Single-Stream Recycling Offers Simplicity But Challenges
Single-stream recycling is a system in which all kinds of recyclables such as plastics, paper, metal, and glass are placed in a single curbside bin by consumers. The recyclables are then collected and transported to a material recovery facility (MRF) where they are sorted and processed. This system is also called commingled or single-sort recycling.
A benefit of this approach is that consumers or the depositors don’t have to separate or sort the recyclables. Rather, they are encouraged to put everything that is not trash into a single bin. This approach helps to increase the quantity of material recovered. However, there are also drawbacks to this system, as it has contributed to higher contamination rates, such as mixed cardboard items containing glues and inks.
Because China is no longer accepting U.S. recyclables, the United States will need to improve upon single-stream recycling to produce cleaner recyclables or come up with an alternate method.
History of Single-Stream Recycling
During the 1990s, several California communities started using single-stream recycling and subsequently the system was adopted by communities across the United States. By 2005, around one-fifth of all locations with recycling programs in the United States were employing the single-stream recycling system. By the start of 2010, the number reached more than two-thirds. By 2012, around 248 MRFs in the United States used a single-stream recycling system. In 2018, the United States had 633 MRFs, which handled a total of 100,000 tons of recyclables a day.
Because recyclables can no longer be sent to overseas recyclers, the United States and Canada must find new, less costly ways to process their recyclables and repurpose the remaining material.
Overview of Single-Stream Recycling
Once the recyclables are put into curbside recycling bins, MRFs collect, sort, and process the recyclables. After processing, similar kinds of recyclables are baled and shipped to recyclers of specific materials, ultimately to be utilized in the production of new products.
The actual sorting process may vary with respect to the automation employed in the system, involving technologies such as conveyors, screens, forced air, magnets, optical material identification, and eddy current.
While single-stream recycling is a simple process for consumers, it is costly for recyclers who have to employ others to work alongside machines to assist with the recycling process.
Single-Stream Recycling Process
The process for single-stream recycling is as follows:
- All the materials are unloaded and placed on a conveyor.
- Non-recyclable items are manually sorted and removed.
- The materials move to a triple-deck screen.
- Items too heavy or light, such as all cardboard, containers, and paper, are removed.
- Heavier containers drop to the bottom level, while lighter items head to the second level.
- A screen breaks the glass containers for the safety and convenience of the workers.
- The remaining materials pass under a powerful magnet to remove tin and steel cans.
- MRF staff watch carefully for specific commodities that may still have inadvertently made it down the line.
- A reverse magnet called an "eddy current" causes the aluminum cans to fly off the conveyor and into a bin.
- MRF workers separate cardboard, newsprint and office paper, and drop each piece into a bunker below. Once all the materials are separated, the materials are baled and shipped to recycling companies for processing.
The entire process of single-stream recycling involves a combination of machines and human workers.
Advantages of Single-Stream Recycling
One of the most notable benefits of single-stream recycling is increased recycling rates. As individuals or consumers don’t have to do the sorting, they are more encouraged to participate in curbside recycling programs. Again, less space is required to store collection containers.
Regarding collection, costs for the hauling process are reduced versus separate pickups for different recycling streams, or the hauler having to place different materials into various truck compartments. This simple process receives greater public approval.
Disadvantages of Single-Stream Recycling
The most notable criticism of single-stream recycling is that it has led to a decrease in the quality of materials recovered. Putting all the materials into a single bin can increase the likelihood of contamination due to broken glass and the propensity to toss non-approved materials into the recycling bin. This ultimately causes significant problems for MRF operators and communities.
Although consumers and depositors are not sorting the materials, someone ultimately has to sort them, making the cost of recycling higher. Therefore, public convenience comes at a cost.
The Bottom line
There are both advantages and disadvantages of single-stream recycling and the battle is between quality and convenience. To this point in time, the popularity of the single-stream recycling process suggests that convenience has trumped quality.
However, the use of the single-stream system has become increasingly controversial in the wake of China's more strict quality requirements for recycled materials. It remains to be seen if there are technological solutions such as leading-edge MRFs that can offer the best of both worlds in terms of convenience, maximum volume recovery, and material quality.