The Truth about Biodegradation in Landfills
‚ÄúFederal environmental regulations require landfills to minimize interaction with water, oxygen, and light,‚ÄĚ (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 This comment is misleading and the precise reason for this is because it is out of date.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‚Äôt 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‚Äôs 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‚Äôs count, there are roughly 2,400 landfills in the US. Of these, 654 (~27%) are categorized as ‚ÄúOperational‚ÄĚ 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 ‚Äď 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‚Äôs 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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