Single-Stream Recycling

One of the most controversial issues in the recycling world is the movement of residential programs to single-stream curbside collection.

Single-stream recycling is separating all recyclables from municipal solid waste (MSW) into a single compartment in a collection truck. With the recyclables in one compartment, this allows for compaction, optimizes payloads and reduces costs.

When curbside recycling became widespread in the mid-'80s, recycling collection vehicles had three to six compartments, and recyclables were hand-separated by the driver.

Single-stream recycling, which first widely emerged in Southern California, requires a more sophisticated materials recovery facility (MRF) with higher operating costs. However, collection cost savings can make up for additional processing costs.

Will residential single-stream recycling yield paper products of high enough quality for the world's paper mills that use it? The paper industry is divided.

One concern with single-stream recovered paper is the mixing of grades, including bleachables (old newspapers and white papers) with unbleachables (OCC and boxboard). For newsprint mills that use washing, deinking technology, mixing coated papers (magazines) with ONP is a paramount issue.

On the paper stream contamination side, the primary focus has been on glass, plastic and metal contamination. In the stock preparation (cleaning and screening) and deinking portion of recycle mills, heavyweight contaminants such as glass regularly are removed. There also are several stages in the mills' recycling processing facilities designed to remove any trapped metals.

The most difficult challenges for a recycle paper mill are plastics and other polymer materials known as stickies. One plastic bag churned up in a mill's pulper can produce thousands of tiny, lightweight particles that are difficult to remove by screening or cleaning. If these particles wind up on a paper sheet, they cause imperfections, breaks and downgraded quality in the product.

In the future, MRF technology will improve, reducing the costs of separating and producing higher-quality materials. However, it's inevitable that the finished commodities produced at the MRF will be a lower valued commodity than the materials produced from highly source-separated material collection.

Residential curbside recycling is here to stay. It is politically attractive, citizens will continue to demand it and many programs will not limit materials or service. But, the public needs education on preparing recyclables so that the materials can be included in single-stream collection.

MRF technology will continue to advance, improving the separation process, producing the highest quality material possible from single-stream collection and minimizing residue loss. Also, recycle paper mill technology routinely advances as the industry adds capacity and mills upgrade.