|Commingling and Single Stream Collection|
Many options exist for collecting recyclable materials, but commingling and single stream collection strategies are becoming increasingly common amongst both municipal recycling programs and campus recycling programs. The terms “single stream” and “commingling” are sometimes used interchangeably to refer to all recyclables (bottles, cans, paper, etc.) being collected in a single bin. “Commingling” may also refer to materials grouped together by category. Office-grade white paper, colored paper, and low-grade paper collected together, or PET, HDPE, PC, and other plastic resins collected together, but still separated from other types of materials are examples of commingled collection systems. For the purpose of this book, single stream collection and commingling will not be used interchangeably. Single stream collection will signify all materials being collected together, while commingling will signify separating materials into similar groups.
A major benefit of single stream collection is that a higher volume of material is collected. However, this material may be highly contaminated and often unfit for use in manufacturing. This is why the waste stream needs to be carefully assessed. Single stream collection may be more viable in a municipal setting as the recyclable materials that are collected are often of a low quality to begin with. This is not the case on a college campus where copious amounts of high quality paper can be collected and will only retain a high quality level if separated from other materials. Paper is an easy material to collect, separate, and sell in order to generate revenue for a college recycling program. Including paper in single stream collection can greatly inhibit a recycling program's ability to profit from recyclable sales. As the market fluctuates, varying degrees of paper quality will be acceptable, but producing a high quality product regardless of market trends will be beneficial in the long term. It is easier to switch to commingling or single stream collection than to begin with single stream and switch to source separation because participants will not be accustomed to separating materials and contamination will occur.
Contamination of recyclables, due to single stream collection, can take on a variety of forms. Trash or organics can be mixed into the recyclables. Another major concern is the effect of single stream collection on valuable paper sources. Broken glass shards are a major hazard to the paper manufacturing process because they significantly increase wear and tear on equipment. If the glass is not fully separated out during the manufacturing process, it may become embedded in the paper and pose a hazard both for employees and future customers. Paper can also become contaminated by liquids left in containers collected as part of a single stream system. Although all plastic and glass containers would preferably be cleaned by the consumer prior to being placed in a recycling bin, there is often leftover liquid in these containers. This skews the weight measurements as wet paper is heavier than dry and also lowers the quality of the paper, sometimes rendering it completely unsuitable for recycling. In this event, what was originally high quality paper becomes waste. While single stream collection may increase the quantity of material collected, it also increases the amount of contamination and therefore trades quality for quantity.
Due to lower quality, costs will be increased at some point in the recycling process. If paper recyclers are receiving huge amounts of low quality materials, they will need to remedy this by placing some of the financial burden back onto the recycling collectors. This could be in the form of increased pick up fees, extra charges to help compensate for damage to equipment from contaminated material, or lower prices per pound of material collected.
Contamination will also make tracking systems more difficult and less reliable. Recyclables are generally measured in weight and volume, but high levels of contamination will skew these results. The weight and volume of contaminants need to be subtracted from the total weight at the time of collection in order to determine the percentage of contaminants and the percentage of recyclable materials. In a single stream system, the collectors (campus recycling programs) will have to rely on manufacturer receipts in determining contamination levels and will not be able to determine which materials to target for increased recycling. Clear material tracking is essential to proving the cost effectiveness of a recycling program as well as identifying educational needs based on what is already being recycled on the campus and what could be recycled, but ends up as waste. Single stream collection also skews tracking systems by counting contaminants as recyclables. There is a major difference between landfill diversion and recycling. Recycling is an ongoing process, whereas waste diversion is temporary. Contaminants will still be landfilled, but will be diverted temporarily. Single stream collection undermines the valuable aspects of material tracking.
It is also important to track where the recyclables from campus are going after being collected. Are materials processed locally? Or, are materials sent overseas for processing? Paper manufacturers in the
Another factor to keep in mind is confidential documents. These cannot be included in single stream collection because they need to remain private. It is inefficient to collect only one type of item separately while single streaming the rest.
Despite the numerous quality and life-cycle drawbacks to single stream separation, many college administrators across the country are clamoring for recycling programs to switch from source separation to single stream collection in order to save upfront collection costs, simplify the system for consumers in order to increase participation, and decrease worker injuries through automating collection processes. While these reasons are valid, they may not be sufficient to justify changing a fully functional source separation system which produces high quality materials to a seemingly simpler system which leads to lower quality items and waste. If pressured or required to switch to a single stream system, compromising with commingling may be an option. For example, paper could be commingled (office grade/white paper, colored paper, and low grade all together) but separated from glass and plastics. While commingling may still lead to a decrease in quality, it will not lead to as significant a decrease as single stream collection.
Commingling should also be considered in composting processes. Just as quality of recyclable materials varies, the quality of compostable materials varies as well. For example, food scraps and yard waste will produce a much higher quality end product than compost made primarily of paper food boats and polylactic acid (PLA) containers. See Chapter 14: Bioplastics for more information about PLA containers. Again, the type of collection depends on the destination of the end use product. If the campus is planning on producing an extremely nutrient rich compost to be used as a soil amendment in campus gardens, it may make sense for food scraps to be collected separately and composted on campus. Since PLA containers will not decompose quickly in a basic compost system and require industrial processes to biodegrade, they could be collected separately from food scraps and sent to an industrial composter. Again, the size of the campus is a major factor in determining the best system. Source separation of organic materials would be feasible on a small or medium sized campus, but sending all organic waste (from food scraps to yard waste to PLA containers) to an industrial composting facility may be the only cost and time effective option on a larger campus.
Container Recycling Institute
Conservatree 2003 Report: Single Stream: “An Investigation into the Interaction Between Single Stream Recycling Collection Systems and Recycled Paper Manufacturing”
Conservatree: “Single Stream Collection: Done Deal or Good Deal?”
EPA Commingled Recycling System Improvement
EPA Region 10: The
Friends of the Earth Briefing: “Recycling Collections- source separated or commingled?”
“Single Stream Best Practices Manual and Implementation Guide”