Type of Document Thesis Author Morales, Jose J. Author's Email Address firstname.lastname@example.org URN etd-11102006-114600 Title Mitigation of Landfill Methane Emissions from Passive Vents by use of Oxidizing Biofilters Degree Master of Science Department Civil and Environmental Engineering, Department of Advisory Committee
Advisor Name Title Tarek Abichou Committee Chair Amy Chan-Hilton Committee Member Jeff Chanton Committee Member Kamal S. Tawfiq Committee Member Keywords
- Methane Oxidation
- Methane Emissions
Date of Defense 2006-11-03 Availability unrestricted AbstractABSTRACT
Decay of waste within landfills is a contributing source to the greenhouse effect due to the production of methane. Larger landfills tend to have gas collection systems, which collect and convert gas into energy or flare it. Older and smaller landfills, however, usually vent this greenhouse gas into the atmosphere through passive vents. This study focuses on the attenuation of methane gas from these passive vents through the use of biofilters containing methanotrophic bacteria. These methanotrophic bacteria can oxidize methane into carbon dioxide, water, and biomass.
Two biofilter designs were explored in this study. The vertical biofilter design has a methane inflow near the bottom which emits the methane upward through the filter medium in which the methanotrophic bacteria reside. The radial biofilter design has a methane inflow source imbedded in the center, vertically, in the filter medium, which emits the methane horizontally. The purpose of the radial design was to increase methane oxidation by increasing the surface area, thus increasing oxygen penetration. The surface area of the radial design was 1.212 m2 compared to 0.264 m2 of the vertical filter design.
Biofilter surface area proved to be a factor in the oxidation of passively vented landfill methane. Although the two filter designs achieved a similar oxidation average for the study period, the radial biofilter design obtained a much higher removal rate at a higher input than that of the vertical design. The better performance of the radial biofilters was due to greater oxygen penetration as verified by probe gas profiles. This increase in oxygen penetration was directly linked to the larger surface area, which had a lower influx than that of the smaller surface area of the vertical design when having the same methane input.
This study also tested the use of two different biofilter media mixtures for oxidizing methane. The mixtures were a combination of recycled tire chips and compost, and a combination of peanut packing foam and compost. The purpose of mixing the compost with the tire chips or the peanut foam was to hopefully increase oxygen penetration and thus, methane oxidation. The study proved that there was statistically no difference in performance between the two media types. Averages of the study period showed a nearly equal methane oxidation average and methane removal rate.
Air temperature, media temperature, and barometric pressure were recorded during testing events for the period of this study. There was an increase in average air temperature through out the study (this was due to a change in seasons, from winter to summer). Average methane outputs from the passive vents studied showed a decreasing pattern throughout the study. This decrease in methane output is due to a decrease in anaerobic decomposition because of the old age of the waste in the section of the landfill studied. It was concluded that there was a direct correlation between biofilter media temperature and methane oxidation by the methanotrophic bacteria. Average oxidation rates of 20% and higher were all within the range of 20-36°C. This temperature range agrees with published research (Visvanathan et al., 1999) that states that this is the optimal soil temperature for methanotrophs to oxidize methane. There was no direct correlation found between atmospheric pressure and landfill methane emissions from passive vents.
This research established that the radial filter design was superior to that of the vertical design for methane oxidation. However, it is important to note that what led the radial design to have a superior performance over that of the vertical design was its increased oxygen penetration and lowered influx of gases due to its larger surface area. Thus, further research of these factors is imperative to ultimately making biofilters viable option for mitigating methane emissions from passively vented landfills.
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