Choosing recycling collection methods

PDF icon Single-stream and Dual-stream Recycling - Comparative Impacts of Commingled Recyclables Processing

In Minnesota, much debate is centered around single-stream and dual-stream recycling systems: What are their comparative advantages and disadvantages?

In its role providing local government and market development assistance, the Minnesota Pollution Control Agency commissioned a study to frame the issue.

The MPCA will use the study to assist local units of government in improving their recycling collection, processing, and marketing. This, in turn, may improve recycling rates by ensuring the most efficient balance among public participation, processing residuals, and marketable quality of materials in local recycling programs.


Single-Stream and Dual-Stream Recycling: Comparative Impacts of Commingled Recyclables Processing (January 2006) is based on research conducted by Tim Goodman & Associates. The project included gathering information about the collection and processing methods of four major materials recovery facilities (MRF) in Minnesota, the quality of materials received at seven major recycling markets and its impacts, and the characteristics and benefits of select recycling equipment. Only one MRF agreed to fully participate in the study, but, when available, existing information about the others was reviewed and included.

Summary of key findings

Collection and processing

  • Glass breaks during both single-stream and dual-stream collection, but can be reduced through the use of collection vehicles and collection methods designed to minimize it.
  • Glass breakage is more prevalent in single-stream processing systems.
  • The amount of processing residuals generated at single-stream facilities in the metro area varies significantly, from around 2 percent up to 17 percent of throughput.

End markets

  • Over 70 percent of end markets interviewed reported seeing more contamination today than 5 years ago.
  • Over 85 percent of the end-markets interviewed said that they have received both good and bad material from single-stream and dual-stream facilities.
  • The major glass market in Minnesota, a glass container manufacturer, has experienced a dramatic decrease in the quantity of clean, color-separated glass cullet, and attributes this decrease to increased single-stream recycling.
  • Most problematic contaminants include glass, plastic bags/film plastic and unacceptable paper grades at paper mills; glass and metal at plastics manufacturers; and ceramics, pottery and mixed glass at glass manufacturers.
  • Most of the paper mills and all of the plastics manufacturers feel that single-stream recycling is a contributing factor to the decline in feedstock quality. Other factors they identified include:
    • contaminated loads from dual stream MRFs
    • feedstock demand and pressures from overseas markets
    • reduction in public education efforts
    • MRFs that emphasize material quantity versus quality.
  • Feedstock contaminants and problem loads of glass are just as likely to come from dual stream MRFs as from single-stream MRFs.

Key recommendations for MPCA staff

  1. Develop educational materials and sponsor workshops for local decision-makers that outline the advantages and disadvantages of different collection and processing methods and discuss options for minimizing problems with any system.
  2. Implement a registration or certification process for MRFs in Minnesota that would give a better understanding of Minnesota's recycling rates and infrastructure by requiring registered MRFs to report certain information.
  3. Clarify to all stakeholders the terms of the Solid Waste Management Tax exemption (Minn. Stat. 297H.06) to ensure adequate compliance.
  4. Conduct further research into the feasibility of using optical sorting technology for processing mixed broken glass from local MRFs, and of possible public/private partnerships for the construction and operation of an optical sorting facility.


Primary author: Mr. Tim Goodman of Tim Goodman & Associates (St. Louis Park, Minn.)

Appreciation goes out to the MRFs, end-markets, and equipment vendors that participated in the study. Many companies and individuals graciously shared their data, thoughts and opinions regarding the issues and impacts associated with the processing of commingled recyclables.

Related research


  • HTML icon Single Stream Best Practices Manual and Implementation Guide

    Materials designed to help recycling managers create and maintain the best program for their goals and local community, as well as for the health of the whole recycling system. Recommendations are directed towards solving problems and maximizing the benefits of this type of recycling program. (Conservatree, 2007)


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Changes in the regional market for recycled glass containers prompted MPCA to commission research on glass uses and outlets. (June 2007){/article}