Microbial Methane Oxidation Processes and Technologies for Mitigation of Landfill Gas Emissions
CHAPTER ONE
OBJECTIVE OF STUDY
The purpose of this report is to provide evidence to allow operators of biodegradable waste landfills to select appropriate methane oxidation techniques over the whole life-cycle of a landfill, in particular when landfill gas production has declined past its peak. In addition, implementing methane oxidation techniques at older, closed landfill sites without active gas control measures presents a challenge, which requires investment (often significant) to install and operate the necessary technology. This report provides evidence for those responsible for such sites on the most appropriate and cost-effective techniques which may be used to mitigate significant passive methane emissions. This report describes these methane oxidation techniques and provides a framework setting out what each can achieve and what conditions each technique is suitable for. The appropriate use of these techniques will help minimise methane emissions from landfills.
CHAPTER TWO
LITERATURE REVIEW
Landfill gas (LFG) is produced by microbial anaerobic degradation of the organic fraction in waste disposed in landfills. The biodegradable organic material in waste mostly includes paper, animal and vegetable matter, and garden waste. The main components in LFG are methane (CH4: 55–60% v/v) and carbon dioxide (CO2: 40–45% v/v). The production of the principal LFG components occurs through three initial sequential phases followed by a phase characterized by stable CH4 and CO2 production (Christensen et al. 1996). The production of LFG will continue until the majority of the organic material in the waste has been degraded, which can take several decades. Both CH4 and CO2 are classified as greenhouse gases (i.e. gases that have a high capacity of absorbing infrared radia tion reflected from the earth’s surface). CH4 has the second largest radiative forcing of the long-lived greenhouse gases after CO2 (Forster et al. 2007). CH4 is however a more powerful greenhouse gas than CO2. Over a time period of 100 years, the global warming potential for CH4 is 25 because of its stronger molar absorption coefficient for infrared radiation and its longer residence time in the atmosphere (Solomon et al. 2007). The global atmospheric concentration of CH4 has increased from a pre-industrial value of about 715 to 1732 parts per billion (ppb) in the early 1990s, and was 1774 ppb in 2005 (IPCC 2007). The atmospheric concentration of CH4 in 2005 far exceeded the natural range of the last 650 000 years (320 to 790 ppb) as determined from ice cores (IPCC 2007). Current atmospheric CH4 levels are due to continuing anthropogenic CH4 emissions accounting for more than 60% of the total CH4 budget (Denman et al. 2007). The current contribution of CH4 to climate change forcing is 18% of the total radiative forcing by all long-lived greenhouse gases (Forster et al. 2007). Landfills, in particular, have been found to be a principal source of CH4 production. Worldwide, the CH4 emission from the waste sector is about 18% of the global anthropogenic CH4 emission (Bogner et al. 2007). In the United States, the second largest anthropogenic CH4 emission originates from landfills, making up 23% of the total anthropogenic CH4 emission. In 2007, US landfill CH4 emissions were approximately 6329 Gg (US EPA 2009). In Europe, landfills are reported as the second largest source of anthropogenic CH4 (22%) with an estimated CH4 emission of 3373 Gg from waste disposal in 2006 (EEA 2008). Worldwide, landfills have been estimated previously to release between 35 and 69 Tg year–1 of CH4 to the atmosphere, out of an estimated annual global emission of approximately 600 Tg CH4 (Denman et al. 2007, Bogner et al. 2007). It is important to note that these projections are based on estimated rates of CH4 production applied to national statistics for landfilled refuse and not on field emission measurements. As recognition of global climate change has increased, the contribution of LFG emissions to anthropogenic greenhouse effects has been seriously considered in many countries. LFG extraction and utilization plants have been made mandatory at all new waste disposal sites. At the same time, research has focused increasingly on development of low-cost technologies that limit LFG gas release from existing landfills where gas collection systems have not been implemented and/or are not economically feasible (Barlaz et al. 2004, Dever et al. 2007, Kjeldsen et al. 2007, Stern et al. 2007). Much of that research has focused on biocovers designed to optimize and sustain CH4 oxidation as a cost-effective technology for controlling emissions from waste disposal sites (Bogner et al. 2007). Over the last two decades research has focused on understanding fundamental processes controlling CH4 oxidation in landfill settings. Laboratory experimental designs have evolved from simple batch experiments for determining CH4 oxidation rates and short-term responses to environmental factors to more advanced column set-ups that more closely resemble the dynamic behaviour in landfill settings and thereby allow long-term performance to be studied. More recently, research has focused on methods to increase CH4 oxidation by improving landfill covers by adding organic-rich materials such as sludge and composts.
CHAPTER THREE
RESEARCH METHODOLOGY
Introduction
This chapter covers the description and discussion on the various techniques and procedures used in the study to collect and analyze the data as it is deemed appropriate
Research Design
For this study, the survey research design was adopted. The choice of the design was informed by the objectives of the study as outlined in chapter one. This research design provides a quickly efficient and accurate means of assessing information about a population of interest. It intends to study the microbial methane oxidation processes and technologies for mitigation of landfill gas emissions. The study will be conducted in Abuja metropolis.
Population of the Study
The population for this study were Geologists in Abuja metropolis, FCT, Nigeria. A total of 134 respondents were selected from the population figure out of which the sample size was determined. The reason for choosing Abuja metropolis is because of its proximity to the researcher.
CHAPTER FOUR
DATA ANALYSIS AND INTERPRETATION
Introduction
This chapter deals with the presentation and analysis of the result obtained from questionnaires. The data gathered were presented according to the order in which they were arranged in the research questions and simple percentage were used to analyze the demographic information of the respondents while the chi square test was adopted to test the research hypothesis.
Table1 above shows the gender distribution of the respondents used for this study. Out of the total number of 100 respondents, 65respondents which represent 65.0percent of the population are male. 35 which represent 35.0 percent of the population are female.
CHAPTER FIVE
CONCLUSION AND RECOMMENDATION
This paper reviews our current understanding of microbial CH4 oxidation in landfill cover soils, biocovers and biofilters, and points out some of the remaining issues. Improving that understanding is important for two reasons. First, in the context of carbon trading, CH4 mitigation might have a commercial value. For that to be implemented, a reliable method for quantifying microbial CH4 oxidation is required. Second, for the design and optimization of landfill biocovers and biofilters, the processes leading to CH4 emission and CH4 oxidation need to be properly understood. One of the major obstacles in the measurement of CH4 oxidation in landfill cover soils is the fact that LFG transport through cover soils is mediated by diffusion and advection simultaneously. Additional research to improve existing measurements techniques is required. To stimulate CH4 oxidation for CH4 emission mitigation an integrated understanding – based on the CH4 mass balance approach – is needed in which all processes controlling the fate routes of CH4 at landfills are included. Considerable research has been carried out to understand CH4 oxidation in soils and lately also in other materials, which may be used in engineered CH4 oxidation facilities. The CH4 oxidation rate in soils depends on several environmental factors such as layer properties (porosity, permeability, and diffusivity), moisture content, and temperature, which are some of the most important factors. However, the most poorly understood factors are N limitation and EPS production. Inorganic N, especially ammonia, usually inhibits CH4 oxidation. However, many methanotrophs need an external source of inorganic N, and these can be stimulated by inorganic N. The understanding of this as well as other factors would benefit from an improved characterization of the main methanotrophic strains responsible for the CH4 consumption. However, the proliferation of newly discovered methanotrophs with widely varying properties indicates that we are far from achieving that goal. More research efforts are needed in this area. There is an increasing awareness of the importance of EPS, which in some cases is produced by the CH4 oxidizing microbial consortia. The EPS may influence the layer properties and examples of significant reduction in the CH4 oxidation capacity of the layer due to EPS formation have been observed in laboratory test systems. There is a lack of detailed understanding of which environmental factors control the EPS formation and thus how it is avoided. Substantial experience is emerging on engineered facilities such as biocovers and biofilters to mitigate the CH4 emission by the CH4 oxidation process. However, research on further development on such facilities is still needed. In particular, there is a need for integrated approaches based on controlling the CH4 mass balance to stimulate CH4 oxidation for CH4 emission mitigation in cases where gas recovery is not a cost-effective option. In such integrated approaches mathematical models could play a major role to optimize the CH4 oxidation process and avoid CH4 emission through imperfect covers or due to off-site migration. Some of the remaining issues here are the effect of pressure cycles on LFG transport, and a better understanding of the link between the activity of biocover/biofilter materials and environmental factors like moisture content.
REFERENCE
- Abichou, T., Chanton, J., Powelson, D., Fleiger, J., Escoriaza, S., Lei, Y. & Stern, J. (2006a) Methane flux and oxidation at two types of intermediate landfill covers. Waste Management, 26, 1305–1312.
- Abichou, T., Powelson, D., Chanton, J., Escoriaza, S. & Stern, J. (2006b) Characterization of methane flux and oxidation at a solid waste landfill. Journal of Environmental Engineering, 132, 220– 228.
- Ahn, Y.M., Park, J.-R., Nam, K. & Kim, J.Y. (2002) A biological barrier for the removal of methane from solid waste landfills. In: Gavaskar, A.R. & Chen, A.S.C. (eds): Remediation of Chlorinated and Recalcitrant Compounds. Proc. of the Third International Conference on Remediation of Chlorinated and Recalcitrant Compounds, Monterey, CA, USA, May 2002. Battelle, Columbus, USA. ISBN 1- 57477-132-9.
- Allen, M.R., Braithwaite A. & Hills, C.C. (1997) Trace organic compounds in landfill gas at seven U.K. waste disposal sites. Environmental Science and Technology, 31, 1054–1061.
- Alvarez-Cohen, L. & Speitel, G.E. (2001) Kinetics of aerobic cometabolism of chlorinated solvents. Biodegradation, 12, 105–126.
- Alvarez-Cohen, L. & McCarty, P.L. (1991) Product toxicity and cometabolic competitive inhibition modeling of chloroform and trichloroethylene transformation by resting methanotrophic resting cells. Applied and Environmental Microbiology, 57, 1031–1037.
