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Chanton J.P.,Florida State University | Hater G.,Waste Management Inc. | Green R.,Waste Management Inc. | Bogner J.,Landfills Inc.
Geotechnical Special Publication | Year: 2010

Microbial methane oxidation in landfill cover soil is a very effective approach for reducing emissions from landfills. Oxidation of methane may be enhanced by the application of materials present on site, such as yard waste or compost. Engineers require a method to quantify methane oxidation in different types of covers. In this paper we will present a simple, effective stable isotope technique for the evaluation of cover soil methane oxidation. The approach exploits systematic variations in the ratio of 13C/ 12C in CH4 prior to and following exposure to methane oxidizing microbes in the soil. The action of the bacteria increases this ratio, due to their preference for utilizing 12CH4 rather than 13CH4. The shift in the ratio following oxidation is proportional to the amount of CH4 oxidized. © 2010 ASCE.

Bogner J.E.,Landfi lls Inc. | Bogner J.E.,University of Illinois at Chicago | Spokas K.A.,University of Minnesota | Chanton J.P.,Florida State University
Journal of Environmental Quality | Year: 2011

Compared wiThnatural ecosystems and managed agricultural systems, engineered landfills represent a highly managed soil system for which there has been no systematic quantification of emissions from coexisting daily, intermediate, and final cover materials. We quantified the seasonal variability of CH4, CO2, and N2O emissions from fresh refuse (no cover) and daily, intermediate, and final cover materials at northern and southern California landfill sites wiThengineered gas extraction systems. Fresh refuse fluxes (g m-2 d-1 [± SD]) averaged CH4 0.053 (± 0.03), CO2 135 (± 117), and N2O 0.063 (± 0.059). Average CH4 emissions across all cover types and wet/dry seasons ranged over more than four orders of magnitude (<0.01-100 g m-2 d-1) wiThmost cover types, including boThfinal covers, averaging <0.1 g m-2 d-1 wiTh10 to 40% of surface areas characterized by negative fluxes (uptake of atmospheric CH4). The northern California intermediate cover (50 cm) had the highest CH4 fluxes. For boThthe intermediate (50-100 cm) and final (>200 cm) cover materials, below which methanogenesis was well established, the variability in gaseous fluxes was attributable to cover thickness, texture, density, and seasonally variable soil moisture and temperature at suboptimal conditions for CH4 oxidation. Thin daily covers (30 cm local soil) and fresh refuse generally had the highest CO2 and N2O fluxes, indicating rapid onset of aerobic and semi-aerobic processes in recently buried refuse, wiThrates similar to soil ecosystems and windrow composting of organic waste. This study has emphasized the need for more systematic field quantification of seasonal emissions from multiple types of engineered covers. © 2011 by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America.

Bogner J.E.,University of Illinois at Chicago | Bogner J.E.,Landfills Inc. | Chanton J.P.,Florida State University | Blake D.,University of California at Irvine | And 2 more authors.
Environmental Science and Technology | Year: 2010

Methane-oxidizing "biocovers" were constructed at the Leon County Landfill (Florida). The primary goal was to determine if a biocover placed above the existing thin (15 cm) intermediate clay cover would be capable of mitigating CH4 and nonmethane hydrocarbon (NMHC) emissions to the atmosphere in this subtropical environment. A secondary goal was to maximize the use of locally recycled materials for biocover construction. The biocovers consisted of 30 or 60 cm of ground garden waste placed over a 15 cm gas distribution layer (clean crushed recycled glass from discarded fluorescent lights). The deep biocover reduced methane fluxes relative to the controls during temporal monitoring over more than a year; in large part, thesereductionswereattributabletoincreasedmethaneoxidation. Both the shallow and the deep biocover exhibited significant percentages of negative fluxes (uptake of atmospheric methane) relative to the nonbiocover controls which had consistently positive fluxes. The overall annual effectiveness/performance of the biocover was limited by seasonally high moisture contents and the thin gas distribution layer. For NMHCs, the deep biocover demonstrated substantial reductions for nonmethane hydrocarbon emissions with high percentages of negative fluxes for several hydrocarbon groups, especially the aromatics, alkanes, and lower chlorinated compounds. Ranges of measured NMHC emissions (10-9 to 10-3 g m-2 d-1) were similar to previous studies in the literature. Conservative calculations based on field data for total NMHC emissions from the 60 cm biocover area indicate that current U.S. Environmental Protection Agency (EPA) regulatory methods overestimate emissions by more than 2 orders of magnitude, suggesting that improved field-validated methods are needed. © 2010 American Chemical Society.

Spokas K.,U.S. Department of Agriculture | Spokas K.,University of Minnesota | Bogner J.,Landfills Inc. | Bogner J.,University of Illinois at Chicago | Chanton J.,Florida State University
Journal of Geophysical Research: Biogeosciences | Year: 2011

We have developed and field-validated an annual inventory model for California landfill CH4 emissions that incorporates both site-specific soil properties and soil microclimate modeling coupled to 0.5 scale global climatic models. Based on 1-D diffusion, CALMIM (California Landfill Methane Inventory Model) is a freely available JAVA tool which models a typical annual cycle for CH4 emissions from site-specific daily, intermediate, and final landfill cover designs. Literature over the last decade has emphasized that the major factors controlling emissions in these highly managed soil systems are the presence or absence of engineered gas extraction, gaseous transport rates as affected by the thickness and physical properties of cover soils, and methanotrophic CH4 oxidation in cover materials as a function of seasonal soil microclimate. Moreover, current IPCC national inventory models for landfill CH4 emissions based on theoretical gas generation have high uncertainties and lack comprehensive field validation. This new approach, which is compliant with IPCC "Tier III" criteria, has been field-validated at two California sites (Monterey County; Los Angeles County), with limited field validation at three additional California sites. CALMIM accurately predicts soil temperature and moisture trends with emission predictions within the same order of magnitude as field measurements, indicating an acceptable initial model comparison in the context of published literature on measured CH4 emissions spanning 7 orders of magnitude. In addition to regional defaults for inventory purposes, CALMIM permits user-selectable parameters and boundary conditions for more rigorous site-specific applications where detailed CH4 emissions, meteorological, and soil microclimate data exist. Copyright 2011 by the American Geophysical Union.

Spokas K.A.,U.S. Department of Agriculture | Spokas K.A.,University of Minnesota | Bogner J.E.,Landfills Inc. | Bogner J.E.,University of Illinois at Chicago
Waste Management | Year: 2011

In order to understand the limits and dynamics of methane (CH4) oxidation in landfill cover soils, we investigated CH4 oxidation in daily, intermediate, and final cover soils from two California landfills as a function of temperature, soil moisture and CO2 concentration. The results indicate a significant difference between the observed soil CH4 oxidation at field sampled conditions compared to optimum conditions achieved through pre-incubation (60days) in the presence of CH4 (50mll-1) and soil moisture optimization. This pre-incubation period normalized CH4 oxidation rates to within the same order of magnitude (112-644μg CH4 g-1 day-1) for all the cover soils samples examined, as opposed to the four orders of magnitude variation in the soil CH4 oxidation rates without this pre-incubation (0.9-277μg CH4 g-1 day-1).Using pre-incubated soils, a minimum soil moisture potential threshold for CH4 oxidation activity was estimated at 1500kPa, which is the soil wilting point. From the laboratory incubations, 50% of the oxidation capacity was inhibited at soil moisture potential drier than 700kPa and optimum oxidation activity was typical observed at 50kPa, which is just slightly drier than field capacity (33kPa). At the extreme temperatures for CH4 oxidation activity, this minimum moisture potential threshold decreased (300kPa for temperatures <5°C and 50kPa for temperatures >40°C), indicating the requirement for more easily available soil water. However, oxidation rates at these extreme temperatures were less than 10% of the rate observed at more optimum temperatures (~30°C). For temperatures from 5 to 40°C, the rate of CH4 oxidation was not limited by moisture potentials between 0 (saturated) and 50kPa. The use of soil moisture potential normalizes soil variability (e.g. soil texture and organic matter content) with respect to the effect of soil moisture on methanotroph activity. The results of this study indicate that the wilting point is the lower moisture threshold for CH4 oxidation activity and optimum moisture potential is close to field capacity.No inhibitory effects of elevated CO2 soil gas concentrations were observed on CH4 oxidation rates. However, significant differences were observed for diurnal temperature fluctuations compared to thermally equivalent daily isothermal incubations. © 2010.

Adams B.L.,University of North Carolina at Charlotte | Besnard F.,University of North Carolina at Charlotte | Bogner J.,Landfills Inc. | Hilger H.,University of North Carolina at Charlotte
Waste Management | Year: 2011

Final landfill covers are highly engineered to prevent methane release into the atmosphere. However, methane production begins soon after waste placement and is an unaddressed source of emissions. The methane oxidation capacity of methanotrophs embedded in a " bio-tarp" was investigated as a means to mitigate methane release from open landfill cells. The bio-tarp would also serve as an alternative daily cover during routine landfill operation.Evaluations of nine synthetic geotextiles identified two that would likely be suitable bio-tarp components. Pilot tarp prototypes were tested in continuous flow systems simulating landfill gas conditions. Multilayered bio-tarp prototypes consisting of alternating layers of the two geotextiles were found to remove 16% of the methane flowing through the bio-tarp. The addition of landfill cover soil, compost, or shale amendments to the bio-tarp increased the methane removal up to 32%. With evidence of methane removal in a laboratory bioreactor, prototypes were evaluated at a local landfill using flux chambers installed atop intermediate cover at a landfill. The multilayered bio-tarp and amended bio-tarp configurations were all found to decrease landfill methane flux; however, the performance efficacy of bio-tarps was not significantly different from controls without methanotrophs. Because highly variable methane fluxes at the field site likely confounded the test results, repeat field testing is recommended under more controlled flux conditions. © 2011 Elsevier Ltd.

Reddy K.R.,University of Illinois at Chicago | Hettiarachchi H.,Lawrence Technological University | Gangathulasi J.,University of Illinois at Chicago | Bogner J.E.,Landfills Inc. | Bogner J.E.,University of Illinois at Chicago
Waste Management | Year: 2011

This paper presents the results of laboratory investigation conducted to determine the variation of geotechnical properties of synthetic municipal solid waste (MSW) at different phases of degradation. Synthetic MSW samples were prepared based on the composition of MSW generated in the United States and were degraded in bioreactors with leachate recirculation. Degradation of the synthetic MSW was quantified based on the gas composition and organic content, and the samples exhumed from the bioreactor cells at different phases of degradation were tested for the geotechnical properties. Hydraulic conductivity, compressibility and shear strength of initial and degraded synthetic MSW were all determined at constant initial moisture content of 50% on wet weight basis. Hydraulic conductivity of synthetic MSW was reduced by two orders of magnitude due to degradation. Compression ratio was reduced from 0.34 for initial fresh waste to 0.15 for the mostly degraded waste. Direct shear tests showed that the fresh and degraded synthetic MSW exhibited continuous strength gain with increase in horizontal deformation, with the cohesion increased from 1. kPa for fresh MSW to 16-40. kPa for degraded MSW and the friction angle decreased from 35° for fresh MSW to 28° for degraded MSW. During the triaxial tests under CU condition, the total strength parameters, cohesion and friction angle, were found to vary from 21 to 57. kPa and 1° to 9°, respectively, while the effective strength parameters, cohesion and friction angle varied from 18 to 56. kPa and from 1° to 11°, respectively. Similar to direct shear test results, as the waste degrades an increase in cohesion and slight decrease in friction angle was observed. Decreased friction angle and increased cohesion with increased degradation is believed to be due to the highly cohesive nature of the synthetic MSW. Variation of synthetic MSW properties from this study also suggests that significant changes in geotechnical properties of MSW can occur due to enhanced degradation induced by leachate recirculation. © 2011 Elsevier Ltd.

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