Over the years, whether during BioCycle Conference tours or editorial trips, we have visited a number of mixed waste composting facilities. These plants are designed to receive mixed MSW, which is sorted (primarily mechanically) and size reduced, and then composted. In the early days (mid to late 1980s), I remember walking along windrows that contained about equal amount of organic and inorganic feedstocks and wondering how that material could be cleaned up enough to make marketable compost.
There are still a handful of mixed waste composting operations in the U.S. that have created sorting and processing lines that yield a salable end product. But the equipment required to successfully sort organics out of mixed waste streams is expensive, and most organics diversion programs opt for source separation over mechanical sorting.
Recently, however, in requests for proposals and in project announcements, we have seen the pendulum starting to swing back toward the mixed waste approach as the solution to diverting organics from disposal. It is widely known that food waste, by weight, accounts for the largest fraction of the MSW stream being thrown away. Perhaps this resurgence of interest in mixed waste streams is due to the widespread adoption of commingled recycling and the ability of the materials recovery industry to utilize technologies that yield recyclables in a form that end markets purchase. The idea is to utilize mechanical sorting, perhaps combined with some human labor, to yield an organics-rich stream that is then anaerobically digested and/or composted. The logic is that municipalities don’t need to rely on residential and commercial source separation, nor run collection trucks to pick up the separated material.
A couple weeks ago I spoke with a municipal recycling office that ultimately believes this approach will yield the highest organics diversion rates. As I sorted out my thoughts after that conversation, I kept coming back to this basic question: What is the end goal in organics diversion? Is it only to keep food waste out of the landfill to prevent methane emissions? Is it to put those heavy tons comprised of yard trimmings and food waste toward meeting zero waste goals — no matter what route those organics take to be diverted? Or is it to create a flow of high quality organics that can be utilized to revitalize soils, reduce chemical inputs in landscaping and agriculture, manage storm water and generate renewable energy?
To create a flow of high quality organics, the materials have to be as free of contaminants as possible. This yields feedstocks with the highest energy value (because nonorganic materials don’t have biomethane potential) and the highest compost value. People will source separate, especially if they understand — and benefit from — the value. Changing behavior isn’t simple, but the fact is that people can and will change when presented with the tools, education and incentives.
In reality, there is no silver bullet to organics diversion. We just know commingling organics and trash — with the idea of capturing the value on the back end — is shortchanging our environment and economy of critically needed resources. We also know that while change is challenging, it can happen. Instead of silver bullets, it is a matter of biting the bullet — enduring the “pain” required to institute change.