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ReLoop: What is Mixed Waste Processing or “All in One/Dirty MRF” Recycling?

Danielle Peacock

As part of our increasing work in recycling and recovery, Project Associate Danielle Peacock and Senior Manager Anne Bedarf continue their recycling blog series, ReLoop, which will address different recycling topics, questions, and concepts. You can check out other posts from the ReLoop series here.

There are three primary ways to collect household recycling: source separation, single stream, and no separation from trash (or “all in one”), and each of these methods provides unique benefits and trade-offs. So far in the ReLoop blog series, we have covered source separated recycling and single-stream recycling. In this blog we take a closer look at “all in one” collection, also known as mixed waste processing (MWP) or using a “dirty MRF.”

MWP is a one-bin system where the consumer places all trash and recyclables in one bin with no separation. This material then proceeds to a sorting facility to glean recyclables. In our previous blog post on single-stream recycling, we discussed how a Material Recovery Facility (MRF) works. These facilities use a combination of machinery and human hands to sort.

MWP uses what is commonly called a dirty MRF because the incoming stream is household trash (also known as Municipal Solid Waste, or MSW). See this report for profiles of different types of sorting facilities, including pictures. This report also estimates that MWP facilities make up less than 5% of all MRFs in the US.

There are varying estimates of the effectiveness of MWP facilities[1]:

  • Kit Strange in Issues in Environmental Science and Technology estimates that 10-30% of waste entering a MWP facility is recovered as commodity grade recyclables, with contamination contributing to this low rate. Contamination is reduced when input comes from homogenous sources like office buildings.
  •  The City of Toronto studied various waste treatment and recovery systems, including dirty MRFs. They found that success relies on a clean and dry stream, and current recovery rates rest around 5–10% with a low quality output due to contamination. They ultimately chose a different course of action.
  • StopWaste.Org (Alameda County, California) calculated the average recovery rate for MWP facilities in California at 19%, compared to 85% at single-stream MRFs.
  • Pinellas County, FL also studied California facilities. They found a maximum recovery rate of around 30%, with a higher rate possible when co-locating with composting. It was not recommended as the primary method of recycling.
  • R3 Environmental planned to co-locate a dirty-MRF with an incinerator in New Hannover County, NC. The project ultimately failed.

As with any recycling system, there are trade-offs:

Good – MWP requires no consumer participation, education, or sorting behavior. It can also be used to recover additional recyclables from the waste stream missed in recycling separation. MWP facilities can also co-locate with single-stream recycling MRFs, waste to energy, or composting facilities to maximize their impact. The quality of materials recovered through MWP is maximized if the source is homogenous, like office waste, or has organics removed prior to disposal.

Bad – The lack of consumer participation can also be seen as a negative, as there are no educational opportunities and consumers are less likely to make the connection to the impacts of their consumption habits. In addition, compared to the other methods, the potential for contamination is very high and the recovery rate is relatively low. Pre-separating organics and investing in technology can improve this process. However, these two options revert to consumer participation and require significant investment in machinery. Use of human labor exacerbates the potential for negative human health impacts on workers. Accepting all municipal solid waste into a MWP facility increases the likelihood of worker being exposed to dirty diapers, spoiled food, sharps, medical waste, and hazardous wastes. In his book Garbage Wars, author David Pellow describes such conditions for workers in a Chicago facility in the mid 1990’s, which used a combination of technology and hand sorting.

Contamination continues to be an important factor in the recycled commodities market. Contaminated materials require extra processing or are rejected outright and sent to landfills. The export market for these lower quality materials is also shrinking. Most recently, China has begun to crack down on unwashed plastic imports and contaminated paper bales.

The Grey Area – Like both of the recycling systems previously discussed in this blog series, decision makers must weigh the pros, cons, and costs of any system. What is the primary goal of the recovery system? Are you using MWP as the sole recycling system? Are you using it to glean additional recyclables from trash after single-stream separation? Are you co-locating with energy recovery or composting? How much are you willing to invest in technology versus human labor?

One East Coast city provides a particularly salient example. In this city, which will remain nameless, transparency is lacking at the local dirty MRF, and processes and recycling rates are unknown. Advertisements from both the dirty MRF and haulers falsely promote a recycling rate of 90%[2], push the dirty MRF as a superior recycling option, and confuse residents by labeling it “single-stream recycling.”  Contamination is billed as “not a problem,” though discussions with local recyclers show significant concern regarding material from this source. Many residents adopted the dirty MRF as their primary recycling option though curbside and drop-off recycling were available.  While some robust local dialogue occurred, there is still a prevailing misconception that the dirty MRF recycles 90% of all waste and is a viable recycling option.

So where does MWP fit? In my opinion, it is not appropriate as a primary recycling option. At present, the best opportunity for MWP is co-location with a landfill or waste to energy facility to provide a final sort of municipal solid waste prior to disposal. Concurrent organics source separation would greatly decrease contamination. This catches missed items and provides a last effort in areas with no recycling ethic or options. However, it should not be billed as a significant recycling option.



[1] For the purpose of this blog, recovery rates are the percentage of materials that enter the facility and are diverted to recycling. The remainder may be landfilled or sent to a waste to energy or incineration facility.

Recovery rate = Amount Recovered for Recycling / Total Input

[2] The facility offers a sorting line designated only for construction and demolition waste. This line achieves approximately 90% recycling as a homogenous and dry stream.

2 Responses to ReLoop: What is Mixed Waste Processing or “All in One/Dirty MRF” Recycling?

  1. I would like to discuss a solution for dirty MRF. Could the public be required to seperate diapers, medical waste, sharps, spoiled foods and hazardous waste into seperate containers inside the garbage? What is your solution to a successful dirty MRF.

    I enjoyed your blog. Excellent!

    Sidney

  2. Danielle Peacock says:

    Hi Sydney,
    These are my conjectures based on the research I have done and our local Charlottesville recycling and waste atmosphere.

    A goal of a dirty MRF is so a consumer does not have to do any separating or to give an extra layer of sorting after recycling. Creating requirements for separation in effect eliminates that benefit. At some point, the lines get gray. If you require separation, why not separate recyclables and put the rest in the trash? At some point, will we have a large can for recyclables, and a small one for trash, with most every item in the recycle bin and the items you list in the trash?

    There’s also a technical side to putting multiple containers inside one trash can. If the waste company wants to truly keep these bags separate, they will need some kind of identifier – a tag, a bag color, etc. At some point they will have to be separated, whether they are manually put in to different places in a truck or separated at a facility. You also have the issue of the bags breaking along the way. If a collection hauler and facility are not set up for this type of separation, then separate containers in one bin will not likely make an impact.

    It seems to me that the path to success includes some sort of separation to preserve the value (and easy ‘sortability’) of materials. This could be a co-located composting program, a recycling program that goes to a traditional MRF with trash going to extra sort at a dirty MRF, a combination of all of those, or some kind of other creative solution.

    Thanks for the comment, it is good food for thought.

    Danielle

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