The SWANA Applied Research Foundation has prepared a new guide to provide solid waste managers with up-to-date information and guidance on an exciting development in the field of solid waste management - namely the bioreactor landfill.

By Jeremy K. O'Brien

The predominant MSW disposal option in use today is the sanitary landfill. Current landfills must meet the requirements of the Resource Conservation and Recovery Act, Subtitle D, the Clean Water Act, the Clean Air Act, and numerous other federal, state, and local regulations. The overall intent and guiding principle of these regulations is to keep wastes "dry," thus minimizing production of leachate and landfill gas (LFG), two of the major byproducts of waste degradation. The containment systems supplied by these the conventional dry Subtitle D landfills are designed to provide environmental protection at least through the end of the 30-year period following the closure of the landfill. At some point beyond the 30-year postclosure period, however, the potential exists that the liner containment systems underlying and overlying the waste might partially fail. The primary environmental issue associated with partial containment system failure and resulting moisture infiltration is the potential associated increase in gas and leachate production and the resulting impact of uncontrolled leachate and/or LFG releases to the environment. The nature and magnitude of the releases exiting the landfill and their resulting impacts are directly related to the amounts of organic waste not yet decomposed. The bioreactor landfill alternative has drawn significant attention in the last several years as a means of addressing this long-term environmental liability issue associated with Subtitle D landfills. A bioreactor landfill is a sanitary landfill that uses enhanced microbiological processes to transform and stabilize the readily and moderately decomposable organic waste constituents within five to 10 years of bioreactor process implementation. The bioreactor landfill significantly increases the extent of organic waste decomposition, conversion rates, and process effectiveness over what would otherwise occur within the landfill. Stabilization means that the environmental performance measurement parameters (LFG composition and generation rate and leachate constituent concentrations) remain at steady levels and should not increase in the event of any partial containment system failures beyond five to 10 years of bioreactor process implementation. As the development of the bioreactor landfill alternative moves from full-scale development to commercial implementation, the management and technical issues associated with the implementation of this new technology on a commercial basis need to be defined and addressed. For example: What is the public's perception of this new technology and how can it be influenced in a positive way? What are the real benefits and risks associated with the bioreactor landfill? More importantly, do the benefits justify assuming the associated risks - especially for public-sector landfills? How will the bioreactor landfill fare in the marketplace? Will it provide a competitive advantage or be seen as a liability by prospective users of the landfill?

To SWANA's knowledge, The Solid Waste Manager's Guide to the Bioreactor Landfill is the first of its kind to address the management-related issues associated with this emerging disposal option. The guide distinguishes between bioreactor landfill and leachate recirculation landfills for a number of compelling reasons. For example, leachate recirculation is currently permitted under Subtitle D regulations while operational approaches needed for bioreactor operations, such as the addition of liquid-waste amendments or the installation of a permeable final cover, are currently prohibited.

The primary objective of leachate recirculation landfills is leachate treatment, with waste stabilization generally viewed as an added benefit. Alternatively, the primary objective of a bioreactor landfill is biostabilization of the landfilled waste mass. The underlying philosophy behind the current Subtitle D regulations is to keep the landfilled waste as dry as possible in an effort to minimize the generation of leachate. The underlying philosophy for a bioreactor landfill is to keep the waste sufficiently wet in order to maximize the biodegradation process. Put another way, the overall goal of the current Subtitle D regulations is waste containment, while the twin goals of the bioreactor landfill are waste containment and treatment. The bioreactor guide provides the solid waste manager with up-to-date technical and management information regarding this new technology in a number of key areas.

Status Report on Bioreactor Landfill Demonstration Projects. There are about 20 full-scale demonstration projects under construction, in startup, or in the early stages of operation. These projects represent millions of dollars invested in the development of this technology. The overriding purpose of these demonstration projects is to define, address, and hopefully resolve the technical and operational issues associated with the implementation of the bioreactor landfill alternative. Current information on each of the demonstration projects is presented along with review of the bioreactor's development history and a characterization of the commercialization status of this technology.

Technical Issues. The bioreactor landfill method is in the full-scale demonstration stage of development. The purpose of this developmental stage is to identify and resolve technical and operational issues associated with applying the bioreactor technology in the real world of commercial landfill operations. The primary technical and operational issues being addressed through the demonstration projects are listed in Table 1. Guide to the Bioreactor Landfill provides the solid waste manager with an understanding of each of these issues and an update on the status of their resolution.

Water Requirements. The amount of water needed for full-scale bioreactor implementation can be substantial. For example, to increase the moisture content of waste from 25% to 45% at a 500-tpd landfill would require almost 12 million gal./yr. of water. The bioreactor guide provides the solid waste manager with basic information regarding the quantities of water that are needed for the operation of a bioreactor landfill and the potential sources of water that can be used to meet bioreactor landfill water needs.

Bioreactor Landfill Benefits. The potential benefits associated with the bioreactor landfill method are substantial. They include waste biostabilization, significant increases in the density of the landfilled waste, and the potential for increased gas recovery, to name a few. Estimates on the amount of landfill airspace that can be recaptured and reused as a result of bioreactor operations range from 13% to more than 30%. The bioreactor guide provides up-to-date information on the benefits associated with the bioreactor landfill alternative.

Drawbacks and Risks. As with the development of any new technology, there are drawbacks associated with the bioreactor landfill alternative in addition to risks associated with its implementation at its present stage of development. Potential drawbacks include increased gas emissions, increased odors, leachate seeps, and sideslope instability. By becoming aware of these risks, the solid waste manager can ultimately assign a probability, as well as a cost, to their negative impacts on a local project and weigh these impacts against the positive benefits of the bioreactor landfill.

Bioreactor Landfill Economics. The solid waste manager should be aware that additional investments - in leachate collection and recirculation piping, enhanced gas recovery systems, and additional permitting requirements - are required to implement the bioreactor option. For example, an estimate of $3.5 million was developed for the leachate recirculation and water distribution system for a 1,200-tpd landfill. Guide to the Bioreactor Landfill presents up-to-date information and data regarding the economic and financial aspects of bioreactor implementation.

Regulatory Issues. Current Subtitle D landfill regulations are based on the philosophy of minimizing the generation of leachate through minimizing the amount of water that is allowed to enter the landfill. These regulations do allow for the recirculation of leachate and LFG condensate back into the landfill. It is difficult, if not impossible, however, to permit a true bioreactor landfill under existing federal regulations. Solid waste managers have two options - one currently available and one that appears imminent - through which a bioreactor landfill permit can be obtained. These options are summarized in the guide, along with the impediments associated with the existing regulatory framework.

Negative Perceptions. Despite the substantial potential benefits associated with the bioreactor landfill, a solid waste manager might have to address negative perceptions associated with this new disposal alternative. To date, these perceptions have focused on two areas: (1) the perception that the bioreactor landfill masks the real issue of whether or not to allow landfilling of nonstabilized wastes and (2) the bioreactor landfill as a competitor to waste composting facilities. Recent developments regarding the definition and resolution of each of these issues are presented in the guide.

Additional technical and management information is provided in the bioreactor guide for each of these important areas associated with the evaluation and implementation of the bioreactor landfill alternative.

The development of the guide was supported through the subscription fees provided by the Applied Research Foundation's disposal group subscribers listed in Table 2. The support of these subscribers, who have decided to make the guide available to SWANA members and other interested individuals at a nominal price, is gratefully acknowledged by SWANA.

To order a copy of The Solid Waste Manager's Guide to the Bioreactor Landfill, please contact Jeremy O'Brien or Todd Von Deak, SWANA's manager of marketing and member services, at 800/467-9262 or visit the SWANA Web store at www.swana.org.

Jeremy O'Brien, P.E., has served as SWANA's director of applied research since February 1999.

MSW - Elements 2004