Compostable plastic is often promoted as a straightforward, planet-friendly alternative to conventional plastic packaging. However, the reality is that the successful decomposition of these materials is entirely dependent on two factors: the specific chemical makeup of the plastic and the environmental conditions provided during disposal. Simply throwing a compostable item into a backyard pile or a standard recycling bin will not lead to its intended breakdown, and in fact, often creates more problems than it solves. Understanding the correct pathway for disposal is necessary to ensure these products fulfill their promise of returning to the earth without causing contamination.
Identifying Truly Compostable Plastic Materials
The terms “biodegradable” and “compostable” are not interchangeable, and recognizing the difference is the first step toward proper disposal. Biodegradable plastic breaks down naturally via microbial action, but this process is unregulated, lacks a specified timeframe, and may still leave behind microplastics or toxic residue. Compostable plastic, by contrast, is a specific subset certified to break down completely into water, carbon dioxide, and biomass within a defined period under managed conditions, leaving no harmful residues.
Most compostable plastics are made from materials like Polylactic Acid (PLA), derived from renewable resources such as corn starch or sugarcane, or Polyhydroxyalkanoates (PHA), produced by microorganisms. To confirm compostability, consumers must look for third-party certification logos verifying compliance with established standards. The most recognized standards include the ASTM D6400 in the United States and the European EN 13432.
A certification logo from organizations like the Biodegradable Products Institute (BPI) or TÜV Austria’s “OK Compost INDUSTRIAL” ensures the material will disintegrate fully in a commercial facility. Without such a logo, a product labeled merely “biodegradable” should be treated as conventional waste, as it requires conditions that do not exist in standard disposal environments.
Steps for Composting in a Home System
The vast majority of certified compostable plastics, especially those made from PLA, are designed for industrial systems and will not easily decompose in a backyard setup. This limitation stems from the specific temperature requirements needed to initiate the breakdown process. For PLA to begin hydrolysis—where water breaks down the polymer chains—it needs to reach a temperature near its glass transition point, around 131°F (55°C).
Home compost piles rarely reach and sustain these high temperatures consistently. Typical home composting temperatures often fluctuate between 110°F and 120°F, meaning decomposition of common compostable plastics will be slow or non-existent. If attempting home composting, the product must carry a “home compostable” certification, such as TÜV Austria’s “OK Compost HOME,” confirming it degrades at lower, ambient temperatures within a year.
If a product is certified as home compostable, preparation is necessary to maximize the chances of successful breakdown. Cutting or shredding the item into very small pieces significantly increases the surface area, making it easier for microbes to act on the material. Integrating these small pieces into a well-managed compost pile that is regularly turned and maintains a proper balance of carbon-rich brown material and nitrogen-rich green material will further accelerate degradation. Even with these efforts, the process will take significantly longer than traditional organic matter, potentially six to twelve months before the plastic is fully dissolved.
Understanding Industrial Composting Requirements
Industrial facilities represent the only reliable pathway for composting most certified compostable plastics. These commercial operations are engineered to provide the highly controlled environment necessary for rapid and complete degradation. They operate under strict parameters, including controlled moisture levels, proper aeration, and a balanced carbon-to-nitrogen ratio, which are difficult to replicate in a backyard setting.
The defining feature of industrial composting is the sustained, high-heat phase necessary to break down durable biopolymers like PLA. Facilities maintain thermophilic temperatures, typically ranging from 131°F to 140°F (55°C to 60°C), for an extended period. This heat accelerates microbial metabolism and initiates the hydrolysis that allows microorganisms to consume the plastic.
The entire process, including active composting and curing, must convert the material to carbon dioxide, water, and biomass within a set timeframe, typically 90 to 180 days, to meet certification standards. Consumers need to confirm whether their local municipality or waste management provider has a program that specifically accepts certified compostable plastics, as these services are not universally available. If a nearby facility exists, the certified items should be placed in the designated organic waste stream, often a green bin, rather than mixed with traditional waste.
Preventing Contamination of Recycling and Waste Streams
Improper disposal of compostable plastic poses a significant threat to established recycling infrastructure. When compostable plastics like PLA are mistakenly tossed into the recycling bin intended for petroleum-based plastics (PET or HDPE), they introduce a material with a different chemical structure and a much lower melting point. During mechanical recycling, the inclusion of even small amounts of PLA degrades the quality of the final recycled product, making it brittle or unusable.
The confusion surrounding these labels also affects general waste streams. Some plastics are marketed as “oxo-degradable” or “photo-degradable.” These are conventional plastics mixed with metal salt additives to accelerate fragmentation when exposed to oxygen or sunlight. These items do not biodegrade into natural components; instead, they break down into increasingly smaller pieces, contributing directly to microplastic pollution.
If an industrial composting facility is not accessible, certified compostable items should be placed in the regular trash rather than the recycling bin. This practice prevents the contamination of valuable recycling streams and maintains the integrity of both composting and recycling programs.