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The Truth about Biodegradation in Landfills

“Federal environmental regulations require landfills to minimize interaction with water, oxygen, and light,” (Section V.C.4.a) according to the Federal Trade Commission (FTC). This comment is misleading and the precise reason for this is because it is out of date.

True, conventional landfills are designed and operated in accordance with the principles described in Subtitle D of the Resource Conservation and Recovery Act (Federal Register, 1991). These conventional landfills generally employ systems that minimize the amount of moisture entering and retained in the waste. The intent is to minimize the risk of groundwater pollution by limiting the amount of leachate and gas that is generated. What is not captured in the above FTC comment is noted in the work of Professor Morton Barlaz in the March 2002 edition of the Journal of Environmental Engineering: this practice often results in high leachate strength and gas generation may persist long into the future (albeit at low rates), requiring long-term management and monitoring of landfills and barrier systems that must function for extensive periods of time. The old, or conventional, way of viewing landfills simply hasn’t kept pace with what modern science is showing us.

The new and emerging waste management trend in the United States is to operate landfills as bioreactors. Bioreactor landfills are operated in a controlled fashion (which often includes the introduction of liquids) with the intent of creating an in situ environment conducive to microbial degradation of waste. Bioreactor landfills are advantageous on several levels. In a 2007 published review of five bioreactor/recirculation landfills, C.H. Benson illustrates benefits such as an increased rate of municipal solid waste (MSW) settlement (i.e. a greater mass of waste can be buried per unit volume of landfill), reduced leachate treatment costs, and enhanced landfill gas production (i.e. improving the viability of gas-to-energy options).

Obviously, it’s not enough simply to accelerate the biodegradation process through the introduction of non-toxic liquids. The landfill gases resulting from this process must be harnessed; this is done through a series of wells which capture the methane and transport it to facilities for treatment, pressurization and conversion to electricity, heat or both.

According to the BioCycle/Columbia survey of MSW, the U.S. generates nearly 400 million tons of MSW every year, 64% of which is landfilled. By the EPA’s count, there are roughly 2,400 landfills in the US. Of these, 654 (~27%) are categorized as “Operational” Bioreactor projects which have ~1610 megawatts (MW) in total Energy Generation Capacity; these projects are estimated to reduce CO2 emissions by ~94 million metric tons (MMT) per year.  More importantly, these projects represent ~54% of the total waste in landfills in the U.S.

In addition, the EPA lists 78 projects currently under construction with total Energy Generation Capacity of 253MW. Once operational, these sites are expected to reduce CO2 emission by 12MMT per year. A further 519 are categorized as candidate sites. This does not take into account the construction of new landfill facilities, many of which will be designed as bioreactors.

There is much innovation taking place around actively fostering biodegradation in landfills to generate energy. Waste Management is the largest owner and operator of landfills in the U.S. Today, they operate LFGE (landfill-gas-to-energy) projects at 100 of their facilities (~33% of the total). These projects harness enough gas to power nearly 400,000 homes (the equivalent of almost 2 million tons of coal or 6.3 million barrels of oil) and avoid production of greenhouse gases and other emissions that would be generated from those alternative sources. By the end of 2012, Waste Management is expected to add generation capacity to power an additional 170,000 homes (a further 230MW per year).

Consumer packaged goods powerhouse SC Johnson operates two gas turbines at its Waxdale, WI, facility which are mostly powered by landfill gas. The company estimates that the gas turbines reduce their reliance on coal-fired electricity and eliminate 52,000 tons of greenhouse gas emissions each year – the equivalent of taking 5,200 cars off the road or returning 298 railroad cars full of coal to the ground annually.

BMW is another industry leader using landfill gas to generate power for its operations: specifically, its Spartanburg, SC, assembly plant. Since installing two new gas turbines in 2009, the company estimates that it has reduced CO2 emissions by 92,000 tons per year or the equivalent benefit of planting over 23,000 acres of trees annually (roughly 30 times the size of New York’s Central Park).

The statistics show that bioreactors are becoming more and more common, making statements to the effect that biodegradation does not occur in landfills simply not accurate. Municipalities and private waste management companies in the U.S. are proving that biodegradation of the contents of their landfills is an on purpose process to generate energy from landfill gas.

One of the challenges faced in building standardized test methods and specifications for biodegradation is making them universally applicable throughout the U.S. There is a high degree of variability in landfill operating conditions from region to region. A key characteristic in fostering necessary conditions for biodegradation is moisture content.  Obviously, a bioreactor site in the U.S. Southeast or Northwest would perform very differently from one in the Southwest.

Our current level of knowledge surrounding MSW landfills does not currently permit the use of landfill biodegradation claims for consumer products. However, research into the performance of materials such as cellulosics and plastics in the bioreactor environment will get us closer. Future developments in the understanding of these processes may allow for testing methods that rely on sound, peer-reviewed science to confidently validate and encourage the development of biodegradable products.

Joseph Mecca is the global commercial lead for the chemicals & plastics business at UL Environment, a wholly owned subsidiary of Underwriters Laboratories. His work has focused on building best-in-class sustainability solutions for leadership partners in the Materials and Consumer Packaged Goods industries. UL Environment aims to play an active role in continued research of how diverse materials behave in actively managed landfill environments throughout the U.S.  Mecca can be reached at (631) 546-2749 or Joseph.Mecca@ulenvironment.com.

William Hoffman, Ph.D., is a senior environmental scientist focusing on the technical basis for the development of standards and guidance for standards within UL Environment including the green chemistry and sustainable chemistry aspects of environmental product performance. Dr. Hoffman can be reached at William.Hoffman@ulenvironment.com.

Stephen Lanus is a project coordinator with the science team at UL Environment, delivering research, providing guidance on, and writing draft sections of sustainability standards for building materials, lighting, and hi-tech devices. Lanus can be reached at Stephen.Lanus@ulenvironment.com.

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7 thoughts on “The Truth about Biodegradation in Landfills

  1. This article should chose a thesis and stick with it. The initial thesis that landfills no longer entomb trash. ie keep it from the environment is OK. Unfortunately the first arguement and discussion supported by Barlaz is that within conventional landfills, the concentration of leachate and the length of time that gas is generated is too long for the materials from which the landfill is constructed. That is an interesting side discussion but has nothing to do with bioreators. The reference to modern science is confusing as no “science” is documented later in the article. The article continues to suggest that regulations were blind to biodegredation. Just because capping systems are introduced, doesn’t mean that landfills will remain dry. When biological matter is consumed by organisms, waste gas (CO2 or CH4) and water will be released. The gas collection systems being installed capture this fuel produced and reduce fugitive emissions, a huge source of CO2 equivalents. This process happens in both conventional landfills and bioreactors.
    The article then gets lost in statistics and numbes of places that produce electricity from the methane. It fails to conclude that CH4 capture is environmentally responsible and can be done in a financially positive manner. It consistently wanders from the original thesis of that water, light and oxygen are now being introduced to the waste. [Light and Oxygen being introduced as part of a bioreactor, where?] and then it then ends abruptly.
    Was their point that there are lots of bioreactors out there, generating a lot of landfill gas? And so? The only thing I concluded from this article is that the authors need to retake 9th grade English to learn how to structure an article to make their point.

  2. I have read previously (I think it was something from the Sierra Club) that more methane is actually emitted to the environment from a landfill that is managed for methane and energy production than from a landfill that is kept dry. This article states the opposite. Which is correct?

  3. This article seems to suggest that encouraging biodegradation in landfills will provide environmental benefits, but the current scientific understanding of landfill gas generation, gas capture efficiency, and the greenhouse gas benefits of energy recovery suggests the opposite.

    Gas collection systems operate very inefficiently until a landfill is closed and capped, but the goal of bioreactors is to prolong the period in which the landfill is open and receiving waste. Bioreactors are essentially maximizing landfill gas generation at the time when gas collection efficiency is at its worst. And a unit amount of municipal solid generates the same amount of landfill gas in any landfill, so it is wrong to assume that bioreactors maximize the amount of generated methane. Academic research and EPA literature show that bioreactors are likely to result in less collected methane and more methane emissions than conventional landfills.

    This article uses a dubiously unreferenced estimation that energy recovery projects reduce CO2 emissions by ~94 million metric tons per year. I suspect that this number is an amalgamation of the amount of landfill methane that was destroyed (which is unfair to count since the landfill methane was human-induced) and the actual benefits of using landfill methane for energy in place of fossil fuel-derived grid energy. Using the benefits calculator of the EPA’s Landfill Methane Outreach program with the amount of landfill gas that was used for energy recovery as reported in the EPA’s most recent Greenhouse Gas Inventory Report, this benefit is closer to 10 million metric tons per year. The same EPA report tells us that atmospheric methane emissions from landfills (in CO2 equivalents) totaled over 117 million metric tons. It is clear that the environmental benefits of recovering energy from landfill gas do not outweigh the harm of landfill emissions, nor will they ever if we continue to minimize gas capture efficiency by using bioreactors (for a more complete discussion of this comparison, see the Sustainable Packaging Coalition’s recently released report at http://www.sustainablepackaging.org). If we’re interested in recovering energy from waste, anaerobic digesters and waste-to-energy plants are undoubtedly better options.

    Bioreactors enhance the economic viability of landfilling waste at the expense of increasing air pollution, and it’s folly to think that the prevalence of bioreactors is increasing due to environmental considerations. It’s time we recognize that biodegradation in landfills is not something to be encouraged and discontinue taking advantage of consumers’ misperceptions by extolling biodegradation in landfills as an environmental benefit.

  4. Operating a landfill as a “bioreactor” will not increase the total volume of gas produced during the lifetime of the space; however, it will “bump up” the curve creating more gas during earlier stages of waste placement.

    That said, I would have to disagree with Alan’s statement that an increase in tons per cubic yard due to the advancement of the biodegradation process occurs at a sacrifice to air quality. Most bioreactors cannot initiate liquid injection/recicruclation processes until an appropriate gas collection system has been implemented and approved. Each well, be it horizontal or vertical, is designed to operate within a designed radius of influence, thereby meeting EPA requirements for collection efficiency for the entirety of the permitted operating space. Further, most B/R landfills are subject to NSPS standards, requiring varying degrees of reporting, surface scans and perimeter monitoring, to name a few, to ensure that there is no harm to the environment.

    In short, a properly implemented and operated B/R facility remains the most appropriate and viable option for extending landfill life spans; a finite volume, at best.

  5. I would hope that every bioreactor landfill operates a gas collection strategy that is much more aggressive than the bare minimum standards imposed by NSPS. According to documentation of the EPA’s WARM program, a bioreactor landfill that operates with a minimum amount of collection as required by NSPS will only collect 53% of its total generated methane. I wouldn’t say that this ensures “no harm to the environment”

  6. There is, in fact, as the article states, widespread agreement that the design basis for EPA’s Subtitle D MSW landfill regulations is fatally flawed. That is because the barrier and liquid/gas removal systems that they are predicated upon have limited lives measured in decades while the waste mass remains an environmental threat for centuries. We are leaving major problems for the future, which will likely lead to major taxpayer bailouts of the waste industry, suggesting major subsidization today.

    However, the rest of this article is factually incorrect and suffers from selective analysis bias, making its conclusions incorrect.

    The article is factually incorrect because it evinces a surface understanding of the details but little of the underlying considerations. In fact, there is no trend to bioreactors, which by definition means the addition of outside liquids in addition to tactics to increase on-site moisture levels by recirculating leachate, delaying installation of a low permeable cover to extend the time for infiltration of precipitation and regrading to maximize surface infiltration. The actual trend is to wet cell operation, which excludes outside liquid addition and relies instead on the other on-site tactics. The GHG Reporting Rule filing at the end of September should provide the first indication of how extensive this change has been.

    It suffers from selective analysis bias by recapitulating the industry position that excludes multitudinous factors that raise serious concerns. While it is widely understood that gas generation will be shifted from the future to the present, the ignored price of shifting gas production from the future to the present by boosting current moisture levels include:

    (1) There will be up to a 40% increase in lifetime methane generation because, contrary to the underlying assumption, the methane concentration ratio is not constant, but rather is a variable as a function of that higher moisture.

    (2) The higher methane ratio combined with gas generation shifts from the future to the present is under conditions that, the literature is quite clear, will seriously degrade gas collection efficiency, and therefore, more gas, more of which is methane, will escape into the atmosphere in the near term when we also confront several irreversible climate tipping points.

    (3) The lower near term leachate concentrations are accompanied by higher fugitive levels of VOCs and di-methyl mercury into the atmosphere, which the reported studies scrupulously ignore.

    (4) Wet cell operation raise its own sets of near and long term safety issues that are also being ignored such as increases in leachate seeps, reductions in factor of safety, leading to significant site stability issues, and increases in mission critical leachate line clogging of the pipes, perforations and gravel beds.

    Of great concern, because the discussion has been dominated by consultants from the landfill industry, the obvious conclusion and proper solution is studiously ignored, which is that decomposable discards cannot be safely managed in the ground and therefore organics should be diverted from landfills to resolve those myriad problems in the first instance. This is precisely what Europe determine in 1999 with its Landfill Directive, ordering EC countries to phase out land disposal of decomposables, and what over 120 cities in North America are aggressively moving towards in the absence of any rational national policy.

  7. Google search says the US uses about 700 GW of electricity on average, so 260MW is only 260/700,000 of total average production — that’s comes out to less than 0.04%. Not enough to even consider, is it? Wind, solar, landfills, etc are all sources of energy for morons and muddleheaded fools (and smart businessmen who can make a quick buck on the emotions of said morons and their politicians).

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