In cradle-to-cradle systems, sustainable material flows are divided into biological and technical metabolisms. A unique characteristic of many renewable materials is that they can be recycled (technically recovered) or composted (biologically recovered). This gives renewable materials a broad array of post-use options not shared by many technical materials, like plastics or metals.

There is increasing interest in the managed composting of organic and renewable materials. In the U.S., landfills are one the most significant man-made sources of greenhouse gas emissions (GHGs) due to the anaerobic decomposition of wet, biodegradable materials (primarily vegetation and food). While studies of landfills have revealed that on the whole, they tend to be tombs rather then composting reactors, these studies have also found that wet, readily degradable materials tend to decompose rapidly, resulting in the evolution of methane—a greenhouse gas 21-times more potent than carbon dioxide. As a consequence, the diversion of wet, organic materials will likely become an important area of focus as the U.S. considers how to reduce its GHGs. San Francisco already has an aggressive, managed composting program that is diverting organic waste from landfills. The resulting compost is used for local agriculture. Several European countries are also pursuing managed composting.

The introduction of bioplastics over the past several years has helped to catalyze the discussion of composting within the packaging community. Along with wet, organic waste, packaging made from renewable and compostable materials will be a likely candidate for landfill diversion. Clearly, recycling is a higher-value recovery option for many renewable materials, but foodservice packaging, which is often contaminated with food and grease and not a candidate for recycling, can be very suitable for composting as long as it is designed with that end in mind. Designing packaging for composting will be especially important to ensure that any coatings, inks or other components are suitable and safe for composting systems. Experience to date suggests that beyond certification of compostability (e.g., Biodegradable Products Institute [BPI] or DIN CERTCO), commercial composters will require validation that packaging is safe and won't compromise the quality of their compost before they accept it at any significant volume.

Managed composting strives to provide the optimal moisture, oxygen and temperature conditions to produce quality compost. Thus, most emissions occur in the form of CO2. Like aerobic biodegradation in nature, managed composting allows organic, renewable materials to be recovered in a carbon-neutral manner and to produce a beneficial soil amendment. For more resources, go to www.packagingdigest.com/info/green8.

Anne Johnson is the director of the Sustainable Packaging Coalition, a project of GreenBlue (www.greenblue.org). For additional information, email [email protected].