Mixed Waste Processing: What it means for energy recovery and waste diversion

As the organization representing America’s plastics makers, the American Chemistry Council (ACC), Washington, spends a considerable amount of time exploring ways to increase recycling and diversion of plastics from landfills. While our nation has made considerable progress and plastic recycling rates continue to grow each year, a large amount of plastics are still buried in landfills. Some of these plastics could have been recycled, and virtually all of them have the potential to be converted into energy. Our view on unrecovered plastic is simple: burying valuable materials is an egregious waste of resources.

To help overcome some of the stumbling blocks to recovering the value inherent in post-use plastics, we’ve sponsored a series of efforts designed to recycle more plastics. These include: research on separating resins at recycling facilities; creation of a uniform language for collecting and selling used plastics; programs to boost recycling of polyethylene films, bags and wraps at retailers and promotion of pyrolysis technologies that convert nonrecycled plastics into fuels. We believe these efforts are helping improve recycling and waste diversion rates—a goal embraced by many communities.
 

Mixed waste processing

Recently we examined evolving systems for capturing recyclable materials at mixed waste processing (MWP) facilities. We are aware that mixed waste processing, in which a facility separates recyclable commodities from municipal solid waste (MSW) instead of collecting recyclables separately, is a relatively new and unproven approach to recycling. Past experience with MWP has raised questions about its utility, purpose and profitability.

But MWP currently is attracting interest as a potential way to address stubbornly low recycling rates, as well as to prepare nonrecycled plastics for conversion into fuels and other products. Advances in technologies at MWP facilities demand a serious inquiry into their potential to capture the recyclables that currently end up mixed with MSW and buried. As the waste stream continues to evolve, we must consider new strategies and innovations to overcome stumbling blocks to higher recycling and recovery rates.

So ACC commissioned the firm Gershman, Brickner & Bratton Inc. (GBB) of Fairfax, Virginia, to review the evolution of MWP and to determine whether technologies and economics exist to recycle and recover significantly more plastics from the waste stream, including plastics that could be converted into fuels and industrial feedstocks. The authors—led by GBB President Harvey Gershman—found that the potential to divert more post-use plastics from landfill does exist, primarily due to improvements in processing technologies. The potential also exists to significantly increase diversion rates of MSW in general if MWP was used to complement an existing single-stream recycling program. However, the authors also identified important questions that need to be answered to realize that potential.
 

MWP potential

The report, “The Evolution of Mixed Waste Processing Facilities, 1970-Today,” notes that MWP facilities currently use a variety of new and existing technologies to separate recyclable commodities from a stream of mixed trash.

In reviewing the evolving technologies, the study’s authors recount how MWP facilities initially were designed to capture high-energy elements of waste for combustion-based energy recovery (typically referred to as waste-to-energy). However, as noted above, today MWP is attracting renewed interest as a means to boost recycling rates.

This is important because even after residents have separated their recycled commodities, many recyclables are left in the MSW stream and thus are currently landfilled. So to be clear, we are not looking at MWP as a substitute for the important role consumers currently play in sorting their recyclables. Rather, we’re looking at the potential to use MWP to recover the valuable items that frequently are missed.

Technological advances make today’s MWP facilities “different and in many respects better” than older versions, the report’s authors say, which could enable communities to recycle at much higher rates than under existing collection systems.

The report notes that sortation technologies in MWP facilities continue to improve, such as the use of optical sensors that can identify and separate plastic resins, enabling higher diversion rates and more recovered materials. The report found that MWP has the potential to increase the recovery rates of high-value materials, such as plastics.

The authors conclude: “Based on its roots in single-stream sortation, today’s MWP technology appears promising. The results in terms of outputs, net revenue and reduced collection costs could be attractive for some communities. The combination of recycling with energy recovery for nonrecycled materials is an excellent approach to managing post-use materials more sustainably.”
 

MWP questions

The report also identifies outstanding issues that need to be addressed to achieve these improvements. For example, in some cases, technologies may deliver more volume of recycled material, but increased contamination could lead to reduced commodity prices. The authors also recognize some have questioned whether energy recovery (not recycling) may be the main driver behind MWP.

“In the early days of MWP when recyclables had less value, energy recovery was the primary driver.” However, the report found that communities without existing curbside recycling programs and with persistent challenges such as multifamily collection and commercial recycling were the best fits for MWP systems. The same was true for communities looking to complement existing recycling programs. Finally, the authors point out the need for better data and case studies to demonstrate realistic recovery numbers for MWP.
 

Increased diversion rates

To tap the potential of MWP, the report authors suggest that coupling MWP facilities with existing large materials recovery facilities (MRFs) could help communities increase diversion rates. To highlight this opportunity, the authors created a series of three hypothetical recovery scenarios based on a material composition study of Fort Worth, Texas, that evaluated materials found in curbside recycling and trash bins:

• Recycling bin – recyclables are processed at a traditional MRF;
• Single bin – all materials are combined and processed at a MWP facility; and
• Dual bins – recyclables are processed at a traditional MRF while trash is processed at a MWP facility. (MRF residue processed at a MWP facility.)

The recycling bin only scenario projected a 19 percent diversion rate of MSW. The single bin scenario projected a 46 percent diversion rate. And the dual bin scenario projected a 54 percent diversion rate.

This analysis led the authors to conclude, “Combining single-stream recycling, mixed waste processing, composting or anaerobic digestion and energy recovery for the nonrecycled plastics and paper residue could achieve high total landfill diversion rates ... GBB finds that combined MRF and MWP systems have the potential to significantly increase both the volume and total revenue from recycling materials. The potential exists to divert 180 percent more high value metals and plastics from landfill than are diverted today.”

MWP by itself also is attractive, the authors note, for communities that do not have an existing single-stream recycling system, due to lower anticipated hauling rates compared with source-separated collection systems. And MWP processing may also contribute to efforts to capture recyclables from multifamily buildings and businesses.
 

Plastics to fuel

As noted above, nonrecycled plastics sourced at MWP facilities potentially could be separated from the waste stream and used at plastics-to-fuel facilities that employ pyrolysis technology to transform these plastics into fuels, petroleum products and chemical feedstocks. Plastics-to-fuel technologies complement ongoing recycling efforts by recovering energy from used plastics that cannot be economically recycled. Increased deployment of these technologies could help reduce the amount of waste sent to landfills and create products. Although the report notes, “The technology has evolved and appears to address historical issues,” some questions remain. The success of MWP will hinge on available markets, the ability to meet growing demand for high-value materials such as plastics, and the ability to reduce costs.

We hope this study by GBB will generate a healthy and productive discussion about the potential for MWP to increase the recovery of post-use plastics (and other materials) and increase diversion rates. At the end of the day, we all share the same goal of diverting more valuable materials from landfill and believe that all potential strategies should be explored and allowed to prove themselves in the marketplace.

Craig Cookson is director of sustainability and recycling for the Plastics Division of the American Chemistry Council, Washington.