes (EN 13432 / ASTM D6400) | Usually no |
| Landfill breakdown speed | Very slow | Very slow |
| Environmental benefit in landfill | Limited | Limited |
Both materials depend on specific environmental conditions to degrade properly.
Landfills do not provide those conditions.
What Happens in Real Landfills?
Modern landfills are engineered systems designed to isolate waste.
Typical conditions include:
Low oxygen (anaerobic)
Compacted layers
Limited heat circulation
Reduced microbial diversity
Under these conditions:
Compostable plastics may remain intact for years
Biodegradable plastics may fragment rather than fully mineralize
Methane may be generated if partial degradation occurs
Methane Risk and Climate Impact
In anaerobic environments, organic materials can generate methane.
Whether compostable or biodegradable plastics produce methane depends on:
Material composition
Landfill gas capture systems
Moisture levels
This means that landfill disposal may eliminate the intended environmental benefits of compostable products.
Are They Better Than Conventional Plastics in Landfill?
Not significantly.
When placed in landfill:
They do not enrich soil
They do not compost
They do not reduce contamination
They behave similarly to conventional plastics
Environmental benefit depends entirely on entering the correct waste system.
Why Compostable Plastics Need Composting Conditions
Compostable plastics are tested and certified to break down under controlled composting conditions, such as:
Sustained high temperatures (usually above 55 °C)
Adequate oxygen
Controlled moisture
Active microbial populations
These conditions exist in industrial composting facilities, not in landfills.
To understand this boundary clearly, see: Home Composting vs Industrial Composting: Key Differences Explained
Where Should Compostable Plastics Go?
Certified compostable plastics are designed for:
Industrial composting facilities
Organics collection systems
FOGO programs
If composting infrastructure is unavailable, landfill becomes the default outcome.
In such cases, material selection should consider system compatibility.
See:
→ How to Dispose of Compostable Plastics
→ Australia FOGO & Council Compostable Bag Requirements
Where Should Compostable Plastics Go Instead?
Best Option: Industrial Composting
Most certified compostable plastics are designed for industrial composting facilities, often accessed through:
Organics bins
FOGO (Food Organics & Garden Organics) systems
Commercial composting programs
If your area has an organics system, compostable plastics may be appropriate only if accepted locally.
For practical guidance, see: How to Dispose of Compostable Plastics
What If My Area Has No Composting Infrastructure?
If industrial composting is not available:
- Compostable plastics usually end up in landfill
- Environmental benefits are minimal
- Compostable may not be the best solution
This is why compostable plastics are system-dependent, not universally eco-friendly.
To understand when compostable products deliver real benefits, see: Are Compostable Plastics Really Eco-Friendly?
Why Certification Still Matters
Even though compostable plastics do not break down in landfill, certification is still essential.
Certification ensures that a product will fully break down when it enters the correct composting system.
To learn how to verify real compostable claims, see: How to Identify Genuine Compostable Products
What This Means for Buyers, Brands, and Councils
- Compostable plastics are not a landfill solution
- They must be matched to existing composting infrastructure
- Incorrect disposal removes environmental value
- Clear definitions and system alignment reduce risk
For Australia-specific waste systems and council acceptance rules, see: Australia FOGO & Council Compostable Bag Requirements
Key Takeaways
- Compostable plastics do not reliably break down in landfills
- Landfills lack the conditions required for composting
- Compostable plastics are designed for composting systems, not landfill
- Environmental benefits depend on correct disposal
- Infrastructure matters more than labels
FAQ
In most cases, no. Landfills lack oxygen and controlled heat required for composting.
Often very slowly. Degradation depends on oxygen, moisture, and microbial activity.
Neither is designed for landfill disposal. Environmental benefit depends on composting access.
No. Compostable materials contaminate recycling streams.
