Methane Emissions From Landfills: Problems And Solution

Project and Seminar Material for Public Health

Abstract

This study was carried out on problems and solutions of methane emissions from landfills. 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 Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC). In municipal solid waste (MSW) landfills, methane is generated as a product of the anaerobic degradation of organic waste. United States Environmental Protection Agency (U.S. EPA) estimated that, in 2016, landfill methane emissions in the U.S. were approximately 107.7 million tons carbon dioxide equivalent (Mt CO2 e). And globally, it was estimated that methane emissions from landfilling of solid waste were 794.0 million tons of CO2 e in 2005. At both the U.S. and the global levels, 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 landfill 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: 1) theoretical maximum methane generation per ton of MSW and actual methane emission per ton of MSW; 2) climate zone statistics about landfill gas generation model parameter, landfill methane generation, emission and recovery; 3) the time series of global landfill methane emissions with regional analysis and per capita analysis. The findings provide both theoretical information and empirical data on landfill methane emissions. 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. In recent years, new methods based on direct measurements have been developed, such as the Back Calculation Method used in the Greenhouse Gas Reporting Program (GHGRP).

Chapter One

Introduction

1.1 Background of the Study

Landfills create a clear and obvious threat to human health as well as a threat to our environment from the hazardous contaminated air emissions emitted from the landfill biodegradation. There are over ten toxic gases released from landfills, of the most serious of which is methane. Methane gas is naturally produced during the process of decay of organic matter. As methane gas is formed, it builds up pressure and then begins to move through the soil. In a recent study of 288 landfills, off-site migration of gases, including methane, has been detected at 83% of these landfill sites. Methane is a more potent greenhouse gas than carbon dioxide.

Studies have shown significantly reduced height among children who live near Love Canal, the chemical waste dump near Niagara Falls, NY. It has also been shown that people living close to landfills suffer from lung and heart diseases from the toxic gasses that are released from the landfill degradation.

The key environmental problem we face as a result of landfills is groundwater pollution from leachates (the liquid that drains or ‘leaches’ from a landfill). Although they intended to protect human beings from toxins, due to natural deterioration the protective barriers only delay the inevitable. When a new municipal landfill is proposed, advocates of the project always emphasize that “no hazardous wastes will enter the landfill”. However several studies have shown that even though municipal landfills may not legally receive “hazardous” wastes, the leachate they produce is as dangerous as leachate from hazardous waste landfills.

Methane, one of the main greenhouse gases (GHGs), has been assessed to have 28 times the global warming potential (GWP) of carbon dioxideover 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.

In municipal solid waste (MSW) landfills, methane is generated as a product of the anaerobic degradation of organic waste. U.S. EPA estimated 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, 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.

As the number of landfills increase the likelihood of leaks increases five-fold. The increase in trash is due to population growth and consumerism. United States population growth is equivalent or marginally lower than most middle to low-middle income developing countries but the American rate of consumption is far greater than any other developed or developing country today. The amount of waste collected in an average American house hold is far greater than that of any developed or developing country in the world today.

1.2 Statement of the Problem

The major issue caused with landfill leachates is the leakage of a large number of toxins into fresh water waterways, which ultimately end up in our homes as drinking water or water for everyday use. Since landfills are most often located in and around large bodies of fresh water or in swamps, the pollution often goes undetected. The compounds submerge to the ground, to the ground water, and inevitably to our dinner tables. The pollution is also severely harmful to animal and plant life.

Groundwater contamination may result from leakage of very small amounts of leachate. TCE is a carcinogen typically found in landfill leachate. It would take less than 4 drops of TCE mixed with the water in an average swimming pool (20,000 gallons) to render the water undrinkable. Some surveys conducted have shown that 82% of the landfills have leaks and up to 41% of the landfills had a leak area of more than one square foot. EPA sponsored research shows that burying household garbage in the ground poisoned the ground water. The EPA has stressed that, even with the double liner landfills, the probability of leaking is very high.

1.3 Objectives of the Study

To examine the effects of methane emissions from landfills
To examine the problems of methane emissions from landfills
To proffer solutions to the challenges of methane emissions from landfills

1.4 Significance of the Study

Chapter Six

Conclusion and Recommendations

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.

Methane Emissions from Landfills – Conclusions

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.