Compostable plastics offer a promising alternative to traditional plastics, aiming to reduce environmental impact by breaking down into natural components. Understanding how these innovative materials work and how to properly manage them is increasingly relevant for consumers seeking sustainable options.
Understanding Compostable Plastics
Compostable plastics break down into natural elements like carbon dioxide, water, and biomass, leaving no toxic residue. This distinguishes them from traditional plastics, which are petroleum-based and persist for centuries, breaking into microplastic fragments. Unlike traditional plastics that photodegrade, compostable plastics biodegrade through microbial activity.
Not all biodegradable plastics are compostable. While all compostable plastics are biodegradable, many biodegradable plastics require specific conditions or extended periods to break down, and some may leave harmful residues. Compostable plastics are certified to decompose completely within a defined timeframe under specific composting conditions, yielding beneficial compost. Their chemical structures, often from renewable plant sources like corn starch, sugarcane, or cellulose, are designed for easier microbial consumption than conventional plastics.
The Process of Decomposition
Compostable plastics break down through a biological and chemical process driven by microorganisms. This process begins when environmental factors like temperature and humidity allow microorganisms to colonize the material’s surface, utilizing it as a nutrient source.
Microorganisms release extracellular enzymes that break down the complex polymer chains into smaller molecules. These molecules are then absorbed and metabolized by the microorganisms, converting them into carbon dioxide, water, and new biomass. This transformation ensures the material fully integrates back into the natural cycle, enriching the soil. The efficiency and speed of this process are influenced by the plastic’s chemical composition, temperature, moisture levels, and microbial diversity.
Home and Industrial Composting
The environment in which compostable plastics are processed significantly impacts their decomposition. There are two primary settings for composting: home composting and industrial (commercial) composting facilities. Each has distinct conditions that affect how effectively compostable plastics break down.
Home composting typically involves backyard bins or piles, where conditions like temperature, moisture, and aeration are less controlled and fluctuate more. Temperatures in home compost bins are generally lower, often around 25°C (77°F) or up to 32°C (90°F), and microbial activity can be less stable due to smaller waste volumes and heat loss. While some specific “home compostable” plastics are designed to break down under these cooler conditions, many certified compostable plastics require the more rigorous environment of an industrial facility. If a compostable plastic is placed in a home compost system without the proper home compost certification, it may not decompose effectively and could persist for extended periods, potentially longer than 18 months.
Industrial composting facilities are large-scale operations with highly controlled conditions optimized for rapid and complete decomposition. These facilities maintain elevated temperatures, typically ranging from 55-75°C (131-167°F), often staying above 60°C (140°F) for at least a week to ensure sanitization and efficient breakdown. They also regulate moisture levels and aeration (oxygen supply) to promote robust microbial activity, including thermophilic microorganisms that thrive in high heat.
The shredded material offers a larger surface area for these microbes to work on, accelerating the process. This controlled environment allows industrially compostable plastics to disintegrate within a few months, typically within 12 weeks, and fully biodegrade within six months, converting over 90% of the material into CO2, water, and biomass.
Identifying and Disposing of Compostable Plastics
Proper identification and disposal of compostable plastics are important to ensure they fulfill their intended environmental benefit. Consumers should look for specific certification labels on products, as these provide assurance that the item will break down under certain composting conditions. Two prominent certification bodies are the Biodegradable Products Institute (BPI) in North America and TÜV Austria, a globally recognized organization.
The BPI certification mark primarily indicates that a product is suitable for industrial composting facilities, meaning it meets ASTM D6400 or D6868 standards for breakdown in high-temperature, controlled environments. These products will not reliably break down in a typical home compost bin. For home composting, consumers should look for the TÜV Austria “OK compost HOME” certification, which signifies that the product is designed to decompose effectively in cooler, less controlled home composting systems. Some products may carry both BPI and TÜV certifications, indicating they can be composted in either environment, but this is not always the case.
Disposing of compostable plastics correctly involves checking local waste management guidelines. If a product is industrially compostable, it should be placed in a food waste or organics collection bin if such a program is available in your community. It is crucial to never put compostable plastics into recycling bins designated for traditional plastics, as they are chemically different and can contaminate the recycling stream, disrupting the process. If industrial composting facilities or collection programs are not accessible, the product may end up in a landfill. While some home compostable plastics might break down in landfills over time, it is not an ideal scenario as landfills often lack the oxygen and conditions necessary for proper biodegradation.