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Zero Waste

Supporting Information for How to Manage Residual Leftovers on your Way to Zero Waste

Read the full report, What is the best disposal option for the "Leftovers" on the way to Zero Waste?

Major assumptions in the report

Landfill gas
Landfill gas capture rates are a contentious issue and a large factor in determining the environmental impacts of burying leftovers, particularly when the leftovers contain high quantities of organic materials. We chose two landfill gas capture rates to reflect the uncertainty in this area. We also chose to model no landfill gas capture for post-MRBT leftovers because the material will not be biologically active and will produce little to no landfill gas. There was not estimated to be enough gas production from the MRBT leftovers to warrant a LFGTE system.

Our decision to run the model at 40% and 80% gas capture rates was to offer some sensitivity analysis around how the rates affected the environmental performance of landfills. Our lifecycle analysis measures the impacts over a 100-year period, and there is no empirical data on landfill gas capture rates over that time period since the technology and practice are relatively new.  The data shows that a landfill with a higher gas capture rate would have a lower environmental impact, but the report does not imply that 80% gas capture is feasible. The report also clearly shows MRBT outperfoms landfill gas to energy systems, even at the assumed high gas capture rates. 

Residue from MRBT process
The residual material after MRBT processing is not considered to be marketable and is sent to a landfill for disposal. Some MRBT facilities may produce a stabilized inert residual that can be used for specific applications such as land reclamation of old mines and landfills, or landscaping along railways and highways, but this was not considered in our study. Using the MRBT residual instead of landfilling could increase the environmental benefits of using MRBT by displacing the use of a substitute material with a higher pollution profile.   

Recovery rates from MRBT
Recovery rates at MRBT facilities vary with the composition of the incoming feedstocks. For example, it may be more difficult to recover market-quality recyclable materials if there are a lot of food scraps in the residuals. This study assumed two different sets of capture rates for recyclables in the MRBT process based on data and conversations with operating facilities. Here's a comparison of our high/low recovery rates for the recyclable materials:

recovery rates for MRBT scenarios

Energy offsets

The energy generated by WTE and LFGTE facilities was assumed to displace electricity that would have otherwise been produced by natural gas. Natural gas is replacing coal as the dominant source of new energy in the US. 

Frequently asked questions

What are "leftovers?"

Leftovers is our term for the materials that remain after recycling and composting. We use "leftovers" instead of "waste" for several reasons:

  1. These are valuable resources, not "trash."
  2. Many of these materials could be recycled or composted but are not sorted properly.
  3. The amount of leftovers decreases in a community with high recovery goals and strong programs for recycling, composting and reuse. What's left over today may not be in a few years or may change in composition as more materials are recovered. This underscores the need to design disposal facilities for fewer and fewer tons, instead of investing in technologies that rely upon a steady stream of tons with high energy content. 


Why did you choose Seattle for your model?

We wanted to model a community on the cutting edge of resource recovery and we also needed a communtiy with good data on what was left in their trash bin. Seattle has one of the best recycling rates in the US and had a recent waste composition on its leftovers so it became our model community. 


Does that mean 70% recycling is the best achievable recycling rate?

Absolutely not. Nearly 90% of a community's discards can be recovered and marketed. Much of Seattle's remaining waste could be recycled or composted instead of ending up in the trash. For example, nearly 29% of Seattle's leftovers was food waste that could have been composted. Almost 19% was paper that could have been recycled or composted. Seattle households could certain reach higher recovery rates and will continue to do so. Their current recycling rate of 70% is a great accomplishment but is not the final goal. 


What do the environmental categories, such as ecotoxicity and eutrophication, represent, and how do you place a monetary value on pollution and health risks?

For more information on the types of pollution assessed and their associated monetary values, please read the background documentation on the MEBCalcTM model.


Where is MRBT happening?

European countries are leading the movement to pre-process leftovers for additional recycling and biological stabilization. This is driven by European Union policy, the Landfill Directive, which reduces the amount of biologically active materials that can be landfilled. Germany has gone one step further in banning the direct landfilling of any materials, requiring all leftovers go through a pre-treatment process. There are more than 330 plants in Europe processing 33 million tons per year, with more than 450 plants expected by 2016.

Can we use MRBT instead of having people separate materials for recycling and composting?

While MRBT facilities are able to recover some recyclables from the leftovers, these facilities are not able to sort and market many of the materials because they are too dirty and contaminated from the other leftovers. For example, the compost from MRBT facilities is often not marketable as a soil amendment and is commonly buried in the landfill. MRBT is a solution for treating leftovers after source separation efforts and is not a substitution for having residents and businesses separate their discards. Source separating materials for recycling and composting, such as cardboard, plastic bottle and food scraps, guarantees the highest economic value and greatest environmental benefits from recovering these materials. 


Why is managing residuals important--shouldn't communities focus on increasing recovery efforts first?

Communities should absolutely give top priority to increasing the availability of and participation in recycling and composting programs to recover materials from their discards. Infrastructure investments are a big part of this effort and it is important for a community to consider how its discards stream will change as recovery rates increase. By looking ahead and considering the best options for managing its leftovers in the present and the future, a community can avoid investing in disposal technologies that are not compatible with a decreasing amount of leftovers or cause excess pollution and environmental health impacts. Pre-processing leftovers through MRBT facilities may also help communities reach their other environmental goals such as minimizing air and water pollution and reducing greenhouse gas emissions.   


For further information about this study and our findings, contact the authors. 

What is the best disposal option for the "Leftovers" on the way to Zero Waste?

Download the report by Dr. Jeffrey Morris, Dr. Enzo Favoino, Eric Lombardi and Kate Bailey

Zero Waste communities push for ever-higher resource recovery rates through a strong emphasis on source-separated recycling and composting, waste reduction and reuse programs. While leading communities continue to progress toward 90% recovery and better, there can still remain many thousands of tons of mixed-waste residuals (a.k.a. “leftovers”) that need to be disposed of, most commonly in landfills. The question before us and addressed in this study is: “What is the best method for managing our residuals in order to reduce the harm and risks to public health and our environment?” To answer this question we took the residual waste from a leading recycling and composting community, Seattle, Washington, and ran it through eight different residual management scenarios, based on the leading technologies in the marketplace today:

1.   Landfill with landfill-gas-to-energy (LFGTE) with three different assumptions for gas collection efficiencies;

2.  Waste-to-energy followed by landfilling (WTE-to-landfill) as practiced today by leading WTE companies as mass burn incineration;

3.  Mechanical Recovery, Biological Treatment followed by landfilling (MRBT-to-landfill) with two different assumptions for therecovery of recyclables and two different assumptions for gas collection efficiencies.

It is also necessary to take into account the likelihood of dependence on Xanax (in extremely rare cases) and when using therapeutic doses of the drug. The risk of drug dependence increases with the combined use of Xanax and benzodiazepines. Read more about this at .

We then used the Measuring Environmental Benefits Calculator (MEBCalcTM), created by Dr. Jeffrey Morris, to assess each leftovers management scenario across seven lifecycle environmental impacts: climate change, acidification, eutrophication, respiratory diseases, non-cancers, cancers, and ecotoxicity. The environmental impacts are caused by the pollution emitted from the various waste management activities used to handle discarded products, packaging and other materials for recycling, composting or disposal.

>> Download the report for our full findings and approach. 

>> Download the press release. 

>> Contact the authors about presenting at conferences or webinars. 


The study found MRBT-to-landfill had the lowest overall environmental and human health impacts of all the disposal technologies. It is reasonable to conclude that the MRBT option is not only the best environmental practice for managing residuals, but is also the best community strategic option as well.

Results showed MRBT had the lowest environmental impacts of all the disposal options.


More information on MEBCalcTM

MEBCalc™ (Measuring the Environmental Benefits Calculator) is Sound Resource Management’s proprietary software for computing the environmental footprint of a community’s municipal solid waste (MSW) management system, from collection through final disposition of each discarded product or packaging material. Environmental impacts covered in the footprint include climate change, public health (respiratory disease, cancer, and toxicity), ecosystem toxicity, waterway nutrification, and acid rain.

Download an overview of MEBCalcTM and the key assumptions used in the model

Download technical documentation for MEBCalcTM

Learn more about MEBCalc and Sound Resource Management. 

Learn more

 Read more about the assumptions for the study and FAQs


Special Reports and Research

>> Boulder Zero Waste Project Multi-Family Unit Outreach (3/16/2015)

>> What's the best way to manage "Leftovers" on the way to Zero Waste?

>> Microplastics in Compost from Food Packaging and Serviceware

>> Stop Trashing the Climate

>> Why waste-to-energy is NOT part of Zero Waste

>> Zero Waste to landfill" is NOT Zero Waste


 What's best to do with "Leftovers" on the way to Zero Waste?

Whether a community is recycling and composting 50%, 70% or 90% of its discards, there still remain thousands of tons of mixed-waste residuals (the “leftovers”) that need to be managed and disposed of, most commonly in landfills. The question before us and addressed in this study is: “What is the best method for managing our residuals in order to reduce the harm and risks to public health and our environment?” 

The study found MRBT-to-landfill had the lowest overall environmental and human health impacts of all the disposal technologies. It is reasonable to conclude that the MRBT option is not only the best environmental practice for managing residuals, but is also the best community strategic option as well.

Read the full report and learn more about the study. 

Microplastics in Compost from Food Packaging and Serviceware

plastics do not disappear when compostedIn several Zero Waste programs across the country, plastic-coated paper products like milk cartons and coffee cups are accepted in compost bins. Eco-Cycle has funded groundbreaking research from the highly-respected Woods End® Laboratories in Maine and international composting expert Will Brinton showing that these  plastic coatings DON’T go away in the composting process. In fact, the plastic breaks down into tiny micro-particles, not visible to the naked eye, that remain in the compost and eventually make their way into our soils and waterways, adding to the growing problem of plastic pollution in the environment. In addition, new research indicates that micro-plastics may be harmful to living organisms in many ecosystems.

View our groundbreaking research and check out our toolkit to help make sense of the different types of food packaging on the market today, what products are safe to include in composting programs, why plastic coatings pose a serious threat to our environment, and now who’s meeting best practices with plastic-coated food packaging. Take action in your community to keep plastics out of our environment. 

Stop Trashing the Climate

stop trashing the climate report

Stop Trashing the Climate, co-authored by the Institute for Local Self-Reliance, Eco-Cycle and GAIA, proves a Zero Waste approach is one of the fastest, cheapest and most effective strategies to protect the climate. Significantly decreasing waste disposed in landfills and incinerators will reduce greenhouse gas emissions the equivalent to closing 21% of U.S. coal-fired power plants. This is comparable to leading climate protection proposals such as improving national vehicle fuel efficiency. Indeed, preventing waste and expanding reuse, recycling, and composting are essential to put us on the path to climate stability.

Read more about the report and download the executive summary, full report and more>>

Why waste-to-energy is NOT part of Zero Waste

The pioneers of the Zero Waste movement in the U.S. —Eco-Cycle among them—were very clear in the mid-90s that zero waste to landfill was not the same thing as Zero Waste. Zero Waste is about making the best choice with our natural resources — from extraction to production to consumption to disposal. It involves a constant evaluation about our materials’ choices and a strong commitment to eliminating waste, not just treating it.

We continue to oppose WTE as a part of Zero Waste because WTE:

  • has the most greenhouse gases (GHG) per fuel type
  • its emissions contain dangerous air pollutants
  • is the most expensive form of electricity
  • fails to create a fraction of the jobs created by recycling and composting
  • produces only a fraction of the energy that can be saved through recycling 

Learn more and download Waste OF Energy: Why Incineration is Bad for our Environment, Economy and Community.


"Zero Waste to landfill" is NOT Zero Waste

air pollution

The business community has embraced the concept of Zero Waste as a way to improve efficiencies, reduce production waste and save money. Unfornately there has been a wave of initiatives under the guise of "Zero Waste to landfill" which are accepting high levels of waste incineration. 

Read our position paper on why Zero Waste to landfill is not Zero Waste.