Hydraulic and earth engineering – Subterranean waste disposal – containment – or treatment – Waste barrier – containment – or monitoring
Reexamination Certificate
1999-12-21
2001-09-04
Bagnell, David (Department: 3673)
Hydraulic and earth engineering
Subterranean waste disposal, containment, or treatment
Waste barrier, containment, or monitoring
C405S129850, C405S129700, C405S129600, C210S747300
Reexamination Certificate
active
06283676
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
This invention concerns landfill bioreactors and methods for their use to accelerate anaerobic and/or aerobic degradation of municipal solid waste in a manner that increases the landfill capacity.
(2) Description of the Art
The bioreactor landfill concept has been examined in lab and pilot scale projects since the 1960's (Merz). Merz found that placing refuse in thick lifts with continuous leachate spraying on the working face can provide increased landfill densities of 35%. He also discovered that a landfill constructed in an aerobic manner with leachate/water addition can increase settlement rates as much as three times that of an anaerobic landfill. In 1969 the U.S. Public Health Service (predecessor to USEPA), funded research to investigate processes that would result in maximum conversion of municipal solid waste (MSW) to gas (methane and CO2). Since energy was cheap at the time, a goal was to reduce the weight and volume (i.e., increase the density) of the solid waste remaining for disposal. However, the state of the first energy crisis started in 1973 led to projects focused on enhanced methane production. Large scale projects were conducted in the early to mid '70s by Leckie & Pacey (1979) and Ham (1982).
Profs. Robert Ham and Fred Pohland have been studying methods to enhance methane production and waste degradation for the last 30 years. Both have used measured increases in methane production and viewed methane as an energy source to be exploited as the primary goal of landfill stabilization. The DOE sponsored several projects in the late '70s during the “second energy crisis” to demonstrate that MSW could provide a renewable source of energy with bioreactor technology (Waste Tec 1986). A bench scale study conducted in Spain (MataAlvarez, 1986) showed that with optimum temperature range of 34-38° C., inoculation of digested pig manure, and moisture contents of 87% by leachate recirculation, more than 90% of biodegradable matter was degraded within 25-57 days. The model for a scaled up landfill showed a landfill life of 1.5-2 years with 95% of the biodegradable matter being reduced during the first year.
In 1988, USEPA in the preamble to the draft Subtitle D rules indicated that leachate recirculation (as allowed by the draft and final Subtitle D regulations) should provide the following benefits: 1. Increases the rate of waste stabilization; 2. Improve leachate quality; 3. Increase the quantity and quality of methane gas production; 4. Provide a viable on-site leachate management method; 5. Maximize rate and quantity of methane energy recovery; and 6. Shorten the duration of methane generation and reduces long term risks.
Matsuto (1991) studied the concept of constantly maintaining an aerobic layer at the bottom of a landfill. Based on bench scale work as well as modeling, with BOD removal from leachatc was achieved in the bottom aerobic layer. This confirmed the work of Stegman (1987) who also observed that the methanogenic stage occurred much faster.
Stessel (1992) conducted unique lab studies using aerobic treatment of all MSW with leachate recycle. This work showed MSW could take up to 70% moisture (wet weight) and achieve 50% settlement. Rapid degradation of waste and leachate could occur within months. He later wrote about and provided conceptual designs of the re-usable landfill and piloted work on landfill mining techniques. No methane is generated in this process therefore no gas collection systems are required. The primary goal of the Stessel study was rapid stabilization and re-use of landfill space.
In 1995 the USEPA Office of Research and Development sponsored the first of two workshops on Landfill Bioreactor Design and Operation. The projects presented in 1995 and 1996 workshops reviewed the “application of leachate recirculating municipal solid waste landfills aimed at reducing environmental risk and optimizing environmental risk and optimizing landfill volume by encouraging active biological decomposition within the contained waste system.” (USEPA, 1995). The ORD also acknowledged that EPA sponsored studies in the early '80s demonstrated that water, leachate recirculation, and sludge addition all enhanced methane production for energy recovery.
A good review of literature on bioreactors is found in two papers by Komilis, Ham, and Stegmann (1999) and in a book by Reinhart and Townsend “Landfill Bioreactor Design &Operation” 1997. An observation made in both references is that maintaining high levels of moisture evenly within the landfill with leachate recirculation is the key to rapid stabilization of leachate and waste. The authors determined that the prior lab scale work focused on leachate recirculation as the primary method of affecting leachate quality, waste stabilization, waste settlement, gas production, attenuation of heavy metals and priority pollutants, and other factors. The parameters that were evaluated were moisture content, pH, temperature, availability of macro- and micro-nutrients and the presence of suitable microorganisms as the main parameters controlling landfill stabilization. Pre-treatment techniques such as thermal, mechanical (i.e., particle size) and biological were also examined. Additives other than leachate were studied. The additives included water, anaerobically digested sludge that ensured suitable anaerobic and facultative microorganisms are present, and other liquids. Some of these studies had contradicted other studies, especially on the importance of adding buffer, nutrients, and sludge in enhancing degradation. Most studies concluded that increasing moisture distribution and content up to 70% on a wet-weight basis optimized the speed of biodegradation.
The most prominent and frequently cited case histories in the literature are: Leckie and Pacey, (1979), Lycoming County, Penn. (1978-'85), Seamer Car Landfill, UK (1979-1984), Delaware Solid Waste Authority (DSWA), numerous sites in Germany started in 1981, but most notably Bornhausen Landfill and reviewed by Stegman and Spendling (1989), Binghamton, N.Y., and SORAB, Sweden.
Leckie and Pacey conducted a demonstration on 6 large test cells at Mountain View, Calif. They found that leachate recirculation resulted in rapid stabilization of the waste as indicated by direct measurements of VS, cellulose content, carbon
itrogen, and carbon/phosphorus ratios. They also concluded that high moisture content and sludge addition increased methane production. Settlement was also measured at 20-25 percent. Some problems were noted with gas leaks and water infiltration.
Lycoming County Landfill was one of the first operating landfills to practice leachate recirculation at full scale. A variety of recirculation methods were tried including spray irrigation, vertical wells, open trenches, and trenches filled with auto fluff or baled fiberglass. The last two methods were most effective in wicking the leachate to larger areas of the refuse. Results were improved waste degradation and methane generation, rapid stabilization of leachate quality (close to pilot-scale studies), and empirical evidence of increased settlement compared to dry areas of the landfill. Also, the importance of eliminating clayey daily cover or pushing back daily cover to allow leachate to drain was discovered.
The Seamer Car Landfill in Britain conducted a full scale demonstration of leachate recirculation by spraying leachate on top of the landfill and enhanced the method with surface furrowing. A low permeability intermediate cover, however, created a perched water table. This created a saturated condition above the base liner of the landfill, but showed that with increased moisture content, there was a more rapid reduction in leachate organic strength. Significant reductions in organics were noted within 2-3 years of operation. They also raised a concern for the residual COD, ammonia and chloride concentrations remaining in the leachate, although the metals and organics were treated.
The Delaware Solid Waste Authority (DSWA) has r
Green Roger
Hamblin Gerard
Hater Gary R.
Bagnell David
Lagman Frederick L.
McDonnell & Boehnen Hulbert & Berghoff
Waste Management Inc.
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