The Effect of Methane Emissions From Landfills in Nigeria
Chapter One
Research Objectives
- To quantify methane emissions from major landfills in Nigeria.
- To assess the environmental and health impacts of methane emissions in surrounding communities.
- To evaluate the effectiveness of existing waste management practices in controlling methane emissions.
- To propose sustainable strategies for mitigating methane emissions from Nigerian landfills.
CHAPTER TWO
LITERATURE REVIEW
Methane, one of the main greenhouse gases (GHGs), has been assessed to have 28 times the global warming potential (GWP) of carbon dioxide over a 100-year time horizon in the IPCC Fifth Assessment Report; its GWP over a 20-year course is 84 times that of carbon dioxide [1]. Table 1-1 shows the 100- Year GWP values of methane assessed in the successive IPCC assessment reports.
In municipal solid waste (MSW) landfills, methane is generated as a product of the anaerobic degradation of organic waste. U.S. EPA estimated [2] that, in 2016, landfill methane emissions in the U.S. were approximately 107.7 million tons carbon dioxide equivalent (Mt CO2 e), accounting for approximately 16.4 percent of total U.S. anthropogenic methane emissions in 2016, and were the third largest source of methane emission, after enteric fermentation (the largest) and natural gas systems. At the global level, it was estimated that methane emissions from landfilling of solid waste were 794.0 million tons of CO2 e in 2005 [3], again, landfilling was the third largest source of methane emissions, after enteric fermentation and natural gas & oil systems.
A broad range of topics about methane emissions from landfills are covered in this report, including the gas-generating processes in landfill, the theories about modeling landfill gas generation and emission, the developed models and the current estimates of landfill emissions, as well as the calculation and analysis on several aspects. The findings provide both theoretical information and empirical data on landfill methane emissions.
Since the United Nations Framework Convention on Climate Change (UNFCCC) [4] requires Annex I Parties (see Section 5.3.1) to use GWP values from the IPCC Fourth Assessment Report (AR4), many of the data referred to in this report were calculated under this requirement. Therefore, when converting units between carbon dioxide equivalent and actual methane emissions, the GWP value of methane used in this report is 25, unless it is stated otherwise.
Gas-Generating Processes in Landfill
Main Processes
In landfills receiving organic waste, the dominating gas-generating process is the microbial conversion of organic carbon to CH4 and CO2, which are the main components of landfill gas; there are very small concentrations of other components.
The gas-generating processes in landfills are classified into aerobic composting, in the presence of ample oxygen and anaerobic degradation, which consists of three phases [5-7]. The most important interactions between the bacterial groups involved, the substrates involved, and the intermediate products in an anaerobic landfill are illustrated in Figure 2-1.
CHAPTER THREE
MATERIALS AND METHODS
Data Acquisition
Historical data on the waste disposal sites such as annual waste acceptance, waste composition, site administration and landfill management facilities was obtained from Lagos State Waste Management Authority (LAWMA) and from reports prepared for LAWMA by Ably Carbon (2012).
Annual waste disposal. The annual waste disposal rates for Olushosun, Abule Egba and Solous 1 WDS are presented in Tables 1-3. Although there was no weigh bridge at this WDS.
CHAPTER FOUR
RESULTS AND DISCUSSION
where T = average temperature (oC) in the waste mass. A value of 0.77 was adopted by assuming that the temperature in the anaerobic zone of the landfill remains constant at 35oC. (Methane correction factor): In non-engineered landfill old landfills, a large part of the deposited waste degrades un- der aerobic conditions. MCF is therefore the part of the land- fill that is left to degrade under anaerobic conditions (Tsatsarelis and Karagiannidis, 2009). MCF varies depending on the depth of the waste and landfill type, as defined by management practices (Aguilar-Virgen et al., 2014). MCF factors recommended by IPCC (2006) are given in Table 5.
CHAPTER FIVE
CONCLUSION
A broad range of topics have been discussed in this report, including the gas-generating processes in landfill, the theories about modelling landfill gas generation and emission, the developed models and the current estimations, as well as the calculation and analysis on several aspects. The findings provide both theoretical knowledge and practical data on landfill methane emissions.
Although as discussed in Section 3.6, the order of the estimation model is not very important, the kinetics order of many existing estimations models is first order. Currently, the most widely used model could be the 2006 IPCC Guidelines First-Order Decay (FOD) Method, which has been used by many countries to develop their national greenhouse gas inventories. And in recent years, new methods based on direct measurements have been developed, such as the Back-Calculation Method used in the GHGRP.
The empirical formula of dry degradable organic waste in the U.S. is estimated as C6H9.21O3.73 when ignoring nitrogen (N) and sulfur (S). Methane generation per ton of MSW in the U.S. has been calculated to be 0.135 ton (or 189 Nm3) at maximum, which is 9% less than the previous estimation.
The actual landfill methane emissions per ton of MSW in the U.S. are much lower than this theoretical maximum generation value. The reason of the gap could be: 1) landfill gas collection systems, landfill gas destruction (flaring) and utilization projects reduce the methane emissions, 2) the intrusion of air at some parts of the landfill diverts the anaerobic degradation to aerobic degradation, 3) the biodegradable components in MSW cannot fully biodegrade due to their intrinsic properties and other limiting factors such as water content, temperature and pH. Under dry basis, the degree of the biodegradation of the biodegradable components in U.S. MSW has been estimated to be 53.6%. At this degree, the expected methane generation would be 0.072 ton CH4 / ton MSW. Besides, the excessive underestimation of the quantity of landfilled MSW in the U.S. in EPA’s annual summary figures and tables of waste management has also been detected.
For methane generation rate k, the order of main climate types, from in which the k value of bulk waste is high to in which that is low, would be warm temperate (C), equatorial (A), snow (D), and arid (B), or ACDB under another calculation option. This indicates that precipitation/water may play a more important role than temperature in the generation of landfill gas. The details are provided in Section 5.2.2 and Annex D.
For methane generation ratio, those based on model estimation show the pattern that, in equatorial
(A) climate, the typical generation ratio is the highest, followed by that in warm temperate (C) climate, snow climate (D) and arid (B) climate. While for those based on measurement, the typical generation ratio in warm temperate (C) and snow (D) climate are very close and are higher than that in equatorial (A) climate, the lowest typical generation ratio is still in arid (B) climate. The lack of sufficient samples in equatorial (A) climate can be a possible reason, while this needs to be further analyzed.
Besides, the methane generation ratios based on measurement are all significantly less than the corresponding ratios based on model estimation, this implies there may exist systematical overestimation in the landfill gas generation model used, which is the 2006 IPCC Guidelines FOD Method.
The typical values of estimated collection efficiency are all relatively high (around 70%) and show small variations in different main climates. An interesting finding is that, the typical values of methane emission ratio show little difference in different main climates. To better understand this, more knowledge about how the landfill operators determine which emission value to report is needed. The details about landfill methane generation ratio, recovery ratio, emission ratio and estimated collection efficiency are provided in Section 5.2.3 and Annex E.
The UNFCCC data and the EDGAR data are two separate sources of landfill methane emissions in different countries. Generally, there are varying degrees of difference between the two data sets in most countries because of the different methodologies used to develop them. After comparison, the EDGAR data are selected as the basis to construct a complete time series of landfill methane emissions at the global level. It is estimated that the global methane emissions from landfills are 727.3 Mt CO2 e in 2012. If there is no significant implementation of landfill methane mitigation measures in the world, the rapid growth of landfill methane in the near future should be expected. Besides, it is estimated that, in 2012, every person on the planet emits 4.10 kg of landfill methane (102.50 kg CO2 e) on average annually.
By world region, the per capita landfill methane emissions in North America and in Europe & Central Asia are significantly higher than those in other regions, among which South Asia region has the lowest per capita emissions. By income group, it has been shown that, for both total emissions and per capita emissions, higher income group emits more than lower income group. The detailed calculation results are provided in Section 5.3.3, Section 5.3.4 and Annex F.
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