Reaping the Best Treasure from Our Trash
When it comes to recycling, collecting more at the curbside doesn’t necessarily mean more waste will actually be recycled.
Let’s examine a decision by the City of Minneapolis to implement a single-sort recycling program aimed at boosting recycling rates. The proposal is an attempt to move the city closer to meeting recycling goals set forth by state resolutions.
Currently, Minneapolis residents are required to separate recycled materials into nine categories: ranging from multiple paper products, to plastic, aluminum and bottles. It’s commonly referred to as source-separated or multiple-sort recycling. On the whole, the city enjoys relatively high recycling participation, but because recycling rules are perceived as onerous, residents recycle fewer materials, leading to a citywide recycling rate (amount recycled as a percentage of total waste generated) that has remained stagnant at 18% for the last decade.
Multi-sort was initially attractive to cities because it traditionally reduced sorting costs for recycling facilities since resident bore the cost of separating the materials themselves. It also resulted in fewer cross-contaminated, damaged, or otherwise unrecoverable materials being sent to landfills, known as residuals.
Moving forward, the city has sought new ways to increase both the quantity recycled and the participation rate while also reducing costs. Michigan-based Resource Recycling Systems conducted a study for the city comparing six metropolitan recycling programs across the country (including Minneapolis and St. Paul). It examined both single (everything in one bin) and dual-sort (separate one item from the rest) options, which consistently fared better than the multi-sort in increasing participation and recycling rates.
In 2002, on the recommendation of a Eureka Recycling study, St. Paul switched from drop-off recycling to a curbside collected dual-sort method, now yielding a 30 percent recycling rate. At the time single-sort was the most costly overall, largely due to higher processing costs. Additionally, single-sort methods showed higher residual rates meaning that more of the material collected for recycling was going to landfills ultimately resulting in higher environmental costs.
However, recent advances in post-collection sorting technology have been a significant factor contributing to the attractiveness of a single-sort system. In the Minneapolis study a decade later, single-sort collections fared the best in terms of both overall cost (collection and processing costs minus revenue from recovered materials) and quantity recycled. It also projected that a switch to a single-sort collection would increase amount recycled by 60% and would raise the recycling rate from 18.1% to 32% (36% and 18.1-25% for dual-sort respectively).
Still, it's curious that the Minneapolis study assumes processing costs to be the same for both dual and single-sort options (comparative rates in the various cities used in this study are not reported). It also suggests that advances in sorting technology over the past 5-10 years have made processing costs at single-sort MRFs competitive with those at dual-sort MRFs.
Perhaps more interesting however, is that the study estimates that residual rates for single-sort municipalities are anywhere from 6-16 times higher than those for St. Paul’s dual-sort program. Furthermore, there is no standard for residual rate reporting and firms that provide such information do so voluntarily. Indeed, according to an independent analysis, one local Material Recovery Facility (MRF) reported a residual rate of 7%, but when questioned further was found to have a rate of nearly 17%. It turns out, the firm was reporting mixed glass (which is not an accepted for end market users, such as bottle manufacturers) as recycled when it was used as landfill cover. Other MRFs have reported using mixed glass for the same purpose.
The report also determined that a significant amount of glass breakage, waste, and contamination arose from single-stream collection and processing systems. However, end-markets also pointed out that blanket statements about the quality of recycled stock from either dual or single-sort MRFs can be misleading since the attitudes of MRF management are also a significant factor in load quality.
On balance, there are strong arguments for and against both dual and single-sort systems. Given that processing costs for single-sort programs are increasingly competitive with dual-sort, then overall costs may be lower for single-sort. Single-sort is also more convenient for residents leading to somewhat higher participation rates and material collected.
On the other hand, dual-sort systems in general tend toward lower residual rates, less contamination, and more beneficial environmental outcomes.
If the city of Minneapolis is committed to implementing a single-sort recycling program, which it plans on doing next year, it is imperative that it includes a certification process for MRFs to ensure quality standards. Contracts should include information on volumes and percentages of recovered materials, set standards for recovery and residual rates, and report on volume and grades of recycling stock (feedstock) sent to end-markets in order to minimize harmful impacts on the environment and assist citizens and appropriate governing bodies in monitoring and evaluating the success of their recycling program.