Waste Wise: Grading Our Composition

There has been significant focus on waste diversion of late. And while initial policy goals focused around recycling, state and local goals are becoming more inclusive, defining overall diversion goals either in concert with or independent of recycling goals. Typically, the term “diversion” is used to indicate the diversion of discards from a landfill and, in some cases, waste-to-energy facilities as well. Thus, the term waste diversion is more broad and includes recycling, as well as other waste management strategies such as composting and waste conversion technologies (both biological and thermal).

One could argue many reasons for this philosophical shift. Perhaps public sentiment to “go green” has catalyzed the inception of these broader goals. Or maybe the realization that waste is now not waste but a resource is the driving factor. The reasons and justifications no doubt vary from city to city. Despite the reasons why, the key question that must be answered is, specifically, how will a city or hauler divert materials? Which technology or processes yield the highest diversion rates?

One way to evaluate the potential for diversion is to consider the limitations imposed by waste composition. When it comes to diversion, waste composition is a critical piece of the equation since typically only limited waste components are acceptable for use with specific technologies. To illustrate this, the table below shows which primary components within the waste discards stream are suitable for typical waste diversion endpoints and how much of the total municipal solid waste (MSW) stream can be processed by that particular diversion technology.

Diversion technologies/processes and their ability to process particular MSW components.

¹ Source: U.S. EPA

² Depends on process and ability to handle moisture contents >10%.

As this table clearly shows, waste diversion based on current technology constraints allow for only 33.7 to 55.7 percent of the total MSW stream to be treated if only one technology or process is used. If two or more processes are used, such as composting and recycling, this number collectively climbs to 88.2 percent. However, this percentage is more of a theoretical maximum value since some specific waste components (e.g. rigid plastics, treated wood, etc.) cannot be readily recycled or composted.

This suggests that appropriate goal setting for waste diversion from a policy perspective should consider the ability to achieve a particular goal based on the technologies or processes that are in place or planned for a particular community or populace. Another issue that exists is that, while the definition of the technologies is relatively clear, there can be substantial disparities between cities, counties and states regarding definitions of what is included in the terms “diversion” and “recycling.” As a result, a stronger coupling between available diversion processes, the fraction of the waste stream that can be utilized by these processes and policymaking should result in goals that are both realistic and practical.