United States
Environmental Protection
Agency
Air and Radiation
(6202 J)
EPA 430-R-93-006
July 1993
&EPA
Options for Reducing Methane
Emissions Internationally
Volume I: Technological Options
for Reducing Methane Emissions
Report to Congress
PROPERTY OF
DIVISION
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Options for Reducing Methane
Emissions Internationally
Volume I:
Technological Options for Reducing
Methane Emissions
Report to Congress
Editor: Kathleen B. Hogan
U.S. Environmental Protection Agency
Office of Air and Radiation
July 1993
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Disclaimer
This document has been reviewed in accordance with the U.S. Environmental
Protection Agency's and the Office of Management and Budget's peer and
administrative review policies and approved for publication. Mention of trade names
or commercial products does not constitute endorsement or recommendation.
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Table of Contents
VOLUME I
Foreword vii
Acknowledgements ix
EXECUTIVE SUMMARY ES - 1
ES.1 Introduction ES - 1
ES.2 Volume I. Assessments of Technological Options ES - 2
ES.3 References ES - 15
CHAPTER ONE
INTRODUCTION 1-1
1.1 Background: The Importance of Methane 1-2
1.2 Technological Options for Reducing Methane Emissions 1-9
1.3 Methane Reduction Options in Countries of Interest 1-11
1.4 Overview of Report 1-11
1.5 References 1-13
CHAPTER Two
LANDFILLS 2-1
2.1 Background 2-1
2.2 Methane Recovery and Utilization 2-5
2.3 Aerobic Landfill Management 2-15
2.4 Reduced Landfilling of Waste 2-21
2.5 References 2-29
CHAPTER THREE
OIL AND NATURAL GAS 3-1
3.1 Background 3-1
3.2 Reduced Venting And Flaring During Production 3-7
3.3 Improved Compressor Operation 3-10
3.4 Improved Leak Detection and Pipeline Repair 3-14
3.5 Low Emission Technologies and Practices 3-23
3.6 References 3-29
CHAPTER FOUR
COAL MINING 4-1
4.1 Background 4-1
4.2 Enhanced Gob Well Recovery 4-7
4.3 Pre-Mining Degasification 4-19
4.4 Ventilation Air Utilization 4-26
4.5 Integrated Recovery 4-31
4.6 References 4-35
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CHAPTER FIVE
FOSSIL FUEL COMBUSTION 5-1
5.1 Background 5-1
5.2 Opportunities for Reducing Methane Emissions 5-3
5.2.1 REDUCTION OF METHANE EMISSIONS FROM STATIONARY SOURCES . . 5-3
5.2.2 REDUCTION OF METHANE EMISSIONS FROM MOBILE SOURCES 5-5
5.3 References 5-9
CHAPTER Six
RUMINANT LIVESTOCK 6-1
6.1 Background 6-1
6.2 Improved Nutrition Through Mechanical and Chemical Feed
Processing 6-10
6.2.1 ALKALI/AMMONIA TREATMENT OF Low DIGESTIBILITY STRAWS .... 6-10
6.2.2 CHOPPING OF Low DIGESTIBILITY STRAWS 6-12
6.2.3 WRAPPING AND PRESERVING RICE STRAW 6-14
6.3 Improved Nutrition Through Strategic Supplementation 6-14
6.3.1 MOLASSES/UREA MULTINUTRIENT BLOCKS 6-16
6.3.2 MOLASSES/UREA MULTINUTRIENT BLOCKS WITH BYPASS PROTEIN . . 6-20
6.3.3 DEFAUNATION 6-23
6.3.4 TARGETED MINERAL/PROTEIN SUPPLEMENTS 6-25
6.3.5 BlOENGINEERING OF RUMEN MICROBES 6-27
6.4 Production Enhancing Agents 6-28
6.4.1 BOVINE SOMATOTROPIN (eST) 6-29
6.4.2 ANABOLIC STEROIDS 6-31
6.4.3 OTHER AGENTS 6-33
6.5 Improved Genetic Characteristics 6-33
6.5.1 CROSSBREEDING IN DEVELOPING COUNTRIES 6-34
6.5.2 CONTINUED GENETIC IMPROVEMENT IN DAIRY CATTLE 6-34
6.5.3 TRANSGENIC MANIPULATION 6-35
6.6 Improved Reproduction 6-35
6.6.1 TWINNING 6-36
6.6.2 EMBRYO TRANSPLANTS 6-36
6.6.3 ARTIFICIAL INSEMINATION AND ESTRUS SYNCHRONIZATION 6-37
6.7 Other Strategies 6-37
6.8 References 6-39
CHAPTER SEVEN
LIVESTOCK MANURE 7-1
7.1 Background 7-1
7.2 Covered Lagoons 7-6
7.3 Small Scale Digesters 7-11
7.4 Larger Scale Digesters 7-19
7.5 References 7-28
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CHAPTER EIGHT
WASTEWATER MANAGEMENT 8-1
8.1 Background 8-1
8.2 Prevention of Methane Production During Wastewater Treatment ... 8-6
8.2.1 AEROBIC PRIMARY TREATMENT 8-6
8.2.2 AEROBIC SECONDARY WASTEWATER TREATMENT 8-10
8.2.3 LAND TREATMENT 8-14
8.3 Recovery and Utilization/Flaring of Methane from Anaerobic Digestion
of Wastewater and Sludge 8-16
8.3.1 ANAEROBIC DIGESTION WITH METHANE UTILIZATION 8-16
8.3.2 FLARING 8-19
8.4 Minimization of Methane Emissions During Treatment, Utilization, and
Disposal of Sludge 8-20
8.5 References 8-25
CHAPTER NINE
BIOMASS BURNING 9-1
9.1 Background 9-1
9.2 Opportunities for Reducing Methane Emissions 9-3
9.3 References 9-7
CHAPTER TEN
RICE CULTIVATION 10-1
10.1 Background 10-1
10.2 International Research Plan 10-3
10.3 References 10-6
in
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List of Exhibits
Exhibit # Page
EXECUTIVE SUMMARY
Exhibit ES-1 Technological Options for Reducing Methane Emissions from Coal
Mining, Oil and Natural Gas Systems, and Fossil Fuel Combustion . . ES - 4
Exhibit ES-2 Technological Options for Reducing Methane Emissions from Ruminant
Livestock, Livestock Manure, and Rice Cultivation ES - 5
Exhibit ES-3 Technological Options for Reducing Methane Reductions from Landfills,
Wastewater, and Biomass Burning ES - 6
CHAPTER ONE
INTRODUCTION
Exhibit 1-1 Global Methane Concentrations 1-5
Exhibit 1-2 Global Contribution to Integrated Radiative Forcing by Gas for 1990 . 1-7
Exhibit 1-3 CO2 and Methane Reduction Comparison 1-8
Exhibit 1-4 Global Methane Emissions from Major Sources 1-9
CHAPTER Two
LANDFILLS
Exhibit 2-1 Summary of the Technical Assessments for Landfills 2-4
Exhibit 2-2 Landfill Gas Recovery Well 2-6
Exhibit 2-3 Co-generation with a Gas Turbine 2-10
Exhibit 2-4 Capital and Operations Costs for Gas-to-Electricity Projects 2-13
Exhibit 2-5 Semi-Aerobic Landfill 2-16
Exhibit 2-6 Recirculatory Semi-Aerobic Landfill 2-18
Exhibit 2-7 Aerobic Landfill 2-19
CHAPTER THREE
OIL AND NATURAL GAS
Exhibit 3-1 Natural Gas Systems 3-2
Exhibit 3-2 Summary of Options for Reducing Methane Emissions from Oil and
Natural Gas Systems 3-6
Exhibit 3-3 Joint Repair with Heat Shrink Sleeve 3-17
Exhibit 3-4 Joint Repair with Urethane Resin Mold 3-18
Exhibit 3-5 Pipe Repair with Polyamide Elastomer Layer 3-19
Exhibit 3-6 Pipe Repair with Epoxy Resin 3-19
Exhibit 3-7 In-Pipe Joint Sealing Equipment 3-20
Exhibit 3-8 Pneumatic Device Bleed Rates 3-23
Exhibit 3-9 Typical Fugitive Emission Rates, Component Numbers, and Facility
Emissions 3-24
Exhibit 3-10 Volume of Gas in Various Size Lines at Different Pressures; Volume of
Gas Saved per Mile of Pipeline 3-26
CHAPTER FOUR
COAL MINING
Exhibit 4-1 Coal Rank and Methane Production 4-2
Exhibit 4-2 Coal Mining and Methane Recovery Techniques 4-3
IV
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Exhibit 4-3 Summary of Options for Reducing Methane Emissions from Coal
Mining 4-6
Exhibit 4-4 Capital Costs for Gob Wells (per well costs) 4-12
Exhibit 4-5 Total Vertical Gob Project Costs in Various U.S. Coal Basins 4-12
Exhibit 4-6 Total Cross-Measure Borehole Project Costs in Various U.S. Coal
Basins 4-13
Exhibit 4-7 Capital Costs for Power Generation 4-14
Exhibit 4-8 Capital Costs for Pipeline Injection All Equipment Needed Between the
Wellhead and a Central Compressor 4-15
Exhibit 4-9 Operating Costs for Pipeline Injection All Equipment Needed Between the
Wellhead and a Central Compressor 4-16
Exhibit 4-10 Capital Costs for Pipeline Injection Gathering Lines to Main Commercial
Pipeline 4-16
Exhibit 4-11 Capital Costs for Vertical Wells (per well costs) 4-23
Exhibit 4-12 Break-Even Energy Costs for Mine Ventilation Air 4-29
Exhibit 4-13 Integrated Recovery 4-32
CHAPTER FIVE
FOSSIL FUEL COMBUSTION
Exhibit 5-1 Summary of Options for Reducing Methane Emissions from Fossil Fuel
Combustion 5-2
CHAPTER Six
RUMINANT LIVESTOCK
Exhibit 6-1 a Summary of Mechanical and Chemical Feed Processing
Optionsrlmproved Nutrition Through Mechanical and Chemical Feed
Processing 6-6
Exhibit 6-1 b Summary of Strategic Supplementation Options:lmproved Nutrition
Through Strategic Supplementation and Other Options 6-7
Exhibit 6-1 c Summary 'of Production Enhancing Agents: Production Enhancing
Agents 6-8
Exhibit 6-1 d Summary of Options for Improved Genetic Characteristics, Improved
Reproduction, and Other Strategies 6-9
Exhibit 6-2 Typical Compositions of Molasses/Urea Multinutrient Blocks 6-17
CHAPTER SEVEN
LIVESTOCK MANURE
Exhibit 7-1 Phases of Anaerobic Digestion 7-2
Exhibit 7-2 Impact on Methane Potential by Manure Management System 7-2
Exhibit 7-3 Summary of the Technical Assessments for Livestock Manure 7-5
Exhibit 7-4 Schematic of a Covered Lagoon Digester System 7-7
Exhibit 7-5 Covered Lagoon Biogas Recovery System 7-10
Exhibit 7-6 Components of an Anaerobic Digester 7-12
Exhibit 7-7 Floating Gas Holder System 7-13
Exhibit 7-8 Fixed Dome Digester System 7-14
Exhibit 7-9 Gas Requirements of End Use Technologies 7-16
Exhibit 7-10 Treatment and Utilization of Digester Effluent 7-16
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Exhibit 7-11 Digester Construction Costs ($/cubic meter volume) 7-17
Exhibit 7-12 Schematic Diagrams of Anaerobic Digesters 7-20
Exhibit 7-13 Plug Flow Digester 7-21
Exhibit 7-14 Complete Mix Digester 7-23
Exhibit 7-15 Estimates of Economically Feasible Projects 7-25
Exhibit 7-16 Digester Design/Manure System Compatibility 7-26
CHAPTER EIGHT
WASTEWATER MANAGEMENT
Exhibit 8-1 Wastewater Treatment Systems and Methane Production 8-2
Exhibit 8-2 Summary of Options for Reducing Methane Emissions from Wastewater
and Sludge Management 8-5
Exhibit 8-3 Conventional Activated Sludge Wastewater Treatment Process .... 8-10
Exhibit 8-4 Trickling Filters Wastewater Treatment Process 8-11
Exhibit 8-5 Rotating Biological Contactors Wastewater Treatment Process .... 8-12
CHAPTER TEN
RICE CULTIVATION
Exhibit 10-1 Methane Production and Emission from Flooded Rice Fields 10-2
VI
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Foreword
I am pleased to transmit the attached report. Options for Reducing Methane Emissions
Internationally. Volume I: Technological Options for Reducing Methane Emissions, in partial
fulfillment of the Congressional mandate in the Clean Air Act Amendments of 1990 for a
series of methane-related reports. This report describes an array of available technologies and
practices which may have been employed to some extent around the world.
I am pleased to ,be transmitting a report that represents the results of a large
international effort. The report was prepared in part for the Response Strategies Working
Group of the Intergovernmental Panel on Climate Change (IPCC) by the U.S. /Japan Working
Group on Methane. As part of this process, much of the information and numerous comments
were submitted by IPCC participating countries.
The report is the most detailed and comprehensive examination of technologies and
practices for reducing methane emissions that has been developed. As such, it will assist
greatly in discussion of how methane emissions can be reduced as part of many countries'
efforts to stabilize their emissions of greenhouse gases.
The report also establishes a strong foundation for the next volume of this report,
Options for Reducing Methane Emissions Internationally. Volume II: International Opportunities
for Reducing Methane Emissions, which assesses the most appropriate technologies for use
in different settings and the types of programs which may be the most effective in
accelerating their adoption.
Paul M. Stolpman
Acting Directory
Office of Atmospheric Programs,
Office of Air and Radiation
VII
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Acknowledgements
This report has been possible due to the efforts of a large number of people. The
report began as an effort by the U.S./Japan Working Group on Methane for the
Intergovernmental Panel on Climate Change's Response Strategies Working Group (Working
Group 3), a group tasked with assessing available options for reducing emissions of
greenhouse gases. As part of this process international experts submitted materials describing
available technologies and circumstances in their countries and regions (as acknowledged at
the end of each chapter) and provided technical reviews of the overall report. These
contributions are greatly appreciated. In particular, the efforts, by Japanese experts as
coordinated by Dr. Katsuya Sato have made a large contribution to this report.
Substantial work was performed to sysnthesize the available information into the final
chapters. This work includes efforts by Jeff Fiedler, Michael Gibbs, Katherine Stenberg, Eric
Taylor, Laura Van Wie and Kwang Liew.
Useful comments were provided by industry, university, and government experts in the
U.S. and other countries, and all comments are greatly appreciated. Comments of particular
importance were provided by Ken Andrasko (USEPA), Lee Baldwin (UC Davis), Bill Breed (US
DOE), Bob Dixon (USEPA), Charles Dixon (Jim Walter Resources Inc.), Gary Evans (USDA),
Jeff Hardy (US DOE), Andy Hashimoto (University of Oregon), Nelson Hay (American Gas
Association), Don Johnson (Colorado State), Ron Leng (Australia), Katsu Minami (Japan), Ron
Munkley (Consumers Gas of Ontario), Heinz-Ulrich Neue (IRRI), Mac Safley (North Carolina
State University), Jeffrey Schwoebel (Resource Enterprises Inc.), Susan Thornelone (USEPA),
Henry Tyrell (USDA), Hilmar von Schoenfeldt (Island Creek Coal Co.), Ted Williams (US DOE),
and Fritz Wolf (Ruhrgas).
IX
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VOLUME I
EXECUTIVE SUMMARY
ES.1 Introduction
Methane currently accounts for over 1 5 percent of expected warming from climate change.
While methane's concentration in the earth's atmosphere is small, it has a sizable contribution
to potential future warming because it is a potent greenhouse gas and because methane's
concentration has been increasing dramatically. Its global concentration has more than
doubled over the last two centuries, after remaining fairly constant for the preceding 2,000
years and continues to rise. Atmospheric methane concentrations are expected to continue
to increase, although the rate of increase appears to have slowed down in the last several
years. The reason for this is not currently understood (WMO, 1990; Steele et al., 1992).
Methane's rising concentration is largely correlated with increasing populations, and currently
about 70 percent of global methane emissions are associated with human activities such as
energy production and use (coal mining, oil and natural gas systems, fossil fuel combustion);
waste management (landfills and wastewater treatment); livestock management (ruminants
and wastes); biomass burning; and rice cultivation.
Reductions in methane emissions of 30 to 40 million metric tons per year, or about 10 percent
of annual anthropogenic (human related) emissions, would halt the annual rise in methane
concentrations. This report identifies technologies and practices which are currently available
for reducing emissions from the major human-related sources of methane, which are profitable
in many cases, and which are appropriate for many countries around the world. It also
examines the potential for reducing methane emissions from some key countries through
further adoption and use of these available technologies. This report has two volumes:
Volume I: Technological Options for Reducing Methane Emissions. This volume was
prepared in part for the Response Strategies Working Group of the Intergovernmental
Panel on Climate Change (IPCC) by the U.S./Japan Working Group on Methane. The
technology assessments were compiled from information and comments submitted by
IPCC participating countries and have been reviewed by government officials and technical
experts in these countries.
Volume II: International Opportunities for Reducing Methane Emissions. This volume
investigates the potential for applying or expanding the use of available technologies in key
countries around the world, for the major methane sources. Key barriers inhibiting the
further use of these technologies and practices are identified, and possible solutions, such
as technology transfer programs, are suggested.
The report has been prepared in response to a Congressional request under Section 603 of
the Clean Air Act Amendments of 1990:
Preventing Increases in Methane Concentrations: Not later than two years after
the enactment of this Act, the Administrator shall prepare and submit to the
Congress a report that analyzes the potential for preventing an increase in
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ES - 2 EXECUTIVE SUMMARY
atmospheric concentrations of methane from activities and sources in other
countries. Such report shall identify and evaluate the technical options for
reducing methane emissions from each of the activities listed in subsection (b),
as well as other activities or sources that are deemed by the Administrator in
consultation with other relevant Federal agencies and departments to be
significant and shall include an evaluation of the costs. The report shall identify
the emission reductions that would need to be achieved to prevent increasing
atmospheric concentrations of methane. The report shall also identify
technology transfer programs that could promote methane emission reductions
in lesser developed countries.1
Another report, Options for Reducing Methane Emissions from Anthropogenic Sources in the
United States, was requested by Congress and is being prepared to examine the applicability
of available options in the U.S.
ES.2 Volume I. Assessments of Technological Options
In general, technological options for reducing methane emissions into the atmosphere are
available for each of the following major methane sources, which represent about 70 percent
of the current emissions from human-related activities:
Oil and Natural Gas Systems;
Coal Mining;
Landfills;
Ruminant Livestock;
Livestock Manure.
Options are also available, for reducing methane emissions from the treatment of wastewater,
although less is known about this source. Efforts are still required to develop and
demonstrate options for reducing methane emissions from rice cultivation and biomass
burning.
Many of the technological options currently available may be cost-effective in many regions
of the world, and have already been implemented to a limited extent. The available options
represent different levels of technical complexity and capital needs and therefore should be
adaptable to a wide variety of country situations. In many cases, furthermore, implementation
of these options provides a range of benefits in addition to methane reductions, including
better air quality, better protection of surface and groundwater, enhanced animal productivity,
reduced risk of explosion and fire, and improved use of energy resources.
Section 603(c)(2) of the Clean Air Act Amendments of 1990.
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EXECUTIVE SUMMARY ES - 3
A summary of the major options for reducing methane emissions into the atmosphere is
provided in Exhibits ES-1, ES-2, and ES-3. Discussions of the available technologies for each
of the major methane sources follow.
Oil and Natural Gas Systems
Methane is the primary constituent of natural gas, and significant quantities of methane can
be emitted to the atmosphere from components and operations throughout a country's natural
gas system. This system generally includes gas and oil wells, processing and storage
facilities, and transmission and distribution systems. Emissions primarily result from the
normal operations of many natural gas system components, such as venting and flaring at oil
and gas wells, compressor station operations, gas processing facilities, gas-operated control
devices, and unintentional leaks (fugitive emissions). Methane emissions also occur during
routine maintenance, with additional emissions from unplanned system upsets. Estimates for
methane emissions froVn oil and natural gas systems worldwide range from 30 to 70
teragrams2 (Tg) per year.3
The technical nature of emissions from natural gas systems is well understood, and emissions
are largely amenable to technological solutions, through enhanced inspection and preventative
maintenance, replacement of equipment with newer designs, improved rehabilitation and
repair, and other changes in routine operations. Reductions in emissions on the order of 20
to 80 percent are possible at particular sites, depending on site specific conditions. These
reduction options can also result in improved safety, increased productivity through reduced
losses, and improved air quality. Identified options include:
Reduced Venting and Flaring During Production: Venting during the production of both
associated and non-associated gas is a controllable release of natural gas. The most
preferable strategy is to fully recover and process associated gas for use as a fuel. Where
demand for gas and an adequate infrastructure do not currently exist, reinjecting gas or
installing inexpensive flares can almost completely eliminate methane emissions while
providing the important benefits of maintaining formation pressure (reinjection only) and
enhancing safety. The use of more efficient flares can also reduce emissions from
unburned gas. Additionally, changes can be made in operating practices to reduce
extraction losses and emissions from wells under development.
Improved Compressor Operation: Enhanced maintenance and monitoring the fuel use of
compressor prime movers can reduce fuel costs while also reducing methane emissions.
Using gas turbines in place of reciprocating engines to power compressors can reduce
methane emissions (per unit of gas used) by over an order of magnitude, as well as
reducing emissions of other pollutants such as CO and NOX. Reductions can also be
achieved by capturing gas that is currently vented during stops and starts, and using
auxiliary power (i.e., hydraulic) for turbine starts (rather than gas pressure).
One teragram is 10 grams, or one million metric tons.
3 Of this total 25 to 42 Tg are estimated for natural gas systems, and 5 to 30 Tg are estimated for oil
systems (IPCC, 199,2).
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EXECUTIVE SUMMARY ES - 7
Improved Leak Detection and Pipeline Repair: Gas pipelines are subject to corrosion and
subsequently develop chronic leaks (i.e., small, continual leaks). Preventing and repairing
these leaks will reduce fugitive emissions. This can be achieved through a number of actions
including improved leak detection and pipeline inspection, preventative maintenance and
replacement programs, and the increased use of corrosion resistant materials (e.g., coated
steels, PVC, PE). In addition, gas releases resulting from line breakages can be reduced with
automatic shut-off valves.
Low Emission Technologies and Practices: Emissions occur from routine operations and
practices, including gas-operated control devices, fugitive emissions from component
joints, and pipeline purging for maintenance purposes. Low emission technologies include
pipeline control devices with reduced or eliminated venting of natural gas ("low-bleed" or
"no-bleed" devices), directed inspection and maintenance programs, and the capturing of
purged gas.
Coal Mining
Methane is produced during coalification (the process of coal formation) and remains trapped
under pressure in the coal seam and surrounding rock strata. This trapped methane is
released during the mining process when the coal seam is fractured. Current annual emissions
of 30 to 50 Tg are expected to rise over the next decades with increases in global coal
production and a continuing trend to deeper mines.
Techniques for removing methane from underground mine workings have been developed
primarily for safety reasons, because methane is highly explosive in air concentrations
between 5 and 1 5 percent and is the cause of numerous mining accidents. These same
techniques can be adapted to recover methane so that the energy value of this fuel is not
wasted. Methane emissions into the atmosphere can technically be reduced by up to 50 to
70 percent at gassy mines using available techniques. Emissions could potentially be reduced
by up to 90 percent at these same gassy mines, depending upon the demonstration of
additional technologies.
Important factors when considering options for reducing methane emissions from coal mining
are: the geologic and reservoir characteristics of the coal basin; mine conditions and mining
method; current mine gas recovery systems; potential gas quality and use options; and
technical and economic capabilities. In particular, the recovery method largely determines the
quality and quantity of gas recovered, which in turn determines the possible utilization
options. Developing uses for recovered methane is required if emission reductions are to be
achieved. The sale and/or use of methane can offset the costs of recovery in certain cases.
Furthermore, improving methane recovery techniques can, result in safer, more productive
mines, with lower ventilation costs. Available recovery and use options are summarized as
follows:
Enhanced Gob Well Recovery: Methane can be recovered from the gob area of a coal
mine - the highly fractured area of coal and rock that is created by the caving of the mine
roof after the coal is removed. Gob areas can release significant quantities of methane
into the mine, and if this gas is recovered before entering the mine, ventilation
requirements can bq reduced. Typically, gob gas is diluted by mine air during production
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ES - 8 EXECUTIVE SUMMARY
so a medium quality gas is obtained (300-800 Btu/cf; 11-29 MJ/m3)4, which can be used
in a variety of applications, including on-site power generation, and residential and
industrial heating. Enhanced gob well recovery can involve in-mine and/or surface wells,
using proven technology that is currently employed in many countries. In many cases, the
capital requirements for these energy development projects are low compared to the
amount of gas that may be produced. Methane emissions from a mine can be reduced by
30 to 50 percent.
Pre-Mining Degasification: This strategy recovers methane before coal is mined. Pre-
mining degasification can be attractive where geologic conditions are appropriate because
methane is removed before the air from the mine workings can mix with it. Pre-mining
degasification typically recovers a higher quality gas (900-1000 Btu/cf; 32-37 MJ/m3)
which can be used as chemical feedstock in addition to being used for power generation
and industrial or residential applications. Pre-mining degasification can be an in-mine or
surface operation. When done inside the mine, boreholes can be drilled anywhere from
six months to several years in advance of mining. Surface drilled vertical wells can be
drilled anywhere from 2 to more than 10 years in advance of mining. Pre-mining
degasification requires more advanced technology and equipment than enhanced gob well
recovery, and therefore has higher capital costs. These higher costs can be justified by
the increased recovery of methane using surface drilling techniques.
Ventilation Air Utilization: Most mine gas is released to the atmosphere in the ventilation
air used in the mine. Ventilation, necessary in underground coal mines for safety reasons,
is achieved with large fans which blow air through the mine. The recovery technology is
basic, but the operating costs of running the fans can be hiqh if the mine is gassy. The
methane content of the vented air must be below 5 percent for safety reasons, and is
frequently as low as 0.5 percent to comply with relevant regulations. In spite of its low
concentration, it appears that there may be opportunities to use ventilation air as
combustion air in turbines or boilers. However, the technical and economic feasibility has
not yet been demonstrated.
Integrated Recovery: The most significant methane emission reductions are likely to occur
by employing a combination of methane recovery strategies. Indeed, many U.S. coal
mines currently use a combination of in-mine and surface recovery methods both before
mining and from gob areas. The technological and capital requirements of such integrated
systems are likely to be moderately high, but it is possible that the additional opportunities
for gas utilization, as well as the enhanced mine safety, could justify the required
investment.
Fossil Fuel Combustion
Methane emissions from fossil fuel combustion are a result of incomplete combustion. Even
if methane (natural gas) is not a component of the fuel, it can be created during the
combustion process. Preliminary estimates indicate that 4 to 5 Tg of methane are released
from this source per year, with the majority of the emissions resulting from stationary
British Thermal Units per cubic foot; million (mega-) joules per cubic meter.
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EXECUTIVE SUMMARY ES - 9
sources. Total emissions are dependent upon such factors as the total amount of fuel
combusted and the extent of incomplete combustion. Several methane reduction options
have been identified, although many of them require further study to estimate the magnitude
of possible reductions. In general, options for reducing methane emissions from combustion
are consistent with efforts to improve energy efficiency and reduce emissions of air pollutants
from both stationary and mobile sources.
Improved Fuel Use Efficiency: The primary method for reducing fuel use is to improve
energy efficiency. Continuing activities to increase fuel use efficiency in all sectors should
contribute to decreases in methane emissions per unit of energy output.
Exhaust Controls: Exhaust controls such as catalytic converters can also be used to
remove methane and other air pollutants (e.g., NOX) from exhaust, thereby reducing
emissions of these gases. The use of catalytic converters in automobiles has already
reduced methane emissions from the transport sector in many countries.
Improved Combustion Efficiency: The amount of methane emitted per unit of fuel used
can be reduced by improving combustion efficiency, ensuring that a higher proportion of
the hydrocarbons are burned completely.
Alternative Fuels: In the longer-term, increased use of alternative fuels, such as solar
power, can reduce fossil fuel use. Reducing the current reliance on fossil fuels will also
improve the energy security of countries which import a significant proportion of the
energy that they use.
Ruminant Livestock
Methane is produced as part of the normal digestion process of ruminant animals (cattle,
buffalo, sheep, goats, 3nd camels). This methane, which is exhaled or eructated by the
animal, represents an inefficiency -- feed energy converted to methane cannot be used by
the animal for maintenance, growth or production. Emissions are estimated to be 65 to 100
Tg per year, with cattle accounting for about 75 percent of the global annual methane
emissions from domestic livestock.
Many opportunities exist for reducing methane emissions from ruminant animals by improving
animal productivity and reducing methane emissions per unit of product (e.g., methane
emissions per kilogram (kg) of milk produced). In general, a greater portion of the energy in
the animals' feed can be directed to useful product, instead of wasted in the form of methane.
This leads to smaller size herds required to produce the same amount of product. With
adequate resources, current and potential future technologies and management practices can
technically reduce methane emissions per unit product by 25 to 75 percent in many animal
management systems.
The conditions under which animals are managed vary greatly by country, especially between
developed and developing countries. Reduction strategies must be tailored to country-specific
circumstances. Despite the differences in animal management practices among various
countries, one common strategy for reducing methane emissions is to increase animal
productivity. Virtually all efforts that improve animal productivity will reduce methane
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ES - 10 EXECUTIVE SUMMARY
emissions per unit product produced. Options for reducing methane emissions from ruminant
livestock include:
Improved Nutrition Through Mechanical & Chemical Feed Processing: Improved nutrition
reduces methane emissions per unit product by enhancing animal performance, including
weight gain, milk production, work production, and reproductive performance. Mechanical
and chemical feed processing options include wrapping and preserving rice straw to
enhance digestibility, chopping straw to enhance animal intake, and alkali treatment of low
digestible straws to enhance digestibility. These options are applicable to accessible
ruminant animals with limited or poor quality feed, and may decrease methane emissions
per unit product on the order of 10 to 25 percent (assuming feed digestibility is increased
by 5 percent), depending on animal management practices.
Improved Nutrition Through Strategic Supplementation: Strategic supplementation
provides critical nutrients such as nitrogen and important minerals to animals on low
quality feeds. Additionally, it may include providing microbial and/or bypass protein to the
animal. Methane emissions per unit product may be reduced by 25 to 75 percent due to
substantial increases in animal productivity, depending on animal management practices.
In particular, applying molasses urea blocks (MUBs) and bypass protein techniques in
tropical areas with phronic feed constraints can produce emissions reductions per unit
product near the high end of the range. The use of chemicals (ionophores) and
defaunation are also possible options, though further efforts to develop better agents and
to demonstrate practical methods of defaunation are necessary.
Production Enhancing Agents: Certain agents can act directly to improve productivity.
These agents are generally most applicable to large-scale commercial systems with well-
developed markets. Emissions reductions per unit product of 5 to 1 5 percent have been
demonstrated. Additional reductions may be achieved by shifts in rumen microbial
patterns. Options include the use of bovine somatotropin (bST) and anabolic steroids.
Improved Production Through Improved Genetic Characteristics: Genetic characteristics
are limiting factors mainly in intensive production systems. Continued improvements in
genetic potential will increase productivity, and thereby reduce methane emissions per unit
product. Emissions reductions from these options remain to be quantified.
Improved Production Efficiency Through Improved Reproduction: Large portions of the
herd of large ruminants are maintained for the purpose of producing offspring. Methane
emissions per unit product can be significantly reduced if reproductive efficiency is
increased and fewer animals are required to provide the desired number of offspring.
Options such as artificial insemination, twinning, and embryo transplants address
reproduction directly. The nutritional options described above can also improve
reproduction.
Other Techniques: Additional options include disease control and the control of product
markets and prices in countries with surplus dairy products.
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EXECUTIVE SUMMARY ES - 11
Livestock Manure
Methane is produced during anaerobic decay of the organic material in livestock manure.
Manure management systems that store manure under anaerobic conditions are the major
contributors to methane emissions from this source. Global emissions are estimated to range
from 20 to 30 Tg per year.
Methane emissions from anaerobic digestion constitute a wasted energy resource which can
be recovered by adapting manure management and treatment practices to facilitate methane
collection. This methane can be used directly for on-farm energy, or to generate electricity
for on-farm use or for sale. The other products of anaerobic digestion, contained in the slurry
effluent, can be utilized in a number of ways, depending on local needs and resources.
Successful applications include use as animal feed and aquaculture supplements, in fish
farming, and as a crop fertilizer.
Additionally, managed anaerobic decomposition is a very effective method of reducing the
environmental and human health problems associated with manure management. The
controlled bacterial decomposition of the volatile solids in manure reduces the potential for
contamination from runoff, significantly reduces pathogen levels, removes most noxious
odors, and retains the organic nitrogen content of the manure.
The selection of successful methane emissions reduction options depends on several
important regional factors, including the ambient temperature and climate; economic, technical
and material resources; existing manure management practices; regulatory requirements; and
the specific benefits of developing an energy resource (biogas) and a source of high quality
fertilizer. Choosing an appropriate strategy is vital to gaining the acceptance of livestock
farmers. With successful implementation, current reduction options can technically reduce
methane emissions by as much as 25 to 80 percent at particular sites. Identified options
include:
Covered Lagoons: The treatment of manure in lagoons is associated with relatively large
scale intensive farm operations. Manure solids are washed out of the livestock housing
facilities with large quantities of water, and the resulting slurry flows into primary lagoons.
The anaerobic conditions treat manure and usually result in significant methane emissions,
provided temperatures remain high enough. Placing an impermeable floating cover over
the lagoon and applying negative pressure effectively recovers methane which can be
cost-effectively utilized for electricity generation, farm heating, and refrigeration. Lagoons
are most common in North America, Europe, and regions of Asia and Australia.
Small Scale Digesters: Digesters are designed to enhance the anaerobic decomposition
of organic material and to maximize methane production and recovery. Small scale
digesters typically require a small amount of manure and are relatively simple to build and
operate. As such, they are an appropriate strategy for regions with technical, capital, and
material resource constraints. Due to the rising cost of commercial fertilizers, the recovery
of high quality fertilizer from digesters can be an even more important benefit than the
energy supplied from biogas. A number of different digester designs have been developed.
These designs are not heated, and while they can operate in colder regions, they are more
appropriate for temperate and tropical regions.
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ES - 12 EXECUTIVE SUMMARY
Large Scale Digesters: The larger, often more technologically advanced digesters
described in this section are usually heated, have larger capacities, require greater capital
investment, and in general are more complex to build and operate. However, advanced
designs can greatly improve the performance of livestock manure digesters, and can
operate in colder regions. This strategy integrates the operation of a digester with current
manure management practices at large livestock operations, typically in more developed
regions. The two primary digester designs are Complete Mix and Plug Flow digesters.
Manure quantity and the percent total solids of the manure are important criteria for
determining the appropriate strategy.
Landfills
Methane is generated in landfills as a direct result of the natural decomposition of solid waste.
The organic component of landfilled waste is broken down by bacteria in a complex biological
process, which produces methane, carbon dioxide, and trace gases. Because the
methanogenic (methane-producing) stage of this process is anaerobic, methane production is
favored in landfills capped with soil or clay that limits air infiltration. However, anaerobic
conditions will exist to some extent in any landfill, whether it is covered or not. Landfills are
estimated to produce 20 to 70 Tg of methane per year. Several options have been identified
that can technically reduce methane emissions from landfills by up to 90 percent. Additional
benefits that result from these strategies include improved air and water quality, reduced risk
of fire and explosion, and the recovery of a clean and convenient fuel.
Methane Recovery and Utilization: Methane can be recovered from landfills, and its energy
value may be put to a profitable use. The recovery of methane from anaerobic landfills
can be a low-cost and relatively low technology option. Recovery efficiencies are typically
as high as 80 percent, with some projects achieving almost complete recovery. Utilization
options for the recovered gas include electricity generation, direct use in industry, and
natural gas supply.
Aerobic Landfill Management: Using a more complex technology, landfills can be designed
to be aerobic so that less methane is produced, as has been done in Japan. Aerobic
designs increase the rate of decomposition, reduce the emissions of harmful and odorous
trace gases, and improve the quality of leachate. These advantages are significant in
terms of pollution reduction and the reclamation of landfill sites. Semi-aerobic landfills
equipped with single air conduction channels have been able to reduce methane emissions
by more than 50 percent. More advanced designs that are still being developed have
achieved reductions of over 80 percent in test applications.
Reduced Landfilling of Waste: The reduced landfilling of waste is an additional option that
reduces the quantity of waste placed in landfills. This can be achieved by recycling and
reusing material, incinerating solid waste and composting organic material, and through
additional technologies under development.
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EXECUTIVE SUMMARY ES - 13
Wastewater Management
Wastewater and its solid byproduct (sludge) can result in methane emissions if they are stored
or treated under anaerobic conditions, and if the methane is subsequently released instead of
being flared. Although data is limited, current estimates for global emissions range from 20
to 25 Tg per year.
The primary sources of methane emissions from wastewater are thought to be domestic
waste streams in developing countries and wastewater from food processing facilities
throughout the world (e.g., fruit and vegetable plants, meat packing plants and
slaughterhouses, distilleries, and creameries). The anaerobic decomposition of the high
organic components in these waste streams results in the production of methane by bacteria.
Wastewater treatment plants in developed countries are not a major source of methane, as
they rely primarily upon aerobic treatment, or anaerobic treatment in enclosed systems where
the methane is recovered and utilized. These treatment practices can be employed in other
regions where unmanaged waste streams and anaerobic storage and treatment practices are
thought to produce significant methane emissions.
Biomass Burning
Methane is produced by incomplete combustion during biomass burning. The most common
sources of anthropogenic biomass burning include agricultural and land management practices,
such as deforestation due to population pressures, swidden ("slash-and-burn", shifting)
agriculture, burning savannah and rangelands to improve livestock forage, and prescribed
burning of unwanted vegetation, logging debris, or agricultural residues. Firewood, charcoal,
agricultural residues and livestock manure are also commonly burned as fuel. Although net
global methane emissions from biomass burning (including deforestation) are not well
quantified due to the lack of data on the amount of biomass burned, fire frequency, and fire
characteristics, estimates range from 20 to 80 Tg annually.
Strategies to reduce methane emissions focus on reducing the amount of forest and
agricultural biomass burned, thus reducing emissions of all greenhouse gases from this source
(i.e., direct greenhouse gas emissions of carbon dioxide (CO2), methane (CH4), and nitrous
oxide (N2O); and tropospheric ozone precursors such as CO and NOX). Such approaches
include sustainable forest management through fire management and deforestation reduction
and alternative agricultural practices which minimize forest clearing and burning of crop
residues. These approaches are largely subsumed under strategies currently being discussed
for maintaining species diversity and reducing rates of deforestation. Other strategies include
promoting efficient combustion devices for biomass fuels, and modification of the types of
stoves and fuels used for burning biomass as an energy source.
Opportunities exist to implement these types of programs, especially in tropical and sub-
tropical regions. These opportunities have not been well characterized, however, and no
estimates of possible reductions have been made.
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ES - 14 EXECUTIVE SUMMARY
Rice Cultivation
Methane is produced in the soils of flooded rice fields, largely from the anaerobic
decomposition of organic material by methanogenic bacteria. The methane that is not
oxidized in the soil or the plant is transported into the atmosphere by plant-mediated transport,
diffusion through the floodwater, leaching, and ebullition. Although much research is needed
to better quantify global methane emissions from rice, it is estimated that rice fields annually
contribute 20 to 1 50 Tg of methane to the atmosphere. These emissions are expected to
grow over the next three decades.
Although the production and emission of methane from rice fields are not fully understood,
present knowledge indicates that various management practices could potentially achieve
significant reductions. Such alternative practices include changes in cultivar selection,
nutrient applications, water management and cultivation practices. Recognizing that
maintaining or increasing rice productivity as well as satisfying other social and cultural
constraints are fundamental objectives, it is believed that 10 to 30 percent reductions from
current levels of methane emissions may be possible over the long term.
Substantial research is necessary to identify, develop, and demonstrate management practices
which are applicable in different rice growing regions. The formation of a research consortium
of the major rice-growing countries has been proposed to help identify the most appropriate
and feasible mitigation opportunities while increasing rice productivity. Options developed
through such research would be available by 2005 to 2010.
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EXECUTIVE SUMMARY ES - 15
ES.3 References
Steele, L.P., E.J. Dlugokencky, P.M. Lang, P.P. Tans, R.C. Martin, and K.A. Masarie (1992),
"Slowing Down of the Global Accumulation of Atmospheric Methane During the 1980's,"
Nature, vol. 358, July 23, 1992, pp 313-316.
WMO (World Meteorological Organization) (1990), Scientific Assessment of Stratospheric
Ozone: 1989. World Meteorological Organization Global Ozone Research and Monitoring
Project - Report No. 20. Geneva, Switzerland.
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CHAPTER ONE
INTRODUCTION
This report evaluates international options for reducing methane emissions from anthropogenic
(human related) sources through the use of technologies that are either currently in use or
under development. This report has been prepared in partial fulfillment of Section 603 of the
Clean Air Act Amendments of 1990, which requires that the EPA prepare and submit to
Congress a series of reports on domestic and international issues concerning methane. As
one of this series of reports, EPA has been requested to evaluate opportunities to reduce
methane emissions in countries other than the United States:
Preventing Increases in Methane Concentrations: Not later than two years after the
enactment of this Act, the Administrator shall prepare and submit to the Congress a
report that analyzes the potential for preventing an increase in atmospheric
concentrations of methane from activities and sources in other countries. Such report
shall identify and evaluate the technical options for reducing methane emissions from
each of the activities listed in subsection (b), as well as other activities or sources that
are deemed by the Administrator in consultation with other relevant Federal agencies
and departments to be significant and shall include an evaluation of the costs. The
report shall identify the emission reductions that would need to be achieved to prevent
increasing atmospheric concentrations of methane. The report shall also identify
technology transfer programs that could promote methane emission reductions in
lesser developed countries.5
This report has two volumes. The first presents technical assessments of the key
technological options for reducing methane emissions, and the second focuses on
opportunities to reduce emissions in some of the key emitting countries.
The first volume, Technological Options for Reducing Methane Emissions, was prepared in
part for the Intergovernmental Panel on Climate Change (IPCC) Response Strategies Working
Group (RSWG), by the U.S./Japan Working Group on Methane. The technology assessments
were compiled from information and comments submitted by IPCC participating countries.
The findings presented in this report indicate that technological options exist for reducing
emissions from most of the major methane sources, including oil and natural gas systems,
coal mines, landfills, ruminant livestock, and livestock manure.
The second volume, International Opportunities for Reducing Methane Emissions, investigates
the potential for applying or expanding the use of available technologies in key emitting
countries around the world6, for the major methane sources. The key barriers in various
countries which are hampering the expansion of methane recovery projects are identified and
Section 603(c)(2) of the Clean Air Act Amendments of 1990.
These are countries other than the United States. Options for reducing methane emissions in the U.S.
are examined separately in USEPA (1993b), "Opportunities to Reduce Methane Emissions in the United
States," Report to Congress (review draft).
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1 - 2 INTRODUCTION
types of technology transfer programs which may address these barriers and achieve emission
reductions are discussed.
1.1 Background: The Importance of Methane
Methane is an important greenhouse gas and a major environmental pollutant. Methane is
also the primary component of natural gas and a valuable energy source. Methane emission
reduction strategies offer one of the most effective means of mitigatinq global warming in the
near term for the following reasons:
Methane is one of the principal greenhouse gases, second only to carbon dioxide (CO2)
in its contribution to potential global warming. In fact, methane is responsible for roughly
18 percent of the total contribution in 1990 of all greenhouse gases to "radiative forcing,"
the measure used to determine the extent to which the atmosphere is trapping heat due
to emissions of greenhouse gases (IPCC, 1992a).7
Methane concentrations are rising rapidly. The atmospheric concentration of methane is
increasing at a rate of about 0.6 percent per year (Steele et al., 1992) (in contrast to CO2
concentrations, which are increasing by about 0.4 percent per year)8, and has more than
doubled over the last two centuries (IPCC, 1992a).
Methane is a potent contributor to global warming. On a kilogram for kilogram basis,
methane is a more potent greenhouse gas than C02 (about 60 times greater after 20
years, 20 times greater after 100 years, and 9 times greater after 500 years).9
Reductions in methane emissions will produce substantial benefits in the short run.
Methane has a shorter atmospheric lifetime than other greenhouse gases: methane lasts
around 10 years in the atmosphere, whereas C02 lasts about 120 years (IPCC, 1992a).
Due to methane's high potency and short lifespan, stabilization of methane emissions will
have a rapid impact on mitigating potential climate change.
Methane stabilization is nearly as effective as stabilizing C02 emissions at 1990 levels.
In order to stabilize methane concentrations at current levels, total anthropogenic methane
emissions would need to be reduced by about 10 percent. This methane concentration
7 Global contribution to radiative forcing by gas is estimated on a carbon dioxide equivalent basis using
IPCC (1990al global warming potentials for a 100-year time horizon, including direct and indirect effects
of methane.
8 Based on measurements taken at Mauna Loa from 1970 to 1990 (Oak Ridge National Laboratory, 1992).
9 Methane is reported to have a direct Global Warming Potential (GWP) of 11 over a one hundred year
timeframe, and to have indirect effects that could be equal in magnitude to its direct effect (IPCC, 1992).
Over a fifty year timeframe, the direct GWP would be on the order of 25 to 30. The GWP reflects the
effect that releasing a kilogram of methane would have over a specified time horizon, relative to releasing
a kilogram of carbon dioxide. While the GWP of methane continues to be uncertain, efforts by the IPCC,
EPA's Office of Research and Development, and others, should begin to resolve these uncertainties over
the next few years.
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INTRODUCTION 1 - 3
stabilization would have roughly the same effect on actual warming as maintaining C02
emissions at 1990 levels (Hogan et al., 1991).
In contrast to the numerous sources of other greenhouse gases, a few large and gassy
facilities often account for a large portion of methane emissions. Therefore, applying
emission reductions strategies to these gassiest facilities would result in a substantial
decrease in estimated current and future methane emissions levels.
Because methane is a source of energy as well as a greenhouse gas, many emissions
control options have additional economic benefits. Methane emissions are usually an
indication of inefficiency in a system. In many cases, methane that would otherwise be
emitted to the atmosphere can be recovered and utilized, or the quantity of methane
produced can be significantly reduced through the use of cost-effective management
methods. Therefore, emissions reduction strategies have the potential to be low-cost, or
even profitable. For example, methane recovered from coal mines, landfills, and livestock
manure systems can be used as an energy source, and options for reducing methane
emissions from livestock can also improve the productivity of each animal.
Well-demonstrated technologies are commercially available for profitably reducing methane
emissions. For the major sources of anthropogenic methane emissions (except rice
cultivation and biomass burning), cost-effective methane reduction technologies are
already commercially available. Additionally, a number of other technologies are under
development. While offering substantial emission reductions and economic benefits, these
technologies have not been implemented on a wide scale in the U.S. or globally because
of financial, informational, and institutional barriers.
The unique characteristics of methane emissions demonstrate the importance of promoting
strategies to reduce the amount of methane discharged into the atmosphere. Understanding
the sources of methane emissions, and in particular the emissions from systems that are
partially controllable, is the first step in identifying cost-effective options for reducing
emissions.
What is Methane?
Methane (CH4) is a radiatively and chemically active trace greenhouse gas.10 Being
radiatively active, methane traps infrared radiation (IR or heat) and helps warm the earth. It
is currently second only to carbon dioxide in contributing to potential future warming. Being
chemically active, methane enters into chemical reactions in the atmosphere that increase not
only the abundance of methane, but also atmospheric concentrations of ozone11 and
stratospheric concentrations of water vapor, which are both greenhouse gases.
10 A trace gas is a gas that is a minor constituent of the atmosphere. The most important trace gases
contributing to the greenhouse effect include water vapor, carbon dioxide, ozone, methane, ammonia,
nitrous oxide, and sulfur dioxide.
11 While methane does not contribute significantly to the formation of urban smog, methane is a major
concern in the formation of ozone in the free troposphere.
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1 - 4 INTRODUCTION
Methane is emitted into the atmosphere largely by anthropogenic sources, which currently
account for approximately 70 percent of the estimated 500 teragrams (Tg) of annual global
methane emissions.12 Anthropogenic sources of methane emissions include: natural gas
and oil systems; coal mining; landfills; domesticated ruminant livestock; liquid and solid
wastes; rice cultivation; and biomass burning. Natural sources of methane, which currently
account for the remaining 30 percent of global emissions, include natural wetlands (e.g.,
tundra, bogs, swamps), termites, wildfires, methane hydrates, oceans and freshwaters.
The concentration of methane in the atmosphere is determined by the balance of input rate,
which is increasing due to human activity, and the removal rate. The primary sink (removal
mechanism) for atmospheric methane is its reaction with hydroxyl (OH) radicals in the
troposphere. In this reaction, methane is converted into water vapor and carbon monoxide,
which is in turn converted into carbon dioxide (C02)- The atmospheric concentration of OH
radicals is determined by complex reactions involving methane, carbon monoxide, non-
methane hydrocarbons (NMHC), nitrogen oxides, and tropospheric ozone. The size of an OH
sink can vary and may actually decrease in response to increasing levels of methane (IPCC,
1992a). A small amount of methane is also removed from the atmosphere through oxidation
in dry soils. Compared to removal by reaction with OH, this oxidation mechanism is believed
to be relatively small. There are no significant anthropogenic activities that remove methane
from the atmosphere. Methane's atmospheric lifetime is presently estimated to be about 10
years (IPCC, 1992a).
Atmospheric Levels of Methane Are Rising
The concentration of methane in the atmosphere has been steadily increasing. The rise in
methane concentrations has been well documented in recent studies and corroborated by
measurements from different locations and several monitoring groups. The principal methods
for estimating methane concentrations over time have been analysis of ice core data and
direct atmospheric measurements.
Analyses of ice cores in Antarctica and Greenland have yielded estimates of atmospheric
methane concentrations of approximately 0.35 parts per million by volume (ppmv) to 0.65
ppmv for the period between 10,000 and 160,000 years ago. Similar analyses of air in ice
cores have placed atmospheric methane concentrations at approximately 0.8 ppmv for the
period between 200 and 2,000 years ago. The level of methane rose to about 0.9 ppmv at
the beginning of this century (IPCC, 1990a).
Direct measurement of the global atmospheric methane concentration was begun in 1978.
At that time, the global atmospheric methane concentration was calculated to be 1.51 ppmv.
In 1990, the level was approximately 1.72 ppmv -- nearly double the concentration level
estimated for the beginning of this century (IPCC, 1990a). A summary of the ice core data
and direct measurement data showing the increase in atmospheric methane concentrations
is provided in Exhibit 1-1. In addition to ice core data and direct atmospheric measurements,
12 The portion of total methane emissions from anthropogenic sources is based on IPCC (1992a). Total
annual methane emissions is based on Crutzen (1991).
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INTRODUCTION
1 -5
analysis of infrared solar spectra has shown that the atmospheric concentration of methane
increased by about 30 percent over the last 40 years (Rinsland et al., 1985).
At present, the atmospheric level of methane is approximately 4,900 Tg (IPCC, 1990a); this
amount is thought to be increasing by about 30 to 40 Tg per year (Steele et al., 1992).
Atmospheric methane concentrations are expected to continue to increase, although global
measurement programs indicate that the rate of increase appears to have slowed in the last
several years (WMO, 1990; Steele et al., 1992). The reason for this is not currently well
understood. Given a continuation of the current annual rate of increase of atmospheric
methane of about 0.0095 to 0.0133 ppmv, the atmospheric concentration of methane would
exceed 2.0 ppmv by the year 2020. Recent models of expected future emissions and
atmospheric processes indicate that without controls, atmospheric concentrations could range
from 3.0 ppmv to over 4.0 ppmv by the year 2100 (USEPA, 1989; IPCC, 1992a), although
these scenarios should be reinvestigated using the most recent information on methane
concentration trends.
Exhibit 1-1
Global Methane Concentrations
1800-
1300-
800-
300-
Stpte fcccoflB
BynJ to core
Dye teŤ core
° ttatok kť core
10ť 10* 10ť 10* 101
Years Before Present (1990 A.D.)
OWri** tnm lot CMPH M4 thi NOAA/CMDL tek
Source: Oak Ridge National Laboratory/Carbon Dioxide Information Analysis Center,
August 1990.
-------
1 - 6 INTRODUCTION
Methane and Global Climate Change
Methane's increasing concentration in the atmosphere has important implications for global
climate change. Methane is very effective at absorbing infrared radiation (IR) reflected by the
earth's surface. By absorbing IR and inhibiting its release into space, methane in the
atmosphere contributes to increased atmospheric and surface temperatures. This process is
commonly referred to as the "greenhouse effect."
A gram of methane is about 35 times more effective at warming the surface of the earth than
a gram of C02 over a 20 year timeframe (IPCC, 1992a). In addition to this direct radiative
forcing, methane's participation in chemical reactions in the atmosphere indirectly contributes
to global warming by influencing the amount of ozone in the troposphere and stratosphere,
the amount of hydroxyl in the troposphere, and the amount of water vapor in the
stratsophere; these reactions are discussed in more detail below. Methane's indirect effect
on global warming resulting from these chemical reactions could be equal in magnitude to its
direct effect, although considerable uncertainty remains (IPCC, 1992a).13
When compared to C02, methane's greater direct and indirect impacts per gram of emissions
is mitigated somewhat by its shorter atmospheric lifetime of around 10 years, compared with
approximately 1 20 years for C02 (IPCC, 1992a). Considering methane's atmospheric lifetime
and its effect on tropospheric ozone, a gram ot methane has a global warming potential (GWP)
21 times greater than a gram of C02 over a 100 year time period (IPCC, 1 992a). It has been
estimated that approximately 18 percent of the greenhouse effect is due to increasing
atmostpheric methane concentrations. The total contribution to radiative forcing of all
greenhouse gases in 1990 is shown in Exhibit 1-2.
Models of atmospheric chemical processes have indicated that increasing methane
concentrations result in net ozone production in the troposphere and lower stratosphere, and
net ozone destruction in the upper stratosphere. It has been calculated that methane's net
effect in these processes is to cause an increase in ozone (Wuebbles and Tamaresis,
1992).14
As the most abundant organic species in the atmosphere, methane also plays an influential
role in determining the oxidizing capacity of the troposphere. Through reactions with
hydroxyl, 80 to 90 percent of methane destruction occurs in the troposphere (Cicerone and
13 The uncertainty in the GWPs for methane result largely from the indirect effects of methane in the
atmosphere, which have not been fully characterized. Some of these uncertainties will be reduced over
the next several years through the efforts of the Intergovernmental Panel on Climate Change as well as
others, including EPA's Office of Research and Development.
14 As described in IPCC (1990a;, "Ozone plays an important dual role in affecting climate. While C02 and
other greenhouse gases are relatively well-mixed in the atmosphere, the climatic effect of ozone depends
on its distribution in the troposphere and stratosphere, as well as on its total amount in the atmosphere.
Ozone is a primary absorber of solar radiation in the stratosphere, where it is directly responsible for the
increase in temperature with altitude. Ozone is also an important absorber of infrared radiation. The
balance between these radiative processes determines the net effect of ozone on climate."
-------
INTRODUCTION
1 - 7
Oremland, 1988). Increasing methane levels could reduce hydroxyl, which would result in a
further increase in the methane concentration. A decrease in the oxidizing capacity of the
Exhibit 1-2
Global Contribution to Integrated Radiative Forcing by Gas for 19901
CH4 18.0%
N20 5.0%
CFCs 11.0%
CO2 66.0%
Note: Estimated on a carbon dioxide equivalent basis using IPCC (1990a) global warming potentials
(GWPs) for a 100-year time horizon. Anthropogenic emissions only.
1 This chart is used to present a general understanding of methane's contribution to future warming based
on the GWPs presented in IPCC (1990a). However, these GWPs are constantly being revised due to a
variety of scientific and methodological issues. It is likely that the contribution of CFCs presented will
decrease and that the contribution of other gases will be about the same or greater upon further
investigation.
Source: IPCC 1990a
troposphere would increase not only the atmospheric lifetime of methane, but also the lifetime
of other important greenhouse gases, and would permit transport of pollutants over long
distances, resulting in atmospheric changes even in remote regions (Wuebbles and Tamaresis,
1992). For example, the atmospheric lifetimes of hydrogenated-CFCs (HCFCs) may be
increased, thereby reducing their desirability as substitutes for CFCs.
Finally, concentrations of stratospheric water vapor (one of the most important greenhouse
gases) should increase as concentrations of methane increase; methane oxidation reactions
roughly produce two moles of water vapor for each mole of methane that is destroyed
(Wuebbles and Tamaresis, 1992). In addition to the impact on global warming, increases in
stratospheric water vapor concentrations as a result of increased methane concentrations
could contribute to the formation of polar stratospheric clouds (PSCs), which have been
-------
1 -8
INTRODUCTION
identified as one factor that enables the chlorine and bromine from chlorofluorocarbons (CFCs)
and halon compounds to cause the severe seasonal loss of stratospheric ozone over
Antarctica (WMO, 1990).
Stabilization of Global Methane Levels and Further Reductions
Since atmospheric methane is currently increasing at a rate of about 30 to 40 Tg per year,
stabilizing global methane concentrations at current levels would require reductions in
methane emissions of approximately the same amount. Such a reduction represents about
10 percent of current anthropogenic emissions. This percentage reduction is much less than
the percentage reduction necessary to stabilize the other major greenhouse gases: CO2
requires a greater than 60 percent reduction; nitrous oxide requires a 70 to 80 percent
reduction; and chlorof luorocarbons require a 70 to 85 percent reduction (IPCC, 1990b).
Because methane has a relatively short atmospheric lifetime as compared to the other major
greenhouse gases, reductions in methane emissions will help to ameliorate global warming
relatively quickly. Therefore, methane reduction strategies offer an effective means of
slowing global warming in the near term. Exhibit 1-3 compares the effects on future
temperature increases of stabilizing methane concentrations versus maintaining CO2 emissions
at 1990 levels. This exhibit illustrates that stabilizing atmospheric concentrations of methane
Exhibit 1-3
CO2 and Methane Reduction Comparison
Actual
T*mpťratun
Roughly Identical oftocta on actual warming
- CO,amlaaiona etaNllzatlon
- CH. Concentration ataHllzation
IPCC-BAU
CH4 stabilization
CO2 capped at 1990
CH4andCO,
1988
2000
2025
2050
2075
2100
Your
Assumas 3° equilibrium warming
HI IIII Constitutes uncertainty range due to NO.
Benefits of Methane stabilization where methane emissions are capped at 540 Tg/yr as compared to
capping CO2 emissions at 1990 levels (and concentrations grow to over 500 ppm by 2100)
Source: Hogan et al. 1991
-------
INTRODUCTION 1 - 9
will have a virtually identical effect on actual warming as capping C02 emissions at 1990
levels. The recent evidence that the rate of annual increase in methane emissions is slowing
(Steele et al., 1992) may mean that reductions on the order of 30 to 40 Tg could reduce
concentrations to the extent that they fall below the level of stabilization. This result would
also have large benefits for the global atmosphere.
1.2 Technological Options for Reducing Methane Emissions
Because methane released by anthropogenic activities is generally a wasted resource,
opportunities may exist for low cost, if not profitable, emission reductions. Depending on the
source, a significant portion of the methane currently emitted to the atmosphere can be
reduced through the use of cost-effective technologies. In this volume, Volume I:
Technological Options for Reducing Methane Emissions, the key options for reducing methane
emissions from the major sources are identified and characterized. An overview of the
emissions from each major source is provided below. Estimates of global emissions from
these sources are provided in Exhibit 1-4.
Exhibit 1-4
Global Methane Emissions from Major Sources
Source
Coal Mining, Natural Gas & Petroleum Industry
Ruminant Livestock
Livestock Manure
Landfills
Wastewater
Biomass Burning
Rice Cultivation
Estimated Emissions -
70-
65 -
10
20
20
20
20 -
Source: IPCC 1992a
a. Emissions from Livestock Manure reflect revised estimates. Emissions for all other
being updated by USEPA (1993a).
120
100
20a
- 70
- 25
-80
150
sources
1990(Tg)
are currently
Oil and Natural Gas Systems
Methane is the primary component of natural gas, and significant methane emissions can
occur during all the major phases of the natural gas system operations: production,
processing, storage, transmission, and distribution. Emissions result from normal operations
(including compressor exhaust emissions, emissions from pneumatic devices and fugitive
emissions); during routine maintenance (including equipment blowdown and venting, well
workovers and scraper operations); and during system upsets when methane is emitted due
-------
1-10 INTRODUCTION
to sudden, unplanned pressure changes or mishaps. Because natural gas is often found in
conjunction with oil, gas leakage during oil exploration and production is also a source of
emissions. Current global emissions from oil and gas systems are estimated to be 33 to 68
Tg per year.15 Reducing these emissions would not only decrease atmospheric
concentrations of methane, but would improve safety, increase productivity through reduced
losses, and improve local and regional air quality.
Coal Mining
Methane and coal are formed together during coalification, a process in which vegetation is
converted into coal by biological and geological forces. Methane is stored within coal seams
and surrounding rock strata and is released to the atmosphere during mining or through natural
erosion. In underground mines, methane is hazardous because it is explosive in low
concentrations (5 to 15 percent) when mixed with air. Therefore, underground mines use
ventilation and degasification systems to remove methane from mine workings; this methane
is usually vented to the atmosphere. In surface mines, methane is emitted directly to the
atmosphere as the rock strata overlying the coal seam are removed. The amount of methane
released from a mine depends mainly upon the type of coal and the depth of the coal seam.
For example, deeper coal can hold more methane. This means that emissions from coal
mining are likely to increase in the future as shallower reserves are depleted, and deeper coal
is mined. Current global coal mine emissions are estimated to be 23 to 47 Tg per year
(USEPA, 1993a). Recovering and utilizing low to high quality methane from gassy mines
would improve mine safety and productivity.
Landfills
Methane is generated in landfills as a direct result of the natural decomposition of solid waste,
primarily under anaerobic conditions (in the absence of oxygen). The organic component of
landfilled waste is broken down by bacteria in a complex biological process that produces
methane, carbon dioxide, and other trace gases. Global emissions are estimated to be 20 to
70 Tg per year. Emission reductions, as well as improved water and air quality, would be
achieved through efforts to reduce methane emissions from this source.
Ruminant Livestock
Ruminant animals (cattle, sheep, buffalo, goats, and camels) produce significant quantities of
methane as part of their normal digestive processes. Ruminant animals are characterized by
a large "fore-stomach" or rumen, in which microbial fermentation converts feed into products
that can be digested and utilized by the animal. The microbial fermentation enables ruminant
animals to utilize coarse forages that monogastric animals, including humans, cannot digest.
Methane is produced by rumen methanogenic bacteria as a byproduct of normal rumen
fermentation, and then is exhaled or eructated by the animal. The amount of methane
15
Of this total, 22 to 52 Tg per year are estimated from natural gas systems worldwide, and 11 to 16 Tg
per year are estimated from oil systems (including associated gas production).
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INTRODUCTION 1-11
produced is dependent upon both animal type and management practices. Global emissions
are estimated to be 65 to 100 Tg per year. Options for reducing these emissions will also
increase animal productivity and animal nutrition.
Livestock Manure
Methane can be produced during the anaerobic decomposition of the organic material in
livestock manure. Many developed countries manage the wastes from large concentrations
of cattle, swine, and poultry, using liquid waste management systems that are conducive to
anaerobic fermentation of the wastes and methane production. Global emissions from
livestock manure are estimated to be 20 to 30 Tg per year. Recovering these emissions for
use as an energy source will also improve environmental and economic conditions at these
farms.
1.3 Methane Reduction Options in Countries of Interest
In many cases, a few countries account for most of the emissions from the major methane
sources. For example, three countries contribute over 70 percent of emissions from global
coal mining activities. Four countries contribute over 80 percent of global emissions from the
production and transportation of natural gas. In some cases, however, such as with ruminant
livestock, methane emissions are fairly evenly distributed worldwide. No individual country
is responsible for more than 10 to 15 percent of global emissions from this source. In these
cases, countries discussed in Volume II were selected primarily according to the feasibility of
achieving reductions, or because these countries are representative of regions of interest.
While a variety of emission reduction technologies are available for each major anthropogenic
methane source -- oil and gas systems, coal mining, landfills, domesticated animals, and
livestock manure -- these technologies have not yet been fully implemented in many countries.
In many cases, existing financial, political, and informational barriers constrain the wider
application of these technologies. Volume II: International Opportunities for Reducing
Methane Emissions focuses on the most important barriers constraining the development of
methane reduction programs and outlines possible actions that could be undertaken to
encourage greater methane recovery and utilization.
1.4 Overview of Report
This report is organized as follows:
Volume I: Technological Options for Reducing Methane Emissions: This volume presents
technical assessments of the principal methane recovery and utilization technologies available
for each of the major sources. The report has separate chapters dealing with technologies to
reduce methane from the following sources:
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1-12 INTRODUCTION
Landfills;
Oil and Natural Gas Systems;
Coal Mining;
Combustion: Mobile and Stationary Sources;
Ruminant Livestock;
Livestock Manure;
Wastewater Management;
Biomass Burning; and,
Rice Cultivation.
For each methane source, the available technologies for reducing emissions are described,
including technical characteristics, costs, availability, applicability, barriers to implementation,
and additional benefits of implementation. These categories were created by the IPCC
Response Strategies Working Group, and the information contained in this volume is a
compilation of submissions by IPCC member countries. These technical assessments have
been reviewed by government officials and experts in these countries.
Volume II: International Opportunities for Reducing Methane Emissions: This report
summarizes the particular conditions of key emitting countries, in terms of the most promising
options for reducing emissions, the possible emission reductions, and the types of technology
transfer programs which may increase the implementation of the cost-effective emissions
reduction technologies. The chapters in this report focus on:
Landfills;
Oil and Natural Gas Systems;
Coal Mining;
Ruminant Livestock; and,
Other Sources (including Livestock Manure, Wastewater Treatment, Biornass Burning,
Fossil Fuel Combustion, and Rice Cultivation.
For each of these sources, the overall emission reduction potential is discussed and case
studies of the key international sources are presented.
-------
INTRODUCTION 1-13
1.5 References
Cicerone, R.J. and R.S. Oremland (1988), "Biogeochemical Aspects of Atmospheric
Methane," in Global Bioqeochemical Cycles, vol. 2, p. 299-327.
Crutzen, P.J. (1991), "Methane's Sinks and Sources" in Nature No. 350 April, 1991.
Hogan, K. B., J.S. Hoffman, and A.M. Thompson (1991), "Methane on the Greenhouse
Agenda," in Nature No. 354 November 21, 1991 pp. 181-182.
IPCC (Intergovernmental Panel on Climate Change) (1990a), Climate Change: The IPCC
Scientific Assessment. Report prepared for Intergovernmental Panel on Climate Change by
Working Group 1, eds. J.T. Houghton, G. J. Jenkins and J.J. Ephraums, Meteorological Office,
Bracknell, United Kingdom.
IPCC (1990b), Methane Emissions and Opportunities for Control, Workshop Results of the
Intergovernmental Panel on Climate Change (IPCC) Response Strategies Working Group.
September, 1990.
IPCC (1992a), Climate Change 1992: The Supplementary Report to the IPCC Scientific
Assessment, report prepared for the Intergovernmental Panel on Climate Change, eds. J.T.
Houghton, B.A. Callander and S.K. Varney, Great Britain: Cambridge University Press.
IPPC (1992b). Technological Options for Reducing Methane Emissions: Background Document
of the Response Strategies Working Group, prepared by the U.S./Japan Working Group on
Methane [Draft - January, 1992]
Lashof, D. (1989), "The Dynamic greenhouse: Feedback processes that may influence future
concentrations of atmospheric trace gases and climate change," in Climate Change No. 14
pp. 213-242. As cited in IPCC, 1990.
Oak Ridge National Laboratory/The Carbon Dioxide Information Analysis Center (1990),
Trends '90, U.S. Department of Energy, Atmospheric and Climate Research Division. Oak
Ridge, Tennessee.
Oak Ridge National Laboratory/The Carbon Dioxide Information Analysis Center (1992),
Trends '91, U.S. Department of Energy, Atmospheric and Climate Research Division. Oak
Ridge, Tennessee.
Prinn, R., D. Cunnold, R. Rasmussen, P. Simmonds, F. Alyea, A. Crawford, P. Fraser, and R.
Rosen (1987), "Atmospheric trends in methylchloroform and the global average for the
hydroxyl radical," in Science No. 238 pp. 945-950. As cited in IPCC, 1990a.
Rinsland, C.P., J.S. Levine, and T. Miles (1985), "Concentration of methane in the
troposphere deduced from 1951 infrared solar spectra," in Nature No. 330 pp. 245-249. As
cited in IPCC, 1990a.
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1-14 INTRODUCTION
Steele, L.P., E.J. Dlugokencky, P.M. Lang, P.P. Tans, R.C. Martin, and K.A. Masarie (1992),
"Slowing Down of the Global Accumulation of Atmospheric Methane During the 1980's,"
Nature, vol. 358, July 23, 1992, pp 313-316.
USEPA (United States Environmental Protection Agency) (1989), Policy Options for
Stabilizing Global Climate. Report to Congress, eds. Daniel A. Lashof and Dennis A. Tirpak,
Office of Policy, Planning, and Evaluation (OPPE). Washington, D.C.
USEPA (1993a), Global Anthropogenic Emissions of Methane, (in progress), USEPA/OPPE
(Office of Policy, Planning and Evaluation), Washington, D.C.
USEPA (1993b), Opportunities to Reduce Methane Emissions in the U.S., Report to Congress
(review draft), USEPA/OAR (Office of Air and Radiation), Washington, D.C.
Vaghjiani, G.L. and A.R. Ravishankara (1991), "New Measurement of the Rate Coefficient
for the Reaction of OH with Methane" in Nature, April 4, 1991 pp. 406-409.
WMO (World Meteorological Organization) (1990), Scientific Assessment of Stratospheric
Ozone: 1989. World Meteorological Organization Global Ozone Research and Monitoring
Project - Report No. 20. Geneva, Switzerland.
Wuebbles, D.J. and J.S. Tamaresis (1992), "The Role of Methane in the Global Environment,"
paper prepared for submittal to the NATO Advanced Research Workshop, NATO-ASI Book:
Atmospheric Methane, Lawrence Livermore National Laboratory, March 19, 1992.
-------
CHAPTER Two
LANDFILLS
2.1 Background
Methane Generation and Emissions
Methane is generated in landfills as a direct result of the natural decomposition of solid waste.
The organic component of landfilled waste is broken down by bacteria in a complex biological
process, which produces mainly CH4 (methane), C02 (carbon dioxide), and trace gases such
as hydrogen sulfide. The methanogenic (methane-producing) stage of this process is
anaerobic (lacking free oxygen), and occurs where there is sufficient organic matter which is
isolated from air infiltration.
The quantity and rate of methane generation in landfills depend upon many factors, including
the following:
Waste composition. Methane is produced from the organic component of the waste;
therefore a larger organic component increases the potential methane generation.
Moisture content. Moisture content is critical for anaerobic decomposition as water
provides the medium for nutrient and bacteria distribution.
Acidity. Living systems are sensitive to pH (a measure of acidity); optimal ranges are
from 6.8 to 7.2, but methane production can occur between 6.5 and 8.0 (Pacey and
DeGier, 1986).
Temperature. Methanogenic bacteria, of which there are many different species, are
affected by temperature; the rate of methane production is maximized between 50 and
60 C (120-140 F), but can occur anywhere from 10 to 60 °C (50-140 FMPacey and
DeGier, 1986).
In addition, the refuse density and consistency, the landfill design, and other site specific
factors can affect the quantity and rate of methane generation.
The majority of gas generated at landfills migrates vertically or laterally until an opening is
reached and the gas can be released into the atmosphere. Through this migration, the landfill
gas presents an explosive hazard. In addition, landfill gas contains hazardous and/or
malodorous gases (e.g., volatile organic compounds - VOCs) that can contribute to air
quality problems in the vicinity of landfills. These problems can be reduced if the landfill gas
is recovered or gas generation is limited.
Because the waste composition, moisture content, temperature, pH, and other characteristics
of landfills vary, the rate and quantity of methane generation vary from landfill to landfill.
Measured landfill gas generation rates have ranged from 0.03 to 1.1 ft3/lb/yr in industrialized
countries (0.002-0.07 m3/kg/yr) (Maxwell, 1990). Gas generation in developing countries
may be either higher or lower, depending on the extent to which air is limited from infiltrating
-------
2 - 2 LANDFILLS
the waste or what portion of the waste is organic, among other factors. Promising research
is underway to improve both measurement and control of methane production.
Methane Recovery. Utilization, and Reduction
There are several options for achieving methane emissions reductions. One option is to
recover the landfill gas by drilling wells into the landfill and applying vacuum pressure to pull
gas from the landfill. The recovered gas can then be used as a fuel. Alternatively, landfills
can be designed to prevent (or reduce the extent of) anaerobic conditions by encouraging the
influx of air and reducing the activity of the methanogenic bacteria. Methane emissions from
landfills may also be reduced by controlling the amount of organic waste entering the landfill,
through source reduction programs or waste incineration.
The strategies presented here to reduce methane emissions from landfills include the
following:
Methane Recovery and Utilization
- Electricity Generation and Co-Generation
- Natural Gas Supply
- Flaring
Aerobic Landfill Management
Reduced Landfilling of Waste
These strategies are briefly discussed below.
Methane Recovery and Utilization: Recovering gas from landfills reduces methane
emissions, while allowing the energy value of the recovered methane to be put to a
profitable use. Recovery efficiencies (the portion of the gas recovered relative to the gas
generated) typically range from 50 to 85 percent, with some projects achieving almost
complete recovery. Technologies for the recovery of methane from landfills are relatively
straightforward: gas wells are drilled into sealed areas of the landfill and the gas is
collected under negative pressure through a series of collection header pipes. After
recovery, the landfill gas must be processed in a manner suitable for the intended
utilization. Experience in the U.S. has indicated that gas utilization may be an attractive
option at landfills with over one million tons of refuse in place (Maxwell, 1 990). Options
for utilizing the recovered landfill gas include the following:
Electricity Generation and Co-Generation. The recovered methane can be used to
power an electricity generator, and the electricity used at nearby sites or sold to a local
electricity supply system. In some cases the recovered gas can be used as part of a
co-generation system, where the waste heat from the prime mover (i.e., the engine)
is used to meet local heating requirements, thereby increasing the overall efficiency of
the system. Electricity generation requires relatively large amounts of landfill gas, and
is therefore suitable for larger landfills. Economic viability depends primarily on the
price at which the electricity can be sold. Historically, 50 percent of landfill energy
projects worldwide have been for electricity generation (K.M. Richards, 1989).
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LANDFILLS 2 - 3
Natural Gas Supply. Recovered landfill gas can be used directly as a fuel in several
ways. Medium quality gas (e.g., 30 to 70 percent CH4) can be used by local industries
after minimal processing, or sold directly to a gas supply system that handles medium
quality gas. Industrial uses include a variety of heating and process needs, with the
end use determining the degree of gas processing required to remove impurities and
corrosives from the landfill gas. Alternatively, if the gas is delivered to a natural gas
utility it usually must be processed extensively to yield high or "pipeline quality" gas
(> 95 percent methane, with minimal impurities).
Flaring. Flaring is the simplest method of reducing methane emissions. The recovered
landfill gas, without treatment or processing, is burned in a combustor. Destruction
efficiency (of all hydrocarbons in the gas) of over 98 percent can be achieved. Initial
capital requirements for flares are small relative to energy recovery strategies and the
technology is simple, but the energy value of the methane is wasted and subsequent
revenues are forfeited. Nevertheless, flaring may be an appropriate method for
controlling emissions at smaller landfills where gas flows will not support an
economically viable project, or as an interim strategy while end uses are developed.
Aerobic Landfill Management: The design of landfills to encourage aerobic conditions has
been an effective method of reducing methane emissions in Japan and other Asian
countries. Although this strategy does not recover methane for use as an energy source,
aerobic designs increase the rate of decomposition, reduce the emissions of harmful and
odorous gases, and improve the quality of leachate. These advantages are significant in
terms of pollution reduction and the reclamation of landfill sites. Emissions reductions of
over 50 percent have been achieved with commercially available designs. More advanced
aerobic landfill designs that are still being developed have achieved methane reductions
of over 80 percent in test applications (JEA, 1991).
Reduced Landfilling of Waste: For given landfill designs and operating conditions, methane
emissions are determined by the quantity of organic material in the landfill. Methods for
reducing the quantity of landfilled organic waste, thereby reducing methane emissions,
include recycling, composting, and incineration.
Exhibit 2-1 summarizes these three strategies. The strategies are described below in detailed
technical assessments. Each technical assessment consists of the following sections:
Reduction/Utilization Technology Description
Costs
Availability
Applicability
Barriers; and
Benefits.
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LANDFILLS 2 - 5
2.2 Methane Recovery and Utilization
Landfills result in the anaerobic decomposition of the organic component of landfilled waste.
Recovery and utilization of this generated methane can greatly reduce the overall methane
emissions associated with landfills. Furthermore, because a valuable energy source is
recovered, this strategy can be profitable in many cases. This section first discusses landfill
gas recovery and purification technologies, as well as possible means of increasing methane
recovery. The options for using the recovered gas are then discussed separately below.
Recovery Technology Descriptions
Landfill gas recovery is essentially the "mining" of trapped methane: wells are drilled into the
landfill; the gas is withdrawn under negative pressure; and the recovered gas is gathered at
a central processing unit. Landfill gas recovery systems share many basic features and
requirements.
Recovery wells are generally drilled once the landfill or individual landfill cell has been capped
by an impermeable layer. Gas recovery is most successful at well-sealed landfills (or sealed
cells within a landfill) for two reasons: 1) gas cannot escape, thus recovery efficiencies are
increased; and 2) oxygen will not infiltrate the landfill, where it would kill the methanogenic
bacteria. A thick layer of soil is sufficient to seal a landfill, although the exact thickness of
this layer depends on the soil type and climate. Landfills using sandy, dry soil, which is more
permeable to gas, require a thicker layer.
The number of wells drilled in a particular landfill depends upon certain characteristics of the
landfill and its contents. Typically, 1 to 6 wells per hectare are installed. If the landfill is deep
and well-sealed, the wells can be spaced further apart because a greater vacuum can be
applied without causing the inflow of air. Denser, less permeable refuse will require more
closely spaced wells (Mahin, 1988).
Recovery wells consist of a number of components. Well shafts, typically 1 to 3 feet (30-90
cm) in diameter, are drilled from the surface to within a few feet of the bottom of the landfill.
A narrow, perforated plastic pipe is then inserted into the well. The shaft is backfilled with
gravel, or other permeable material; the top is sealed with concrete, or an impermeable block,
to prevent the inflow of air; and finally the pipehead is connected to the collection system
(Mahin, 1988) (see Exhibit 2-2).
Gas is collected from the wells by the gas collection header. The wells are connected by
horizontal pipes on or just below the surface of the landfill. Compressors (simple
motor/blower units) create the negative pressure necessary to gather the gas at a central
collection point. Most collection systems filter out particulates, and drain water and other
condensed liquids, to prevent clogging of the system. Some facilities also remove corrosive
impurities such as hydrogen sulfide. (Purification systems required for particular uses of the
landfill gas are described in more detail in the following sections.)
Because methane control systems are necessary at many sealed landfills, this technology is
currently widely available. The recovery efficiency will vary with the design and operation of
-------
2- 6
LANDFILLS
the system. Well-designed systems in Europe and the U.S. have achieved almost complete
recovery in some cases, with recovery efficiencies often around 70 to 80 percent (Maxwell,
1990; USEPA, 1993a). The methane content of recovered gases ranges from 40 to 60
percent (Maxwell, 1990; Thorneloe, 1992b).
It is also possible to recover methane from unsealed landfills. In any situation where large
quantities of waste are dumped, it is likely that anaerobic conditions will exist within the
"landfill," and that methane is therefore being generated. While wells sunk into sealed
landfills have better recovery rates, less technologically sophisticated systems have
successfully recovered and utilized gas generated from decomposing waste (USEPA, 1993b,
Volume II; Monteiro, 1992).
Exhibit 2-2
Landfill Gas Recovery Well
VALVE
SPECIAL BACKFILL
HEADER PIPE CONCRETE PLUG
TO PUMP SOLID PLASTIC PIPE
COMPACTED FILL
VARIES
PERFORATED PLASTIC PIPE
CAP
BOTTOM OF TRASH
Source: Mahin, 1988
-------
LANDFILLS 2 - 7
Purification Technologies
Recovered gas is typically a 50:50 mixture of methane and carbon dioxide (a non-combustible
gas), and is therefore a medium quality gas (approximately 500 Btu/cf, 18 MJ/m3) suitable
for numerous energy applications. However, in addition to CH4 and CO2, landfill gas often
contains variable amounts of water, particulates, hydrocarbons, halogen compounds and other
impurities. These impurities may interfere with the operation of recovery and end use
equipment. Therefore, after recovery and collection, the gas must be processed and purified
before it is used or sold. In particular, particulates, water and corrosive compounds must be
removed.
Particulates. Particulates must be removed because they can clog pumps or cause
excess wear as they move through the gas piping system. Also, particulates can
accumulate inside engines and reduce engine life. Filters and water wash scrubbers
are the two primary methods for removing solids. Filters are simpler than water wash
scrubbers, but because they are a physical barrier they cause a larger pressure drop
in the system than scrubbers (GRCDA, 1990).
Water. Large quantities of drainage water can be removed with trap mechanisms at
the well head. However, landfill gas also contains significant amounts of water vapor
which must be reduced before the gas is used in an engine or turbine. Several vapor
removal methods are available, including direct chilling, glycol treatment, and dry
desiccants (Thorneloe, 1992; GRCDA, 1990). Direct chilling of the gas will cause
water vapor (and often heavy hydrocarbons) to condense out as a liquid. Glycol and
dry desiccants (e.g. silica gel and activated alumina) work because they have a greater
affinity for water than the gas; water is removed from the moist gas when a desiccant
and a gas are placed in contact. However, desiccants must either be regenerated or
replaced when they become saturated. For example, glycol is frequently separated
from water by distillation, and some dry desiccants can be regenerated by heating
(evaporation). Chilling can typically remove 80 to 95 percent of the water and
contaminants down to a dew point of 1 °C (34°F). Glycol and dry desiccants can
almost completely remove any water; typical systems can achieve a dew point of as
low as -14°C (6°F) (GRCDA, 1990). These techniques can also be combined,
depending upon the requirements for gas end use.
Corrosive Compounds. Trace gases can react chemically with engine parts, pipeline
components, and desiccants, causing corrosion and therefore increased maintenance
and replacement costs. In particular, sulfur compounds (e.g. H2S) will result in the
formation of sulfuric acid and sulfur oxides. Halogenated hydrocarbons can form acids
(HCI, HF), and possibly dioxins. Sulphur compounds can be removed with impregnated
(activated) carbon filters, or absorption onto iron oxide. Some hydrocarbons are
removed in the chilling process used to remove water; others are removed using
carbon filters, or through the use of selective physical solvents (i.e., no chemical
reaction is involved in the removal of the contaminant) (GRCDA, 1990). The degree
of purification, and thus the cost of the purification system, must be balanced against
the cost of any corrosive damage that may occur; at some point it becomes more cost-
effective to increase the maintenance of end use equipment than to further purify the
gas.
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2 - 8 LANDFILLS
Methane Generation Improvement Techniques
Increasing methane generation can improve the profitability of recovery projects. There are
technologies available that increase the quantity of gas generated and recovered. Although
more research is necessary to identify the factors that influence methane generation and to
understand their effect, the role of several key factors has been examined. For example,
keeping the moisture content high increases decomposition as long as the field capacity (the
point at which water begins to drain through the landfill) is not exceeded (Pacey and DeGier,
1986). Recirculating leachate liquid both maintains water content and acts to control the pH
of the landfill. Shredding waste to create a smaller particle size increases the relative surface
area on which bacterial activity may occur, thereby increasing the rate of decomposition.
Techniques for initiating methanogenic bacterial activity have been developed, including the
application of previously digested solids or sewage sludge to provide bacteria for the landfill
and removal of oxygen from the landfill through nitrogen purges (Pacey and DeGier, 1986;
Kinman et al., 1987).
Utilization Technology Descriptions
There are three types of end use options for the medium quality gas typically recovered from
landfills. First, recovered landfill gas can be used to generate electricity on-site or at a nearby
power plant, using internal combustion engines, gas turbines, or emerging technologies such
as fuel cells. Second, landfill gas can be used directly as a fuel source without conversion to
electricity. Landfill gas can be sold with little or no processing as a medium quality gas for
local industrial, residential or commercial heating and energy needs. Alternatively, landfill gas
can be processed into high quality gas and sold to natural gas supply systems. Third, landfill
gas can be flared where there is insufficient gas to justify an energy project, or as an initial
step before implementing utilization options.
The following utilization options are discussed below:
Electricity Generation and Co-Generation
Natural Gas Supply
Flaring
Electricity Generation and Co-Generation Technologies: There are several available
technologies for generating electricity from landfill gas. Internal combustion engines (ICs)
and gas turbines are the most commonly used prime movers for landfill gas energy
recovery projects, with efficiencies of approximately 25 to 30 percent. Cogeneration, the
additional use of waste heat for local uses, can result in overall efficiencies exceeding 80
percent and improved economics (Williams and Larson, 1 990). Other technologies such
as fuel cells are being explored for use with landfill gas, and may be commercially available
in the near term. Fuel cells achieve conversion efficiencies of around 40 to 60 percent,
and close to 90 percent when combined with heat recovery (Woo, 1990).
The anticipated landfill gas flow rate is particularly important in choosing an appropriate
prime mover to generate electricity. An approximate guideline is that 0.65 m3 of landfill
gas per hour (23 ft3/hour) is required for every kW of generating capacity, although this
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LANDFILLS 2 - 9
figure will vary with operating efficiency, rated capacity, and gas quality.16 Gas
turbines are typically available in sizes from 500 kW to 10 MW, corresponding to 300 to
7000 m3/h. Internal combustion engines are available in smaller sizes, e.g. 30 to 2000
kW. It is more common to expand capacity with multiple units rated at several hundred
kW to several MW than to install a single large turbine or 1C engine (because of the greater
flexibility of modular expansion).
Internal Combustion Engines. Internal combustion engines are stationary engines,
similar to conventional automobile engines, that can use medium quality gas to
generate electricity. While they can range from 30 to 2000 kilowatts (kW), 1C engines
associated with landfills typically have capacities of several hundred kW. 1C engines
are a proven and cost-effective technology. Their flexibility, especially for small
generating capacities, makes them the only option for smaller landfills.
1C engines have proven to be reliable and effective generating devices. However, the
use of landfill gas in 1C engines can cause corrosion due to the impurities in landfill gas
(Thorneloe, 1992). Impurities may include halogenated compounds that can react
chemically under the extreme heat and pressure of an 1C engine. Experience has
shown that adequate gas processing and regular engine maintenance can successfully
overcome this problem (Thorneloe, 1 992; GRCDA, 1990). In addition, 1C engines are
relatively inflexible with regard to the ainfuel ratio, which fluctuates with landfill gas
quality. Some 1C engines also produce significant NOX emissions, although designs
exist to reduce NOX emissions.
Gas Turbines. Gas turbines can use medium quality gas to generate power for sale to
nearby users or electricity supply companies, or for on-site use. Gas turbines typically
require higher gas flows than 1C engines in order to be economically attractive, and
have therefore been used at larger landfills; they are available in sizes from 500 kW to
10 MW, but are most useful for landfills when they are 2 to 4 MW (Anderson, 1991).
Where adequate gas volumes are available, gas turbines have several advantages over
1C engines. Gas turbines have a continuous combustion process and are therefore
much better at coping with fluctuating heat values. Also, gas turbines are constructed
from high-temperature alloys that are much more resistant to corrosion. Gas turbines
also emit less NOX.
Cogeneration/Combined Cycle. Cogeneration and combined cycle systems can greatly
increase efficiencies and improve the attractiveness of gas utilization. In cogeneration,
waste heat from various stages of the gas combustion system is recovered and used
for on-site or other local heating needs. Combined cycle systems use recovered waste
heat from the prime mover to produce steam, which is in turn used to power a steam
turbine and generate electricity. Cogeneration can be carried out in a combined cycle
system (see Exhibit 2-3). Without cogeneration, both turbines and 1C engines have
efficiencies in the region of 30 percent. The remainder of the energy content of the
fuel (i.e., landfill gas) is typically unutilized, and escapes as heat. Cogeneration and
combined cycle systems can raise overall process efficiency to above 80 percent
(Williams and Larson, 1990), and are proven and cost-effective utilization options for
16 A gas flow rate of 0.65 m3/hr assumes medium quality gas (20 MJ/m3) and a system efficiency of 28%.
-------
2-10 LANDFILLS
landfill gas (GAA, 1992). They have been used successfully in a number of countries
around the world (Gendebien, 1992).
Exhibit 2-3
Co-generation with a Gas Turbine
Fuel Cells. Fuel cells are similar to batteries, in that they convert chemical energy into
usable energy such as electricity and heat. Most fuel cells have three subsystems: a
fuel processor, in which gas reacts with steam to produce hydrogen and carbon
monoxide; a power section, which electrochemically consumes the hydrogen from the
gas and the oxygen from the process air system, producing direct current (DC)
electricity; and a power conditioner, which converts the unregulated DC output power
into regulated AC power if DC cannot be utilized directly.
Fuel cells have several advantages as electricity generators. Most fuel cells achieve
fuel-to-electricity conversion efficiencies of 40 to 60 percent, and can approach
efficiencies of 90 percent if waste heat is used in cogeneration schemes (Thorneloe
and Spiegel, 1990). In addition, their small labor requirements and modular design
make fuel cells a promising option for small landfills. However, the use of fuel cells
to date has been limited by their costs, which are estimated at $2500/kW for turn-key
operations; prices should become competitive in the future with technological and
manufacturing advances. Fuel cells have not been demonstrated with landfill gas,
although such a demonstration should be completed over the next several years by the
USEPA's Office of Research and Development (Thorneloe, 1992b). A recent study
concluded that about 750 landfills in the U.S. have sufficient gas potential to utilize
2 MW fuel cells, with a total generating capacity of 6000 MW (EPRI, 1992).
Natural Gas Supply: As an alternative to electricity generation, medium quality landfill gas
can be used directly for other energy applications. In addition, landfill gas can be enriched
by removing the carbon dioxide along with other impurities, and sold as high quality gas.
Depending upon gas prices and purification costs, revenues from sales can make these
projects feasible.
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LANDFILLS 2-11
Medium Quality Gas Use. Landfill gas can be used to supplement existing fuel supplies
for firing boilers, space heating, and a variety of other uses in industrial, commercial
and residential applications. Landfill gas can also be co-fired with other fuels. Medium
quality gas can often be economically transported via pipeline if the user is near the
landfill (i.e., within several miles) (Thorneloe, 1992b). The degree of processing will
depend on the requirements of the end user, with typical applications needing only a
minimum of purification. In some cases, pipeline systems accept medium quality gas.
High Quality Gas Use. To use landfill gas for high quality gas uses it is necessary to
remove most of the carbon dioxide and trace impurities. This is a more difficult and
hence more expensive process than removing other contaminants. Technologies
include pressure swing adsorption with carbon molecular sieves, amine scrubbing, and
membranes (USEPA, 1991).
Flaring: Flaring landfill gas is a strategy that simply and effectively reduces emissions from
landfills. This strategy can reduce safety hazards and environmental problems using low
cost technology. However, flaring landfill gas eliminates the potential to generate revenue,
as the energy value of the methane is wasted. Nevertheless, flaring may be the optimal
control strategy for small landfills or those with minimal emissions.
Flaring is simply the combustion of the recovered landfill gas. The gas will readily form
a combustible mixture with air, and requires only an ignition source to ensure combustion.
Flares are usually designed for gas flows of around 8 to 20 m3 per minute (300-700 cubic
feet per minute), and can handle as much as 100 m3 per minute or more. The flame can
burn openly or can be enclosed.
Open Flame Combustors. Open flame combustors (e.g., candle or pipe flares) are the
simplest flaring technology. They consist of a pipe through which the gas is pumped,
a pilot light to spark the gas, and some means of regulating the gas flow. Possible
complications include unstable flames leading to inefficient combustion, aesthetic
complaints, and the difficulty of testing emissions from open flames. Some open flame
combustors are covered, both hiding the flame from view and allowing relatively
accurate monitoring for low flow rates. However, this does not increase control over
the flame.
Enclosed Combustors. Enclosed combustors successfully overcome all of the problems
associated with open flame combustors. Because the air flow can be adjusted, the
combustion is more reliable and more efficient. As a result, unburned hydrocarbon and
hazardous material emissions are reduced. Furthermore, because the combustor has
an exhaust flue, emissions testing is simpler and more accurate. The flame is
completely hidden from view.
Costs
Costs of using landfill gas are highly dependent on the specific technologies used.
Nevertheless, the costs for all uses include three major components: recovery costs;
purification costs; and costs for the electricity generation or gas supply equipment.
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2-12 LANDFILLS
Recovery Costs: Installation costs for gas recovery systems are typically $5,000 to
$10,000 per acre (Maxwell, 1990; Anderson, personal communication; USEPA, 1991).
These capital costs include surveying, drilling wells, and construction of the surface
collection system. Operating costs of the recovery system will vary greatly with the
complexity and scope of the system. A hypothetical landfill, with capital costs of roughly
$1 million, is estimated to have annual operating costs of $83,000 to $94,000 (USEPA,
1991).
Gas Purification Costs: Purification costs for use in an 1C engine or turbine will largely
depend upon the required pressure of the gas. Costs will be lowest for low-pressure 1C
engines (5 psi), higher for high-pressure engines (45 psi), and greatest for gas turbines,
which require around 160 psi. For typical flow rates of several hundred cubic feet per
minute (e.g., 100-200 kW generating capacity), costs will range from $50,000 to
$300,000 for a system removing liquids and particulates (GRCDA, 1 990). Costs will rise
significantly if other impurities must be removed. As indicated above, these costs must
be balanced against the associated reduction in engine maintenance costs. Gas
enrichment (carbon dioxide removal) processes range from $0.60 to $2.00 per MMcf
(Soot, 1991b).
Electricity Generation Equipment Costs: End use equipment for generating electricity from
recovered landfill gas must include sufficient gas purification systems, a prime mover, a
generator, and auxiliary equipment such as engine controls and gas monitors. Capital
costs for these components vary widely depending on the gas flow, the generating
capacity, the type of prime mover, as well as other factors such as gas quality and system
specific criteria.
Prime mover capital costs are typically a large portion of total costs. 1C engines, exclusive
of other cost components, are estimated to be $350 to $500 per kW (Anderson, personal
communication; Soot, 1991 a). Operation and maintenance costs are estimated at up to
20/kWh. Capital costs for gas turbines, for a 6 MW system, are estimated to be $700/kW
(Sturgill, 1991). Operation and maintenance costs are estimated at 0.60/kWh.
Typical capital and operating costs for "turn-key" gas-to-electricity engine-generator
equipment operated in the U.S. are summarized in Exhibit 2-4. These costs include
necessary gas purification and compression, prime mover, generator equipment, site
preparation and auxiliary equipment. Low-pressure 1C engine-generator packages range
from $1,100 to $1,700 per kW. A high-pressure 1C package, which requires gas
compression, costs $2,000 per kW (Anderson, personal communication).
Gas Supply Costs: The supply of landfill gas typically involves existing end-use facilities.
Therefore, the significant costs for this option are for the construction of a gas distribution
pipeline, gas blower, and gas purification equipment. Landfill gas supply pipelines (and
requisite gas blowers), which might typically be 10 to 1 5 inches in diameter, and operate
at 10 to 15 pounds per square inch of pressure, have construction costs ranging from
$200,000 to $300,000 per mile (Thorneloe, 1992a). These costs depend on several
related factors, including the distance to the user, gas flow, pipeline diameter and material,
blower capacity, and the terrain over which the pipeline is laid. Gas supply for these
applications is likely to be competitive for users within several miles of the facility
(Thorneloe, 1992b).
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LANDFILLS
2 - 13
Exhibit 2-4
Capital and Operations Costs for Gas-to-Electricity Projects
Engine Type
1 1C Engine;
Low Pressure
2 1C Engines;
Low Pressure
2 1C Engines;
High Pressure
1 Turbine
Initial Capital
(xlOOO)
$1,300
$1,700
$3,600
$4,600
Gas
Consumption
(xlOOO scf/day)
450
900
900
2,000
Net kW
Capacity
770
1540
1460
2700
O & M
in C/kWh
2.1
1.5
1.7
1.1
Source: Anderson, personal communication.
Flaring: The cost of flares depends on the design and the required gas flow rate. For a
typical flow rate of 8 to 20 m3 per minute (300-700 cubic feet per minute), costs range
from $15,000 for an open-flame combustor to $90,000 for enclosed combustors
(Anderson, personal communication; USEPA, 1991).
Availability
Most technologies for landfill gas recovery and use are widely available. Emerging
technologies, such as fuel cells, are expected to become available or commercially feasible in
the near future.
Recovery and Purification Equipment: The recovery of landfill gas and subsequent
processing for the supply of medium quality (non-enriched) gas involves technologies that
are well developed and commercially available. These technologies have been successfully
demonstrated in projects worldwide, under a range of conditions (USEPA, 1993b).
Enrichment of landfill gas to high quality gas, however, depends on processes that are
commercially available but currently uneconomic or impractical for use in many landfill gas
applications. Continuing progress and experience is expected to improve the feasibility of
gas enrichment technologies.
Generating and Gas Supply Equipment: The technologies for using landfill gas to generate
electricity are generally well developed, as are other off-site uses such as in industrial
boilers. In addition; gas supply equipment such as pipe, blowers, and meters are readily
available. The use of fuel cells and other emerging technologies requires further
development and demonstration before they become widely available. It is expected,
however, that these technologies will be added to the list of available options by the end
of the decade.
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2-14 LANDFILLS
Flares: Flares are a simple, proven, and commercially available technology. The necessary
equipment can be manufactured in most countries.
Applicability
The applicability of methane recovery and use depends on the quantity of gas that is being
generated by a landfill and the local demand for gas or generated electricity. Applicability is
therefore discussed in terms of recovery, end-uses, and flaring.
Gas Recovery: Gas recovery has been commercially successful primarily in large sanitary
landfills (which are covered with a thin layer of soil or clay), where 1) anaerobic conditions
can be easily maintained and 2) large amounts of methane are generated. However,
anaerobic conditions are also likely to exist in any sufficiently dense or deep landfills, and
methane recovery does not rely upon technologically advanced landfill management.
Recovery systems are available in a wide range of technical complexity. Therefore,
methane can be recovered from landfill sites under a wide range of conditions, if a suitable
utilization such as electricity generation or direct use of medium Btu gas is feasible.
Electricity Generation and Gas Supply: The applicability of specific end-uses depends
primarily on the local demand for and price of electricity or gas. Low energy demand
reduces project feasibility. Where sufficient local demand exists, all or a portion of the
available landfill gas may be utilized; if necessary, the remaining demand for gas or
generated electricity may be met by other sources.
The applicability of supplying high quality gas is somewhat different than for medium
quality gas. Due to the high processing cost, high quality landfill gas is competitive only
where the market price of natural gas supplies is quite high.
Flaring: Recovering and flaring gas is feasible for most landfills, especially where
emissions of methane and VOCs are a local environmental or safety problem. Flares are
relatively simple technologically and require low capital investment. Moreover, flaring can
often be an initial step before implementing other utilization options.
Barriers
The primary barrier to landfill gas recovery and use in developed and developing countries is
often artificially low regional energy prices (Thorneloe, 1992). Conditions governing both
electricity and natural gas prices, such as government energy policies, subsidies, and tax
incentives, can have an important effect on the viability of landfill gas projects. A second
problem, especially for developing countries, is the availability of technical expertise,
equipment, and other resources. In particular, there is a need for monitoring equipment to
assess potential gas flow rates and qualities, in order to determine viable end uses for
recovered gas.
Site-specific barriers include the proximity to local industrial users, with the cost of
transporting the gas becoming prohibitively high as distance increases, and the high cost of
emerging technologies such as enrichment, fuel cells, and some purification technologies.
-------
LANDFILLS 2-15
Flaring does not provide any revenue, and therefore may only be feasible when combined with
other utilization options, or where environmental or safety regulations require that landfill gas
emissions be controlled.
Benefits
In addition to reducing methane emissions into the atmosphere, the recovery and flaring of
landfill gas creates other benefits:
Landfill safety will be improved. Methane poses a serious explosive hazard, especially
if it migrates beyond the landfill boundaries. Recovering the methane from a sealed
landfill can significantly reduce this danger.
Reduced emissions of hazardous materials. Landfill gas contains significant quantities
of VOCs, in addition to methane. Both methane and VOCs are implicated in urban air
pollution, and many VOCs are also toxic. Recovery of landfill gas can reduce these
emissions.
Reduced odor problems. Landfills frequently emit gases that cause odor problems.
Recovery systems reduce these emissions.
Methane Recovery and Utilization
methane recovery of 60-90%
clean energy source
improved safety
improved air quality
reduced odor problems
2.3 Aerobic Landfill Management17
The Japanese have demonstrated that it is possible to suppress the generation of methane
by creating aerobic or semi-aerobic landfill conditions. Aerobic landfills enhance the
biodegradation of waste in the landfill site, limit the generation of harmful and odorous gases
such as methane and hydrogen sulfide, and prevent groundwater pollution by improving the
quality of leachate from the landfill site. In addition, aerobic landfill sites can be reclaimed for
a variety of land uses more quickly than conventional landfills.
17 This section is based on information supplied in Japan Environment Agency, 1991.
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2 - 16
LANDFILLS
Technology Description
Aerobic options are classified into semi-aerobic, recirculatory semi-aerobic, and fully aerobic
landfill designs. These designs are characterized by reduced methane generation and
increased decomposition rates. Studies have shown that total methane emissions from each
of the aerobic landfill designs over a ten year period are lower than for anaerobic systems.
The semi-aerobic landfill system is commercially available; the re-circulatory system and fully
aerobic system are still in the research and development stage.
Semi-Aerobic Landfill: In this system, air is supplied to the landfill through the leachate
collection pipes and is diffused through the landfill layers to maintain semi-aerobic
conditions. As shown in Exhibit 2-5, the leachate collection pipes are installed at the
bottom of the landfill site to collect leachate and transport it to the leachate collection pit.
The leachate can be drained by pump or natural flow. The water level in the pipes is
monitored to ensure that the pipes are not blocked and that air is able to flow through the
pipes into the landfill. The pipes have a larger diameter than conventional leachate pipes
to ensure an adequate supply of air. The amount of methane generated by a semi-aerobic
system has been shown to be roughly 50 percent less than that generated by an anaerobic
landfill.
Exhibit 2-5
Semi-Aerobic Landfill
Runoff Collection Duct
Cover Soil
Solid Wast
Gate
\
Pump Pit
Impermeable Layer
Leachate Collection Pipes
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LANDFILLS
2 - 17
Re-Circulatory Semi-Aerobic Landfill: The re-circulatory semi-aerobic landfill system is an
improved version of the semi-aerobic system. The rate of decomposition and purification
of leachate are faster in this system than in the semi-aerobic. As shown in Exhibit 2-6,
a recirculatory semi-aerobic landfill consists of a leachate recirculation system and the
leachate collection system of the semi-aerobic process. The collected leachate is returned
to the landfill site and recirculated to encourage bacterial growth through increased oxygen
and nutrient supply. This process enhances decomposition of solid waste in the landfill
layers, improves leachate quality, stabilizes the landf illed wastes, and reduces the methane
generation. Based on demonstration projects, the methane generated by a re-circulatory
semi-aerobic system can be as much as 80 percent less than that generated by an
anaerobic landfill.
Exhibit 2-6
Recirculatory Semi-Aerobic Landfill
Cover Soil
Solid Waste
Leachate
Facility
Landfill Site
- Leachate
Aerobic Landfill: The aerobic landfill system uses an air blower (see Exhibit 2-7) to force
air into the landfill layers. The air passes through pipes which lie slightly above the
leachate collection pipes at the bottom of the landfill site. The system is operated and
controlled so that the conditions maintained in the landfill site are more aerobic than those
of a semi-aerobic system. According to demonstration project evaluations, the methane
generated by an aerobic system can be nearly 90 percent less than that generated by an
anaerobic landfill.
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LANDFILLS
Exhibit 2-7
Aerobic Landfill
Runoff Collection Duct
Cover Soil
Solid Waste
Air Supply Pipe
Air Supply Pipes
Leachate Collection Pipes
Costs
Costs for aerobic landfill management vary substantially according to the composition of the
wastes, the size of the landfill site, the amount of precipitation, and the social conditions of
the country concerned. The following costs are typical for landfill sites operated in Japan,
where semi-aerobic landfill techniques are widely used.
Installation costs for semi-aerobic landfill systems are approximately $0.60/ton of landfilled
waste. Estimated installations costs for an air blowing system for an aerobic landfill system
are approximately $0.50/ton of landfill waste and operating costs are approximately
$0.40/ton, assuming that the air blower is operational for 15 years. In regions with light
rainfall, maintenance and operating costs can be significantly controlled by adopting the semi-
aerobic landfill system with natural leachate drainage and natural aeration.
Availability
The semi-aerobic landfill technology is developed and proven. It is commercially available and
in use in Japan and East Asia. The re-circulatory semi-aerobic and fully aerobic landfill
systems are in the research and development stage and should be commercially available
around 1995.
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LANDFILLS 2-19
Applicability
The use of aerobic and semi-aerobic landfill technology may be most appropriate for small-
capacity landfill sites in which methane recovery is not economically feasible. Aerobic landfill
management is best conducted at landfills designed for this strategy because aerobic systems
require air-feed pipes, or, at a minimum, leachate collection pipes, at the bottom of the landfill
site. It can be extremely difficult to retrofit existing landfills with these pipes. Semi-aerobic
conditions can be achieved in some sites in which leachate collection pipes have already been
installed, especially if these pipes are larger than required for leachate collection, or if
additional measures are instituted to ensure adequate leachate water level control.
Barriers
Barriers to the implementation of these methane reduction strategies can be both economic
and technical. In the semi-aerobic landfill system, it is necessary to have an equally dense
arrangement of vertical air ventilation pipes as leachate collection pipes. Moreover, in cases
where the landfill is very deep, maintaining a large aerobic zone will require additional
ventilation pipes. Monitoring the operation of these sites is an important component of the
overall system since there is always the potential for methane concentrations to fall into the
explosive range.
Economic factors will be a major consideration at large landfill sites, which likely require air
blowers to ensure aerobic conditions. As the landfill size increases, so will the costs of the
air blower equipment and general operating and maintenance costs, including electric power
costs. Also, in such large-scale landfill sites, it is difficult to achieve a uniform air supply at
the bottom of the landfill, requiring development of an improved air-supply system.
Benefits
After making allowances for the cost aspects, the aerobic landfill systems can be classified
in the following order according to relative advantages they offer: the semi-aerobic as most
advantageous, followed by the re-circulatory landfill system, and then the aerobic system.
Aerobic and semi-aerobic landfill systems offer the following advantages as compared with
the anaerobic landfill systems which are currently in general use:
Ability to reduce the pollution load of the leachate;
Reduced formation and generation of hazardous gases such as hydrogen sulfide;
Earlier stabilization of the landfill site;
Prevention of groundwater pollution; and,
Lower cost of leachate control than in anaerobic sites.
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2 - 20 LANDFILLS
Aerobic Landfill Management
proven methane reductions of 50%
improved pollution control
earlier stabilization
technology currently available
(semi-aerobic)
2.4 Reduced Landfiliing of Waste
Changes in human lifestyle resulting in rising per capita waste generation, and continued
population growth, steadily increase the total amount of waste that is generated worldwide
each year. The proper disposal of this solid waste is an important environmental and human
health issue in both developed and developing countries. The majority of solid waste is
disposed of in landfills (Carra and Cossu, 1990) where the organic component (e.g., paper
products, food waste, and yard waste) decomposes over time and produces methane if
decomposition occurs anaerobically.
Because only the organic component of solid waste decomposes to produce methane, the
amount of methane generated from landfills can be reduced by decreasing the amount of
organic material placed in landfills. This can be achieved by: 1) source reduction and
recycling; 2) composting; 3) incinerating the waste (with potential energy recovery); or 4)
using the waste in other energy production technologies (e.g., anaerobic digestion;
fermentation; pyrolysis). These strategies can often be implemented as part of a larger solid
waste management system.
Design and implementation of a solid waste management system requires that many regional
factors be taken into account. These factors include: characteristics of the waste, such as
volume, composition (e.g., organic component), and moisture content; status of current
collection equipment and management systems including landfill management; and the state
of markets for non-conventional energy sources, recycled materials, and other potential
products such as compost (organically enriched soil amendments). Trends in these factors
must be anticipated so that regionally appropriate and adaptable systems are instituted.
Reducing the amount of waste that is placed in landfills yields significant benefits. In
developed countries, short term savings can be realized from the avoided cost of tipping fees
(i.e., landfill charges), and in the longer term, the demand for new landfill capacity is
decreased or delayed.- In developing countries the costs of managing landfills and other
sectors of the waste management system, which are typically borne by municipalities, can
also be reduced. In general, reduced landfilling of waste decreases the magnitude of
environmental risk associated with landfills, such as surface- and groundwater pollution and
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LANDFILLS 2-21
air emissions. In addition, many of the strategies presented here produce valuable products
such as energy and compost.
Reduction Technology Descriptions
The major strategies for reducing the landfilling of wastes and thereby avoiding methane
emissions are described below.
Source Reduction and Recycling: The source reduction and recycling of organic material
reduces methane emissions. The most promising materials for this strategy are paper
products. While other organic materials (e.g., food waste) can be composted, they do not
readily lend themselves to recycling or reduced generation. Paper products comprise a
significant proportion of solid waste in developed countries (e.g., 40 percent in the U.S.)
and a growing proportion of solid waste in some urban centers in developing countries
(typically 5 to 20 percent) (Mahin, 1988; Vogler, 1984). Paper products can be easily
recycled by paper mills into a variety of products, depending on the quality of the
recovered material. Markets are, in most cases, identical to those for virgin paper
products.
Recycling can be accomplished through technologies and practices of greatly varying
technical complexity. In developing countries, where labor costs are low and equipment
costs are relatively high, recycling often occurs informally, uses relatively unsophisticated
machinery, and involves intensive manual labor (e.g., for baling and sorting). In contrast,
developed countries typically use more complex labor saving machinery requiring higher
operator skill levels for collection, sorting, and processing. The differing levels of
complexity do not have a large effect on the overall capacity or effectiveness of these
operations (Vogler, 1984). In all cases, the quality of the recovered material is the most
important factor, and is controlled to the degree necessary by paper mills accepting
recovered paper.
Composting: Composting is the controlled biological decomposition of organic material,
usually under aerobic conditions, the end products of which are stabilized organic material
and carbon dioxide. If aerobic conditions are maintained then no methane will be formed.
The stabilized (oxidized) organic material is suitable for use as a soil amendment that can
improve soil's physical, chemical, and biological properties (Kashmanian, 1991; Biocycle,
1991). Composting can be easily integrated with other waste reduction practices such
as recycling non-organics and incineration in a comprehensive waste management system.
Composting operations vary considerably according to available space, technology, capital,
capacity, and material to be accepted (Biocycle, 1991). Composting can be carried out
either "in-vessel" (i.e., confined within a specially designed container), or more simply in
elongated piles referred to as windrows, which are laid out in large open spaces. Windrow
composting is sometimes carried out in covered barn-like structures to protect the
windrows from the wind and rain. In-vessel composting allows close management of
important variables, especially aeration, but is usually more complex to build and operate.
Windrow composting uses bulldozers, front-end loaders, or specially designed mechanical
turners to aerate the material. Both processes may also use forced aeration, alone or in
combination with turning.
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2 - 22 LANDFILLS
The composting process is affected by a number of physical, chemical, and other
environmental factors which may, with varying degrees of effort, be monitored and
managed to control the composting process (Biocycle, 1991). Of primary importance are
characteristics of the organic material (e.g., particle size and chemical structure of the
organic compounds) which control the availability of nutrients to the microorganisms that
decompose the waste. For example, cellulose, hemicellulose, and lignin contained in wood
and paper (high carbon content) are less digestible than meat and vegetable waste (high
nitrogen content). The nutrient balance of the organic material is typically measured by
1) the ratio of carbon to nitrogen, as organisms require nitrogen to process available
carbon, and 2) the availability of certain necessary macro- and micro-minerals (e.g.,
potassium, phosphorus). To control these factors, facilities carefully select and often pre-
process waste before it is accepted. Other factors that are monitored and controlled
include process temperature, pH, aeration, and moisture.
In order to produce a clean and valuable compost, there are a number of important
operational considerations in addition to the factors listed above. For example, it is
necessary to provide a clean substrate for the composting process; this is particularly true
when composting municipal solid waste (MSW) because of the wide variety of non-organic
components (e.g., glass, metals, and large objects such as appliances). Extensive
separation equipment is required when handling mixed wastes, and the separation process
can be designed to recover recyclables and/or produce a "refuse-derived-fuel" for use in
an incinerator (see below). If a pre-separated waste such as yard waste is composted,
then significantly less equipment is needed to sort the waste. Many operations also shred
the incoming waste to enhance the composting process, and screen the final product to
remove any remaining non-organics (Biocycle, 1991).
Markets for compost include landscapers, nurseries, agriculture, land reclamation, and
landfill cover (Kashmanian, 1991). Different markets have different specifications for
compost properties such as acidity, particle size, and moisture content. The product must
consistently meet these criteria to sell successfully. Potential markets should be identified
early in the planning stage to ensure that the composting process can accommodate these
requirements.
Incineration: Incineration of waste will also reduce methane emissions from waste
management. Other benefits of incinerating waste are volume reduction (where land
availability is an important consideration) and potential energy recovery. The extent of
volume reduction will depend on the initial compactness and combustibility of the waste,
but as a rule of thumb incineration reduces the waste to 10 percent of its original volume
(Mahin, 1988). The remaining ash must still be landfilled.
Incineration has been used for many years, and a large number of incineration plants (or
municipal waste combustors) are currently operating successfully in developed countries.
In the U.S., 14 percent of all solid waste was incinerated in 1988 (Kaldjian, 1990); Japan
incinerates almost 70 percent of its solid waste because limited land availability increases
the attractiveness of reducing the volume of landfilled waste (Carra and Cossu, 1990).
Reduced land availability and the potential for energy recovery are increasing interest in
this technology in many countries, although stack emissions and ash disposal are still an
issue.
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LANDFILLS 2 - 23
Solid waste can be incinerated in either a "mass-burn" or "RDF" process. Mass-burn
technology burns unsorted or minimally sorted waste in specially designed boilers.
Alternatively, waste can be sorted and shredded before incineration to produce a "refuse-
derived fuel," or RDF. A wide variety of processes have been developed to prepare RDF,
and significant research efforts are improving the quality and reducing the cost of RDF
(Goodman and Walter, 1991). RDF is a higher quality fuel than unsorted waste because
it contains less inert matter, has a smaller particle size, and can fire or co-fire a
conventional (or slightly modified) boiler. For example, RDF may have an energy value of
6,000 to 7,500 Btu/lb (3,300 to 4,200 kJ/kg), as compared to an average value of 4,500
Btu/lb for unsorted waste in developed countries. Additionally, sorting removes metals
and glass that may be recycled and sold to generate revenue. Both mass-burn and RDF
technologies have been implemented in many countries.
Most plants that recover energy use the hot gases from waste combustion to produce
steam, which in turn is used to power a steam turbine (which generates electricity) or to
directly supply local heating needs. Capacities typically range from 500 to 3,000 tons of
waste per day, with a generating capacity of 10 to 80 MW (Mahin, 1988).
A number of factors have made incineration less technically feasible in developing regions.
First, waste in these regions tends to have a lower heat value (e.g., 1,500-3,000 Btu/lb;
3,500-7,000 kJ/kg) than the drier and more combustible waste in developed countries
(e.g.,4,500 Btu/lb; 10,500 kJ/kg). Second, the moisture content of wastes in developing
countries is typically in excess of 40 percent, greatly increasing the capital cost of
combustion systems and, in some cases, making combustion impossible (Mahin, 1988).
In many cases, mass-burn and RDF technologies designed for use in developed countries
have encountered difficulty when used without modification in developing countries.
Some incineration projects in developing countries have attempted to overcome these
problems by co-firing wastes with fossil fuels or other biomass fuels, using rotary kiln
combustors with pre-heated combustion air to dry moist waste, and in some cases using
separation and RDF equipment to improve fuel quality (Mahin, 1988).
Alternative Processes: Several emerging technologies are being developed which may
reduce methane emissions from waste management. The primary alternative waste
management technologies are 1) controlled anaerobic digestion (i.e., biogasification) to
produce methane; 2) hydrolysis and fermentation to produce ethanol; and 3) pyrolysis (i.e.,
thermal conversion) to produce oil or gas. These are described below.
Anaerobic Digestion. Organic waste maintained in a controlled anaerobic environment
will undergo the same process of decomposition that occurs naturally in a sealed
landfill. Carrying out the biochemical reactions in a digester vessel allows greater
control over the process, reducing reaction times, improving efficiency, and facilitating
gas collection. Solid waste digesters have been used in Europe, where several facilities
have operated successfully for years (Platt et al., 1988). As with composting, only
organic material can be digested, requiring separation equipment to remove non-
organics from mixed wastestreams.
Ethanol Production. Converting solid waste to ethanol involves the following steps:
separation of the organic material (if necessary); hydrolysis to form sugars;
fermentation of sugars to ethanol; and distillation to purify the ethanol. Ethanol is a
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2 - 24 LANDFILLS
high octane liquid fuel that can be used independently or as a gasoline additive, and
can also be sold as a chemical feedstock. Emerging technologies are making this type
of conversion of solid waste increasingly feasible and economically attractive (Logsdon,
1991).
Pyrolvsis. Pyrolysis is the thermal degradation of organic material (usually in the
absence of oxygen), changing its chemical structure to produce combustible gases or
a petroleum-like product called biocrude. Biocrude can be distilled to yield gasoline and
similar energy products, which can be used in existing equipment without modification.
Thermal yields from this process have exceeded 70 percent for some materials
(Goodman, 1991). Further research is needed to apply this technology to solid waste.
The ability of these technologies to reduce methane emissions depends directly on the
quantity of organic material that is available (i.e., diverted from landfills) and the proportion
of this organic matter that would likely have decomposed anaerobically and produced
methane. Emission reductions associated with specific projects are highly variable but, in
theory, organic material can be completely removed, thereby achieving reductions of up to
100 percent. The practical limitations discussed in more detail below constrain the actual
reductions in methane emissions that are achieved in practice.
The capital and operating costs for projects that reduce the landfilling of waste are highly
dependent on local factors. The costs are also dependent on the size of the facility, the
planning of which must consider a range of important factors such as the limits (and imposed
costs) of local infrastructure (e.g., transportation services, roads, technical skills) and markets.
Composting: Capital costs for solid waste composting facilities are highly variable,
depending on many factors such as the level of technological complexity, characteristics
of the waste source, local conditions, and the desired quality of the product. Capital costs
per unit of capacity vary by an order of magnitude. For example, a survey of large U.S.
facilities found a range from $1.5 million for a 300 ton/day plant, to $45 million for a more
complex 550 ton/day plant that also co-composts sewage sludge. Operating costs range
from $9 to $85 per ton, but are generally around $20 to $40 per ton (Biocycle, 1991).
These operating costs are competitive with average landfill tipping fees of $ 10 to $65 per
ton (NSWMA, 1990).
Yard waste composting facilities, which are typically smaller, less complex, and do not
require as sophisticated sorting equipment as MSW composting facilities, have lower
capital costs. In the U.S., these costs range from $80,000 to $2 million for plants
handling from 2,000 to 60,000 tons per year of waste, and operating costs of roughly
$18 to $20/ton ($3-4/cubic yard) (Biocycle, 1991).
Incineration: Capital costs for boilers and steam generators range from $60 to $300
million for 10 to 80 MW facilities (Mahin, 1 988), or approximately $ 1 25,000 per ton/day
capacity for mass-burn or RDF plants (Nollet, 1 989). RDF typically costs $2.50 to $2.90
per MMBtu (Goodman and Walter, 1991)
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LANDFILLS 2 - 25
Alternative Technologies: Biogasification has shown promise as a cost-effective option.
Although the production of ethanol from MSW has not achieved commercial application,
this technology is projected to be profitable in some applications in the near term
(Logsdon, 1991). Pyrolysis demonstration projects have not yet produced fuels at
competitive prices, and require further development and demonstration (Goodman and
Walter, 1991).
Availability
Recycling, composting, and incineration are technologies that have been successfully
implemented under a variety of operating conditions, and are commercially available
technologies. Continuing technological development and increasing operating experience will
improve the availability of these practices. Of the alternative technologies described here,
only biogasification has proven technically feasible in full-scale application; other technologies
have proven feasible in small-scale demonstration projects. Further developments are
expected to increase the availability, feasibility, and economic attractiveness of these
alternative technologies.
Applicability
The applicability of these technologies and practices varies for the different regions of the
world. The majority of these technologies has been developed for application in developed
countries. Due to differences in waste composition (and other physical factors); limitations
in financial, technical, and infrastructure resources; regulatory incentives; and cultural
practices, the applicability of waste management technologies and practices presented here
must be carefully considered in the context of developing nations. In general, waste
management alternatives that are less technically complex, more labor intensive, and rely
primarily on indigenous resources will be more successful in developing nations. Rapidly
increasing energy demand in these countries can also spur waste management technologies
that produce energy.
Many of the technologies discussed in this section are receiving renewed application and
research as the issue of solid waste management is addressed in both developed and
developing countries. The management of solid waste is a rapidly growing industry often
driven by government legislation and regulation. The approaches discussed here can
successfully accommodate highly variable site-specific criteria and regional needs to provide
a comprehensive waste management system. Planners in Europe and North America are
increasingly relying on a regionally or locally tailored mix of options to handle municipal solid
waste (Kaldjian, 1990; Platt, 1988).
Barriers
None of these technologies and practices is a panacea for the problem of waste management;
each option has drawbacks when applied in certain situations. However, these drawbacks
are sometimes cited as barriers to implementation without proper comparison to the problems
of existing or alternative waste management practices. With proper planning and
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2 - 26 LANDFILLS
management, cost-effective and environmentally beneficial solutions can be developed. With
this caveat in mind, the following are the most commonly identified problems with each
technology:
Recycling: Recycled paper products must be priced competitively with virgin products to
be successful. Competitiveness largely depends on the regional cost of virgin wood pulp;
countries with large, often subsidized supplies of wood pulp have a disincentive for
recycling. As with many products derived from solid waste, recycled paper products may
also be perceived as being of inferior quality.
Composting: Poorly managed composting operations may be partly anaerobic, creating
odor and plant pathogen problems; however, these problems are much less common as
operating experience develops (Biocycle, 1991). Other anticipated problems include
gaining and maintaining product acceptance; identifying and penetrating new markets; and
in some cases, contamination with pesticides and heavy metals.
Incineration: The main limitation to this technology has been concern over air emissions,
which has made it difficult to site incinerators near the urban centers where waste is
generated. The ash that remains after combustion may contain significant quantities of
heavy metals, potentially causing problems if disposed of in a poorly designed landfill.
Also, in developing countries, the low energy and high moisture of most waste makes
combustion infeasible without modified technology.
Alternative Technologies: These technologies are in various stages of development and
acceptance. In all cases, further research and demonstration will increase efficiencies and
acceptance, and decrease costs.
Benefits
In addition to reducing the potential for methane emissions from landfilled organic material,
the processes described above have the following benefits:
Source Reduction/Recycling: Reducing the amount of waste that must be handled by
other methods, such as landfilling or incineration, can remove the strain on waste
management systems and effectively increase system capacity. Moreover, recycling
provides a valuable product that can generate revenue.
Composting: The use of compost as a soil amendment can improve soil porosity and
water retention, erosion resistance, and tilth. By encouraging plant growth (and
uptake of nitrogen), nutrient runoff is reduced. Furthermore, some compost has been
shown to suppress plant disease (Kashmanian, 1991).
Incineration: Incineration can greatly reduce the volume of landfilled waste, thereby
alleviating the pressure for new landfill construction while providing a valuable source
of energy.
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LANDFILLS 2 - 27
All of the technologies that reduce landfilled waste will reduce the potential
environmental and health risks associated with landfills, such as air quality problems
and surface- and groundwater contamination.
Reduced Landfilling of Waste
methane reductions dependent on
quantity of reduced organics up to
100%
reduced need for landfill capacity
flexible, appropriate practices
technologies currently available
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2 - 28 LANDFILLS
2.5 References
Contributions were made by:
Masataka Hanashima, Faculty of Engineering, Fukuoka University, Japan
Yasushi Matsufuji, Faculty of Engineering, Fukuoka University, Japan
Kurt Roos, USEPA, USA
W. T. Morris, Department of Energy, Energy Technology Division, United Kingdom
Additional information may be found in the following:
Anderson, C. (1991), Waste Management of North America, personal communication,
October 8, 1991.
Biocycle (1991), The Art and Science of Composting. JG Press, Emmaus, Pennsylvania.
Carra, Joseph S. and Raffaello Cossu, eds. (1990), International Perspectives on Municipal
Solid Wastes and Sanitary Landfillinq. International Solid Wastes and Public Cleansing
Association, Academic Press, London, England.
Cointreau, Sandra J. (1982), Environmental Management of Urban Solid Wastes in Developing
Countries. World Bank, Washington, D.C.
EPRI (Electric Power Research Institute) (1992), Summary of Landfill Gas Potential: 2 MW
Molten Carbonate Fuel Cells, prepared by Resources Management International, Inc.,
September 1992. EPRI TR-1 01-068-Project 1677-21 (Interim Report).
Gendebien, A., M. Pauwels, M. Constant, M.J. Ledrut-Damanet, E.J. Nyns, H.C. Willumsen,
J. Butson, R. Fabry, and G.L. Ferrero (1992), Landfill Gas: From Environment to Energy
(1 992) - Final Report, Commission of the European Communities.
Goodman, Barbara J. and Donald K. Walter (1991), "Opportunities for Energy from Municipal
Waste Technology," in Energy Sources, volume 1 3, pp.1 79-1 88.
Governmental Advisory Associates, Inc. (GAX\) (1992), 1991-2 Methane Recovery from
Landfill Yearbook, prepared by Eileen Berenyi and Robert Gould, GAA, NY.
Governmental Refuse Collection and Disposal Association (1990), Proceedings of the 13th
Annual International Landfill Gas Symposium, Silver Spring, Maryland, GLFG-0018.
Japan Environment Agency (JEA) (1991), personal communication, provided by Hanashima
and Matsufuji, Fukuoka University, Japan.
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LANDFILLS 2 - 29
Kaldjian, Paul (1990), Characterization of Municipal Solid Waste in the United States: 1990
Update. U.S. Environmental Protection Agency, Washington, D.C., EPA/530-SW-90-042.
Kashmanian, R. M. (1991, draft), Markets for Compost. Office of Policy, Planning, and
Evaluation, U.S. Environmental Protection Agency, Washington, D.C.
Logsdon, Gene (1991), "Producing Ethanol from Solid Waste," in Biocvcle, July. 1991, pp.71-
72.
Mahin, D.B. (1988), Prospects in Developing Countries for Energy from Urban Solid Wastes.
Office of Energy, U.S. Agency for International Development.
Maxwell, Greg (1990), "Will Gas-to-Energy Work at Your Landfill ?," in Solid Waste and
Power, June 1990.
Monteiro, Penido (1992), coordinator of landfill gas projects in Rio De Janeiro and Manaus,
personal communication.
National Solid Wastes Management Association (NSWMA) (1990), 1990 Landfill Tipping Fee
Survey, prepared by S. Sheets and E. Repa, NSWMA, Washington, D.C.
Nollet, Anthony (1989), "Designing Shredding Plants That Don't Go Up in Smoke," in World
Wastes, June 1989.
Pacey, J.G. and J.P. DeGier (1986), "The Factors Influencing Landfill Gas Production,"
presented at Energy from Landfill Gas, sponsored by UK DOE/US DOE, 28-31 October, 1 986.
Platt, B. A., Neil Seldman, Bernd Franke, and Bernd Mayer (1988), Garbage in Europe:
Technologies. Economics, and Trends, Institute for Local Self-Reliance, Washington, D.C.
Richards, K.M. (1 989), "Landfill Gas: Working with Gaia," in Biodeterioration Abstracts. Vol.
3, No. 4, December 1989.
Soot, P.M. (1991 a), "Power Generation Using Small Internal Combustion Engines," prepared
for the Global Change Division, USEPA, 1991.
Soot, P.M. (1991b), "Enrichment of Dilute Methane through Adsorption," prepared for the
Global Change Division, USEPA, 1991.
Sturgill, C. (1991), "Power Generation: On-Site Use and Sale to Utilities," prepared for ICF
Inc., April 1991.
Taylor, Alison C. and Richard M. Kashmanian (1988), Yard Waste Composting: A Study of
Eight Programs, U.S. Environmental Protection Agency, Washington, D.C., EPA/530-SW-89-
038.
Thorneloe, S.A., and R. Spiegel (1990) (draft), Global Climate Mitigation: Use of Fuel Cell
Power Modules to Recover Energy from Landfill Gas, AEERL/ORD, USEPA, May 1990.
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Thorneloe, S.A., D. Augenstein, J. Pacey (1992a), Landfill Gas and Energy Utilization:
Technology Options and Case Studies, prepared by EMCON Associates for AEERL/ORD,
USEPA, Research Triangle Park, NC. EPA-600/R-92-11 6, June 1992.
Thornleloe, S.A., (1992b), "Landfill Gas Recovery/Utilization: Options and Economics,"
presented at the 16 Annual Conference by the Institute of Gas Technology on Energy from
Biomass and Wastes, Orlando, Florida, March 5 ,1992.
USEPA (United States Environmental Protection Agency) (1 991), Air Emissions from Municipal
Solid Waste Landfills - Background Information for Proposed Standards and Guidelines.
OAQPS, March 1991, EPA-450/3-90-011a.
USEPA (1993a), Anthropogenic Methane Emissions in the United States. Report to Congress,
USEPA/OAR (Office of Air and Radiation), Washington, DC.
USEPA (1993b), Options for Reducing Methane Emission Internationally - Volume II:
International Opportunities for Reducing Methane Emissions, Reportto Congress, USEPA/OAR,
Washington, DC.
Valenti, Michael (1992), "Tapping Landfills for Energy," in Mechanical Engineering, January
1992.
Vogler, Jon A. (1984), "Waste Recycling in Developed Countries," in Holmes, John R, ed.,
Managing Solid Wastes in Developing Countries. John Wiley and Sons, Chichester, England.
Williams, R.H. and E.D. Larson (1990), "Power Generation with Natural Gas Fired Turbines,"
in Natural Gas: Its Role and Potential in Economic Development, eds. W Vergara, N.E. Hay,
and C.W. Hall, Westview Press, 1990.
Woo, M.Y.C. (1990), "PAFC Fuel Cell - A Unique Solution to Clean Air," presented at the
California Clean Air and New Technologies Conference, October 15-17, 1990.
-------
CHAPTER THREE
OIL AND NATURAL GAS
3.1 Background
Methane Emissions
Methane is the primary constituent of natural gas, and significant quantities of methane can
be emitted throughout a country's natural gas system. This system generally includes gas
and oil wells, processing and storage facilities, and transmission and distribution systems
(presented schematically with additional explanation in Exhibit 3-1). Emissions primarily result
from the normal operations of many natural gas system components, such as venting and
flaring at oil and gas wells, compressor station operations, gas processing facilities, gas-
operated control devices, and unintentional leaks (fugitive emissions). Methane emissions also
occur during routine maintenance, with additional emissions from unplanned system upsets.
These sources are described in more detail below.
Many oil production facilities also produce associated gas which is often flared or
sometimes vented. In addition, an undetermined quantity of natural gas is released
during the drilling of oil and gas wells before wellhead gathering equipment is installed,
and before the well is plugged and suspended or abandoned.
Gas processing plants typically vent methane while reclaiming the dehydrator
chemicals, often glycol. These gas plants contain a high density of control devices
(valves, etc.), which also contribute to emissions through normal operation.
Reciprocating engine and turbine compressors are used throughout gas systems to
pressurize the gas, and to generate electricity and provide motive power for various
facilities. These engines typically use pipeline gas for fuel. Methane emissions result
from incomplete combustion and from venting during engine stops and starts.
Pneumatic or gas-operated devices use the pressure of pipeline or process gas to
power their operating mechanisms. Emissions occur when the gas used to run the
devices is vented to the atmosphere. These devices include pressure regulators, valve
positioners, and actuators.
Fugitive emissions are leaks in pipelines or other components. They typically occur at
connections between components and in valves where seals or gaskets fail, through
the corrosion of pipelines, and from end-use equipment such as residential gas
appliances and industrial furnaces, and power generators.
Methane emissions also occur during routine maintenance, when gas from facilities or
equipment is purged to the atmosphere. These activities include the venting (blowdown) of
equipment and pipeline sections for periodic testing and repair, and the launching and
receiving of scrapers and pigs. Also, releases occur during well workovers - the routine
maintenance of production wells.
-------
3 - 2
OIL AND NATURAL GAS
Exhibit 3-1
Natural Gas Systems
Production
Injection/Withdrawal
Storage
Residential Commercial Industrial
Electric
Utility
-------
OIL AND NATURAL GAS 3 - 3
Exhibit 3-1 (cont.)
Natural Gas Systems
Natural gas production is generally categorized as "associated" or "non-
associated" production, where associated gas is produced in association with oil,
and non-associated gas is produced from dedicated gas fields. Both associated
and non-associated production facilities withdraw the gas from underground
formations and collect it at a central location for processing before injection into
the transmission system. Significant volumes of natural gas are often produced
with the oil taken from petroleum reservoirs, and oil production facilities that do
not utilize natural gas must either vent, flare, or re-inject the gas.
Natural gas processing plants ensure that the characteristics of the gas are
suitable for the transmission system and the intended end-use. This involves
removing heavier hydrocarbons (referred to as condensate), moisture, and
impurities such as sulfur compounds, particulates, and carbon dioxide.
Storage systems are used to meet seasonal fluctuations in demand without
similar fluctuations in production. During periods of low demand, the excess
production is injected into depleted oil and gas fields, salt domes, and other
suitable formations. When demand rises, the stored gas is withdrawn,
processed, and injected into the transmission system.
The transmission system is a network of high pressure pipelines used to
transport the gas from the production, processing, and storage facilities to the
distribution networks. In addition to the pipelines, transmission systems include
metering stations, maintenance facilities (e.g., pig-launching), and compressor
stations. Compressors are used to maintain pressure throughout the natural gas
system, and are located at regular intervals along the pipeline. Compressors are
usually driven by reciprocating or gas turbine engines which use the pipeline gas
as fuel.
The distribution system is an extensive network of pipelines supplying natural
gas to end users. The pipelines are generally of smaller diameter and lower
operating pressures than transmission pipelines. Gas enters the distribution
system at gate stations, or "city gates," where the gas pressure is first reduced.
The gas pressure must be reduced from approximately 1000 pounds per square
inch (75 Bar) in the transmission pipeline to about 0.5 psi (30 mBar) for
residential applications. Commercial, industrial, and public utility requirements
for gas pressure vary by application, and are typically around 10-200 psi (1-15
Bar). This pressure reduction usually occurs in steps through different sections
of the distribution network.
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3-4 OIL AND NATURAL GAS
Unplanned events such as pressure surges and line breakages contribute to the release of
natural gas. Pressure relief systems often vent gas directly to the atmosphere, rather than
flaring or returning relieved gas to the pipeline. Line breakages are usually caused by external
forces such as construction or land subsidence, but also as a result of corrosion.
Methane Emission Reduction Strategies
Emissions from normal operations account for the majority of releases worldwide, although
the emissions from each system will depend on the specifics of that system. The technical
nature of emissions from natural gas systems is well understood, and emissions are largely
amenable to technological solutions, through enhanced inspection and preventative
maintenance, replacement with newer designs, improved rehabilitation and repair, and other
changes in routine operations and maintenance.
The economic cost (i.e., lost revenues) of venting methane to the atmosphere may provide
an incentive for changed practices. In some regions, air quality regulations controlling the
release of hydrocarbons apply to natural gas systems, and changes are legally required.
Concerns over safety, and occasionally the noise of venting at gas facilities, can also motivate
efforts to reduce emissions.
Emissions reduction strategies presented in this assessment are:
Reduced Venting and Flaring During Production: Venting during the production of both
associated and non-associated gas is a controllable release of natural gas. The most
preferable strategy is to fully recover and process associated gas for use as a fuel. Where
demand for gas and an adequate infrastructure do not currently exist, reinjecting gas or
installing inexpensive flares can almost completely eliminate methane emissions while
providing the important benefits of maintaining formation pressure (reinjection only) and
enhancing safety. The use of more efficient flares can also reduce emissions from
unburned gas. Additionally, changes can be made in operating practices to reduce
extraction losses and emissions from wells under development.
Improved Compressor Operation: Enhanced maintenance and monitoring the fuel use of
compressor prime movers can reduce fuel costs while also reducing methane emissions.
Using gas turbines in place of reciprocating engines to power compressors can reduce
methane emissions (per unit of gas used) by over an order of magnitude, as well as
reducing emissions of other pollutants such as CO and NOX. Reductions can also be
achieved by capturing gas that is currently vented during stops and starts, and using
auxiliary power (i.e., hydraulic) for turbine starts (rather than gas pressure).
Improved Leak Detection and Pipeline Repair: Gas pipelines are subject to corrosion and
subsequently develop chronic leaks (i.e., small, continual leaks). Preventing and repairing
these leaks will reduce fugitive emissions. This can be achieved through a number of
actions including improved leak detection and pipeline inspection, preventative
maintenance and replacement programs, and the increased use of corrosion resistant
materials (e.g., coated steels, PVC, PE). In addition, gas releases resulting from line
breakages can be reduced with automatic shut-off valves.
-------
OIL AND NATURAL GAS 3 - 5
Low Emission Technologies and Practices: Emissions occur from routine operations and
practices, including gas-operated control devices, fugitive emissions from component
joints, and pipeline purging for maintenance purposes. Low emission technologies include
pipeline control devices with reduced or eliminated venting of natural gas ("low-bleed" or
"no-bleed" devices), directed inspection and maintenance programs, and the capturing of
purged gas.
Exhibit 3-2 summarizes information on these four strategies, which are described in more
detail in the individual technological assessments.
The assessments consist of the following sections:
Reduction Technology Description;
Costs;
Availability;
Applicability;
Barriers; and
Benefits.
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OIL AND NATURAL GAS 3 - 7
3.2 Reduced Venting And Flaring During Production
The technologies and practices presented here reduce methane emissions from the production
of oil and natural gas. The largest reductions can occur from using associated gas production,
rather than venting or flaring this gas. Additional small reductions can occur from general
improvements in operating practices. (Fugitive emissions and venting from pneumatic devices
in production and processing are addressed in section 3.5).
Reduction Technology Description
Both oil and natural gas fields produce natural gas. In the case of dedicated natural gas
production (non-associated gas), the release of gas, intentional or accidental, is a clear loss
of a valuable resource. On the other hand, gas produced from oil fields (associated gas) is not
the primary product, and is sometimes viewed as an inconvenience rather than an energy
resource. As a result, most studies agree that methane emissions from oil production are
higher than those from gas production (Barns and Edmonds, 1990).
Oil Production: The environmentally preferable strategy for reducing methane emissions
from oil production is to fully recover and process the associated gas for local fuel use or
for sale to a pipeline. This strategy not only eliminates the emissions but also takes
advantage of the energy value of the gas. However, this strategy requires a gas supply
infrastructure and demand for natural gas as an energy source.
Where demand for gas and an adequate infrastructure do not currently exist, gas produced
from oil fields is flared, vented, or reinjected. (Also, gas may be vented or flared if the
wellhead pressure is too low to be brought up to adequate transmission pressure with
existing compressor equipment.) In each case, the gas is separated from the oil and
directly released (venting), burned off (flaring), or reinjected into the field to help maintain
formation pressure. Reinjection prevents emissions as long as the exhausted well is
plugged properly so that it does not leak once production ceases. Flaring is preferable to
venting because even an inefficient flare will destroy the majority of the methane (usually
more than 98 percent). However, it is important to install flares that will either burn
continuously or be self-igniting so that venting from flares is minimized. Effectively flaring
or reinjecting gas that is currently vented could significantly reduce methane emissions
from production facilities.
Estimates of the proportions of gas vented, flared and reinjected are difficult to develop
due to incomplete data. Flaring and venting has been estimated to be around 5 percent
of world natural gas production, with 20 percent of this being vented (Barns and Edmonds,
1990). However, this estimate is very uncertain. A similar amount, 6 to 7 percent of
world production, is thought to be reinjected (Barns and Edmonds, 1 990; US DOE, 1992).
In general, flaring and venting of associated gas is more prominent in young extraction
industries that do not have a gas infrastructure or demand. Encouraging the use of natural
gas and the development of infrastructure can help reduce emissions from oil production.
Baudino and Volski (1991) estimate that a 50 percent reduction in emissions from venting
and flaring is readily achievable.
-------
3-8 OIL AND NATURAL GAS
Gas Production: Emissions from gas production arise during exploration, extraction losses,
and system upsets. Reducing emissions from these sources involves marginal
improvements in existing practices -- better housekeeping -- that will also reduce safety
hazards from methane leaks and reduce lost product. Extraction losses worldwide are
thought to be approximately 5 percent of production (Barns and Edmonds, 1990), although
there are large differences between sites. The reductions achieved at individual sites will
depend on current emissions and the success of changes in operating practices.
The costs for reducing methane emissions are highly dependent on regional and site specific
factors. As an example, India recently received a $450 million loan to build the infrastructure
necessary to reduce the annual venting and flaring of approximately 116 bcf of gas from the
Bombay High offshore oil field. This gas will be used in onshore factories (Banerjee, 1991).
The fuel cost savings are expected to cover the cost of the loans. Existing technology,
equipment, and practices will all affect the cost and feasibility of various reduction options.
Where the market for gas exists, utilizing natural gas as an energy source will generate
revenue from gas sales, and will encourage infrastructure development. Alternatively,
reinjection can improve well production sufficiently to be a cost effective option where there
is adequate drilling technology to support the development of reinjection wells. Where gas
is currently vented, the installation of rudimentary flares is relatively inexpensive. However,
because flaring does not utilize the gas as fuel and emits CO2 and CH4, it is the least
environmentally beneficial option, but remains preferable to venting.
Availability
The technology and expertise exist to develop uses and the necessary infrastructure for
transporting the associated gas. Efficient flaring and reinjection are also common practices.
Beneficial changes in operating practices and/or equipment that reduce fugitive emissions and
extraction losses are also available technologies.
Applicability
Utilizing the gas as a fuel is applicable where the infrastructure and demand for gas exists,
and the quantity is sufficient to recoup the investment through fuel substitution (i.e. gas for
oil). Encouraging demand and infrastructure growth will enhance this development.
Reinjection is economical where the reservoir structure (geology) supports the enhanced
recovery of hydrocarbons through repressurization. Without the proper structure, this option
is very costly. Where associated gas is currently vented, simple flares can achieve major
reductions of methane emissions at a low cost. Regions that do not utilize, reinject or flare
the gas likely include the Middle East, Africa, Latin America, China, and certain areas of Asia
(Barns and Edmonds, 1990). As an interim step, flaring should be encouraged over venting.
More general improvements in operating practices that reduce emissions from exploration and
other fugitive emissions, and improve the efficiency of flares, are applicable in most regions.
-------
OIL AND NATURAL GAS 3 - 9
Barriers
The primary barrier to reducing the release of methane into the atmosphere is generating
demand for associated gas, and the infrastructure to supply the market. Historically, this
development has lagged behind oil production. Developing sufficient infrastructure requires
capital and the availability of appropriate technology. Additionally, institutional inertia can
delay changes in the energy supply.
Changes that reduce emissions can be driven by the value of the recovered gas. However,
many regions that vent and flare gas do not have convertible currencies or free market pricing
mechanisms for gas, making investments difficult to pay off. Compared to oil from these
regions, which is exported for hard currency, the gas saved would produce little cash return.
The other benefits of reducing methane emissions are less directly realized (non-cash), and
are not typically analyzed when considering changes in current operating practices.
Benefits
Reducing methane emissions from oil and natural gas production will have the following
benefits:
Improved safety. Reducing releases of methane, which is potentially explosive, will
reduce the risk of accidents.
Use of a clean and efficient fuel. Methane is a convenient and clean energy source,
producing less CO2 per unit energy than other fossil fuels, and also producing smaller
amounts of local air pollutants such as particulates, nitrogen oxides, and sulfur oxides.
Increased energy productivity. Reducing the venting and flaring of gas by using
associated gas, and also reducing extraction losses from both oil and gas production,
will effectively increase the available energy supply.
Reduced Venting and Flaring
methane reductions of up to 50%
optimize energy supply
reduce risks
technology currently available
clean energy source
-------
3-10 OIL AND NATURAL GAS
3.3 Improved Compressor Operation
This strategy reduces the methane emissions in the exhaust of gas-fired compressors, which
arise because a portion of the fuel remains unturned during the combustion process. The
most widely applicable method will be to reduce the amount of fuel used by compressors
(thereby decreasing emissions even if the emissions factor remains constant). Importantly,
reducing fuel use can result in significant savings. A second option is to use gas turbines,
which have much lower methane emissions, as compressor prime movers in place of
reciprocating engines wherever economically, operationally, and technically feasible. In
addition, altering other practices such as engine starts and stops can reduce the amount of
natural gas that is vented to the atmosphere.
Reduction Technology Description
Most compressors are used in transmission pipelines to maintain the pressure in the pipelines.
Energy is lost due to friction as gas flows through transmission pipelines, resulting in a gradual
drop in pressure; a compressor compensates for these frictional losses. Energy must also be
expended to bring gas up to pipeline pressure from gas fields and storage facilities, and
compressors also are used for this purpose. The basic components of a compressor station
are a prime mover, a gas compressor, and auxiliary equipment.
Prime Mover: A prime mover is an engine which supplies power to the gas compressor.
Reciprocating (internal combustion) engines and gas turbines are most common, although
electric engines and steam turbines have also been used. Reciprocating engines and
turbines usually use pipeline gas as fuel.
Gas Compressor: Compressors use the energy supplied by the prime mover to increase
the pressure of the gas. This is done either by compressing an enclosed volume of gas
(e.g., in a piston), or increasing the velocity of a continuous gas flow.
Auxiliary Equipment: This includes starter systems, piping, filters, cooling systems,
instrumentation, and buildings.
Methane is released from a number of sources in compressor operations, although almost all
emissions are associated with the prime mover. The majority of methane emissions from
compressors result from incomplete combustion of the natural gas used for fuel. Large
volumes of methane can also be released if the pressurized pipeline gas is used in starter
motors or to start gas turbines directly. Starts and stops vent significant quantities of
unburned fuel for safety reasons. Emissions can be improved by reducing fuel usage, using
gas turbines where feasible, by changing the method of starting engines, and by reducing the
number of engine stoppages.
Reduced Fuel Use: Fuel use can be improved by better maintenance practices and through
more efficiently engineered engines. First, improving the analysis of gas-fired compressor
engine efficiency can reduce fuel use by several percent, thereby reducing methane
emissions (for a given emissions factor). One such system, instituted by Northwest
Pipeline, involved enhanced monitoring of engine performance to track fuel use and
-------
OIL AND NATURAL GAS 3-11
compare it with predicted fuel use. The continuous monitoring of fuel consumption
enabled operators to identify performance inefficiencies and to correct problems quickly
(Zebelean, 1991). Improved maintenance can improve thermal efficiencies, as well as
reduce fuel use.
Second, exhaust emission levels can also be reduced with the use of more efficiently
engineered engines. For example, lean burn engine technology enables an internal
combustion engine to run on a more dilute air-fuel mixture, reducing fuel use and also
reducing emissions of particulates and carbon monoxide. Similarly, rich burn engines can
be modified with improved air-fuel ratio controllers.
Combustion Efficiency - Prime Mover Choice: The two most, common types of prime
mover engine are gas turbines and gas-fired internal combustion (reciprocating) engines.
As a rough approximation, methane emissions in the exhaust are an order of magnitude
lower for gas turbines than for similarly rated reciprocating engines, largely due to the
greater air flow into the combustion chambers of gas turbines. Thus, potentially the most
effective reduction option is to install gas turbines, as opposed to internal combustion
engines, where technically and operationally feasible. For example, recent estimates for
emissions from reciprocating engines, weighted by actual fuel use, are approximately 500
kg of methane per MMcf of fuel used, whereas turbines emit 6 to 12 kg of methane per
MMcf used (USEPA, 1 993a). Designing new pipeline systems to maximize the use of gas
turbines or replacing reciprocating engines with turbines can therefore reduce emissions
at a given location by upwards of 90 percent. The decision to install one or other type of
engine, or to swap out an existing engine, will depend on the economics and site specific
operational requirements.
Engine Starts: Starting an engine can require up to 10 percent of its rated power, and this
power is often supplied by utilizing the pressure of pipeline gas in gas driven starter
motors for both reciprocating engines and gas turbines (AGA, "Compressors"). The gas
that is used in these motors is usually vented to the atmosphere. These emissions can be
reduced if the gas is captured, or if alternative power sources such as electricity,
compressed air, or hydraulic pressure are considered.
When engines are started and shut down there are periods when fuel passes through the
engine without being burned. Reducing the number of stoppages, and improving engine
starts (e.g., by increasing starting motor capacity) can reduce the quantity of gas that is
vented.
Costs for these technologies and practices vary considerably, being highly dependent on site
specific factors. Under a wide range of conditions, however, some of these options provide
a return on investment through fuel savings.
Reduced Fuel Use: The fuel use monitoring program instituted by Northwest Pipeline has
proven cost-effective, potentially reducing fuel costs by $1 28,000 per year and methane
emissions by approximately 30 metric tons per year, in a 7,000 mile pipeline system with
a mainline capacity of 2 bcf per day (Zebelean, 1991).
-------
3-12 OIL AMD NATURAL GAS
Prime Mover Choice: Gas turbines are becoming increasingly economically competitive
for large transmission compressor stations. Capital costs for a 6 MW gas turbine prime
mover are estimated to be about $700/kW. Operation and maintenance costs are
0.60/kWh. A larger system of 17.5 MW would have a capital cost of $600/kW,
demonstrating some economies of scale, with operation and maintenance costs of
0.70/kWh (Sturgill, 1991). In comparison, capital costs for internal combustion (1C)
engines are estimated to be $400 to $800/kW, with operation and maintenance costs of
2C/kWh (Soot, 1991). Gas turbines become more cost competitive for larger systems.
(These figures are for engines alone, and do not include the cost of the compressors and
auxiliary equipment, which may not have to be switched.) Total installed costs will vary
considerably by location and specific application.
Other: Alternative strategies include the use of lean burn 1C engines and air-fuel ratio
controllers, non-gas powered starters, and capturing vented gas. These technologies and
practices have typically been installed only where there are regulatory incentives, as the
efficiency gains usually are only marginally economic. Any alteration in practices that
does not require significant new equipment, such as capturing vented gas or improving
compressor seals, is more likely to be economically justified; often the most important
factor is the cost of the lost gas (or alternative energy supplies).
Availability
Compressor station technology is well developed, and continuous developments in high
efficiency and low emissions engines are being made. In particular, these developments will
increase the availability of appropriate and economically viable gas turbine technology.
Applicability
The operating characteristics of gas pipeline systems will vary greatly by design, and the
applicability of the technologies described here must be evaluated individually for each
system. However, closer monitoring of fuel use and improved maintenance and efficiency is
a widely applicable technique. While it is likely that some improvements can be made virtually
everywhere through enhanced fuel use inspection programs, the most significant
improvements are expected in countries with older and less technologically sophisticated
systems, as these systems typically will be using more inefficient prime movers (with shorter
lifetimes).
Currently, the economics and operating characteristics of turbines make them an attractive
choice as prime mover for larger transmission stations (e.g., above 8-10,000 hp; 10-13 MW)
(Ervin, personnel communication).
In general, new technologies must be economically attractive and able to perform at least as
effectively as existing equipment. In some cases, external incentives such as air quality
regulations may drive the installation of new equipment. Because of the high capital cost of
installation, advanced equipment will not immediately replace existing equipment, but will
gradually be installed in new pipeline construction and during the scheduled replacement of
compressors.
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OIL AND NATURAL GAS 3-13
Barriers
Installing new equipment, such as prime movers and other equipment for emissions control,
monitoring fuel use, and alternative starting practices, may involve a relatively high initial
capital investment. In these cases, the availability of funds can be a barrier to installing
equipment that will be more economic in the long term. Also, the long lifetimes of well-
maintained equipment can limit the speed with which new technology is introduced.
Many technologies and operating practices do not require significant investment in equipment,
and are therefore more likely to be introduced quickly. However, a lack of information or
technical experience may hinder adoption of certain practices.
Benefits
In addition to reducing methane emissions from compressor stations, this strategy has the
following benefits:
Reduced natural gas losses: Some systems are estimated to use a significant
proportion of total throughput for compressors. Installing more efficient compressors
can increase actual energy supply by reducing the fuel used by compressor stations.
Improved pipeline performance: The installation of more advanced and reliable
technologies will improve the overall performance of the natural gas system.
Improved air quality: Reducing gas losses reduces the effect that such emissions have
on local air quality. In addition, improving compressor operations lowers the emission
of other pollutants such as NOX.
Compressor Operation
methane reductions of up to 90%
reduced transmission losses
cost-competitive practices
technology currently available
improved air quality and safety
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3-14 OIL AMD NATURAL GAS
3.4 Improved Leak Detection and Pipeline Repair
This assessment describes technologies and practices to improve leak detection, to prevent
corrosion of pipelines, to repair pipelines when they do fail, and to replace those sections of
pipeline that cannot be cost-effectively maintained. Techniques for both transmission and
distribution pipelines are discussed.
Reduction Technology Description
Natural gas pipeline systems are divided into transmission and distribution networks.
Transmission networks are high pressure (typically 1000 psi; 75 Bar) pipelines used to
transport gas from production, processing, and storage facilities to the distribution networks.
Distribution pipelines carry gas from the transmission pipeline to the end user. The gas
pressure is reduced in steps through different sections of the distribution network, from 1000
psi at the connection to the transmission system down to less than 0.5 psi for typical end
uses. Common pipe materials include cast iron, steel, and plastic (PVC, PE).
Leaks occur from pipelines as a result of corrosion, pipe joint failures, and fractures.
Corrosion of the pipe material can occur internally or externally, causing pinhole leaks, or
weakening the pipe and eventually causing structural failure. Transmission pipelines are
constructed by welding pipe sections together, while in distribution pipelines the pipe sections
are usually joined using mechanical joints. Mechanical joints are susceptible to failure through
deterioration of the sealant material and/or movement of the pipe sections. Fractures are
breaks in the pipe resulting from externally applied forces, such as construction, heavy road
traffic, and subsidence.
Leaks from these pipeline systems may be reduced by improving existing leak minimization
practices and introducing additional technologies and methods that have been proven
successful elsewhere under similar operating conditions. Methods for reducing methane
emissions from leaking pipelines include improved leak detection, preventative methods such
as corrosion control and appropriate material selection, pipeline repair and replacement, and
the use of automatic shutoff valves.
Leak Detection: Methods to detect gas leaks include techniques that attempt to directly
detect the presence of abnormally high gas concentrations, techniques to identify material
defects in the pipeline or pipeline coating, system pressure monitoring, arid analysis of
historical records of leaks in a given system to identify problem areas.
The most common detection method for both transmission and distribution systems makes
use of Combustible Gas Indicators and Hydrogen Flame Ionizers which can detect
concentrations (by volume in air) of approximately 5000 ppm and 1 ppm, respectively
(Weynand, personal communication). These two pieces of equipment are used to conduct
regular ground surveys above pipelines. Mare recently developed techniques include laser
and thermal detection of leaks from remote and largely inaccessible transmission pipelines
using helicopter-mounted equipment (Weynand, personal communication).
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OIL AND NATURAL GAS 3-15
A number of techniques exist to detect flaws in the pipe and coating material. These
techniques typically involve the insertion of magnetic or acoustic sensors into the pipeline
(e.g., using specially designed pigs) and have been principally applied to large-diameter
transmission pipelines (AGA, n.d.). However, similar methods have been developed to
detect the external corrosion of small and medium diameter pipe (2-12 inches; 50-300
mm). Magnetic and acoustic sensors have been used to detect areas of corrosion as small
as 10 mm in diameter (JGA, 1991).
When the integrity of pipe coating begins to fail, the amount of cathodic protection
required to maintain minimum levels of protection must be increased. Measuring the level
of cathodic protection is one indication of the pipeline's level of resistance to corrosion,
and regulations in many nations require such periodic surveys (Hall, 1991). Cathodic
protection is commonly measured as the pipe-to-soil potential using a reference cell placed
on the soil surface above the pipeline. This potential difference should be maintained at
between -0.85 v and -1.5 v (Stevens, 1991). An alternative method to detect coating
failures uses a 220 Hz transmitted signal between the pipeline and a magnesium anode
placed in the soil (Japan Gas Association, 1991). The signal will flow through the
surrounding soil from the anode to any area of the pipeline with a coating defect, up to
2 km away. This flow in the vicinity of defects can be detected by a travelling receiving
unit on the surface. Defects as small as 0.1 cm2 can be detected on some coatings.
In addition to gas leak and coating defect detection methods, many operators of
transmission and distribution systems use historical records of leak location and frequency,
"unaccounted-for-gas" estimates, and pressure data to identify high risk areas of their
pipeline networks (Miller, 1991). Monitoring programs range from simple statistical
surveys to the use of sophisticated computer-based leak prediction systems. For example,
CIMOS (Cast-Iron Maintenance Optimization System), developed under a GRI grant, uses
data on past leaks, details of the present system, and economic information to prioritize
maintenance and replacement programs (Ahrens, 1991). Significant savings can be
realized using such advanced tools to guide system protection efforts.
Continuous monitoring of gas systems is often performed using automated pressure trend
analyses. This practice monitors the temperature-corrected pressure at points throughout
the system, and compares this to the anticipated performance of the system based on
past trends. This practice can detect pressure fluctuations in the system which may
indicate the presence of undetected leaks.
Preventative Methods: Preventing leaks from natural gas systems requires selecting
appropriate materials, and protecting the pipe materials from the effects of corrosion and
mechanical or third party damage. Steel is the favored material for transmission pipelines,
being sufficiently strong to handle high pressures and more resistant to corrosion than
iron, although steel requires extensive protection. Distribution pipelines, especially the
lower pressure sections, are increasingly constructed from plastics such as PVC and PE
which are inexpensive, easy to work with, and extremely resistant to corrosion. PVC and
PE pipe sections can be joined by heat-fusion, reducing the number of mechanical joints
and subsequently the number of joint failures. Despite the trend toward using plastics in
distribution systems, many older systems which were built with cast iron or uncoated
steel are still in use today.
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3-16 OIL AND NATURAL GAS
Steel and iron pipelines can be protected from the effects of corrosion with external and
internal coatings, and cathodic protection. External corrosion is usually galvanic
(electrochemical) -- for example, rusting in ferrous metals - and is exacerbated by
certain environmental conditions (e.g., soil types, moisture, external currents),
construction, and material flaws. Internal corrosion occurs through the action of
contaminants in the pipeline gas, such as sulfur, hydrogen sulfide, and carbon dioxide,
especially if water or moisture is present to act as a reaction medium. Corrosion can also
occur through erosion from particulates and liquid molecules in the gas stream.
Preventative methods include the following (AGA, undated).
External Coatings. Coatings can be an extremely effective protection method. The
primary role of the coating is to provide a barrier to the electric currents that are set
up between the piping and the soil and which cause electrochemical corrosion.
Coatings should also have good adhesion and be resistant to soil chemicals and water.
Coating materials include coal tars, asphalt enamels, epoxy resins, plastic tapes, and
mastics.
Internal Coatings and Inhibitors. The potential for internal corrosion increases if the
gas stream contains significant concentrations of impurities (e.g., S, H2S, CO2).
Reducing the concentration of these impurities and drying the gas is the most effective
protection strategy. Internal coatings have been used in some situations, although
they are more difficult to apply than external coatings. Internal coatings are also more
likely to be eroded by contaminants and particles in the gas stream. Inhibitors have
been used; they are chemicals injected into the gas stream to reduce the corrosive
reactivity of gas impurities.
Cathodic Protection. Galvanic corrosion is the loss of metal through an
electrochemical process, whereby metal ions are formed at an anodic area on the
surface of the pipe and pass into solution in the surrounding soil. Metal loss will occur
at any point where current leaves the pipe. Corrosion can occur when two dissimilar
metals are placed in contact, when dissimilar soil conditions exist along the pipeline,
or when stray currents flow through the pipeline (e.g., from electric rail systems,
induced current from high voltage lines). There are two types of cathodic protection.
Impressed protection uses external power to force a DC current onto the pipeline
structure to balance any corrosive current flowing from the material; Galvanic
protection attaches a more electrochemically active metal (sacrificial anode) to the
pipeline structure.
Pipeline Repair: Although high quality construction and protection will greatly reduce the
rate of corrosion of new pipelines, effective repair is a necessary aspect of reducing gas
leaks. Repair techniques include external sleeves, clamps, and seals, and internal inserts.
Some success has also been achieved by reconditioning pipe joint seals with gas stream
additives.
High pressure transmission leaks are typically repaired by welding or bolting on steel
sleeves, which can either partially or completely encircle the leaking pipe section (Corder,
1991). Large areas of corroded pipe may be repaired by completely cutting out a section
of pipe; smaller areas of corrosion can be repaired by grinding the affected area smooth.
When coatings become too deteriorated to resist corrosion the pipe must be dug up,
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OIL AND NATURAL GAS
3 - 17
cleaned, and recoated. Repairing leaks is often faster, less disruptive, and less expensive
than replacing sections of pipeline.
Low pressure distribution systems also utilize similar methods of external repair using
clamps and sleeves on corroded pipe sections. Joint leaks in these systems can be
repaired using a heat shrinking polyethylene tube or encasing the joint in a urethane resin
mould (See Exhibits 3-3 and 3-4). These and similar techniques have been used
successfully for many years.
Exhibit 3-3
Joint Repair with Heat Shrink Sleeve
Bell-and-spigot joint
W type repair tube
Mastic bar
G type repair tube
Gas type joint
Socket
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3 - 18
OIL AND NATURAL GAS
Exhibit 3-4
Joint Repair with Urethane Resin Mold
Sealer
Polycover
In addition to external repairs on distribution systems, a number of new processes have
been developed that attach an internal, impermeable layer to the inside of the pipeline
(JGA, 1991). These systems greatly reduce the amount of excavation required to fix the
leak and allow entire sections of pipeline to be rehabilitated during one repair (as opposed
to single joints or corroded areas). The concept of the repair is to insert flexible material,
coated with adhesive, into the pipeline from a single excavation point and inflate it with
pressurized gas. This creates a smooth layer of impermeable material within the pipeline.
(Exhibits 3-5 and 3-6). Pipe diameters ranging from 20 to 750 mm (approximately 1-35
inches) have been treated using this practice. An alternative method that has been used
successfully involves inserting PE pipe inside existing metal pipelines that have corroded
(Pipeline Industry, 1991; P&GJ, 1990). Diameters of 2 to 20 inches (approximately 4-45
cm) have been repaired in this manner. Reconditioning the sealant material in joints has
been accomplished by adding chemicals to the gas stream (Mitchell & Sweet, 1990), and
by using an in-pipe sensor that can apply sealant directly to the joint (Exhibit 3-7) (JGA,
1991). Both methods allow full operation of the pipeline while the repair is made.
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OIL AND NATURAL GAS
3 - 19
Exhibit 3-5
Pipe Repair with Polyamide Elastomer Layer
Adhesive
>Ť.. Layer
Polyamide
Elastomer
Layer
Winch
Adhesive
Layer
Polyamide
Elastomer
Layer
Exhibit 3-6
Pipe Repair with Epoxy Resin
Basin - Injector Tank
Generator
Suction Machine Resin Injector Blower compressor
Winch
Lining Pig Unlng Pig \ Removing Pig
Carrying Pig
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3-20
OIL AND NATURAL GAS
Exhibit 3-7
In-Pipe Joint Sealing Equipment
CompcMioc Unrt
ConMIPml
Pipeline Replacement: In some cases, age, materials, and hostile environmental conditions
make it cost effective to replace existing pipe with more corrosion resistant materials
rather than continue repairs.
Minimizing gas leakages requires a comprehensive system of monitoring pipeline conditions
and leak detection, repair, and replacement with suitable materials. Application of
appropriate techniques such as those described in this assessment can greatly reduce the
leakages from some pipeline networks. For example, recent estimates of leakage from
pipeline systems giye a world average of between 1 and 2 percent of production.
However, the wide range of regional estimates, from 0.5 percent to as high as 1 2 percent
of production, indicates that large reductions are possible using existing technology and
practices (Rabchuk, 1991; Baudino & Volski, 1991). Feasible reductions may be 60
percent worldwide with some systems able to reduce up to 80 percent of emissions from
pipeline leaks (USEPA, 1993c).
Automatic Shutoff Valves: Automatic shutoff valves can reduce emissions from system
mishaps. These valves are simple piston-spring or ball valves which close when there is
a surge in the gas flow through the valve, and are often known as excess flow valves
(EFV). In distribution systems, automatic shutoff valves are most commonly used on
residential service lines where the risk of third party damage from excavation is greatest
(LaShoto, 1989). EFVs have proven effective at reducing leakage and improving safety
in instances of catastrophic line failure. Most designs reset themselves when the gas flow
returns to normal. Due to operating characteristics, these devices have been less
commonly used on lines with pressures below several psi (Bernhardt, 1992). Automatic
shutoff valves are also widely used in transmissions systems, at citygate and compressor
stations, and offtake lines.
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OIL AND NATURAL GAS 3-21
Pipeline networks are expensive to build and maintain. In the U.S., a transmission pipeline can
cost up to $1 million per mile (roughly $0.6 million per km), and with proper maintenance can
stay in service 40 to 50 years. The maintenance costs for existing transmissions systems are
generally less than the cost of new pipeline. Furthermore, much of the emphasis on system
maintenance is driven by additional important concerns such as minimizing risk to nearby
populations.
Distribution systems are also extremely expensive to install, primarily because of the difficulty
of underground construction in urban areas. As a result, operating companies have found it
cost-effective to emphasize extensive maintenance in order to avoid wholesale replacement.
For example, Washington Gas, a typical U.S. distribution company, has a system protection
group of 40 people and a budget of $5.5 million to maintain their 20,000 mile (12,000 km)
pipeline system (gas throughput of 3.67 bcm). Adequate protection and effective
maintenance can therefore improve profitability by reducing repair costs and extending the
useful lifetime of distribution pipelines.
Availability
The techniques and materials discussed here are commercially available. Continual
improvements are expected through research, development efforts and demonstration.
Applicability
Each of the approaches described in this assessment -- leak detection, preventative
measures, pipeline repair or replacement, and automatic shutoff valves have the common
goal of cost-effectively reducing gas leakage. Individual technologies within these approaches
are applicable under certain conditions, and for particular stages of gas systems. In
combination, these technologies provide an integrated strategy for controlling methane
emissions applicable across a range of conditions.
Leakages in a given region are related to the length, condition, and type of pipeline system.
The largest impact on methane emissions will be the application of improved leak detection
and repair techniques to large, high-pressure pipeline systems in relatively poor condition.
However, gas leaks are a safety hazard and a lost resource throughout all the stages of a gas
system, and continued improvements can be made in monitoring and effective repair.
These technologies are applicable in both developed and developing countries. Developing
countries with gas infrastructures typically have smaller systems in relatively poor condition.
Here, the transfer of available technology, and the financing to adopt it, can significantly
reduce methane emissions. Although developed countries typically have high integrity pipeline
systems, considerable variation between regions, and even within networks, makes
improvements possible.
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3 - 22 OIL AND NATURAL GAS
Barriers
Implementation of these techniques requires the availability of technology, financing, and
proper incentives to reduce leakages. The lack of proper economic incentives and capital are
often the cause of existing poor quality pipeline networks.
Benefits
In addition to reducing methane emissions into the atmosphere, these strategies will:
Improve safety. Methane leaks can cause fires and explosions. Reducing gas leaks
from pipelines, especially transmission and distribution networks, will improve the
safety of these systems.
Reduce energy losses. Gas leaks are lost energy, which can be recovered through
improved construction and repair.
Increase pipeline longevity. Improved repair can increase the useful lifetime of gas
pipelines, reducing the effective cost of such systems.
Improved Leak Detection and Pipeline
Repair
methane reductions of up to 80% from
some pipeline networks
reduced losses
reduced risks
technology currently available
cost-effective technology
-------
OIL AND NATURAL GAS
3 - 23
3.5 Low Emission Technologies and Practices
A number of routine operations and practices result in the release of natural gas from all
stages of the gas system. The primary sources of these methane releases are gas-operated
pneumatic regulators and controlling devices, flanges and seals at various component joints,
and pipeline operating and maintenance procedures which vent gas. The techniques and
types of equipment presented here are intended to reduce these releases cost-effectively while
contributing to efficient operation.
Reduction Technology Description
Low emission technologies and practices which may cost effectively reduce methane
emissions include low- and no-bleed pneumatic devices, directed inspection and maintenance
programs at above-ground facilities, and methods for capturing purged gas during
maintenance.
Pneumatic Devices: These devices are used throughout the natural gas system to control
the flow of gas. They include regulators, valve operators (actuators), valve controllers,
valve positioners, and pressure transmitters. Because these devices are used to control
gas pressure and flow, engineering simplicity has led to designs which operate directly off
of gas pressure, allowing devices to derive both their power needs and their informational
input from the same source - gas pressure. The devices take gas directly from the pipe
to drive their operating mechanisms. Numerous designs exist, many of which allow for
(or require) gas to be vented from the operating mechanisms once it has performed its role
of activating the device. The gas is typically released to the atmosphere. However, it is
possible to design devices which either bleed significantly less gas or do not vent gas at
all. Some designs reinject the used gas back into the pipeline downstream of the device;
others use compressed air or electric power, which must be supplied from an auxiliary
source. Exhibit 3-8 shows representative examples of bleed rates from high and low-Weed
devices.
Exhibit 3-8
Pneumatic Device Bleed Rates
Device
Valve Positioner
Valve Actuator
Regulator
Bleed Rates (ft3/min)
Low-Bleed1
0.0283
0.0113
0.0064
High-Bleed2
0.628
0.085
0.268
Difference
0.5997 (95%)
0.0737 (87%)
0.2616 (98%)
1 PSI, 1990
2 PG&E, 1990
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3 - 24
OIL AND NATURAL GAS
An initial estimate derived from extensive surveys by two U.S. gas companies indicates
that pneumatic devices may result in annual releases of approximately 38,000 cubic feet
per mile of pipeline (PG&E, 1990; SOCAL, 1992). The potential for reducing emissions
depends upon the number and design of devices in a particular system. In general,
determining this will require system-specific surveys; the two U.S. company surveys
estimated that there is roughly one high-bleed pneumatic device every 2 miles. As shown
in Exhibit 3-8, replacing individual devices can result in emission reductions of 80 percent
and higher. Releases from pneumatic devices also occur in wellhead, gathering,
processing, storage, and distribution systems, and these areas will also offer the
opportunity for emissions reductions.
Directed Inspection and Maintenance Programs: In addition to pneumatic devices, above-
ground gas system facilities also contain a number of components which potentially leak
gas. These include flanged joints, other mechanical joints and connections, valves,
pressure relief valves, and seals in pumps and compressors.
Flanged joints rely on a gasket tightened between two flanges to maintain a gas-tight seal.
The joint will leak when the gasket is damaged or deformed, which primarily occurs
through poor installation, corrosion (typically from the gas stream), or thermal stress
(USEPA, 1983).
Similarly, relief valves form a seal between the valve head and a seat, with the necessary
pressure usually provided by a spring. Corrosion of the head or seat, or misalignment, can
result in leaks.
Process valves, compressors, and pumps all have moving parts - the valve stem or
compressor shaft - which must pass through the casing of the device. Thus, in each
case, a seal which separates the process fluid and the atmosphere must be formed
between the stationary casing and a moving shaft. These seals are inherently more prone
to wear, corrosion, and ultimately failure than simple flange gaskets or relief valve seals.
As shown in Exhibit 3-9, although the leakage from individual components is relatively
Exhibit 3-9
Typical Fugitive Emission Rates, Component Numbers, and Facility Emissions
Component
Valves
Relief Valves
Seals
Flanges & Connections
Emission Rate
(kg/day)
0.384
3.6
5.12
0.021
Typical Number of
Components
750
12
12
3,000
Plant Emissions
(kg /day)
288
43
30
62
Source: EPA, 1983
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OIL AND NATURAL GAS 3 - 25
small, the large number of components in a typical plant may make total plant emissions
significant.
Directed inspection and maintenance programs are designed to identify the source of these
leaks, and prioritize and plan their repair in a timely fashion. Therefore, any plan to reduce
emissions from an individual facility will be comprised of a number of components,
including a method (or methods) of leak detection, a definition of what constitutes a leak
(e.g., a particular meter reading), set schedules and targeted devices for leak surveys, and
allowable repair time. These components must be defined to institute a reliable and
effective inspection and maintenance program. The details of a program will depend on
site-specific factors, and can be tailored to fit the needs and limitations of the site.
For example, such a program may require quarterly, monthly, or even weekly monitoring;
may monitor any or all of the components (e.g., valves, relief valves, connections,
compressor seals, and pump seals); may use portable or fixed instruments such as
hydrogen flame ionizers or OVAs, visual inspection, or applied soap solutions; and may
provide a flexible response to leaks depending upon their magnitude and location within
the facility.
Analyses of typical programs have determined that cost-effective emission reductions on
the order of 70 percent or more are feasible (Radian, 1992; USEPA, 1983). These
programs could result in net savings. However, diminishing returns (i.e., decreasing
marginal emission reductions for additional program cost) indicate that properly designed
programs are necessary to maximize benefits and overall cost-effectiveness.
Capturing of Purged Gas: Routine maintenance work on transmission pipelines requires
a large reduction in gas pressure in the pipeline section to be repaired to ensure safe
welding conditions. Typically, a pipeline section undergoing repairs is isolated and vented
to reduce pressure, resulting in the release of the gas to the atmosphere. However, it is
technically feasible and may be cost-effective to use a portable compressor unit to transfer
this gas to another section of the system.
A Canadian gas pipeline operating company with over 8,000 miles of pipeline has
successfully used two truck-mounted turbine-gas compressor units to capture gas that
would otherwise have been vented during maintenance (NOVA, 1985). Each unit consists
of a natural gas fired turbine (rated at between 3 and 4 MW), a gas compressor (with a
compression ratio of 5:1), necessary auxiliary equipment such as air intake and exhaust
filters and silencers, fuel gas filters, electric power units, control stations, all mounted on
a standard "lowboy" trailer. A support truck carries the necessary pipe and fittings to tie-
in the compressor unit to the pipeline. A total crew of 3 or 4 is needed to transport, set-
up, and operate the unit. The result is a fully-mobile, self-contained compressor unit
which can reach any point in the system within 2 to 10 hours, and set-up in 4 hours.
In operation, the portable unit can evacuate a 20 mile section of 30 inch pipeline from a
pressure of 800 psi down to 160 psi in approximately 10 hours. The compression ratio
of 5:1 means that the pipeline cannot be completely evacuated; the remaining gas,
approximately 1/5 of the total volume, is then vented. However, emissions are reduced
by roughly 80 percent. Exhibit 3-10 shows the amount of gas saved per mile for different
size pipelines.
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3 - 26
OIL AND NATURAL GAS
Exhibit 3-10
Volume of Gas in Various Size Lines at Different Pressures; Volume of Gas Saved per
Mile of Pipeline
Pipe Size
(inches)
10
12
16
20
24
30
36
42
MSCF of Gas/Mile
at 800 psi and
60°F
186.22
267.41
431.72
687.53
1003.27
1587.70
2305.53
3157.37
MSCF of Gas/Mile
at 1 60 psi and
60°F
35.90
51.55
83.24
132.55
193.43
306.11
444.50
608.74
MSCF of Gas
Saved per Mile
150.32
215.86
348.48
554.98
809.84
1281.59
1861.03
2548.63
Source: NOVA, 1985 ,
Costs
These practices and technologies all generate cost savings through capturing gas or otherwise
reducing gas leakage, thereby offsetting program costs. In some cases, depending on site
specific factors, these cost savings can recoup capital and operating costs (USEPA, 1 993b).
Low-bleed Pneumatic Devices: The cost-effectiveness of replacing existing devices
depends on several factors, including the avoided cost of lost gas, and the incremental
cost of low/no-bleed devices above that of high-bleed equipment. In some cases, lower-
bleed devices are less expensive than other designs. Some success has already been
achieved in replacing devices where expected avoided costs from preventing gas leaks is
larger than incremental costs. For example, a U.S. gas company installed low- or no-bleed
gas control station equipment at five locations, and expects to save over 800,000 mcf of
gas over a ten year period, with direct benefits of over $4 million (Cowgill, 1991).
Cumulative incremental investments were in fact negative, indicating reduced replacement
costs over high-bleed devices for these applications.
Directed Inspection & Maintenance Programs: Experience in the US indicates that
programs can achieve per component monitoring costs of $0.30 to $1.00; these costs
are based on monitoring rates of 200 to 800 components per man-day (USEPA, 1983).
Capturing Purged Gas: The best available information on the costs of capturing natural
gas vented during pipeline repair is from the Canadian experience. The two Canadian units
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OIL AND NATURAL GAS 3 - 27
were deployed in 1979 and 1 983, at a cost of 2.3 million Canadian dollars and 4.5 million
Canadian dollars respectively. From 1979 to 1984, 490 to 760 mmcf of gas were
captured annually, for net savings of 750,000 to 1,560,000 Canadian dollars. Annual
operating costs ranged from 102,000 to 285,000 Canadian dollars (NOVA, 1985). These
costs and savings are highly dependent upon the average volume of gas released during
pipeline blowdowns and the number of blowdowns that are actually planned, thereby
allowing for deployment of the units.
Availability
Designs for pneumatic devices which bleed less gas have been developed and installed in
numerous applications. In many cases these designs are not marketed explicitly as low-bleed
designs, and choosing these designs requires a certain level of awareness on the part of those
planning maintenance. However, the availability of low-bleed devices is not seen as a barrier
to implementation.
The technical equipment for directed inspection and maintenance, such as portable or fixed
monitoring devices, is readily available. Furthermore, there is a growing body of experience
in implementing these programs.
Trailer-mounted turbine-compressor units are not commonly available as integral units.
However, the individual components are widely available in a variety of configurations,
requiring custom work 6nly for the trailer mounting. (The Canadian gas company worked
closely with the compressor manufacturer to install the components satisfactorily on the
trailer.)
Applicability
In general, the options presented here are suitable for most natural gas systems.
Low-bleed pneumatic devices are applicable in almost all situations where high-bleed
devices are currently installed. Since their average lifetime is about seven years before
being replaced, significant methane reductions could be expected over the next
decade. However, there are some applications of pneumatic devices where the high-
bleed feature is necessary for system performance.
Directed inspection and maintenance programs are applicable for any surface
installation, especially processing and gathering facilities, compressor stations, and gas
transfer points. These facilities contain numerous connections, seals, and other
components which emit gas. Regular planned inspection and timely repair can reduce
these emissions.
Capturing otherwise vented gas is most likely to be applicable on transmission
pipelines, which have large internal volumes and high pressures. However, there is
potential for similar (scaled down) equipment to hot-tap into distribution or service lines
and capture otherwise vented gas.
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3 - 28 OIL AND NATURAL GAS
Barriers
These technologies have proven successful and cost-effective in a variety of situations.
Barriers to wider implementation include the availability of information, the existence of
necessary incentives to save gas, and inertia in accepting new practices.
Operators often do not realize the magnitude of emissions that may be occurring at their
facilities, and the overall economic cost of these losses. In other cases the cost of lost or
unaccounted for gas is not fully born by the facility operator, weakening the incentive to alter
operating procedures. In general, there is resistance to change and new equipment and
procedures only slowly gain acceptance.
Benefits
In addition to reducing methane emissions into the atmosphere, these strategies will:
Improve safety: Methane leaks cause fires and explosions. Reducing gas leaks will
improve the safety of these facilities.
Reduce energy losses: The installation and use of more advanced technologies will
reduce the energy otherwise lost through gas leaks.
Improve air quality: Reducing gas losses reduces the effect that such emissions have
on local air quality.
Low Emission Technologies and Practices
methane reductions of up to 80% in
typical facilities and applications
reduced losses
cost-competitive practices
technology currently available
improved air quality and safety
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OIL AND NATURAL GAS 3 - 29
3.6 References
Contributions were made by:
Ed Caldwell, Environment Canada, Canada
Bruce Craig, Oil and Natural Gas Systems, USEPA, USA
Charles Ervin, Southwest Research Institute, USA
Katsuya Sato, Global Environment Department, Japan Environment Agency, Japan
Gordon Weynand, Oil and Natural Gas Systems, USEPA, USA
Additional information may be found in the following:
Ahrens, Frank (1991), "Getting a Fix on Repairs," in American Gas. July 1 991.
AGA (American Gas Association), Gas Engineering and Operating Practices Series, Arlington,
Virginia.
Banerjee, N. (1991), "Compressor Scheme Will Reduce Gas Flaring in India's Oil Fields," in
Oil and Gas Journal. April 22 1991.
Barns, David W. and J.A. Edmonds (1990), An Evaluation of the Relationship Between the
Production and Use of Energy and Atmospheric Methane Emissions, U.S. Department of
Energy, Washington, D.C., DOE/NBB-0088P.
Baudino, Mario and Edward Volski (1991), Abating Methane Emissions by Reducing Natural
Gas Leakages, presented at the International Symposium on Environmentally Sound Energy
Technologies and their Transfer to Developing Countries and European Economies in
Transition, Milan, Italy, 21-25 October, 1991.
Bernhardt, Todd (1992), "Examining EFVs," in American Gas, May 1992.
Corder, Ian (1991), "On-Line Repair Using Epoxy-Filled Shells," in Pipeline Industry, July 1991.
Cowgill, R.M. (1991), Pacific Gas and Electric Company, personal communication, September
26, 1991.
Hall, Charles (1991), "Computerized System for Corrosion Control," in Pipeline and Gas
Journal, October 1991.
Japan Gas Association (JGA) (1991), "Catalogue of Technological Options for Methane
Emissions of Natural Gas Systems in Japan," submitted by JGA October 18, 1991.
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3 - 30 OIL ANO NATURAL GAS
LaShoto, Paul (1989), "Automatic Shut-Off Valves," in Pipeline and Gas Journal. November
1989.
Miller, Robert J. (1991), "Maintaining a Cast Iron System," in Pipeline and Gas Journal.
September 1991.
Mitchell, Catherine and Jim Sweet (1990), A Study of Leakage from the U.K. Natural Gas
Supply System with Reference to Global Warming, prepared for Greenpeace U.K. by Earth
Resources Research, London, England.
NOVA (1985). Portable Pipeline Evacuation Compressor, prepared by John Matemisi, Alberta,
Canada, 1985.
PG&E (1990), Unaccounted for Gas Project Summary Volume. Pacific Gas and Electric,
Research and Development, San Ramon, CA, 1990. GRI-90/0067.1.
Pipeline and Gas Journal (Staff) (1990), "Renovating the Paris Gas System'" in Pipeline and
Gas Journal, November 1990.
Pipeline Industry (Staff) (1991), "PE Pipe Insertion Through Cast-Iron Main Saves Money," in
Pipeline Industry, July 1991.
Rabchuk, V. I., N. I. Ilkevich, & Y. D. Kononov (1991), A Study of Methane Leakage in the
Soviet Natural Gas Supply System, prepared for US DOE/EPA, November 1 991; Washington,
DC.
Radian (1992), US Natural Gas Industry Methane Emissions Mitigation and Cost-Benefit
Analysis. Austin, TX.
SOCAL (Southern California Gas Company) (1 992), Unaccounted for Gas Project - Summary
Volume, in preparation, Southern California Gas, Los Angeles, CA, 1992.
Soot, P.M. (1991), "Power Generation Using Small Internal Combustion Engines," prepared
for ICF Inc., 1991.
Stevens, Ralph W. (1 991), "Cathodic Protection Vs. Recoating," in Pipeline and Gas Journal.
March 1991.
Sturgill, C. (1991), "Power Generation: On-Site Use and Sale to Utilities," prepared for ICF
Inc., April 1991.
US DOE (US Department of Energy) (1992), International Energy Annual - 1990. DOE/EIA-
0219(90), Washington, DC.
USEPA (United States Environmental Protection Agency) (1983), Equipment Leaks of VOC
(Volatile Organic Compounds) in Natural Gas Production Industry - Background Information
for Proposed Standards, US Environmental Protection Agency, Research Triangle Park, NC,
December 1983, PB84-155126.
-------
OIL AND NATURAL GAS 3-31
USEPA (1993a), Anthropogenic Methane Emissions in the United States. Report to Congress,
USEPA/OAR (Office of Air and Radiation), Washington, DC.
USEPA (1993b), Opportunities to Reduce Methane Emissions in the United States. Report to
Congress (review draft), USEPA/OAR, Washington, DC.
USEPA (1993c), Options for Reducing Methane Emissions Internationally - Volume II:
International Opportunities for Reducing Methane Emissions. ReporttoCongress, USEPA/OAR,
Washington, DC.
Webb, Mike (1992), personal communication, May 8, 1992.
Zebelean, D.C. (1991), "Compressor-Fuel Engine Analysis Locates Inefficiencies," in Oil and
Gas Journal. August 12, 1991.
-------
CHAPTER FOUR
COAL MINING
4.1 Background
Methane Production. Storage, and Emissions
Methane is produced during coalification (the process of coal formation) and remains trapped
under pressure in the coal seam and surrounding rock strata. This trapped methane is
released during the mining process when the coal seam is fractured. Methane released in this
fashion will escape into the mine works, and will eventually be emitted into the atmosphere.
The production of methane during coalification may exceed the adsorptive capacity of the
coal. For example, although the highest gas content measurements for U.S. anthracite coal
are only 21.6 cubic meters per metric ton, 180 cubic meters of methane may be produced
during coalification (Diamond et al., 1986). As a result, significant quantities of methane seep
into and are stored in the rock surrounding the coal seam. This methane seeps back into the
mine working as the coal is mined. Mine air containing methane is removed from the mine
workings, and is generally vented directly into the atmosphere.
The quantity of methane emitted per tonne of mined coal depends upon several characteristics
of the coal, the most important of which are: 1) gas content, 2) permeability and gas
diffusion rates, and 3) method of mining. The gas content of coal depends upon its rank and
geological history. Coal rank is a measure of the degree of coalification; as coal rank
increases, the amount of methane produced also increases (see Exhibit 4-1). Furthermore,
higher ranks of coal have greater adsorptive capacities and will tend to contain more gas.
Because pressure increases with depth, deeper coal seams generally contain more methane
than shallow coal seams of similar rank. Thus, deeper mines with coal of a higher rank will
typically contain larger quantities of methane.
Permeability and diffusion rates are also important because they determine how quickly gas
can migrate through the coal and into the mine workings. After coal is mined, the strata
overlying the mined coal are allowed to cave in, causing the formation of a rubbleized area,
termed a "gob." This fracturing increases the permeability of the methane-containing strata
and facilitates the release of methane. Because more coal is removed during longwall mining
and fewer pillars remain, the caving associated with longwall mining is generally more
extensive, and thus methane released per tonne of coal is generally higher with longwall
mining than with room and pillar mining.
Methane Recovery and Utilization Strategies
Techniques for removing methane from underground mine workings have been developed
primarily for safety reasons, because methane is highly explosive in air concentrations
between 5 and 15 percent. These same techniques can be adapted to recover methane so
that the energy value of this fuel is not wasted. Where methane utilization is combined with
recovery, methane emissions into the atmosphere are reduced.
-------
4- 2
COAL MINING
Important factors when considering options for reducing methane emissions from coal mining
are: the geologic and reservoir characteristics of the coal basin; mine conditions and mining
method; current mine gas recovery systems; potential gas quality and use options; and
technical and economic capabilities. In particular, the recovery method largely determines the
quality and quantity of gas recovered, which in turn determines the possible utilization
options. Developing uses for recovered methane is required if emission reductions are to be
achieved. The sale and/or use of methane can offset the costs of recovery in certain cases.
Furthermore, improving methane recovery techniques can result in safer, more productive
mines, with lower ventilation costs (Dixon, 1987).
Exhibit 4-1
Coal Rank and Methane Production
1600
Yield cf/ton
3200
Coal Rank
4800
5400
High
Volatile
Bituminous
Med-volatile
Bituminous
91 136
Yield m3/ton
z
o
n
m
o
o
33
Z
*
Source: USEPA, 1990.
-------
COAL MINING
4 -3
Exhibit 4-2
Coal Mining and Methane Recovery Techniques
Longwalt Mining
/ Machine
Train
haulage
(a) Longwall Mining
(b) Room-and-pillar Mining
(c) Vertical Gob Well
(d) Vertical Degasification Well
(e) Cross Measure and
Horizontal Boreholes
(f) Surface Equipment
-------
4 - 4 COAL MINING
Because the quality of gas that is recovered determines the possible gas utilization options,
each of the four techniques presented here is a complete project based on a particular
recovery method and its associated utilization options. Additionally, these strategies are
structured according to technological and economic criteria and overall applicability. The four
strategies presented are:
Enhanced Gob Well Recovery;
Pre-Mining Degasification;
Ventilation Air Utilization; and
Integrated Recovery.
Enhanced Gob Well Recovery: This strategy recovers methane from the gob area of a coal
mine -- the highly fractured area of coal and rock that is created by the caving of the mine
roof after the coal is removed. Gob areas can release significant quantities of methane
into the mine, and if this gas is recovered before entering the mine, ventilation
requirements can be reduced (see Exhibit 4-2, Coal Mining and Methane Recovery
Techniques). Typically, gob gas is diluted by mine air during production so a medium
quality gas is obtained (300-800 Btu/cf; 11-29 MJ/m3). This type of gas can be used in
a variety of applications, including on-site power generation, gas distribution systems, and
industrial heating. Enhanced gob well recovery can involve in-mine and/or surface wells
using existing technology that is currently employed in many countries. In many cases,
the capital requirements for methane recovery are low compared to the amount of gas that
may be produced. The capital cost associated with gas utilization can vary significantly,
being quite high for electricity generation, particularly where gas turbines are used.
Pre-Mining Degasification: This strategy recovers methane before coal is mined. Pre-
mining degasification can be attractive where geologic conditions are appropriate because
the methane is removed before the air from the mine workings can mix with it. Pre-mining
degasification typically recovers a higher quality gas (900-1000 Btu/cf; 32-37 MJ/m3)
which can be used as a chemical feedstock in addition to being used for power generation
and industrial or residential applications. Pre-mining degasification can be an in-mine or
surface operation. When done inside the mine, boreholes can be drilled anywhere from
six months to several years in advance of mining. Surface drilled vertical wells can be
drilled anywhere from 2 to more than 10 years in advance of mining. Pre-mining
degasification requires more advanced technology and equipment than enhanced gob well
recovery, and therefore has higher capital costs.
Ventilation Air Utilization: Most mine gas is released to the atmosphere in the ventilation
air used in the mine. Ventilation, necessary in underground coal mines for safety reasons,
is achieved with large fans which blow air through the mine. The recovery technology is
basic, but the operating costs of running the fans can be high if the mine is gassy. The
methane content of the vented air must be below 5 percent for safety reasons, and is
frequently as low as 0.5 percent to comply with relevant regulations. In spite of its low
concentration, it appears that there may be opportunities to use ventilation air as
combustion air in turbines or boilers (Granatstein etal., 1991; ESA, 1991). However, the
technical and economic feasibility has not yet been demonstrated.
-------
COAL MINING 4 - 5
Integrated Recovery: The most significant methane emission reductions are likely to occur
by employing a combination of methane recovery options. Indeed, many US coal mines
currently use a combination of in-mine and surface recovery methods both before mining
and from gob areas (Soot, 1990). The technological and capital requirements of such
integrated systems are likely to be moderately high, but it is possible that the additional
opportunities for gas utilization, as well as the enhanced mine safety, could justify the
required investment.
Exhibit 4-3 summarizes information on these four coalbed methane recovery and utilization
strategies. The four strategies are described in more detail in the individual technological
assessments.
The assessments consist of the following sections:
Recovery Technology Descriptions;
Utilization Technology Descriptions;
Costs;
Availability;
Applicability;
Barriers; and
Benefits.
-------
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-------
COAL MINING 4 - 7
4.2 Enhanced Gob Well Recovery
Enhanced Gob Well Recovery is an approach that seeks to improve and augment methane
recovery techniques that are already in place at a mine so that recovery is more efficient. This
strategy builds on local experience and methods of operation.
Gob areas consist of fractured rock and coal that have collapsed into mined-out areas. Since
these areas are considerably more permeable than intact coal and rock, methane stored above
and below the coal seam is released during and after the creation of this gob area. The
proximity of the gob area to the lower pressure of the mine can result in the flow of
significant quantities of methane into the mine workings. This released methane is typically
emitted into the atmosphere, rather than being utilized.
In many deep coal mines, methane concentrations in the mine air cannot be maintained at safe
levels through ventilation alone without reducing coal production. Coal mine operators seek
to maximize the amount of coal they can safely produce by employing additional methane
removal techniques to supplement ventilation. These systems are quite common; for
example, 100 state-owned underground mines in China, 18 Polish mines, at least 145 Russian
and Ukrainian mines, and about 35 U.S. mines use some type of advanced methane recovery
technique (JP International, 1990; Pilcher et al., 1991; Zabourdyaev, 1992;USEPA, 1993a).
Mines in many other countries including Czechoslovakia, Germany, Canada, the United
Kingdom, Japan, Australia, South Africa and India - also use these techniques.
The most common of these techniques are performed during mining operations (as opposed
to pre-mining degasification), and include vertical gob wells drilled from the surface and
boreholes drilled from in-mine workings into gob areas. Enhanced Gob Well Recovery will
improve the efficiency of existing recovery systems and expand the use of these techniques.
Based on reported emissions data from a variety of countries, it appears that anywhere from
10 to 50 percent of the total methane emissions may be recovered with these technologies,
depending upon the site-specific geologic conditions, and the design of the degasification
program.
Recovery Technology Description
The two techniques described here are cross-measure boreholes and vertical gob wells. These
techniques are carried out in conjunction with active mining operations, and, as shown in
Figure 2, they recover gas from the caved-in or "gob" area. Removing methane from the gob
area can be technically complex and must be integrated with mining operations. Because the
gob area is located within the mine and is surrounded by ventilated mine workings, medium-
quality gas is typically produced using these techniques.
In-Mine Boreholes: Boreholes have been used in coal mining since the 1800's. This
technology consists of drilling boreholes from the mine workings into unmined areas of the
coal seam and surrounding rock. Cross-measure boreholes, angled into the rock and coal
strata above and below the mine workings, are used to recover methane from the gob
areas. These boreholes are typically tens to hundreds of meters in length. The boreholes
-------
4 - 8 COAL MINING
are connected to an in-mine vacuum piping system, through which recovered methane is
transported out of the mine (USEPA, 1990).
To maximize gas production the boreholes are operated under negative pressure, and in
the process mine air is drawn into the gob area and ultimately into the gas stream. The
quality of gas recovered will vary greatly depending on such factors as local geology, coal
rank, and the efficiency of the recovery system. Previous experience indicates that
medium quality gas (300-800 Btu/cf; 11-30 MJ/m3) will be recovered. Total methane
production will vary according to local factors and the length of the borehole. Various
experiments in the U.S. have yielded production rates of 800 m3/day to 2,800 m3/day for
boreholes of 100 to 200 meters in length (Garcia and Cervik, 1985; Baker et al., 1986).
Typically, 20 to 50 percent of the methane contained in the gob area may be recovered
through the use of in-mine boreholes (USEPA, 1990).
Japan and other countries practice a variant of this method of gob well recovery (Higuchi,
personal communication). When a longwall panel (typically 150-250 m wide and several
hundred meters long; 500-825 ft by 3000 ft) is completed, the resulting collapsed gob
area is sealed to reduce methane leakage into the mine workings. A steel pipe is inserted
into this sealed area and connected to an in-mine piping system enabling large quantities
of methane to be recovered.
Vertical Gob Wells: A second method of removing the methane from the gob area is to
drill vertical wells into the gob from the surface. Prior to mining, wells are drilled to a point
2 to 15 vertical meters above the coal seam (USEPA, 1990). As the working face passes
under the well, the methane-charged coal and rock strata collapse to form the gob. The
methane can be recovered under vacuum, rather than being released into the mine
workings. The main advantage of this technique is that it avoids the difficulties of
working in the mine, and possibly interfering with the mine operations. However, the use
of vertical gob wells requires relatively advanced drilling techniques and may be difficult
to integrate with multiple seam coal extraction.
Typically, the gas quality is similar to that of the in-mine systems, although it may be
easier to produce high quality methane using vertical gob wells. As with in-mine
boreholes, surface gob wells can be operated under negative pressure, drawing mine air
into the gob and diluting the recovered methane. Through careful monitoring of the gas
quality, and adjustment of the vacuum pressure, it is possible to maintain a higher and
more consistent gas quality (one company's mines in Alabama, U.S., produce gas with
over 95 percent methane from the gob wells) (Dixon, 1989). Over time, the quality will
decline as air from the mine workings seeps into the gob area. Vertical gob wells alone
may recover 30 to 40 percent of the methane contained in the gob area (USEPA, 1990).
Typical production figures are 2,800 m3 per day (100,000 cf), but are highly dependent
on site-specific factors (Baker at al., 1988; USEPA, 1990). One mining operation in
Alabama, U.S., recovers 849,000 m3 per day from 80 surface gob wells (Dixon, 1987).
The choice between in-mine and surface recovery techniques depends upon site-specific
factors that affect how cost-effective and appropriate these two techniques are for a
particular mine. These factors include mine depth, mining method, drilling costs, availability
of technology, surface activities, and terrain.
-------
COAL MINING 4 - 9
Where the techniques described above are already in place, it is often possible to increase the
recovery efficiency and improve gas quality through improved drilling techniques, improved
pumping and in-mine piping systems, and the use of more advanced monitoring and control
systems.
Drilling Techniques: Inappropriate drilling technology can slow the drilling of gob wells and
boreholes to the point where it is no longer feasible to implement these technologies.
However, adequate technology currently exists, and is in use in many countries. Where
improvements would be useful, those countries with oil and gas industries may be able to
adapt existing drilling capabilities; otherwise this technology must be imported, raising
project costs. Drilling improvements may include the use of diamond bits for rock, and
the capacity to drill bore holes with larger diameters and longer lengths.
In-Mine Piping: In some mines, the overall quality of the in-mine piping system can be
improved to reduce leakage. One important improvement is to ensure the integrity of the
piping by installing safety devices to shut down the system in the event of mining
accidents. In some cases, increasing the capacity of the piping system will increase the
quantity of methane that can feasibly be recovered.
Pumping: Gas pumps with higher pressures and greater capacities increase the efficiency
of methane recovery. In general any improvements in reliability and lifetime will be
beneficial.
Monitoring: The placement and spacing of boreholes and vertical wells is extremely
important for the effectiveness of a recovery program. Monitoring the recovery system
in operation can also improve the efficiency of the system. Both of these important
factors involve relatively low-technology solutions. For example, each borehole can be
equipped with a shutoff device that activates when the gas quality drops below 25
percent CH4. Many monitoring techniques are currently available and in use.
Utilization Technology Description
There are four main options for utilizing medium quality gas: on-site power generation with
turbines, on-site power generation with internal combustion engines, sale to a distribution
system, and industrial use in boilers. In each case, the sale or direct use of energy can often
justify the initial investment in generating equipment. The anticipated gas flow rate and gas
quality (e.g., impurity levels and methane concentration) are particularly important in selecting
the appropriate utilization option.
On-site Gas Turbines: Gas turbine systems can use medium quality gas to generate power
for on-site use or for sale to nearby electricity users or supply companies. Selection can
be made from among several gas turbine system configurations, depending on factors
such as energy needs, technical capabilities, and capital availability.
Simple cycle gas turbine systems can operate with efficiencies ranging from 1 5 to 40
percent, increasing in efficiency as size increases (Williams and Larson, 1990). Combined
cycle turbine systems use the exhaust heat from a gas turbine to produce steam in a
boiler, which is then used to power a steam turbine. Alternatively, or in addition, waste
-------
4-10 COAL MINING
heat can be used for various local heating needs (i.e., co-generation). When combined
with a heat recovery system, energy efficiencies can exceed 80 percent. Energy
efficiencies in the region of 50 percent can be achieved in combined cycle systems
without heat recovery.
Gas turbine systems have certain properties which make them a particularly attractive
utilization option for coal mines: 1) turbines come in a range of sizes, depending on the
required generating capacity; 2) the turbine combustion process is continuous, which
results in a high combustion efficiency and greater tolerance to deviations in fuel quality;
and 3) waste heat from the turbines can be used for industrial purposes, such as coal
drying at the mine. Gas turbines usually require higher gas flows in order to be
economical, and typical applications at coal mines would use one or more 1 to 5 MW
turbines (Sturgill, 1991). Gas turbines are running on medium quality mine gas in
Australia, China, Germany, and Japan.
On-site Internal Combustion Engines: Internal combustion (1C) engines provide an
alternative method for burning medium quality mine gas for power generation. A
stationary engine can turn a generator which produces electric energy, with operating
efficiencies ranging from 25 percent to 35 percent. With a heat recovery system, energy
efficiencies can reach as high as 80 percent (Williams and Larson, 1990). 1C engines are
widely used to generate power from medium quality gas, and they tend to be better suited
than turbines to low gas flows or irregular use. Although variations in methane
concentration previously caused some problems with the use of mine gas in 1C engines,
modern integrated control systems allow fluctuations in gas quality to be accommodated
in the operation in the engine (Pilcher et al., 1991). 1C engines are available in sizes from
around 30 kW up to several MW, but are typically rated at several hundred kW.
Gas Distribution System: In developing countries, as well as some other regions, medium
quality mine gas can be distributed in residential and commercial gas supply networks and
used for cooking and heating. Many mines in China, for example, currently transport
medium quality methane short distances to residential consumers (JP International, 1990).
The system can be very simple, consisting of pipes and rudimentary stoves which can
burn natural gas. High efficiency gas burners will use fuel more efficiently and will also
reduce the emissions of uncombusted methane. Care should be taken in the construction
of new pipelines so that leakage is minimized.
In some countries, such as Poland, it may also be possible to distribute coalbed methane
in low-methane natural gas (LMNG) or coke-oven gas pipeline systems (Pilcher et al.,
1991). These medium quality gas pipelines are extremely attractive because they can be
used to transport gas that would not otherwise be considered "pipeline quality," (e.g.,
pipeline quality gas must be 95 percent methane in the U.S.) In general, these types of
systems transport gas that is 50 to 70 percent methane.
Industrial Use: Medium quality gas may also be used as a combustion fuel for industrial
boilers. The gas can be supplied to nearby industries and used on its own or in
conjunction with other fuels in a boiler. Medium quality methane from coal mines is used
by local industries in several countries, including Czechoslovakia, Poland, and Ukraine.
The use of medium quality gas may require minimal conversion of existing boiler
equipment, but in many cases requires no significant changes.
-------
COAL MINING 4-11
Costs
Preliminary figures for the costs of recovery and utilization options are presented below. The
prices are U.S. figures and do not reflect the added cost of importing technology, lower labor
costs in developing countries, or other local factors. All costs are in U.S. dollars.
Recovery Costs: Recovery costs will vary depending on the recovery technique being
used and various site-specific factors such as mining depth and coal permeability. Per well
recovery costs are presented below for vertical gob recovery projects. The full costs
associated with hypothetical U.S. vertical gob well and cross-measure borehole projects
are also summarized. The costs are based on U.S. conditions and U.S. state-of-the-art
technology. Simpler technologies may require less capital investment, but may also incur
larger operating costs. Furthermore, improvements in existing technology may be
significantly less expensive than indicated by the costs below.
Vertical Gob Wells. Exhibit 4-4 summarizes the potential range of capital costs on a
per well basis for vertical gob wells in various U.S. coal basins. The number of wells
drilled by a given mine will depend on site specific conditions. In addition, the capital
costs for vertical gob wells vary between and within coal basins due to differences in
well depths (drilling costs), equipment costs, and costs for surface rights (which can
vary significantly on a site-specific basis depending on terrain and land use in the area).
Vertical gob wells are assumed to have fixed annual operating costs associated with
recovering -- but not utilizing - methane. Recovery costs include all manpower,
materials, and power costs for the operations, maintenance, and administration of
producing wells. The likely range of operating costs for vertical gob wells is $4,000
to $8,000 per well (ICF, 1992).
Project costs for hypothetical methane recovery projects using vertical gob wells in
different U.S. coal basins have been estimated by the U.S. Bureau of Mines (Baker,
1988). These costs are for complete methane recovery projects associated with five
years of coal mining. Specific characteristics of the projects, such as the depth of the
wells, the number of wells per longwall panel, the rate of mining, and the productive
life of the wells, were assumed to vary by coal basin. Estimated project costs include
all planning, site development, equipment, drilling and subsequent operating costs, and
general overhead for each project. These costs include only the recovery portion of
the project. Exhibit 4-5 summarizes the total costs of these hypothetical projects in
the selected coal basins (Baker, 1988). No gas production values are provided, so the
USBM study cannot be used to determine production costs on a $/mcf basis.
Based on potential capital and operating costs, however, and with some assumptions
about gas production over the life of the wells, it is possible to make rough estimates
of methane recovery costs in terms of $/mcf. In general, the costs for vertical gob
well recovery could range from a low of $0.50/mcf to levels of $3.00/mcf or higher.
Some U.S. vertical gob well projects have reported costs on the order of $0.75/mcf
to $1.00/mcf, not including the value of cost savings in the mining operations.
-------
4 - 12
COAL MINING
Exhibit 4-4
Capital Costs for Gob Wells (per well costs)
Basin
Central
Appalachian
Northern
Appalachian
Illinois
Warrior
Western
Low
$80,000
$60,000
$50,000
$90,000
$100,000
Medium
$130,000
$110,000
$100,000
$140,00
$150,000
High
$190,000
$170,000
$160,000
$200,000
$210,000
Note: Capital costs for gob wells include all costs for surface drilling rights, site development and
preparation, and costs for drilling, completing and equipping the wells.
Sources used to develop ranges: 1) USEPA 1990; 2) ICF Resources, 1990b; 3) Baker, Garcia, and Cervik
Cost Comparison of Gob Hole and Cross-Measure Borehole Systems to Control Methane in Gobs (USBM
Report of Investigations, 1988).
Exhibit 4-5
Total Vertical Gob Project Costs in Various U.S. Coal Basins
Location
Central Pennsylvania
Northern West Virginia
Southern Virginia
Northern Alabama
Capital Cost
($ millions)
1.0
1.1
6.1
3.8
Operating Cost
($ millions)
0.3
0.3
0.2
0.5
Project Cost
{$ millions)
1.3
1.4
7.2
4.2
Note: Costs are undiscounted and represent the sum of all costs incurred over the life of the project,
which was assumed to be five years and one year of development.
Source: Baker, 1988.
Cross-Measure Boreholes. In general, cross-measure borehole recovery projects will
have lower capital costs but higher operating costs than vertical gob recovery, as a
result of the greater complexity of drilling within the mine. Cross-measure boreholes
are not a common degasification technique in the United States, although they are
widely used in other countries.
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COAL MINING
4 - 13
No costs from actual U.S. cross-measure boreholes projects have been published. In
general, costs for in-mine piping systems will be similar to those for horizontal
boreholes, or about $5/foot of pipe (ICF Resources, 1990a). Drilling costs may be
lower than for horizontal boreholes, however, because the holes are shorter and less
powerful drilling equipment can be used. On the other hand, the shorter cross-measure
boreholes require proportionately more setup time and, because they are drilled through
hard strata rather than coal, could have slower penetration and higher drill bit wear
rates.
The U.S. Bureau of Mines has investigated the costs of hypothetical cross-measure
boreholes systems in four U.S. locations: central Pennsylvania, northern West Virginia,
southern Virginia, and northern Alabama (Baker, 1988). Costs for each area were
specific to anticipated local methane production rates and to local labor and material
costs. The USBM benefitted from some information provided to them by mining
operators in these regions. However, this study only estimated investment and
operating costs over a five-year period for a system with fixed methane capacity. No
estimate of actual production from the boreholes over time was provided. Therefore,
it is not possible to evaluate the economic viability of such a system using the USBM
costs alone. The results of the USBM analysis are summarized in Exhibit 4-6.
Exhibit 4-6
Total Cross-Measure Borehole Project Costs in Various U.S. Coal Basins
Location
Central Pennsylvania
Northern West Virginia
Southern Virginia
Northern Alabama
Capital Cost
($ millions)
0.3
0.4
1.8
1.2
Operating Cost
($ millions)
1.2
1.2
3.6
1.5
Project Cost
($ million)
1.5
1.6
5.4
2.8
Note: Costs are undiscounted and represent the sum of all costs incurred over the life of the
project, which was assumed to be five years and one year of development.
Source: Baker, 1988.
Utilization Costs: Utilization costs are presented for four options: power generation using
gas turbines; power generation using 1C engines; pipeline injection; and use in industrial
boilers. The costs are presented in U.S. dollars, based on U.S. applications and
technology. Costs in other countries could vary significantly depending on specific
conditions.
Power Generation in Turbines. The cost of using methane from coal mines in gas
turbines could range from $0.04/kwh to $0.07/kwh or higher. Key variables are the
size of the turbine, its efficiency, and the market for waste heat. The cost of fuel
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4 - 14
COAL MINING
supplied to the turbine can also be an important cost item; where coal mine methane
is used, however, it is assumed that the only fuel costs are those associated with
transporting and preparing the methane for use.
The equipment required for on-site power generation includes a turbine generator and
the gathering lines between the wellhead and the generator. For off-site sale of power
to a utility, transmission line upgrades or an interconnection facility may be needed to
feed power generated at the mine into the main transmission line. A range of capital
costs for power generation are shown in Exhibit 4-7.
Exhibit 4-7
Capital Costs for Power Generation
Equipment
Gathering lines between
wellhead and generator
Gas Turbine1
Off-site Transmission2
Low
$10,000 per well
$800 per kw installed
$100,000 per project
Medium
$25,000 per well
$1,000 per kw installed
$300,000 per project
High
$40,000 per well
$1,200 per kw installed
$500,000 per project
1 Both 1C engines and gas turbines were examined in the analysis. However, for sizes above 4 MW, it was
assumed that a mine would prefer a gas turbine. Since projects less than 4 MW were not shown to be
profitable, 1C engine costs are not included here.
2 Off-site transmission costs are for costs of an interconnection facility and/or line up-grades. The low
costs assume that an interconnection facility would not be needed and that line up-grades would be
minimal.
Sources used to develop ranges: 1) Carl Sturgill Power Generation: On-site Use and Sale to Utilities
(Prepared for USEPA April, 1991); 2) "Opportunities for Power Generation from Methane Recovered During
Coal Mining" (Draft Report Prepared for USEPA by ICF Resources, 1990a); 3) Bill Wolfe and Greg Maxwell,
"Commercial Landfill Gas Recovery Operation: Technology and Economics" in Klass, Energy from Biomass
and Wastes XII (Institute of Gas Technology, 1990); 4) Personal Communication with Allison Gas Turbines.
Power Generation in 1C Engines. The cost of generating power using 1C engines is
likely to be slightly lower than for turbines. In general, the capital costs of 1C engines
are lower, with estimates ranging from $350 to $500 per kilowatt (Soot, 1991;
Anderson, 1991). Operation and maintenance costs are generally higher than for
turbines, however, typically around $0.02/kwh.
1C engines are best suited to smaller power generation projects, with typical sizes
ranging from a few hundred kilowatts to 2 or 3 MW. Project financial analyses in the
U.S. have indicated that the most economic coal mine generation projects would range
in size from 4 MW to 20 MW. For projects of greater than 4 MW it appears that mines
would prefer gas turbines.
Pipeline Distribution. The costs associated with pipeline distribution will include: (1)
the gas gathering system, between the wellheads and the central
compression/processing location; (2) compression; (3) processing; (4) enrichment, if
necessary; and (5) the transportation system from the compression point to the
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COAL MINING
4 - 15
commercial pipeline. Capital and operating costs for each of these components are
discussed below, based on U.S. experience.
The capital costs for gathering lines, compression, and processing and treatment of the
recovered gas are summarized in Exhibit 4-8. As the table shows, for certain system
components capital costs are presented in terms of the gas production ($/mcf) because
gas production will determine the size of these components.
Exhibit 4-8
Capital Costs for Pipeline Injection All Equipment Needed Between the Wellhead and a
Central Compressor
Equipment
Gathering lines
between wellhead and
Central Compressor
Compressor(s)
Processing/Treatment
Low
$10,000 per well
$1 80 per mcf/day
$10 per mcf/day
Medium
$45,000 per well
$190 per mcf/day
$20 per mcf/day
High
$100,000 per well
$200 per mcf/day
$30 per mcf/day
Note: Capital costs for compressor and processing/treatment are based on maximum gas production per
day. Equipment costs for enrichment of gob gas are included in the total $/mcf operating costs.
Sources used to develop ranges: 1 ) USEPA 1 990; 2) A Technical and Economic Assessment of Methane
Recovery from Coal Seams (Prepared for USEPA by ICF Resources Inc., 1990b); 3) The Potential Recovery
of Methane from Coal Mining for Use in the U.S. Natural Gas System (Prepared by ICF Resources, Inc. for
USEPA, 1990); 4) W.W. Sykes "Gathering Systems Concepts-Planning, Design and Construction"
Proceedings of the 1 989 Coalbed Methane Symposium (The University of Alabama at Tuscaloosa); Warren
R. True "Pipeline Economics" Oil & Gas Journal Special (November 26, 1990).
In addition to capital costs, there will also be operating costs associated with
compression and processing, as shown in Exhibit 4-9. These operating costs are
based on annual gas production.
The capital costs for the gas pipelines that transport gas from the point of compression
to the commercial pipeline are presented in terms of their cost per mile. Costs will
vary between or within coal basins depending primarily on terrain and land use
patterns. Exhibit 4-10 presents a range of costs, which reflects pipeline construction
experience in several U.S. coal basins.
Finally, in some countries or at some mines it may be necessary to enrich gob gas
before it can be injected into pipelines. This will be the case in situations where
medium quality pipelines do not exist and where the mine cannot maintain pipeline
quality gas through monitoring and management of the gob recovery system.
Enrichment costs are quite uncertain and there has been limited experience with the
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4 - 16
COAL MINING
Exhibit 4-9
Operating Costs for Pipeline Injection
All Equipment Needed Between the Wellhead and a Central Compressor
Equipment
Compressor(s)
Processing/Treatment
Low
$.06 per mcf
$.02 per mcf
Medium
$.07 per mcf
$.03 per mcf
High
$.08 per mcf
$.04 per mcf
Sources used to develop ranges: 1) ICF Resources 1990a; 2) Warren R. True "Pipeline Economics" Oil &
Gas Journal Spec/a/ (November 26, 1990).
Exhibit 4-10
Capital Costs for Pipeline Injection
Gathering Lines to Main Commercial Pipeline
Basin
Central Appalachian
Northern Appalachian
Illinois
Warrior
Western
Dollars per Mile
Low
$650,000
$450,000
$200,000
$500,000
$650,000
Medium
$750,000
$550,000
$300,000
$600,000
$800,000
High
$850,000
$650,000
$400,000
$700,000
$950,000
Sources used to develop ranges: 1) ICF Resources 1990; 2) Warren R. True "Pipeline Economics" OH &
Gas Journal Special (November 26, 1990).
enrichment of mine gas. Current estimates for these costs range from $1.00/mcf to
$2.00/mcf for various enrichment approaches. Some new technologies are under
development that could have lower costs of $0.50/mcf, but these have not been
demonstrated.
Industrial Boilers. The cost of adding capacity for gas combustion at industrial facilities
will depend on the site and the retrofit requirements. Retrofits for full boiler conversion
(to 100 percent capacity with gas) can range from $ 1,500/kJ to $3,000/kJ, with sizes
ranging from 40 kJ to 250 kJ (Glickert, 1992). It would thus cost about $200,000
to convert an average sized boiler rated at 120 kJ to gas. Additional costs would
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COAL MINING 4-17
include the gathering of the gas, any necessary compression and processing, and
transportation from the point of compression to the boiler site.
Availability
All of the above technologies are commercially available and are in use in various countries.
In countries where the equipment is not locally manufactured it may be possible to import
used equipment or modify existing equipment.
Applicability
Enhanced gob well recovery, when combined with suitable utilization options, is an
appropriate strategy for mines where more advanced techniques are not already in use or are
found to be impractical. In many cases, recovery and utilization techniques will build upon
existing practices.
Medium quality gas can be used in many countries for a wide range of utilization options.
Some countries, especially developed countries, may have gas quality standards which
prohibit the distribution of a medium quality gas for residential fuel use and therefore reduce
the overall marketability of non-pipeline quality gas. In these countries, power generation or
on-site industrial uses (e.g., coal-drying) may be the most feasible options. In countries with
fewer restrictions on medium quality gas use, the full range of options may be applicable.
Barriers
Barriers to the development of these recovery and use options will depend on the country and
the technology used, but frequently include: investment capital shortages, lack of resources,
difficulties in maintaining gas quality, and regulatory or institutional barriers related to a
country's coal mining or energy sector. To address the technical difficulties, methane content
can be carefully monitored and methods to compensate for heat value variations can be
implemented. Overcoming regulatory, legal or institutional barriers may require changing
legislative or legal frameworks. To the extent that particular policies have reduced the
economic attractiveness of projects, moreover, it may be necessary to remove energy
subsidies, rationalize prices, and/or provide incentives to encourage methane utilization.
Benefits
In addition to the reduction of methane emissions into the atmosphere, other benefits will be
seen from the recovery and use of coalbed methane:
Mine safety will be improved. Because methane drainage is improved with the
enhanced gob well recovery strategy, the methane concentration in the mine is
reduced, which may result in fewer methane-related accidents at mines.
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4-18 COAL MINING
Ventilation costs will decrease. One mining company in Alabama, U.S. has been able
to increase coal production white decreasing ventilation costs by using improved
methane recovery techniques. This mine has estimated that capital expenditures of
$15 million would have been required for additional ventilation shafts and fans
necessary to ventilate the same amount of methane which is now being recovered at
a profit (Dixon, 1989).
A more efficient energy source will be used. Methane can be a more efficient fuel than
coal, particularly in residential cooking and heating end-uses. Many countries,
including China, use coal extensively for residential purposes (JP International, 1990).
Coal combustion cannot respond efficiently to low load operation, nor is it easy to start
and stop operation as the heating load swings. In comparison, gas can respond
instantaneously to heat demand and can be used for low load operation, thereby
providing a more efficient fuel source.
Less S02, NOX, and particulate emissions will be produced by the displacement of coal
with gas. Natural gas combustion produces virtually no SO2 emissions, no particulate
emissions, and lower NOX emissions. A 10 percent increase in gas use in a retrofitted
coal-fired burner will result in a 10 percent decrease in S02 and particulate emissions.
In many countries, expanded natural gas use is being aggressively pursued in response
to serious local air pollution problems (Pilcher et al., 1991; Bibler et al., 1992).
Enhanced Gob Well Recovery and
Utilization
up to 50% methane reduction
improved mine safety
improved mine productivity
competitive with alternative gas
sources
augments existing practices
technology currently available
clean energy source
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COAL MINING 4-19
4.3 Pre-Mining Degasification
Pre-Mining Degasification is a strategy that produces methane from targeted coal seams prior
to active mining. Unmined coal of high rank, such as bituminous coal, may contain as much
as 10 to 20 cubic meters of methane per metric ton of coal (Kim, 1977). Additionally, larger
quantities of methane are stored in the surrounding rock strata. During mining operations, this
methane can also flow into the mine workings where it may create a severe safety hazard.
Conventional methods for removing mine gas dilute the gas and vent it into the atmosphere.
Pre-mining degasification recovers this otherwise wasted resource before mining begins,
thereby increasing utilization options and reducing the methane emissions associated with
future mining activities.
Recovery Technology Description
The two primary recovery technologies are in-mine horizontal boreholes and vertical wells
drilled from the surface. Both techniques can be implemented anywhere from six months to
several years prior to the commencement of active mining operations, depending upon the
amount of degasification required and various geologic factors such as the methane content
and permeability (USEPA, 1 990). Drilling horizontal boreholes is an in-mine technique; vertical
wells are drilled from the surface. Both techniques remove methane from areas of the coal
seam that are not yet exposed to ventilated mine workings, and as a result typically produce
higher quality gas than the "Enhanced Gob Well Recovery" approach. Furthermore, unlike gob
gas recovery, pre-mining degasification does not depend on active mining operation to
stimulate methane emissions. As a result, gas production can be more reliable over longer
periods of time.
Horizontal Boreholes: Horizontal boreholes have been used extensively for methane
drainage, especially in the United States and some European countries. These boreholes
are drilled into the unmined coal seam itself, in contrast to cross-measure boreholes which
are angled up into coal and rock strata at the boundary of the gob area (see "Enhanced
Gob Well Recovery"). The boreholes are typically a few hundred meters long. All
horizontal boreholes are drilled and produce methane prior to mining.
In general, horizontal boreholes are longer than cross-measure boreholes and therefore
require more powerful drilling equipment. They can be drilled in two ways: 1) into the
longwall panel, or 2) into mine development areas prior to the preparation of panels for
mining. In the first case, horizontal boreholes are drilled across the width of a developed
longwall panel and typically produce gas for a period of several months until they are
mined through. These boreholes are generally a few meters shorter than the width of the
longwall panel. In the second case, much longer boreholes can be drilled into the coal
reserves from development headings and drain gas for several years in advance of mining.
As with cross-measure boreholes, horizontal boreholes are connected to an in-mine piping
system often operated under negative pressure to remove the gas. However, the gas
quality is higher, typically over 95 percent methane. Production volumes vary with local
geology and borehole length, and have ranged from 700 to 5,000 m3/day (Trevits and
Finfinger, 1986; Baker et al., 1986; Kline et al., 1987). Useful production lifetimes are
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4 - 20 COAL MINING
reported to be from six months to several years. The production lifetime is limited by how
far in advance the mine is developed or the longwall panels are defined and laid out.
Horizontal boreholes are not as effective for degasification when coal seams are steeply
inclined or have very low permeability, as is the case in many of the world's coal
producing countries such as Japan and China. In these countries, pre-mining
degasification is carried out using cross-measure boreholes drilled from a gallery under the
coal seam (Higuchi, personal communication). Boring stations are typically located every
50 to 100 m (1 60 to 330 ft) along the gallery, and a number of boreholes are drilled from
each station. Borehole spacing depends on coal and geologic characteristics, and they are
usually spaced 10 to 25 m (30 to 80 ft) apart.
Vertical Wells: Degasification using vertical wells drilled from the surface is a more
recently developed technology that has been commercially demonstrated in independent
gas production and coal mining operations. Vertical degasification wells are similar to
conventional oil and gas wells and are drilled into the coal seam several years in advance
of active mining. This technology is more advanced than the use of in-mine boreholes
because of the greater depth of drilling, the need to drill through rock rather than coal, and
the need to stimulate the reservoir in order to produce gas. Despite this, suitable
technologies have been developed and are widely available. The advantages of drilling
from the surface include avoiding working in the mine, and the ability to degasify the coal
seam many years prior to mining.
Because of the vertical orientation of the well, only a few meters of the coal seam will be
exposed (i.e., the height of the coal seam), in contrast to the hundreds of meters exposed
to an in-mine borehole. Depending on the permeability of the coal seam this may limit the
desorption rate of the methane into the well, thereby limiting overall recovery potential.
In order to overcome this, fractures can be induced in the seam by hydraulic fracturing (or
stimulation), a process in which a sand and water mixture is pumped under pressure into
the wellbore. This fracturing process increases the permeability of the seam by creating
pathways through which the gas can flow.
Care must be exercised in the design and execution of hydraulic fracturing to ensure that
the future mineability of the coal is not jeopardized. Many coal miners are concerned that
uncontrolled fracturing could weaken roof rocks and reduce mine safety when the area is
mined through. Experiments in U.S. mining regions have shown that hydraulic fractures
can be controlled and should not adversely affect future mining (Deul, 1986). In fact,
several coal mines in the U.S. are using vertical degasification and hydraulic fracturing to
recover methane in advance of mining (Consolidation Coal Company, 1992; Oxy USA,
1992). When these technologies are used in other basins, however, care must be taken
to protect the integrity of the coal.
After fracturing, water must be removed from the coal formation in order to produce gas.
Removing water (which is naturally occurring and also added during hydraulic stimulation)
decreases the hydrostatic pressure on the coal seams, thereby allowing gas to desorb from
the coal. Coalbed methane wells usually produce substantial quantities of water during
the first year of production, after which water production decreases and stabilizes over
a long period of time. Methane production peaks after the initial dewatering, and declines
slowly (10-20 percent/yr) over the lifetime of the well (USEPA, 1990). Recovered water
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COAL MINING 4 - 21
must be disposed of by direct land application, discharge into streams or rivers, deep well
injection, or in evaporation pits.
The quality of produced water varies depending on geologic characteristics; in some cases
the water is potable, while in other cases it has high concentrations of dissolved salts and
other solids. The quantity and quality of the produced water, as well as applicable
regulations, will determine what disposal or treatment method is required. Where large
quantities of water, poor quality, or local regulations necessitate advanced treatment (such
as deep well injection or desalination) the disposal costs can be substantial.
Pre-mining degasification using vertical wells may be a very effective method of reducing
the methane content of coal seams and could consequently reduce the emissions from
mining operations. Recovery rates of up to 70 percent over a 10 year period have been
documented using this technique (USEPA, 1990). Gas quality is high (over 90 percent
methane) because the methane is not diluted with ventilation air. Production rates depend
on reservoir and geological factors, the success of hydraulic stimulation, coal rank, and
well spacing.
Where the techniques described above are already in place, it is often possible to increase
recovery efficiency through improved drilling techniques, improved pumping and in-mine piping
systems, and the use of more advanced monitoring and control systems. These
improvements have been discussed above (see "Enhanced Gob Well Recovery").
Utilization Technology Description
Pre-mining degasification typically yields high quality gas, with a heat value greater than 32
MJ/m3 (950 Btu/cf). The recovered gas can be used in any of the applications described
above for medium quality gas (in "Enhanced Gob Well Recovery"), including electricity
generation, gas distribution systems, and industrial heating. High quality gas will be a
preferred fuel because it does not cause some of the technical problems associated with
burning fuel with a lower heat value. In addition to the previously described uses, gas that
consistently contains 95 percent methane is "pipeline quality," and can be sold in high quality
pipeline systems (e.g., in the U.S.). This high quality gas may be transported long distances
or used as a chemical feedstock, in addition to its other uses.
Pipeline Distribution: Conventional natural gas is generally processed, gathered, and
compressed on its way from the wellhead to the pipeline. As with conventional gas
production, methane recovered from coal mines will also require these steps, although the
specifics of these activities may differ slightly.
Processing involves the removal of impurities. For most coalbed methane, the principal
contaminants are water and sand, which can be easily removed. Some coal seams may
also contain significant concentrations of C02, which must also be removed from the gas
prior to pipeline injection. In cases where rare trace gases (e.g., helium) are found,
separation techniques can be used to remove the gases and these by-products can then
be sold. Water and sand are removed at the wellhead; trace gases and C02 are usually
separated at a central processing location after the gas is gathered. Gathering lines are
laid between the wellhead and the processing plant of pipeline.
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4 - 22 COAL MINING
The gas is compressed and propelled through the gathering lines to the pipeline. The
required compression is a function of the compressor's inlet pressure, outlet pressure, and
rated capacity. Pressures typically range from 200 to 800 psi (ICF Resources, 1990c).
Chemical Feedstock: Methane is a feedstock (i.e., a raw material) in several important
chemical processes, such as the synthesis of ammonia, methanol, and acetic acid. In very
gassy areas, pre-mining degasification can recover the large quantities of consistently high
quality methane required to supply chemical plants. The smallest plants typically require
about 5 to 10 million standard cubic feet per day (280,000 cubic metersMXytel
Technologies, 1992), although smaller plants may be feasible. Alternatively, coalbed
methane from several mines could be collected at a central location in order to meet this
required volume.
Total project costs will include both the costs associated with methane recovery and the costs
associated with gas utilization. A range of costs associated the two pre-mining recovery
technologies - vertical wells and in-mine boreholes -- are summarized below. Many of the
utilization costs have already been presented in the discussion of gob well costs, but those
costs associated with unique utilization options, such as chemical feedstock, are also
presented in this section.
Recovery Costs: The costs associated with recovering methane in advance of mining
using vertical wells and in-mine horizontal boreholes are summarized below. These costs
are based on U.S. experiences and technology and they are presented in U.S. dollars.
VerticaLWells. The costs associated with recovering methane in advance of mining
using vertical wells are higher than for gob wells, because these wells require
additional completion and hydraulic stimulation and because it is necessary to dispose
of the produced water. As with vertical gob wells, the capital costs will vary between
and within basins depending on the depth of the wells and site specific conditions,
which can influence the completion method used, the type of stimulation, the amount
of water produced, and the method of water disposal required.
Exhibit 4-11 summarizes the capital costs associated with vertical well drilling,
completion and stimulation in the United States. The costs of surface rights and site
development are also included in these figures. The costs associated with coal basins
in the eastern United States tend to be lower as compared to western basins because
the eastern basins are usually shallow.
The operating costs of vertical wells will depend on the number of wells in operation
and on annual gas and water production. The per well recovery costs are associated
with the operation, maintenance and administration of the producing wells. They
should be quite similar to those for vertical gob wells and are assumed to remain fixed
over the lifetime of the well regardless of the amount of methane recovered. The
operating costs could range from $4,000 per well to $8,000 per well, depending on
site specific conditions (ICF, 1992).
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COAL MINING
4 - 23
Exhibit 4-1 1
Capital Costs for Vertical Wells (per well costs)
Basin
Central Appalachian
Northern Appalachian
Illinois
Warrior
Western
Low
$60,000
$50,000
$45,000
$90,000
$320,000
Medium
$140,000
$125,000
$115,000
$190,000
$450,000
High
$225,000
$205,000
$195,000
$290,000
$580,000
Note: Capital costs for vertical wells include all costs for surface drilling rights, site development and
preparation, drilling, completing and equipping the wells and hydraulic fracture treatment.
Sources used to develop ranges: 1 ) USEPA 1 990; 2) A Technical and Economic Assessment of Methane
Recovery from Coal Seams (Prepared by ICF Resources, Inc. for USEPA, 1990); 3) The Coalbed Methane
Resource and the Mechanisms of Gas Production (Gas Research Institute, 1989); 4) Economics and
Financing of Coalbed Methane Ventures (Ammonite Resources, 1991); 5) Hunt and Steele Coalbed
Methane Technology Development in the Appalachian Basin (prepared for Gas Research Institute, 1991);
Market Study of Future Coalbed Methane Activity (Spears and Associates, 1991).
Vertical wells typically produce significant quantities of water during the first months
of operation, which must be disposed of in an environmentally safe manner. Water
disposal costs will vary for individual mines depending on geologic conditions and
applicable environmental regulations.
The capital costs for water disposal systems can range from $0.30/barrel of water to
$3.30/barrel of water. The low end of this range is associated with stream discharge
with little treatment, a practice that is sometimes practiced in the Warrior basin.
Medium costs of $0.90/barrel of water would be associated with stream discharge
with treatment, or land application with treatment, as is practiced in the Warrior basin.
The high end of this range is associated with the cost of disposal wells or evaporation
pits, which are often necessary, as is the case in the Western U.S.
The operating costs for water disposal can vary significantly depending on the disposal
method used. Generally, the stream or river discharge disposal method has the lowest
operating costs. Evaporation pits, surface application, and stream or river discharge
with treatment, deep well injection and commercial off-site disposal have higher
operating costs. Operating costs for water disposal can range from $0.40/barrel of
water to $1.00/barrel.
The methane production costs (in $/mcf) will vary significantly depending upon
numerous site-specific factors, such as depth of drilling, completion and stimulation
methods used, water disposal requirements, and gas production. Low costs could be
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4 - 24 COAL MINING
in the range of $1.00/mcf, and high costs could reach $3.50/mcf or more. As
production costs increase, project economics become less attractive.
In-Mine Boreholes. The costs for in-mine horizontal boreholes have been estimated by
the U.S. Bureau of Mines and others (Baker, 1986; ICF Resources, 1990a). The total
system costs associated with several U.S. projects -- including the boreholes, methane
collection system, gas transmission system, and methane sensing system --are
reported to range from $25/foot of borehole to $35/foot of borehole. These costs
include both amortized investment and system operating costs. Capital and operating
costs for drilling alone are reported to range from $10 to $15 per foot of borehole.
The cost of in-mine piping systems may be about $5/foot of pipe.
The costs of in-mine systems will of course be highly site-specific. Conditions within
the mine will determine the number of boreholes drilled and their gas production rates.
Likely gas production costs could range from $1.00/mcf to $4.00/mcf or higher.
Utilization Costs: The utilization costs for several options ~ including power generation
with turbines and 1C engines, pipeline distribution, and use in industrial boilers - were
summarized in the section on gob well recovery. One additional utilization option may be
attractive where high-quality methane is recovered: the use of methane as a chemical
feedstock. The costs for this option will include the costs associated with the process,
as well as costs related to collecting and transmitting the methane to the point of use.
These costs will be highly variable depending upon the feedstock process selected and the
amount of gas to be processed.
Availability
All of the above technologies are commercially available, but may not be feasible in certain
regions for technical or economic reasons. In countries where the equipment is not locally
manufactured, it may be possible to import used equipment or modify existing equipment.
Factors affecting applicability and barriers to implementation are discussed in the following
sections.
Applicability
Pre-Mining Degasification is an appropriate strategy for very gassy mines where more
advanced techniques are already in use, or may be easily introduced. In many cases, recovery
and utilization techniques will build upon existing practices.
High quality gas is a valuable energy source or raw material that can be used in many
countries. Developed countries, in particular, are likely to have pipeline infrastructures which
would allow the distribution of high quality gas for commercial sale and/or residential fuel use.
The price for natural gas varies considerably from region to region, however, and can have
a large effect on the applicability of commercial sale as an option (including use as a chemical
feedstock). Using high quality gas as a chemical feedstock would be attractive for gassy
mines in countries with substantial domestic petrochemical markets (e.g., China and India are
both increasing their domestic demand for ammonium fertilizers).
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COAL MINING 4 - 25
Barriers
Barriers to the development of these recovery and use options will depend on the country and
the technology used. Frequently encountered barriers include investment capital shortages,
lack of local resources, lack of technical experience, low gas prices, and legal or regulatory
constraints. Some of the barriers can be overcome through technology demonstration,
training, and technical assistance in regulatory development. In other cases, it may be
necessary to restructure energy sectors, rationalize energy prices, and provide assistance in
the development of viable gas markets. Additionally, because the use of recovered methane
as a feedstock requires transport to the point of sale, feasible proximity to commercial users
must be considered.
Benefits
In addition to reducing methane emissions into the atmosphere, pre-mining degasification will
result in several other benefits:
Mine safety will be improved. Because methane drainage is greatly improved through
pre-mining degasification, the methane concentration in the mine is reduced, which
may result in fewer methane-related accidents.
Ventilation costs will decrease. One mining company in Alabama, U.S. has been able
to increase coal production while decreasing ventilation costs by using improved
methane recovery techniques. This mine has estimated that capital expenditures of
$15 million would have been required for additional ventilation shafts and fans
necessary to ventilate the same amount of methane which is now being recovered at
a profit (Dixon, 1989).
A more efficient energy source will be used. Methane can be a more efficient fuel than
coal, particularly in residential cooking and heating end-uses. Many countries,
including China, use coal extensively for residential purposes (JP International, 1990).
Coal combustion cannot respond efficiently to low load operation, nor is it easy to start
and stop operation as the heating load swings. In comparison, gas can respond
instantaneously to heat demand and can be used for low load operation, thereby
providing a more efficient fuel source.
Less S02, NOX, and particulate emissions will be produced by the displacement of coal
with gas. Natural gas combustion produces virtually no SO2 emissions, no particulate
emissions, and lower NOX emissions. A 10 percent increase in gas use in a retrofitted
coal-fired burner will result in a 10 percent decrease in S02 and particulate emissions.
In many countries, expanded natural gas use is being aggressively pursued in response
to serious local air pollution problems (Pilcher et al., 1991; Bibler et al., 1992).
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4 - 26 COAL MINING
Pre-Mining Degasification
up to 70% methane reduction
high quality gas
long production lifetime
improved mine safety
improved mine productivity (up to
25% at gassy mines)
competitive with other gas sources
technology currently available
clean energy source
4.4 Ventilation Air Utilization
Ventilation air utilization presents an opportunity to use the considerable volume of mine gas
that is currently vented into the atmosphere in low concentrations from all underground
mines. Developing uses for ventilation air can significantly reduce methane emissions to the
atmosphere from coal mining.
The release of methane into the mine workings presents a safety hazard for all deep coal
mines, because methane is explosive at concentrations of 5 percent to 1 5 percent in air.
Most countries have regulations which require that methane concentrations be kept below 1
percent. The most common method of achieving this safety level is to dilute the methane
through the ventilation of the mine with large fans. Although additional techniques can be
used, ventilation is a necessity in all underground mines. As a result, large quantities of air
are removed which contain methane at an average concentration of about 0.5 percent
methane. At gassy U.S. mines, between 5 and 23 tons of air may be ventilated per ton of
coal mined (Skow et al., 1980). Total methane emissions in ventilation air range from 0.5 to
1 5.0 million cubic feet a day of methane for gassy U.S. mines (Trevits et al., 1991). Recent
estimates for the U.S. indicate that the venting of mine gas accounts for 50 to 75 percent of
all methane releases from coal mining, and 75 percent of emissions from underground mines
(USEPA, 1993a).
Although the methane in ventilation air is dilute, its energy value may still be profitably
recovered. Efforts to reduce methane emissions from this source must focus on developing
uses for air that contains low concentrations of methane. The utilization techniques described
here involve using ventilation air as a supplemental or secondary fuel for the generation of
electricity in steam boilers and gas turbines. Depending on its concentration and the generator
technology, ventilation air could supply between 7 percent and 1 5 percent of a generator's
energy (or higher if methane concentrations are in excess of 0.5 percent), thereby reducing
primary fuel requirements and contributing to the electricity need of the mining operation
(ESA, 1991).
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COAL MINING 4 - 27
Recovery Technology Descriptions
Recovery of the methane is not a factor in this strategy. As noted above, ventilation of the
mine will occur as a matter of course in any underground mine, and utilizing the ventilation
air should have no negative economic or practical effect on mining operations. Since this
utilization option has not yet been demonstrated, however, it is important to design the
system in a manner that does not jeopardize the ability of the mine to dilute and remove the
methane from the mine workings. In addition, this option must be implemented in a manner
consistent with mine safety regulations.
Utilization Technology Description
The utilization option discussed in this section involves substituting low concentrations of
methane in air for combustion air in coal-fired boilers or gas turbines. In either case the basic
concept is the same: generators obtain energy by burning a fuel/air mixture, with the fuel
being coal or gas. Because ventilation air from coal mines contains methane, it has a heat
energy value which could reduce the amount of fuel required to create an explosive fuel/air
mix of combustion in a boiler or turbine.
For both coal-fired boilers and gas turbines, the ventilation air must be ducted from the
ventilation shaft to the generating facility. Preliminary technical analyses indicate that the air
supply system can be readily constructed from galvanized steel ducts, typically 7 to 1 2 feet
(2 to 4 m) in diameter (ESA, 1991). Fans and motors will likely be necessary if the supply
distance is over 1000 feet (300 m). The energy needs of the fan motors must be balanced
against the energy value of the mine gas - at some point, depending on duct length, capacity,
and pressure, more energy will be required to transport the gas to the generating facility than
can be recovered during combustion. It appears that this distance is on the order of 3 miles
(5 km).
Coal-Fired Boilers: Coal-fired boilers burn pulverized coal mixed with large amounts of
combustion air to produce steam, which in turn is used to generate electricity. Typically,
13 pounds of air are needed for every pound of coal that is burned (i.e., a 13:1 mass
ratio). This translates to approximately 140 standard cubic feet (4 m3) of combustion air
per hour for each kilowatt (SCFH/kW) of generating capacity, but the ratio will vary with
coal type, boiler efficiency, and the amount of excess air used in combustion (ESA, 1 991).
Preliminary technical feasibility studies indicate that ventilation air can be transported
through the air ducts of most types of boilers without compromising safety or otherwise
affecting standard operation. The methane should therefore be easily introduced into the
boiler, where it will burn and produce heat. 140 standard cubic feet of ventilation air (i.e.,
the approximate amount needed to produce 1 kWh of electricity), containing 0.5 percent
methane, has a heat value of 700 Btu (740 kJ). Ventilation air containing 0.5 percent
methane could provide 7 percent of the boiler's energy (ESA, 1991). Replacing the
primary fuel, coal, with methane could also improve boiler economics through reduced fuel
purchasing, handling, and preparation costs, less furnace slagging and ash production, and
lower emissions of particulates, sulfur dioxide and nitrogen oxides.
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4 - 28 COAL MINING
Gas Turbines: A gas turbine uses heat obtained from the combustion of a fuel/air mixture
to raise the temperature of compressed air. The hot compressed gas powers a turbine
which generates electricity. Gas turbines use large quantities of combustion air in the
fuel/air mixture, typically 350 SCFH per kW of generating capacity for turbines with
capacities between 1 and 100 MW. Based on ventilation air containing 0.5 percent
methane, 350 SCFH would provide 1750 Btu/kWh, or about 15 percent of a typical
turbine's energy requirements (ESA, 1991).
Because turbines use larger quantities of combustion air than coal-fired boilers, and thus
gain a higher energy contribution from ventilation air they are an attractive option for
ventilation air use. Additionally, the simpler technology, lower capital and maintenance
costs, shorter construction lead times, and the large range in available generating
capacities make turbines extremely suitable for use at coal mines.
The applicability of these techniques must be determined by an analysis of many site-specific
factors, including the compatibility of the volume of ventilation air with combustion air
requirements, the mine operation power requirements and/or local energy markets, and the
proximity and design of the generating plant. A discussion of relative energy costs is
presented in the following section.
The underlying factor in choosing to use ventilation air as combustion air is the relative energy
cost of supplying ventilation air. If low concentration methane is to replace some percentage
of the primary fuel requirements for electricity generation, the ventilation air must be supplied
at a lower cost per unit of energy than the primary fuel.
In terms of fuel costs, supplying low quality methane is attractive if the combustion devices
are located in close proximity to the mine. In this situation, the capital costs of the ducting
should be low and the operating costs associated with running fan motors minimized. For a
range of air flows from 2 MMSCFH to 80 MMSCFH (compatible with turbine sizes of 5 MW
to 230 MW respectively), costs are estimated to be $0.08 to over $1.60 per MMBtu,
depending on the distance and methane concentration (ESA, 1991). To the extent that new
ventilation shafts are opened as mining proceeds, it may be necessary to move the fans and
ducting every few years, which could increase costs. In comparison to current U.S. costs of
$1.50 to $4.00/MMBtu for conventional turbine fuels (e.g., natural gas and #2 fuel oil) the
economics of supplying ventilation air to mine-site gas turbines appear attractive in many
cases (ESA, 1991).
Energy costs rise when the ventilation air is transported some distance from the mine site.
In this situation, higher methane concentrations and flow rates will increase the overall
attractiveness of the project. For example, supplying air containing 0.5 percent methane at
a flow rate of 40 MMSCFH (compatible with a 285 MW coal-fired boiler) would cost
approximately $1.25 MMBtu at a distance of 3 miles (ESA, 1991). In comparison, delivered
coal costs are approximately $1.50/MMBtu in the U.S., rising to $1.75- $2.00/MMBtu if costs
for preparation, pollution control and ash disposal are included. Exhibit 4-12 shows estimated
break-even energy costs for ventilation air use based on duct length, methane content, and
air flow.
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COAL MINING
4- 29
Exhibit 4-12
Break-Even Energy Costs for Mine Ventilation Air
Distance
(miles)
Concentration
(% CH4)
< 0.5
1.0
3.0
< 0.5
1.0
< 0.5
1.0
3.0
Gas Flow (mmscfh)
Turbine Capacity (MW)
Boiler Capacity (MW)
2
6
14
20
57
143
40
114
286
80
229
572
|| || Break-Even Energy Cost ($/mmbtu)
0.5
0.5
0.5
0.25
0.25
1.0
1.0
1.0
0.8
> 1.6
> 1.6
n/a
n/a
n/a
n/a
n/a
0.25
0.55
> 1.6
n/a
n/a
n/a
n/a
n/a
0.18
0.35
1.25
0.5
0.8
0.08
0.18
0.5
0.13
0.28
1.25
n/a
n/a
0.08
0.13
0.42
Source: ESA, 1991.
Availability
The recovery, transportation, and combustion of ventilation air uses equipment and
technology that is commercially available and accessible. However, this concept has not yet
been demonstrated and pilot projects should be undertaken to determine if this strategy is
feasible.
Applicability
Large quantities of ventilation air are vented by every operating underground mine. These
emissions constitute an untapped energy resource that can potentially be utilized. If a
technical demonstration is successful, the utilization of ventilation air should be considered
for every mine. However, there are economic and practical requirements that will limit the
number of feasible project locations. The crucial factors are whether the methane in the
ventilation air can be reliably supplied to the combustion device in sufficient quantity at an
energy cost lower than the primary fuel, and whether the project can be implemented in a
technically feasible manner that does not adversely affect mine safety or the safety of
powerplant operation.
Ventilation air use may be economically attractive in certain locations if it is proven technically
feasible. Additionally, where primary fuel is available and electricity demand is expected to
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4 - 30 COAL MINING
grow, meeting this demand by installing gas turbines in the vicinity of underground coal mines
may be a feasible strategy that more efficiently utilizes local resources.
Barriers
Despite the potential for utilizing this resource, there are several barriers to implementation.
Most importantly, the technical viability of this utilization option has yet to be demonstrated.
Institutional interest and awareness of the potential is often lacking, as are incentives to
consider ventilation air as an energy source. In addition, the massive volume of low quality
gas that is produced is itself a barrier. Generally, utilizing all the ventilation air produced by
a mine would necessitate a larger generator than is required for mine operations alone. As
a result, full utilization of mine ventilation air requires external electricity markets and a
transmission infrastructure; this reliance on specific conditions in other sectors of the local
energy market may present a barrier to project implementation.
Benefits
In addition to the reduction of methane emissions into the atmosphere, other benefits will be
seen from the utilization of ventilation air:
Reduced use of primary energy sources and/or increased generating capacity. The use
of ventilation air in electricity generation can reduce primary energy source use by up
to 30 percent. This is a more efficient use of energy resources, and can reduce
reliance on foreign energy sources.
Less SO2, NOX, and paniculate emissions will be produced by the displacement of coal
with gas. Natural gas combustion produces virtually no S02 emissions, no particulate
emissions, and lower NOX emissions. A 10 percent increase in gas use in a retrofitted
coal-fired burner will result in a 10 percent decrease in S02 and particulate emissions.
In many countries, expanded natural gas use is being aggressively pursued in response
to serious local air pollution problems (Pilcher et al., 1991; Bibler et al., 1992).
Ventilation Air Utilization
10-90% methane reductions
efficient use of energy resources
competitive energy costs
augments existing practices
technology currently available
demonstration projects necessary
clean energy source
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COAL MINING 4 - 31
4.5 Integrated Recovery
An integrated system of methane recovery and utilization can take full advantage of all the
available strategies for reducing methane emissions from coal mining. In many mines, using
two or more methane recovery approaches (e.g., pre-mining degasification with horizontal
boreholes and vertical gob wells) can: 1) optimize mine degasification, achieving the
maximum improvements in mine safety and productivity; and 2) realize economies of scale
as fixed costs are shared (Exhibit 4-13).
Recovery Technology Description
Developing the capability to implement a variety of methane recovery techniques enables an
optimal response to site-specific field conditions. The available methane recovery
technologies have each been described in the technical assessments above. Each technology
can effectively reduce methane concentrations in mines. Nevertheless, due to certain
geological or technological factors it may be desirable to implement a combination of
strategies. For example, if methane reductions of 50 percent are required to maintain coal
production most economically while ensuring mine safety, an optimal strategy may be to
combine gob well recovery with pre-mining drainage. This has been the experience of at least
one mining operation in the United States (Dixon, 1987), and many mines in the U.S. and
throughout the world use a variety of degasification techniques to optimize methane recovery.
In addition to technical advantages, economies of scale may be realized in integrated projects.
Utilization Technology Description
As with recovery technologies, the utilization technologies that have been previously
described may be combined to optimize gas use. The compatible combination of end uses can
improve technical and economic feasibility.
Costs
Integrated recovery projects will typically be larger than projects employing single strategies;
capital costs are expected to be correspondingly larger. However, unit costs may be lower
due to economies arising from the implementation of mutually beneficial technologies.
Economies of Scale: Several of the techniques use similar technology, equipment, or
drilling practices, and require similar technical capabilities. In-mine piping and surface
gathering and processing equipment are often compatible with different projects.
Therefore, certain fixed costs associated with capital expenditures, support facilities,
training, and maintenance may be spread over several types of methane recovery. Even
where this is not the case, common costs of project planning and overhead can be shared
for integrated strategies.
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4- 32
COAL MINING
Economies of Scope: The most promising potential for integrated systems lies in the
mutual benefits of coordinating utilization strategies. For example, one of the significant
barriers to utilizing ventilation air as a supplementary combustion fuel is the supply of
competitively priced primary fuel for gas turbines (see "Ventilation Air Utilization").
Conventional supplies of gas turbine fuel, natural gas or #2 fuel oil, can cost between
$1.50 and $4.00 per MMBtu, which is often enough to make the installation of a turbine
uneconomical. However, coordination of a degasification or gob well recovery project
with the combustion of ventilation air can provide a significantly less costly supply of
primary fuel; medium quality gas (as low as 30 percent methane) is sufficient to power
a gas turbine. The integrated recovery and use of both low and medium/high quality gas
provides a direct demand for the medium quality gas, and removes a barrier to utilizing
ventilation air; independent of one another, these projects may not be feasible.
Exhibit 4-13
Integrated Recovery
Gas use
To Power
Generation (tor use i
combustion air)
Gas use
Note: not drawn to scale
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COAL MINING 4 - 33
Mutual advantages may also exist for issues of technical feasibility. Active gob gas recovery
will reduce the volume of ventilation air necessary to maintain mine safety. As a result, a
smaller and less costly turbine can be used, or a more significant proportion of the ventilation
air can be consumed. Coordinating the production from both projects can optimize total
project economics and feasibility.
Availability
Technologies for reducing methane emissions are available. However, certain countries may
need technical assistance in assessing the trade-offs between approaches for developing
optimal integrated systems.
Applicability
There are significant benefits associated with developing integrated methane recovery and
utilization projects. However, it is important to realize that these benefits are attained through
the implementation of larger and more technically advanced projects. This fact has a direct
impact on the suitability of integrated recovery projects. It is likely that integrated projects
will only be suitable for large mining operations working in relatively gassy coal seams. The
current trend in coal mining is towards deeper, and thus gassier mines, making the
implementation of integrated projects increasingly likely.
Barriers
The barriers for integrated recovery will be similar to those facing any methane recovery
project, though larger because of the additional scope, cost, and complexity. As a direct
result of the size and technical sophistication of these larger projects, capital expenditures and
operating costs will be correspondingly higher even though the long-term economics may be
more favorable. Similarly, equipment and training needs will be more advanced, as will
technical and planning expertise. Integrated projects will likely only be implemented by mining
operations that have significant previous experience, or with technology transfer assistance.
Benefits
In addition to the reduction of methane emissions into the atmosphere, other benefits will be
seen from the integrated recovery and use of coalbed methane:
Mine safety will be improved. Because methane drainage is improved with the
enhanced gob well recovery strategy, the methane concentration in the mine is
reduced, which may result in fewer methane-related accidents at mines.
Ventilation costs will decrease. One mining company in Alabama, U.S. has been able
to increase coal production while decreasing ventilation costs by using improved
methane recovery techniques. This mine has estimated that capital expenditures of
$15 million would have been required for additional ventilation shafts and fans
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4 - 34 COAL MINING
necessary to ventilate the same amount of methane which is now being recovered at
a profit (Dixon, 1989).
A more efficient energy source will be used. Methane can be a more efficient fuel than
coal, particularly in residential cooking and heating end-uses. Many countries,
including China, use coal extensively for residential purposes (JP International, 1990).
Coal combustion cannot respond efficiently to low load operation, nor is it easy to start
and stop operation as the heating load swings. In comparison, gas can respond
instantaneously to heat demand and can be used for low load operation, thereby
providing a more efficient fuel source.
Less S02, NOX, and particulate emissions will be produced by the displacement of coal
with gas. Natural gas combustion produces virtually no S02 emissions, no particulate
emissions, and lower NOX emissions. A 10 percent increase in gas use in a retrofitted
coal-fired burner will result in a 10 percent decrease in SO2 and particulate emissions.
In many countries, expanded natural gas use is being aggressively pursued in response
to serious local air pollution problems (Pilcher et al., 1991; Bibler et al., 1992).
Degasification will be optimized. The integrated use of suitable recovery technologies
can result in up to 90 percent methane reduction. Greater reductions can be achieved
while improving project economics.
Integrated Systems
up to 90% methane reduction
optimization of degasification
economies of scale
economies of scope
augments existing practices
technology currently available
clean energy source
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COAL MINING 4 - 35
4.6 References
Contributions were made by:
E. Dowdeswell, Environment Canada, Canada
Roger Glickert, Senior Engineer, Energy Systems Associates, USA
Kiyoshi Higuchi, Hokkaido University, Japan
Robert Kane, Global Climate Program Manager, U.S. Department of Energy, USA
Dina Kruger, Project Manager for Coalbed Methane, USEPA, USA
Carl Sturgill, Independent Consultant, USA
Additional information may be found in the following:
Ammonite Resources (1990), "Economics and Financing of Coalbed Methane Ventures,"
presented by G.W. Hobbs and R.O Winkler, at The Eastern Coalbed Methane Forum.
Tuscaloosa, AL, January 16, 1990.
Anderson, C. (1991), Waste Management of North America, personal communication,
October 8, 1991.
Baker, E.G., R.H. Grau III, G.L. Finfinger (1986), Economic Evaluation of Horizontal Borehole
Drilling for Methane Drainage from Coalbeds, 1986, 1C 9080.
Baker, E.G., F. Garcia, J. Cervik (1988), Cost Comparison of Gob Hole and Cross-Measure
Borehole Systems to Control Methane in Gobs, U.S. Bureau of Mines, 1988, Rl 9151.
Bibler, C.J., J.S. Marshall, and R.C. Pilcher (1992), Assessment of the Potential for Economic
Development and Utilization of Coalbed Methane in Czechoslovakia, prepared by Raven Ridge
Resources, Inc., Grand Junction, CO, for USEPA, in press.
Consolidation Coal Company (1992), update on Consol/Conoco project in Buchanon County,
VA, delivered at the Fall 1992 Pittsburgh Coalbed Methane Forum Meeting, October 14,
1992, Morgantown, WV.
Deul, M., A.G. Kim (1986), Methane Control Research: Summary of Results, 1964-80, U.S.
Bureau of Mines, 1986, B-687.
Diamond, W.P., J.C. Lascola, and D.M. Hyman (1986), Results of the Direct Method
Determination of the Gas Content of U.S. Coalbeds. U.S. Bureau of Mines, 1C 8515, 36 pp.
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4 - 36 COAL MINING
Dixon, C.A. (1987), "Coalbed Methane -- A Miner's Viewpoint," in Proceedings of the 1987
Coalbed Methane Symposium, Tuscaloosa, Alabama.
Dixon, C.A. (1989), Maintaining Pipeline Quality Methane from Gob Wells. Pittsburgh Coalbed
Methane Forum, April 4, 1989, 7 pp.
ESA (Energy Systems Associates)(1991), "Opportunities for the Utilization of Mine Ventilation
Air," prepared for Global Change Division, USEPA, Washington, D.C. January, 1991.
Garcia, F., and J. Cervik (1988), Review of Membrane Technology for Methane Recovery from
Mining Operations, U.S. Bureau of Mines Information Circular/1988, 1C 9174, 6 pp.
Glickert, R. (1991), Energy Systems Associates, personal communication, August, 1991.
GRI (Gas Research Institute) (1989), "The Coalbed Methane Resource and the Mechanisms
of Gas Production" Topical Report prepared by ICF Resources, Inc. for Gas Research Institute,
Contract Number 5984-214-1066, November, 1989.
Granatstein, D.L., A.L. Crandlemire, J.C. Campbell, P.P. Preto, B.C. King (1991), "Utilization
of Coal Mine Methane at Lingan Generating Station," presented at the 19th Stack Gas/Energy
Technologies Meeting, Battelle Laboratories, Columbus, Ohio, September, 1991.
Higuchi, Kiyoshi, Hokkaido University, Japan, personal communication, 1992.
Hunt, A.M. and D.J..Steele (1991), Coalbed Methane Technology Development in the
Appalachian Basin. Topical Report prepared by Dames and Moore for Gas Research Institute,
Contract Number 5089-214-1783, January, 1991.
ICF, Inc. (1992), Options for Reducing Methane Emissions from Coal Mining. Draft Report,
prepared for USEPA by ICF, Inc. (in preparation), 1992.
ICF Resources (1990a), Opportunities for Power Generation from Methane Recovered During
Coal Mining. Revised Draft Report, prepared for USEPA by ICF Resources, Inc. with
contributions from ICF Kaiser Engineers, September 30, 1990.
ICF Resources (1990b), A Technical and Economic Assessment of Methane Recovery from
Coal Seams, prepared for USEPA/OAR (Office of Air and Radiation).
ICF Resources (1990c). The Potential Recovery of Methane from Coal Mining for Use in the
U.S. Natural Gas System, prepared for the USEPA/OAR.
IPCC (1990), Methane Emissions and Opportunities for Control: Workshop Results of
Intergovernmental Panel on Climate Change, U.S. Environmental Protection Agency,
Washington, D.C., EPA/400/9-90/007.
JP International (1990), Opportunities for Coalbed Methane Recovery and Utilization in China.
prepared for the U.S. Environmental Protection Agency, September, 1990.
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COAL MINING 4 - 37
Kim, A.G. (1977). Estimating Methane Content of Bituminous Coalbeds from Adsorption Data,
U.S. Bureau of Mines, Rl 8245, 22 pp.
Kline, R.J., L.P. Mokwa, and P.W. Blankenship (1987), "Island Creek Corporation's Experience
with Methane Degasification," in Proceedings of the 1987 Coalbed Methane Symposium,
Tuscaloosa, AL, pp. 279-284.
Moerman, A. (1982), "Internal Report on Gas Storage in Peronnes-Lez-Binche, Belgium, S.A.
Distrigaz," 19 pp.
Oxy USA (1992), Update on Oxy USA project in Buchanon County, VA, delivered at the Fall
1992 Pittsburgh Coalbed Methane Forum Meeting, October 14, 1992, Morgantown, WV.
Pilcher, R.C., C.J. Bibler, R. Glickert, L. Machesky, J.M. Williams (1991), Assessment of the
Potential for Economic Development and Utilization of Coalbed Methane in Poland. Prepared
for the U.S. Environmental Protection Agency, Washington, D.C., August, 1991, EPA/400/1 -
91/032.
Skow, M.L., A.G. Kim, and M. Deul (1980), Creating a Safer Environment in U.S. Coal Mines.
U.S. Bureau of Mines, Impact Report, 50 pp.
Soot, P. (1990), Survey of U.S. Coal Mine Degasification Processes, prepared by Northwest
Fuel Development Inc., Portland, OR. Prepared for the USEPA.
Soot, P.M. (1991), "Power Generation Using Small Internal Combustion Engines," prepared
for ICF, Inc., 1991.
Spears & Associates, Inc. (1991), Market Study of Future Coalbed Methane Activity.
Summary to Producers, prepared by Spears and Associates, Inc. Tulsa, OK 74135. January
10, 1991.
Sturgill, C. (1991), "Power Generation: On-Site Use and Sale to Utilities," prepared for ICF,
Inc., April, 1991.
Sykes, W.W. (1989), "Gathering Systems Concepts-Planning, Design and Construction" in
Proceedings of the 1989 Coalbed Methane Symposium. The University of Alabama at
Tuscaloosa. April 17-20, 1989.
Trevits, M.A. and G.L. Finfinger (1986), "Results Given of Studies Concerning Methane
Extraction from Coalbeds," Mining Engineering. August, 1986, pp. 805-808.
Trevits, M., G. Finfinger and J. Lascola (1991), "Evaluation of U.S. Coal Mine Emissions," in
Proceedings of the Fifth U.S. Mine Ventilation Symposium. Society for Mining, Metallurgy and
Exploration, Inc., Littleton, CO.
True, W.R. (1990), "Pipeline Economics," in Oil and Gas Journal Special. November 26, 1990.
USEPA (United States Environmental Protection Agency) (1990), Methane Emissions from
Coal Mining: Issues and Opportunities for Reduction. USEPA/OAR (Office of Air and
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4 - 38 COAL MINING
Radiation), Washington, DC. Prepared by ICF Resources, Inc., September 1990, EPA/400/9-
90/008.
USEPA (1993a), Anthropogenic Methane Emissions in the United States. Report to Congress,
USEPA/OAR, Washington, DC.
USEPA (1993b), Opportunities to Reduce Methane Emissions in the U.S.. Report to Congress
(review draft), USEPA/OAR, Washington, D.C.
Williams, R.H. and E.D. Larson (1990), "Power Generation with Natural Gas Fired Turbines,"
in Natural Gas: Its Role and Potential in Economic Development, eds. W. Vergara, N.E. Hay,
and C.W. Hall, Westview Press, 1990.
Wolfe, B. and G. Maxwell (1990), "Commercial Landfill Gas Recovery Operations: Technology
and Economics" in Energy from Biomass and Wastes XIII. Edited by Donald L. Klass. Institute
of Gas Technology. Chicago, Illinois.
Xytel Technologies (1992), "Acetic Acid from Methane Gas," Prepared by Xytel
Technologies, Mt. Prospect, IL, July, 1992.
Zabourdyaev, V. (1992), data tables received by Raven Ridge Resources during April 1992
visit to Moscow, Russia.
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CHAPTER FIVE
FOSSIL FUEL COMBUSTION
5.1 Background
Methane Emissions
Fossil fuel combustion releases methane in addition to other greenhouse gases. Fossil fuels,
which include coal, oil, natural gas, shale oil, and bitumen, provide almost 90 percent of the
energy used by stationary combustion sources (power plants, industrial boilers, residential
heating and cooling) and mobile combustion sources (automobiles, trucks, airplanes and ships)
in industrial nations.
When fossil fuels are burned, carbon is released in the form of carbon dioxide (CO2), carbon
monoxide (CO), methane (CH4) and other hydrocarbons (HC), and other trace substances.
The amount of methane in these emissions is determined to a large extent by the
completeness of the combustion process. As methane is slower to react in combustion than
most other hydrocarbons (HC), the release of methane is proportionally greatest during
incomplete combustion.
The magnitude and composition of combustion related methane emissions vary according to
the following factors:
Amount and type of fuel combusted;
Methane content of the fuel;
Completeness of the combustion process (i.e., amount of HC passing through the
engine unburnt);
Type and condition of engine; and
Use of exhaust control technologies.
Methane emissions from combustion can be reduced by altering the combustion processes
to reduce the amount of gases produced or by using exhaust control technologies, such as
catalytic converters, to reduce emissions of some gases after the combustion process has
taken place. Unless such exhaust control technologies are employed, the gases produced
during combustion of fossil fuels are emitted to the atmosphere. Estimates of global methane
emissions from this source, although very uncertain, range from 4 to 5 teragrams per year
(USEPA, 1993).
Methane Emissions Reduction Strategies
A number of options exist to reduce methane emissions from stationary and mobile fossil fuel
combustion sources. The feasibility of some of these options has not yet been demonstrated
and, in many cases, the potential for reducing methane emissions has not been well
quantified. Nevertheless, many of these technologies are being implemented or are likely to
be implemented because of other beneficial effects, such as increased energy efficiency and
reduced emissions of air pollutants and other greenhouse gases.
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FOSSIL FUEL COMBUSTION 5 - 3
As these various options are assessed further, efforts will be needed to provide a
comprehensive accounting of the greenhouse gas balance, and to identify technologies which
are appropriate and economically feasible in different regions. Exhibit 5-1 summarizes the
options described in the technical assessments which follow.
5.2 Opportunities for Reducing Methane Emissions
Strategies for reducing methane emissions from fossil fuel combustion are described below.
Stationary and mobile combustion sources are discussed separately, as the factors which
influence methane emissions and appropriate emission reduction technologies differ for these
two types of categories.
5.2.1 REDUCTION OF METHANE EMISSIONS FROM STATIONARY SOURCES
Stationary sources of fossil fuel combustion include industrial boilers and facilities which
generate electricity to supply energy for industry and for commercial and residential lighting,
heating and cooling processes. These sources represent the majority of methane emissions
from fossil fuel combustion. Methane emissions from stationary sources vary widely
according to the nature and scale of the process and the fuel used. Emissions have been
estimated to range from 0.03 grams per gigajoule (g/GJ) energy output for distillate oil boilers
to 6 g/GJ for gas turbines (OECD, 1991; Radian Corporation, 1990; USEPA, 1985). Possible
emission reduction options, including increasing energy efficiency, optimizing engine
performance, using exhaust controls, and using alternative fuels, are discussed below.
Increase Energy Efficiency
Increasing the efficiency of industrial combustion, electricity generation, and energy use can
significantly reduce the amount of energy input required for global energy needs, thus
reducing emissions from fossil fuel combustion. The following technologies for improving
combustion efficiency and enhancing energy use efficiency are appropriate for new buildings
and homes, as well as for retrofitting in older structures.
Residential and Commercial Sectors: More efficient building insulation, appliances,
lighting, and heating and cooling equipment are commercially available. The use of these
technologies is being advanced by EPA programs such as Green Lights, which has
achieved lighting energy cost reductions of 50 percent in existing commercial buildings,
and Energy Star Computers, which will introduce computers using 90 percent less
electricity. It is technically feasible with available technologies to reduce energy use in
new homes by 50 percent, and in new commercial buildings by 75 percent (Lashof and
Tirpak, 1990). These buildings may require advanced ventilation systems, however, to
prevent increases in indoor air pollution. Strategies such as using shade trees to cool
residential buildings can also save energy.
Industrial Sector and Electricity Generation: Large potential exists for recycling waste heat
and improving combustion efficiency in power plants. Some examples of available
-------
5 - 4 FOSSIL FUEL COMBUSTION
technology include cogeneration (i.e., using waste heat from electricity generation to
produce steam for other uses); advanced combined cycle (ACC) turbines, during which
steam produced from waste heat is fed to a turbine to produce additional electricity;
variable-speed drives to reduce motor electricity use; and efficiency measures similar to
those discussed for residential lighting and space conditioning. Another important option
is the widespread recycling of inorganic waste materials (e.g., bottles and aluminum cans),
which can conserve substantial amounts of energy in the industrial sector if recovered
materials are used to produce steel, aluminum and glass products. Some emerging
technologies include the use of fuel cells in power plants, and various clean coal
technologies. Estimates of total feasible industrial energy savings from these strategies
range from 20 percent to 50 percent (Lashof and Tirpak, 1990).
Optimize Engines
Because methane emissions, along with other HC and CO emissions, are often highest from
old or poorly tuned engines, these emissions can be reduced by requiring regular maintenance
and timely engine replacement. Engine use can be optimized by tuning engines to ensure an
efficient air-fuel ratio, and replacing them at optimal times to prevent declines in efficiency due
to age and wear. In addition, maximizing engine use during operating hours by reducing the
number of start-ups and the times of idle operation can reduce emissions of methane and
other gases.
Implement Exhaust Control Technologies
Emissions of methane, other HC, NOX, and CO from stationary internal combustion (1C)
engines can be reduced using catalytic converters. These devices, which are placed in engine
exhaust pipes, promote chemical reactions to complete the oxidation of unburned methane,
other HC, and CO into C02 and water and, in some cases, the reduction of NOX into nitrogen
and ammonia. Non-selective catalytic reduction (NSCR) technologies, used for rich-burn (low
oxygen) applications, substantially reduce these emissions; oxidation/selective catalytic
reduction (SCR) technologies, more appropriate for lean-burn operations, may almost eliminate
methane and other HC emissions. As methane is the most difficult hydrocarbon to oxidize,
significant reductions in methane emissions are achieved only when the exhaust gas reaches
temperatures exceeding 900°F (temperatures should not exceed 1400°F). These higher
temperatures can be encouraged by placing the converter closer to the engine and insulating
the exhaust piping. Catalytic converters can be used with engines which run on a range of
fuels, including gasoline, natural gas, landfill gas and diesel fuel.
Increase Use of Alternative Fuels
Enhanced use of alternative fuels in stationary combustion can reduce emissions of methane
and other exhaust gases by minimizing fossil fuel use. Alternative fuel technologies suitable
for stationary applications include solar thermal, wind energy, and photovoltaic (PV) cells.
These technologies are available, and further developments are expected to extend their range
of practical applications. Hydroelectric, geothermal, and nuclear energy are also options, but
their application is limited to appropriate sites. The widespread use of nuclear fission could
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FOSSIL FUEL COMBUSTION 5 - 5
contribute to reduced greenhouse gas emissions if concerns about safety, nuclear proliferation
and waste disposal were satisfied, and if costs were reduced. The environmental and social
impacts of developing each of these options must be considered.
In addition to switching to alternative fuels, shifting to fossil-derived fuels (e.g., methanol and
ethanol converted from coal, oil shale and natural gas) can result in lower direct emissions of
methane and other exhaust gases; their production, however, requires energy consumption
and may thus result in large net greenhouse gas emissions. The use of diesel fuel produces
very low emissions of hydrocarbons, but can result in high NOX and particulate emissions.
5.2.2 REDUCTION OF METHANE EMISSIONS FROM MOBILE SOURCES
Although emissions of methane from mobile sources are significantly lower than stationary
source emissions, mobile source emissions still provide abundant opportunities to reduce total
emissions. Over 25 percent of global energy consumption each year is used for
transportation; most of this energy is provided by oil. Road transport (i.e., cars and trucks),
which accounts for over 80 percent of this mobile fuel consumption in many countries,
presents the largest potential for methane emission reductions. Most road vehicles, which
generally use spark-ignited, gasoline-fueled engines, emit exhaust gases which contain large
amounts of hydrocarbons, of which about 14 percent is methane (approximately 0.2 grams
of methane are emitted per kilometer travelledXOECD, 1 990). Total methane emissions from
non-road mobile sources (e.g., farm and construction equipment, railway locomotives, ships
and jets) are much lower than emissions from road sources, primarily because of the smaller
number of vehicles. Many non-road sources also use more efficient diesel-fueled compression
engines, which emit about one-tenth as much methane as spark-ignition engines.
Near term opportunities exist to cost-effectively reduce methane emissions by improving the
efficiency of mobile fuel consumption and controlling exhaust gas emissions. Over the longer
term, additional reductions in energy consumption may be possible by shifting to alternative
modes of transportation. These options are discussed below.
Increase Fuel Efficiency
Increasing the fuel efficiency of mobile sources (i.e., the distance traveled per unit volume of
fuel) reduces fuel use and, other factors being constant, reduces emissions of all exhaust
gases in proportion to the exhaust composition. Several currently available technologies have
the potential to significantly increase the fuel efficiency of new light-duty vehicles (e.g.,
passenger cars), which account for over 60 percent of current transportation energy use. Fuel
efficiencies for gasoline engines currently range from about 1 5 to 55 miles per gallon (mpg)
on the road, and studies indicate that these values can be increased by up to 35 percent by
the year 2005 (Plotkin, 1991).
Finally, efficiency improvements can be achieved by reducing vehicle weight, although there
is concern that this strategy may compromise vehicle safety, comfort and/or performance.
Fuel efficiency can be enhanced through technologies such as low friction tires, five-speed
automatic transmissions, and improved aerodynamic designs. Continuously variable
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5 - 6 FOSSIL FUEL COMBUSTION
transmissions (CVT) can reduce energy losses during shifting by allowing the engine to
operate closer to full load at varying speeds. Using diesel engines, which are more fuel-
efficient, can also reduce methane emissions, although this benefit may be offset by increased
emissions of particulates.
Opportunities for efficiency improvements are also available for freight transport (i.e., diesel
trucks, which use 14 percent of oil consumed from transportation in OECD countries) and
non-road vehicles. Adiabatic diesel truck engines, for example, may achieve 50 percent
efficiency increases by retaining heat in the combustion chamber and harnessing high pressure
exhaust gases. New technologies for ships have shown 30-40 percent efficiency increases,
and studies show possible aircraft fuel use reductions of 50 percent per passenger mile by the
year 2010 (Lashof and Tirpak, 1990).
Improve Combustion Efficiency
Improving the efficiency with which an engine burns fuel increases the completeness of
combustion, thereby reducing emissions of methane, CO and other gases which are highest
during incomplete combustion. Combustion efficiency (CE) depends both on the air-fuel ratio
during combustion and on the type of engine. Methane emissions are generally highest when
air-fuel mixtures are "rich" (i.e., less oxygen is available than is required for complete
combustion). Tuning an engine to create a "leaner" (high-oxygen) air-fuel mixture ensures
that a higher proportion of the HC is completely burned, thus reducing the amount of methane
emitted per unit of fuel burned. Using reformulated gas, in which additives (e.g., ethanol,
methanol) increase the oxygen content of the gasoline, can also ensure lean fuel mixtures.
The possible negative effects of raising air-fuel ratios (e.g., increasing nitrogen oxides
emissions) can be prevented using exhaust control technologies, such as catalytic converters,
or electronic engine management systems which minimize emissions by precisely controlling
air-fuel mixtures.
Combustion efficiency can also be improved through the development and use of more
efficient engines. Compression ignition engines using diesel fuel generally burn fuel more
efficiently than gasoline engines, although they emit greater quantities of NOX and/or
particulates. One highly-efficient gasoline engine under development is the Stirling engine,
an external combustion engine designed to achieve extremely low HC, NOX and CO exhaust
emissions by preheating combustion air in a continuous combustion process. Stirling engines
should soon be available for commercial applications (Bennethum et al., 1991).
Optimize Engines
As with stationary combustion sources, engine optimization and proper maintenance can
reduce emissions of methane and other exhaust gases from mobile combustion sources.
Tuning engines regularly also helps to maintain an optimal air-fuel (stoichiometric) ratio for
high combustion efficiency. Programs to encourage driving at more efficient speeds (e.g.,
strict enforcement, sequenced traffic lights, improved roads) can also enhance the optimal use
of vehicle engines.
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FOSSIL FUEL COMBUSTION 5 - 7
Implement Post-Combustion Exhaust Control Technologies
Emissions of methane and other exhaust gases can be reduced or eliminated by using post-
combustion exhaust control technologies such as catalytic converters and air injection.
Automobile catalytic converters are similar to those used in stationary applications, and have
been shown to reduce HC emissions from a range of gasoline vehicles by as much as 70 to
95 percent. As in stationary engines, the most significant reductions in methane emissions
are achieved at temperatures between 900° and 1400°F. These higher temperatures can be
encouraged through such methods as placing the converter close to the engine and insulating
the exhaust piping.
Automotive converters generally use one or more of the following two catalysts: oxidation
catalysts, which reduce only CO and HC emissions; and three-way catalysts, which also
reduce NOX emissions. A variety of precious metals including platinum, palladium and
rhodium are used to provide sites for the reactions, and base metals can be added to improve
stability. Regular engine maintenance and the use of lead-free fuel are essential to avoid
exposing the catalysts to contaminants or excessively high temperatures.
Air injection, a non-catalyst method of controlling HC and CO exhaust emissions from mobile
sources, involves injecting air into the exhaust manifold to enhance the oxidation of these
gases.
Increase Use of Alternative Fuels
Increasing the use of alternative fuels can significantly reduce emissions of methane and other
exhaust gases, while improving the energy security of countries which rely on imported fuels,
by minimizing fossil fuel use. Non-fossil automotive fuel technologies such as solar and
hydrogen fuels have been successfully demonstrated, and may be cost-effective for light-duty
vehicles in the long term. Several fuel cell technologies are also being researched and tested.
Electric cars and trains are another feasible option, although the generation of electricity for
their use results in some greenhouse gas emissions. Vehicles which use alcohol fuels
(methanol or ethanol) converted from biomass (e.g., agricultural wastes, wood products) are
also available.
The practice of converting solid energy resources (e.g., coal, oil shale) into gaseous and liquid
fuels (e.g., methanol ethanol) is also growing. The use of these fossil-derived fuels can result
in lower direct emissions of methane and other exhaust gases if vehicles are optimized for
their use. Greenhouse gas emissions can be high, however, during the production of such
synthetic fuels.
Reduce Scale of Emission Source
Another option for reducing methane emissions is to reduce the scale of mobile emission
sources by optimizing transportation systems to minimize total vehicle miles travelled (VMT).
Strategies include improving public mass transit facilities and encouraging reductions in the
use of personal vehicles through the promotion of carpooling and the introduction of high
occupancy vehicle (HOV) lane highway restrictions. The continued development and use of
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5 - 8 FOSSIL FUEL COMBUSTION
advanced telecommunications systems (e.g., teleconferencing, electronic mail, electronic
banking) may decrease the need for transportation in the future, thereby reducing fossil fuel
combustion from mobile sources (Lashof and Tirpak, 1990). The implementation of these
strategies may be justified solely on the basis of traffic congestion and/or air quality problems.
Although total methane emissions from stationary and mobile sources are significant on a
global scale, methane is a comparatively small component of fossil fuel combustion exhaust
gas. Other gases released during combustion, such as NOX, CO and other HC's, contribute
to problems such as global warming, smog, tropospheric ozone production, and acid rain on
a much greater scale. Currently, many nations are developing and enforcing stricter
regulations governing exhaust emission levels of these gases. As a result, technologies aimed
at reducing emissions of these gases and increasing energy efficiency will have the ancillary
benefit of reducing methane.
Many strategies discussed above are cost-effective because they significantly reduce fuel use.
In addition, many technologies are currently available (e.g., catalytic converters, alternate-
fueled vehicles and advanced engines), although substantial improvements are possible with
ongoing research and development. A number of technologies are still in the development
stage (e.g., Stirling engines, hydrogen-fueled vehicles), and will require further work before
they will be economically feasible and commercially available. A combination of these fuel
use reduction strategies, fuel switching, and emissions reduction technologies will most
successfully achieve reductions of methane and other gases resulting from fossil fuel
combustion.
Reducing Methane Emissions from Fossil
Fuel Combustion
some technologies available; others
under development
many cost-effective strategies
implementation likely in order to
comply with emissions limits on NOX,
CO and other HCs
methane reductions of 80%-98%
possible with some technologies
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FOSSIL FUEL COMBUSTION 5 - 9
5.3 References
Contributions were made by:
Robert Bruetsch, Technology Development Group, USEPA/Office of Mobile Sources,
U.S.A.
Robert Heavenrich, Technology Development Group, USEPA/Office of Mobile Sources,
U.S.A.
Leonard Johansson, Stirling Thermal Motors, Inc., U.S.A.
James McDonald, Johnson Matthey Inc., U.S.A
Steve Plotkin, Office of Technology Assessments, U.S.A.
Susan Stefanek, Regulation Development and Support Division, USEPA/Office of Mobile
Sources, U.S.A.
Additional information may be found in the following:
Bennethum, James E., Thomas D. Laymac, Lennart E. Johansson, and Ted M. Godett
(1991), "Commercial Stirling Engine Development and Applications," SAE Technical Paper
Series 911649 for Future Transportation Technology Conference and Exposition, Portland,
Oregon August 5-7, 1991.
Clement, Raymond and Ron Kagel, eds. (1990), Emissions from Combustion Processes:
Origin, Measurement, Control, Boca Raton: Lewis Publishers.
Drehmei, Dennis C. and Charles B. Sedman (1989), Recent Developments of Emission
Control Technology in the United States for Fossil Fuel Combustion Sources, Air and Energy
Engineering Research Laboratory.
IPCC (Intergovernmental Panel on Climate Change) (1990), Climate Change: The IPCC
Response Strategies, prepared by the Response Strategies Working Group, with WMO and
UNEP. Geneva, June 9, 1990.
Lashof, Daniel A. and Dennis A. Tirpak, eds. (1990), Policy Options for Stabilizing Global
Climate: Report to Congress. U.S. EPA/OPPE, December 1 990.
OECD (Organization for Economic Co-operation and Development) (1991), Estimation of
Greenhouse Gas Emissions and Sinks: Final Report from the OECD Experts Meeting, 18-21
February 1991, Prepared for IPCC, August 1991.
OECD (1990), "Greenhouse Gas Emissions: The Energy Diversion," Joint IEA/OECD Project.
Paris, drafted February 2, 1990, Working Document.
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5-10 FOSSIL FUEL COMBUSTION
Plotkin, Steve (1991), OTA, personal communication.
Radian Corporation (1990), Emissions and Cost Estimates for Globally Significant
Anthropogenic Combustion Sources of NOx, N20. CH^, CO. and C02. prepared by Air and
Engineering Research Laboratory for EPA/OPPE (Office of Policy, Planning and Evaluation),
May 1990.
USEPA (United States Environmental Protection Agency) (1 985), Compilation of Air Pollution
Emission Factors, AP-42, Fourth Edition. September, 1985.
USEPA (1993). Global Anthropogenic Emissions of Methane, Report to Congress (in progress),
USEPA/OPPE.
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CHAPTER Six
RUMINANT LIVESTOCK
6.1 Background
Methane Production and Emissions
Methane is produced as part of the normal digestion process of ruminant animals. These
animals are characterized by a large "fore-stomach" or rumen, in which microbial fermentation
converts feed into products that can be further digested and utilized by the animal.
Approximately 200 species and strains of microorganisms are present in this anaerobic rumen
environment, although a much smaller number are dominant. The microbial fermentation
performed by the rumen microorganisms enables ruminant animals to utilize coarse forages
which monogastric animals, including humans, cannot utilize.
Methane is produced by rumen methanogenic bacteria as a byproduct of the normal rumen
fermentation process. This methane, which is exhaled or eructated by the animal, represents
a sink for a portion of the feed energy consumed by the animal. Typically from 4 to 9 percent
of gross energy intake is lost through methane production. This methane loss, therefore,
represents an inefficiency -- feed energy converted to methane cannot be used by the animal
for maintenance, growth or production.
The level of methane production in ruminant animals is influenced by the quality and quantity
of feed consumed. On the one hand, higher levels of feed intake and higher quality feeds are
associated with increased rumen fermentation, and hence higher absolute levels of methane
production (e.g., kg of methane per head per year). Alternatively, higher levels of feed intake
and higher quality feeds are also associated with lower relative levels of methane emissions
per amount of energy consumed (e.g., percentage of gross energy intake converted to
methane).
These two examples demonstrate that methane production in ruminants can be expressed in
a variety of ways. For the purposes of evaluating options for reducing methane emissions,
these emissions should be expressed per unit of product (e.g., methane production per kg of
milk produced). When viewed in this manner, options can be assessed in terms of their ability
to reduce methane emissions per unit of product produced.
Methane Reduction Strategies
The conditions under which livestock are managed vary greatly by country, especially
between developed and developing countries. Reduction strategies must be tailored to
country-specific circumstances. Despite the differences in animal management practices
among various countries, one common strategy for reducing methane emissions is to increase
animal productivity (e.g., milk production in cows, reproductive efficiency of brood cows).
Virtually all efforts that improve animal productivity will reduce methane emissions per unit
of product produced.
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6 - 2 RUMINANT LIVESTOCK
The ability to reduce methane emissions per unit product produced has been demonstrated
in various countries with intensive animal production systems. High quality feed, selective
breeding, and associated intensive management techniques have greatly increased
productivity. Coupled with saturated demand market conditions, these developments have
resulted in decreases in methane emissions per unit product, and, therefore, in absolute
methane emission reductions. Strategies for further reductions from intensively managed
livestock may involve more advanced productivity enhancers.
To date, similar productivity improvements have not been achieved in most developing
countries. Over the past 40 years, increased demand for animal products has been met
primarily by increases in the number of animals, as opposed to increases in animal
productivity. Given the variety of cultural and economic factors that shape animal production
practices in the developing countries, strategies for reducing methane emissions from
ruminant animals in developing countries must: 1) increase production; 2) be cost effective
under current economic conditions; and 3) be consistent with local traditions and systems of
production.
The following strategies for reducing methane emissions from ruminant livestock are described
in these technical assessments, and are summarized in Exhibit 6-1.
Improved Nutrition Through Mechanical and Chemical Feed Processing: Improved nutrition
reduces methane emissions per amount of product produced by enhancing animal
performance, including weight gain, milk production, work production, and reproductive
performance. Methane emissions per amount of digestible energy consumed by the animal
may also be reduced. This option is applicable to accessible ruminant animals with limited
feed resources. Assuming that feed digestibility is increased by 5 percent, methane
emissions per unit product produced may decrease on the order of 10 to 25 percent,
depending on animal management practices.
Alkali/Ammonia Treatment of Low Digestibility Straws. This is a proven technique that
improves feed digestibility and consequently animal performance (Owen and
Jayasuriya, 1989). Many field trials have demonstrated its effectiveness. This
process has been only partially implemented however, since it can be difficult to
implement at the village level because it requires handling caustic materials.
Additionally, adequate nitrogen in the animal's diet is required to take advantage of the
increased digestibility.
Chopping of Low Digestibility Straws. Chopping of straws can increase feed intake
and consequently animal performance in some cases. This practice is limited in some
areas due to lack of chopping equipment, which requires a moderate capital
investment.
Treat and Wrap Rice Straw. A small-scale mechanized procedure for cutting, treating
and wrapping rice straw is being developed. Essentially an ensiling process that uses
urea as a nitrogen source, the process improves rice straw digestibility and
consequently animal performance. Losses due to spoilage may also be reduced. The
small-scale mechanized process may enable larger numbers of small scale farmers to
improve their feed resources. The process is not yet commercial, and testing is
ongoing. Recycling options for wrapping materials need to be investigated.
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RUMINANT LIVESTOCK 6 - 3
Improved Nutrition Through Strategic Supplementation: Improved rumen function will
reduce methane emissions per amount of feed consumed. Also, by providing additional
microbial and/or by-pass protein to the animal, emissions per amount of product produced
will be reduced by enhancing animal performance, including weight gain, milk production,
work production, and reproductive performance. Improved rumen function may reduce
methane emissions by about 5 to 10 percent. In addition, emissions per unit product may
be reduced by 25 to 75 percent due to substantial increases in animal productivity that
are anticipated under specific conditions (Leng, 1991 a).
Molasses/Urea Muitinutrient Blocks. Balancing rumen function by supplying key
supplements in a molasses-urea block (MUB) is a well described technique that may
be targeted to animals on diets that lead to deficient rumen ammonia levels.
Numerous field trials have been performed. Improved microbial growth improves the
protein energy ratio for the animal and reduces methane production directly while
improving animal performance. Currently, implementation is limited by infrastructure,
manufacturing, and farmer education levels.
Molasses/Urea Blocks with Bypass Protein. By-pass protein feeds (BPF) may be
combined with the MUBs. BPFs improve the protein energy ratio for the animal and
improves animal performance. The BPF source must be available locally, and ideally
should come from by-products of existing activities, such as distillery wastes or fish
processing wastes. Currently, implementation is limited by a lack of evaluations of
potential BPF sources as well as infrastructure, manufacturing, and farmer education
levels.
Defaunation. Defaunation is the removal of rumen protozoa that consume rumen
microbes. Primarily applicable to grazing animals, defaunation improves the microbial
protein supply to the animal. Defaunation agents are not yet available commercially.
Defaunation is not suitable for animals on high energy, high grain diets.
Targeted Mineral/Protein Supplements. Mineral/protein supplements may be targeted
to specific circumstances to correct deficiencies in the diet. This technique has been
applied primarily to grazing animals in the U.S., and has successfully enhanced
reproductive efficiency in beef cows. A lack of understanding of critical deficiencies
combined with current market and pricing arrangements have limited implementation.
Bioenqineering of Rumen Microbes. Bioengineering may be possible in the long term.
Microbes that can utilize feed more efficiently may be developed. Additionally,
techniques for suppressing methanogenesis may be feasible.
Production Enhancing Agents: Certain agents can act directly to improve productivity.
As a result, methane emissions per unit product will be reduced.
bST. Bovine Somatotropin (bST) is a naturally occurring growth hormone produced by
the cow's pituitary gland. Recombinant DNA techniques developed over the last 10
years now allow large quantities of bST to be synthesized. Development tests indicate
that bST can improve milk productivity by 10 to 20 percent per lactation (Blayney and
Fallert, 1990). It is also effective in promoting feed efficiency and repartitioning
-------
6 - 4 RUMINANT LIVESTOCK
growth to lean tissues. The commercial use of bST has been approved in several
countries and is under consideration in many others.
Anabolic Steroid Implants. Implants are a proven and commercialized technique for
improving feed efficiency and repartitioning growth in beef production (USDA, 1987;
Ensminger, 1983). However, these agents were recently banned in the EC.
Other Agents. Other agents are being developed, and may be available in the short to
long term.
Improved Production Through Improved Genetic Characteristics: Genetic characteristics
are limiting factors mainly in intensive production systems. Continued improvements in
genetic potential will increase productivity, and thereby reduce methane emissions per unit
product.
Crossbreeding in Developing Countries. The overall effectiveness of this technique is
still a matter of dispute. Some claim that native breeds perform better under existing
environments, and that genetic characteristics are not a limiting factor in production.
As nutrition is improved genetic factors may increase in importance.
Continued Genetic Improvement in Dairy Cattle. The genetic characteristics of dairy
cattle are expected to continue to improve in the future. The major dairy countries
have significant breeding programs in place. Detailed recording systems are used to
perform quantitative assessments of the genetic potential of cows and bulls. Embryo
cloning and transplanting techniques, expected to be applied in the mid-term future,
have the potential to accelerate improvements in the genetic potential of dairy herds.
Transgenic Manipulation. Over the long term it will be possible to transfer desirable
genetic traits among species. This technique holds great promise for improving the
efficiency of production in large ruminants.
Improved Production Efficiency Through Improved Reproduction: Large numbers of
ruminants are maintained for the purpose of producing offspring. Methane emissions per
unit product can be significantly reduced if reproductive efficiency is increased. The
nutritional options described above can improve reproduction. Additionally, the following
options address reproduction directly.
Twinning. Techniques are being developed to produce healthy twins from cattle (e.g.,
inhibin vaccine). When combined with adequate nutrition for the mother and offspring,
twinning can substantially reduce the total number of mother cows required to produce
calves.
Embryo Transplants. Embryos produced by superovulated, genetically superior cows
can be transferred to foster cows of lesser genetic merit. This frees the superior cow
from the long term pregnancy, redirecting energy towards increased ovulations. This
technique has the potential to improve overall reproductive efficiency.
-------
RUMINANT LIVESTOCK 6 - 5
Artificial Insemination and Estrus Synchronization. These are well known techniques
that improve reproductive efficiency. Their implementation is limited to intensive
systems where frequent contact with the cows is possible.
Other Strategies:
Milk Marketing in Surplus-Producing Countries. Eliminating surplus production will
reduce methane emissions. Additionally, changing the pricing systems to reduce
incentives for surplus fat production would potentially lead to modifications in feeding
practices that would, as a side benefit, reduce methane emissions per amount of milk
produced.
Disease Control. Disease control will enhance productivity by reducing mortality rates
and improving growth rates and reproductive efficiency.
Beef Marketing: U.S.. Re-orienting the beef marketing system to reduce the amount
of trimmable fat produced will reduce methane emissions per unit product. Efforts are
underway to emphasize "value-based marketing" which will have this effect.
Overall, the assessments indicate that there are many opportunities for reducing methane
emissions at relatively low cost. Exhibits 6-1 (a-d) summarize these assessments. Each
technical assessment contains the following sections:
Reduction Technology Description;
Costs;
Availability;
Applicability;
Barriers; and
Benefits.
-------
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6-10 RUMINANT LIVESTOCK
6.2 Improved Nutrition Through Mechanical and Chemical Feed
Processing
Mechanical and chemical processes have been developed that improve the nutritive value of
low quality crop byproducts, principally rice straw. Large quantities of rice straw and other
crop byproducts are produced throughout the world. In many tropical countries with limited
feed resources, these crop byproducts are the main source of feed for ruminant livestock.
The nutritive value of most crop byproducts, and straws in particular, is limited by their
relatively low level of digestibility. These byproducts possess both physical and chemical
characteristics that impart resistance to biological degradation in the rumen. The primary
factor that has been correlated with low levels of digestibility is lignin content.
While lignin has come to mean somewhat different things to various disciplines (Van Soest,
1987, p. 120), lignin can be considered to be a group of substances that exhibit inhibitory
effects on digestion, either by interfering with animal metabolisms or by interfering with
rumen microbes. True lignin, the major component of this class of compounds, limits the
availability of cell wall carbohydrates to rumen microbes.
Chemical and physical treatment methods have been developed that either remove the lignin
or neutralize its effects. These treatments result in improved digestion of the crop
byproducts, and hence improved animal performance. By improving digestion and animal
performance, methane emissions per unit product are reduced.
Two well established techniques for improving the nutritive value of crop byproducts are
discussed below: chemical treatment with alkali and ammonia; and chopping. Additionally,
a new process under development for wrapping and preserving rice straw is discussed.
6.2.1 ALKALI/AMMONIA TREATMENT OF Low DIGESTIBILITY STRAWS
Chemical treatment of low quality roughages such as straw and other crop byproducts to
improve their digestibility and intake by ruminant animals has been intensively researched
since the mid-1960s (Owen and Jayasuriya, 1989). During the 1980s there has been
enormous interest in applying these techniques in the developing countries of the tropics and
subtropics which produce large amounts of crop byproducts.
While a variety of chemicals have been investigated, including various alkalis, acids, salts, and
oxidizing agents, sodium hydroxide and ammonium hydroxide treatments have dominated
research and development efforts. To date, these two treatments have been found to be the
most beneficial and cost effective methods available. Nevertheless, the implementation of
these methods has been somewhat limited.
Research is continuing to improve chemical treatments for upgrading the nutritive value of
crop byproducts and to promote their use more effectively. As improved methods become
available, they may displace the sodium hydroxide and ammonium hydroxide treatments that
are currently preferred. However, for purposes of this assessment, the discussion focuses
on these two treatment methods.
-------
RUMINANT LIVESTOCK 6-11
Reduction Technology Description
Chemical treatments to improve the nutritive value of crop byproducts generally involve
mixing given quantities of the chemical and the byproduct, and allowing them to remain in
contact for a specified period of time. The sodium hydroxide "dip method" is the simplest
approach and includes the following:
a mixture of 14-15 grams of sodium hydroxide (NaOH) per liter of water and 10 grams
of urea per liter of water is prepared;
the straw is placed into the mixture for 30 minutes; and
the straw is removed from the mixture and stored for 5 days.
Using this process, the digestibility of the straw may increase from about 50 percent to as
much as 75 percent, and the nitrogen content may increase from about 3 gN/kg dry matter
(DM) to as much as 15 gN/kg DM. Other NaOH processes have been investigated, including
spraying the solution on chopped straw, soaking the straw under pressure, and soaking the
straw under pressure and heat (Owen and Jayasuriya, 1989).
Ammonium hydroxide treatments are similar, and also involve urea. In the tropics, treatment
with ammonia generated from the hydrolysis of urea during a 10-25 day ensiling period is
most favored (Owen and Jayasuriya, 1989). The extent to which improved digestibility of
the forage versus additional rumen ammonia leads to improved animal performance has not
been established. In general, however, these chemical treatment methods may be
implemented in a fashion that is complementary to the application of strategic
supplementation techniques discussed below.
The primary cost of chemical treatment of straws and other byproducts is the cost of the
chemicals themselves. Because NaOH and urea are relatively low cost, the NaOH-urea
treatment methods are preferred. When animal products are marketed, the value of the
increased production of animal products due to improved feeding will generally exceed the
cost of the chemical treatment.
Availability
Chemical treatment techniques have been verified and promoted in many regions.
Consequently, the information and resources necessary to implement the treatments are
considered to be generally available. There are, however, several barriers that have limited
the adoption of these techniques (see below).
-------
6-12 RUMINANT LIVESTOCK
Applicability
Chemical treatment to upgrade the nutritive value of crop byproducts is applicable in virtually
all situations where large quantities of crop byproducts are produced. Although generally
discussed as a method of improving feed resources in tropical and subtropical developing
countries, NaOH treatment is also practiced in Europe, for example.
Barriers
To date, the use of chemical treatment has been promoted in developing countries at the farm
level. With this approach, individual farmers would treat their own crop byproducts. Farm
level acceptance has reportedly been slow, however, for several reasons. The need for large
quantities of water often creates an unrealistic water collection burden, and a reluctance to
handle caustic and poisonous chemicals has discouraged widespread acceptance of these
techniques. Options that require less water and chemical treatment are being investigated.
However, widespread adoption of these chemical treatment techniques in many countries may
require a more centralized implementation approach, such as involving the feed milling sector.
Under such a centralized implementation approach, transportation cost issues would have to
be addressed.
Benefits
The principal benefit of upgrading the nutritive value of crop byproducts is the improvement
in animal nutrition and performance using the same feed base. Methane emissions per unit
product are reduced due to increased productivity.
Chemical Feed Processing
methane reduced 10 % or more per unit product
technology currently available
low costs
improves animal productivity
6.2.2 CHOPPING OF Low DIGESTIBILITY STRAWS
Physical modification of straws and other byproducts, such as by chopping and milling, can
improve feed intake and animal performance. Chopping and grinding are the cheapest and
most cost effective approaches that can be applied at the farm level. Heat treating and
steaming are also options, but are not cost effective in most developing countries.
-------
RUMINANT LIVESTOCK 6-13
Chopping and grinding improve the intake of digestible energy by mechanically isolating the
carbohydrate in the feed from the lignin. Although digestibility of the feed may in fact be
reduced as a result of grinding, increased feed intake more than compensates so that total
digestible energy intake improves. When straw is the principal feed, digestible energy intake
reportedly increases on the order of 30 percent as the result of grinding (Nour, 1986).
Reduction Technology Description
Chopping and grinding is accomplished using specialized grinding equipment such as a
hammer mill or other implement. The straw or other byproduct is generally ground
immediately prior to its use.
The primary cost of chopping and grinding is the grinding equipment and the labor necessary
to operate it. When animal products are marketed, the value of the increased production of
animal products due to improved feeding will generally exceed the cost of the grinding.
Availability
Chopping and grinding are simple techniques that have been implemented in many areas. The
up-front costs of the necessary equipment often prevent this option from being implemented.
Applicability
As in the case of chemical treatment, chopping and grinding to upgrade the nutritive value of
crop byproducts is applicable in virtually all situations where large quantities of crop
byproducts are produced. Although generally discussed as a method of improving feed
resources in tropical and subtropical developing countries, chopping, grinding and other feed
processing methods are commonly practiced in Europe, North America, and elsewhere.
Barriers
To date, the principal barrier to the implementation of this strategy has been the up-front cost
of the chopping and grinding equipment. The development of lower-cost equipment suitable
for individual farm usage may assist in implementation of this option.
Benefits
The principal benefit of upgrading the nutritive value of crop byproducts is the improvement
in animal nutrition and performance using the same feed base. Methane emissions per unit
product are reduced due to increased productivity.
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6-14 RUMINANT LIVESTOCK
Chopping and Grinding
methane reduced 10% or more per unit product
technology currently available
improves animal productivity
6.2.3 WRAPPING AND PRESERVING RICE STRAW
As discussed in the previous two sections, significant improvements in the nutritive value of
straw can be achieved through chemical and physical treatments. A new device for wrapping
and preserving rice straw is being developed that may enable these benefits to be realized by
many farmers.
Devices operated by hand and animal power are currently being tested that will cut rice straw,
mix it with urea, and wrap it into small "bales." At the time of harvest, green straw has a
digestibility of 50-60 percent, which is reduced to 40-45 percent after it is dried. By
wrapping freshly cut and treated straw, its nutritive value is retained and spoilage is prevented
(Leng, personal comm., 1992). The process may be useful for improving the nutritive value
of rice straw because large amounts of water or caustic chemicals are not required, and it is
expected to be more effective than simple chopping and grinding.
Because development is ongoing, it \s premature to assess the costs and benefits of this
option. If developed successfully, the principal value of this device may be its ability to be
more widely accepted and implemented than has been the case with other existing treatment
techniques.
6.3 Improved Nutrition Through Strategic Supplementation
Improving the basic nutrition of animal feeds through strategic supplementation will improve
animal productivity and reduce methane emissions per unit product. Many of the world's
ruminant livestock survive primarily on low digestibility feeds. While the low energy content
of these feeds can limit animal productivity, the problem is exacerbated for many ruminant
livestock by deficiencies in key nutrients which make the animal unable to utilize as fully as
possible the energy that is potentially available in the feed. Supplementation to correct the
deficiencies can improve the digestibility of the feed and the productivity of the animal.
Additionally, in some areas, ruminant livestock suffer from specific mineral deficiencies that
reduce production levels. These mineral deficiencies can also be addressed through
supplementation. In all cases, supplementation must be designed to address local needs.
-------
RUMINANT LIVESTOCK 6-15
Microbial Growth in the Rumen
The rumen is a complex living environment that supports microorganisms which digest plant
matter (cellulose). A deficiency of nutrients needed by these microorganisms will reduce the
microbial mass, thereby reducing both the rumen's ability to digest cellulose and the protein
available to the animal from microbial outflow (from the rumen). An important priority for
feeding ruminant animals is to ensure the availability of essential nutrients for microbial
growth in the rumen.
The efficiency of microbial cell growth (typically measured as microbial growth per unit of
digestible carbohydrate entering the rumen) is limited primarily by the concentration of
ammonia in the rumen, and by the availability of sulfur, phosphorus, and certain other trace
minerals. However, the absence of any nutrient required in the growth of rumen
microorganisms will result in low cell growth.
Deficiencies of ammonia and other essential nutrients in the rumen of animals fed poor quality
forage can be corrected by supplying molasses/urea multinutrient blocks. This strategy is
described in more detail below.
A second factor affecting animal nutrition is the supply of protein (in the form of amino acids)
to the digestive tract of the host animal. Amino acids are vital for growth and productive
functions such as milk and wool production, as well as a large number of important biological
processes within the animal.
The principal source of protein for grazed and forage-fed animals is microbial outflow from the
rumen. In addition to increasing microbial outflow (as above), the available protein can be
increased through protein feed supplements. To derive the maximum benefit from protein
feed supplements, the protein should be in a form that prevents its degradation in the rumen.
Protein that is insoluble or that has a high component of disulfide bonds tends to bypass the
rumen undigested (bypass protein), and is therefore available for use by the animal.
The availability of useful protein is measured as a ratio of protein to energy (i.e., P/E ratio).
The higher the P/E ratio in the nutrients absorbed, the more efficient the animal becomes in
utilizing the available energy for growth and productive functions. For diets that are low in
protein but have an adequate energy content, supplementation with bypass protein stimulates
the efficiency of feed utilization.
Protozoa in the Rumen
The role of protozoa in the rumen is still somewhat controversial. For animals consuming high
grain diets, protozoa rapidly assimilate sugars and starches, thereby acting as a valuable pH
buffer for the rumen. In these circumstances defaunation (i.e., removal of these protozoa) is
not recommended. However, in animals on forage diets, protozoa appear to interfere with
rumen efficiency by ingesting bacteria and reducing microbial protein flow out of the rumen,
and hence the P/E ratio. Also, protozoa are thought to increase the degradation of protein in
-------
6-16 RUMINANT LIVESTOCK
the rumen. Defaunation will improve the efficiency of feed utilization and will therefore reduce
methane emissions per unit product. The possibilities for successful defaunation are
discussed later in this section.
The following strategies for improving animal nutrition through strategic supplementation are
presented in this section:
Molasses/Urea Multinutrient Blocks (MUB) provide ammonia and other essential
nutrients to rumen microorganisms, increasing rumen efficiency;
MUB with Bypass Protein both increases rumen efficiency and provides protein for the
improved utilization of energy;
Defaunation increases microbial growth and reduces protein degradation;
Targeted Mineral/Protein Supplements improve animal performance by correcting
specific performance-limiting deficiencies; and
Bioengineering of Rumen Microbes enhances the efficiency of feed utilization.
6.3.1 MOLASSES/UREA MULTINUTRIENT BLOCKS
The efficiency of digestion in the rumen requires a diet that contains essential nutrients for
the fermentative microorganisms. When the available feed lacks these nutrients digestion will
be less efficient, lowering productivity and raising methane emissions per unit product.
Strategic supplementation of missing nutrients can greatly improve the efficiency of digestion
without requiring a change in the basic diet. The use of molasses/urea blocks is a proven and
cost effective diet supplementation strategy.
Reduction Technology Description
For grazing animals and those fed low quality diets, the primary limitation on efficient
digestion is the concentration of ammonia in the rumen. It has been accepted that the
optimum level of ammonia in the rumen was 50-60 mg/l. However, more recent studies have
shown that digestibility is maximized above 80 mg/l, and feed intake increases at levels up
to 200 mg/l (Perdok et al., 1 988). Supplying ammonia can therefore greatly increase digestive
efficiency and utilization of available energy.
Ammonia can be supplied by urea, chicken manure, or soluble protein that degrades in the
rumen. Urea is broken down in the rumen to form ammonia, and adding urea to the diet has
been the most effective method of boosting rumen ammonia levels demonstrated to date.
Chicken manure, which has a high uric acid content, has been used in some regions, where
available. While protein in the feed can provide rumen ammonia, sources of protein are often
scarce, and where possible should be processed and used as a bypass protein (see
"Molasses/Urea Multinutrient Blocks with Bypass Protein").
-------
RUMINANT LIVESTOCK
6- 17
In addition to ammonia, there are numerous nutrients that must be present in the diet to
support the microbe population in the rumen. The most common nutrients required are
sulphur and phosphorus, although this will vary greatly by region.
Urea and other supplemental nutrients are mixed with molasses to make it palatable to
livestock. In addition, molasses provides the energy needed in order to realize the improved
microbial growth that can result from enhanced ammonia levels. Demonstration projects have
added the molasses/urea mixture directly into the feed or have supplied the supplement as a
pre-mixed lick block. The molasses/urea block (MUB) is easy to use and can be produced in
large quantities and transported easily.
The exact composition of the blocks will depend on local needs and available materials.
Important factors are: 1) the level of urea, which must be effective but not toxic; 2) the
quantity of molasses, which must cover the bitter taste of the urea and provide adequate
energy; and 3) the hardness of the block, which must deter chewing, and yet be soft enough
to allow easy intake. In addition to molasses, urea, and supplemental nutrients, blocks
contain a binding agent to ensure correct consistency, and often contain a locally available
source of soluble protein such as wheat or rice bran. A typical MUB composition is shown
in Exhibit 6-2:
Exhibit 6-2
Typical Compositions of Molasses/Urea Multinutrient Blocks
Ingredient
Molasses
Urea
Lime
Mineral/Vitamins
Wheat/Rice Bran
Amount {%)
40-60
4-15
8-10
1-15
20-30
Function
Palatability and Energy
Ammonia Source
Binding Agent
Nutrient Supplements
Soluble Protein
Sources: Leng, 1991a; Saadullah, 1991.
The application of MUBs has been extremely successful in improving productivity, such as
milk yields, growth rates, and reproduction (International Atomic Energy Agency, International
Symposium on Nuclear and Related Techniques in Animal Production and Health, 1991).
MUBs have been used as the sole supplement in many countries including India, Pakistan,
Indonesia, and Bangladesh. Typical results have been:
Milk yields increased by 20-30 percent
Growth rates increased by 80-200 percent
Increased reproductive efficiency.
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6-18 RUMINANT LIVESTOCK
Based on these results, methane emissions per unit product are expected to be reduced by
up to 40 percent.
The use of MUBs has consistently proven to be a successful and cost effective investment.
The application of molasses/urea blocks and the associated increase in feed intake per animal
does increase the cost of feed for managed livestock; case studies typically report increased
costs of 30 percent. However, this investment results in higher productivity; in one study the
cost per kilogram of liveweight gained decreased by 60 percent. Overall, the cost
effectiveness of this technology has attracted considerable interest in many areas of the
world.
Availability
The technology of strategic supplementation with molasses/urea blocks is well understood,
and its effectiveness has been demonstrated both in research and applied case studies. The
results of regional case studies are also increasing awareness and acceptance of this
technique. Additional research is needed to design applicable projects and overcome local
barriers to implementation, such as quality control of the MUB production process and the
structure of agricultural extension services.
Applicability
Strategic supplementation with molasses/urea multinutrient blocks will be most effective in
regions where constraints on feed resources decrease animal productivity below genetic
potential. Because molasses/urea blocks primarily act to increase the ammonia levels in the
rumen, they are most applicable in regions where the base diet results in deficient ammonia
concentrations. In general, molasses/urea blocks will be most appropriate where the base
feed is:
Low digestibility crop residues, cut/carry grass and agro-industrial byproducts; or
Grazed forage:
~ in monsoonal climate, especially during the dry season;
- on tropical grasslands on infertile soils (e.g.. South America);
-- on semi-arid pastures (e.g., Southern U.S., Northern Australia).
To be cost-effective, the use of molasses/urea blocks should be implemented in situations
where farmers can realize the value of the increased productivity caused by the blocks.
Therefore, the blocks are most applicable to situations where adequate cash flow is generated
through the sale of animal products such as meat, milk, wool, calves, or draft power.
Barriers
Acceptance of new animal management techniques will always face institutional and cultural
barriers. These can be overcome through successful demonstration projects and grassroots
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RUMINANT LIVESTOCK 6-19
level education. Where investment in new techniques or more expensive feed may not pay
off for several years, or are subject to risk from animal losses, favorable finance and insurance
schemes can overcome initial resistance. Also, local ingredients must be available to
manufacture a suitable block.
The simplicity of the block formulation and manufacture enables the block to be used virtually
anywhere. Complex technology and capital costs are not anticipated to be barriers to the
applicability of this technique.
Benefits
In addition to the reduction of methane emissions, strategic supplementation can provide
several other benefits:
Animal productivity is increased. In countries where feed resources are limited,
improving the productivity per unit feed can improve a country's ability to meet its
demand for animal products.
Reduced payment of foreign exchange for animal product imports. A secondary
benefit of increased productivity and better supply of animal products is the reduction
of food imports.
Increased draft power. Improved health, reproductive efficiency, and increased
liveweight all act to increase available draft power. Increased draft power can be
expected to lead to more efficient cropping.
Increased equity for small farmers. Small farmers are typically limited to grazing on
public lands where forage is poorer than on private land. More efficient utilization of
poor quality forage allows poor farmers to better maintain their herds. The generally
improved health and efficiency of livestock also reduces susceptibility to famine during
drought conditions.
Molasses/Urea Multinutrient Blocks
methane reduced 40% per unit product
milk production increases up to 30%
technology currently available
low costs; high returns
significant additional benefits
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6 - 20 RUMINANT LIVESTOCK
6.3.2 MOLASSES/UREA MULTINUTRIENT BLOCKS WITH BYPASS PROTEIN
Proteins provided by rumen microorganisms are generally adequate to support tissue growth
and low levels of lactation in low to moderately producing animals. Animals capable of higher
yields and faster growth rates, however, need a greater supply of amino acids than the
microorganisms can provide. Valuable amino acids contained in many feeds are wasted when
unprotected protein is metabolized in the rumen. Bypass proteins, also called "escape
proteins," escape degradation in the rumen and are digested in the lower gut. These proteins
must pass through the rumen very quickly or have physical or chemical characteristics that
inhibit microbes from metabolizing them, Providing supplements of molasses/urea
multinutrient blocks with bypass proteins can greatly increase milk yields and liveweight gains
of animals on straw/forage based diets.
Reduction Technology Description
The combined use of molasses/urea blocks with bypass protein addresses the two critical
aspects of ruminant nutrition: microbial growth and the protein/energy ratio. Both
supplements are manufactured from locally available resources, are tailored to local conditions
and practices, and have proven to be effective in boosting productivity.
Molasses/Urea Multinutrient Blocks: These are hard lick-blocks containing urea, which
boosts rumen ammonia levels and therefore increases digestive efficiency. The typical
ingredients and their effects are described in more detail in the previous section.
Bypass Protein: Protein that is insoluble or high in disulfide bonds will be most resistant
to degradation in the rumen, and will therefore be available for digestion in the intestine
of the host animal. Here, protein is digested in a similar manner to monogastric animals.
Protein is broken down into constituent arnino acids, which are necessary for growth and
other important biological processes.
Protein meals from oilseed production are the most promising sources of high quality bypass
protein. For example, cottonseed and linseed meal contain 50-75 percent bypass protein.
Also, fishmeal has been used with some success. High quality cereal crops are one source
of bypass protein; however, these crops are not typically available for animal feed. Other
sources of protein contain varying amounts of bypass protein, but can be treated to protect
the available protein from digestive action in the rumen. These protein sources include
sunflower and safflower seeds, guar, groundnut, soybeans, lupins, peas, and beans. Where
treatment is necessary to protect the protein, three potential treatment processes exist: 1)
formaldehyde; 2) heat; and 3) xylose/glucose and heat.
Where suitable sources are available they may be incorporated into the MUBs directly,
provided separately as a "cake," or mixed into the feed. The appropriate level of supplemental
protein varies considerably with animal type, base diet, and protein source.
Case studies using this strategy have found that productivity is increased beyond the effects
of molasses/urea blocks alone. In the Kaira district of India a cottonseed meal (30 percent
bypass protein) replaced a conventional "concentrate" supplement and was supplied with a
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RUMINANT LIVESTOCK 6-21
molasses/urea multinutrient block. The recommended feeding level of the bypass protein
supplement was only 50 percent of the previously recommended feeding level for the
concentrate supplement. The result of the change was a 30 percent increase in milk
production for the local dairy area. It was estimated that methane production decreased 60
percent per unit product.
The potential long term benefits of this project should also be noted. The age taken to reach
maturity was reduced from 4 to 1.5 years, and the inter-calving interval from 2 years to 12
to 15 months. Increasing the reproductive rate in this manner, to approximately one calf per
year, can nearly double milk production. One researcher has calculated that demand for milk
in India can be met by 27 million animals (assuming that demonstrated cross-breeding
practices are applied), which could also produce the 13 million draft animals required each
year (Leng, 1991 a). These increases in animal productivity would greatly reduce the number
of animals needed to satisfy consumer demand, thereby reducing the costs of milk and meat
production.
The experience in the Kaira district in India indicates that, although the price of the bypass
feed supplement was about 30 percent higher than the previously-used concentrate
supplement, the reduction in the recommended feeding level led to an overall reduction in the
cost of feed. A cost-benefit analysis prepared for the Kaira project by Fleming (1991)
estimates an overall internal rate of return of over 100 percent, using conservative
assumptions. A qualitative assessment of costs in this same study indicates that although
research costs were high, the cost of production inputs and extension services were moderate
to low.
Availability
The importance of protein meals for productivity and growth has been demonstrated through
research and field applications, such as the Kaira project. The successes of MUBs and bypass
protein are increasing the awareness and acceptance of this technique. Currently, bypass
protein feeds are becoming increasingly available. However, significant efforts are needed to
identify and evaluate suitable sources of bypass protein in many areas.
Applicability
As with MUBs, supplementation with bypass protein and MUBs in combination will be most
effective in regions where constraints on feed resources decrease animal productivity below
genetic potential. In general, this technique will be most appropriate where the base feed is:
Low digestibility crop residues, cut/carry grass and agro-industrial byproducts; or
Grazed forage:
- in monsoonal climate, especially during the dry season;
-- on tropical grasslands on infertile soils (e.g., South America);
- on semi-arid pastures (e.g., Southern U.S., Northern Australia).
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6 - 22 RUMINANT LIVESTOCK
In comparison to supplying MUBs on their own, the capital investments necessary for
supplying, processing, and distributing bypass protein feed supplements may be large, and
may only be economically justifiable when adequate physical and financial infrastructure
enables the value of the increased production to be realized. The total investment required
will depend largely on the size and flexibility of the existing infrastructure for milling and feed
processing.
Barriers
The use of MUBs in combination with bypass protein will face barriers similar to the barriers
applicable to the use of MUBs alone. Farmers will accept this combined technique where they
realize the value of rapid increases in production. Consequently, adequately developed
markets for the animal products must exist. Even where benefits are clearly demonstrated,
demonstration projects and extension services may be necessary to overcome institutional and
cultural barriers.
An additional barrier to this strategy is the development of an economic supply of bypass
protein. This supply depends upon: 1) identifying a local protein source; 2) possessing the
means to process bypass protein; and 3) distributing the feed supplements to farmers. In
many regions, such as those already processing animal feed, it may already be possible to
satisfy these requirements; the extent to which they constitute barriers will depend upon
regional circumstances.
Benefits
In addition to the reduction of methane emissions, strategic supplementation can result in
several other benefits:
Animal productivity is increased. In countries where feed resources are limited,
improving the productivity per unit feed can improve a country's ability to meet its
demand for animal products.
Reduced payment of foreign exchange for animal product imports. A secondary
benefit of increased productivity and better supply of animal products is the reduction
of expensive food imports.
Increased draft power. Improved health, reproductive efficiency, and increased
liveweight all act to increase available draft power. Increased draft power can be
expected to lead to more efficient cropping.
Increased equity for small farmers. Small farmers are typically limited to grazing on
public lands where forage is poorer than on private land. More efficient utilization of
poor quality forage allows poor farmers to better maintain their herds. The improved
health and efficiency of livestock also reduces animal mortality during drought
conditions.
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RUMINANT LIVESTOCK 6 - 23
MUBs with Bypass Protein
methane reduced 60% per unit product
milk production increases up to 50%
technology currently available
low costs; high returns
* significant additional benefits
6.3.3 DEFALCATION
For animals grazing on forage or fed similar poor quality diets, protozoa in the rumen are
thought to decrease the efficiency of digestion. The strategy described here uses targeted
dietary supplements to remove protozoa, increasing digestion efficiency and productivity and
reducing methane emissions per unit product. Some supplements are currently being tested
and, along with further expected developments, may be available for application in the mid-
term future.
Reduction Technology Description
The rumen is populated by many different species of microorganisms. In a symbiotic
relationship, bacteria ferment carbohydrates to gather energy for their own maintenance and
growth, and then provide the host animal with a source of protein when they flow from the
rumen into the intestine. This process allows ruminant animals to utilize otherwise
undigestible feed.
Protozoa, a type of microorganism in the rumen, derive a portion of their energy by ingesting
bacteria and, in doing so, reduce the outflow of microbial protein. Because intensively
managed animals on grain-based diets typically receive large quantities of protein in their feed,
they rely to a lesser extent upon microbial outflow from the rumen to provide protein.
Therefore, protozoa do not significantly interfere with the nutrition of the animal, and are
thought to have the beneficial effect of buffering the pH in the rumen.
Alternatively, microbial growth and subsequent microbial protein outflow from the rumen is
the primary source of protein for many animals raised on poorer quality feed. In this case, the
ingestion of bacteria by protozoa reduces microbial growth with the dual effect of decreasing
rumen efficiency and reducing the protein to energy ratio. Furthermore, protozoa are thought
to promote the degradation of protein in the rumen. Defaunation - the removal of protozoa
and maintenance of the defaunated state -- is expected to improve productive efficiency in
these animals.
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6 - 24 RUMINANT LIVESTOCK
Anti-protozoal properties have been discovered in at least one type of natural forage.
Preliminary trials indicate that small amounts of this forage can successfully defaunate the
rumen (Leng, 1991 a). Pharmaceutical companies are also actively screening chemicals for
this purpose.
Defaunation may increase microbial cell outflow from the rumen by 25-50 percent among
animals on poor-quality forage-based diets. Such an increase may reduce methane emissions
per unit of carbohydrate fermented by approximately 25 percent. Additionally, defaunation
will improve the protein to energy ratio in nutrients available to the animal and increase
productive efficiency.
Costs
Defaunation agents are not commercially available. Consequently costs are not estimated at
this time.
Availability
Trials are underway to test practical methods of applying this technique, which will lead to
full-scale demonstrations. If successful, this strategy may be commercially available within
several years.
Applicability
Protozoa are thought to have the largest negative impact on animals whose primary source
of protein is microbial outflow, as opposed to protein contained in the feed. Therefore,
animals fed low-protein crop residues and agro-industrial byproducts, and animals grazing on
relatively dry or infertile pastures are the principal candidates.
Barriers
The primary barrier is currently the need to identify and demonstrate an effective defaunation
agent that can be delivered in a cost effective manner. Once appropriate defaunation agents
and delivery methods are demonstrated, generating adequate supply of the supplements in
targeted regions and gaining farmer acceptance will be important objectives.
Benefits
In addition to the reduction of methane emissions per unit product, it is anticipated that
defaunation will result in several other benefits:
Animal productivity will increase. Defaunation will improve the digestive efficiency of
grazing ruminants and increase productive efficiency. These improvements can
improve a country's ability to meet the demand for animal products.
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RUMINANT LIVESTOCK 6 - 25
Reduced payment for animal product imports. Increased productivity and better supply
of locally produced animal products can reduce expensive food imports.
Improved resistance to drought conditions. The improved health and efficiency of
livestock also reduces animal mortality during drought conditions.
Defaunation
methane reduced up to 25% per unit product
expected productivity increases
trials underway
* significant other benefits
6.3.4 TARGETED MINERAL/PROTEIN SUPPLEMENTS
Many regions of the world have extensive ranching operations for beef production. The
reproductive efficiency of beef cows and, in some cases, the efficiency of weight gain of
calves and steers on grazing systems, are adversely affected by specific dietary deficiencies.
In many areas protein is deficient seasonally. Additionally, specific minerals are deficient
throughout the year or seasonally. Supplements targeted to these deficiencies can improve
productivity and reduce methane emissions per unit product.
Reduction Technology Description
The expanded use of both protein and minerals supplements is being investigated.
Protein Supplements: Seasonal deficiencies in protein availability are often encountered
in extensive grazing operations. For example, in the U.S. mature warm season grasses
and crop residues used in the winter may be lower in protein than is recommended for
reproductive performance and adequate milk yield. Protein supplementation (e.g., with
cottonseed cakes or meals) can keep grazing beef cows in good condition and promote
reproductive efficiency and the production of healthier and heavier calves.
Mineral Supplements: Mineral elements have been shown to be essential for maintaining
animal productivity. Macrominerals (those required in greater quantities and present in
animal tissues at higher levels) include calcium, phosphorus, sodium, chlorine, potassium,
magnesium, and sulfur. Trace minerals (those required in smaller amounts) include cobalt,
copper, iodine, iron, manganese, molybdenum, selenium, and zinc.
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6 - 26 RUMINANT LIVESTOCK
Mineral deficiencies in ruminant diets are known to occur to various degrees throughout
the world. For example, copper deficiencies have been identified in many areas, due in
some cases to the interference of excess levels of molybdenum with the ability of the
animal to absorb copper. Similarly, although toxic in large quantities, selenium deficiencies
are known to occur in many areas, including the United States. Mineral deficiencies can
reduce animal productivity, including reproductive performance among beef cows. Mineral
supplements can remove these deficiencies and improve animal performance.
When mineral deficiencies are identified, it is usually cost effective to provide mineral
supplements to eliminate the deficiency. Supplements are available commercially, although
they may not always provide the best mix of supplements required for a given producer's
situation. Custom formulation of supplements can further improve animal performance and
avoid the purchase of ingredients that are not required. However, custom mixing is often not
cost effective for small producers.
Mineral deficiencies are not always easy to identify. Seasonal evaluations of forage quality
and intake levels can be used to assess whether supplementation is needed to correct mineral
and protein deficiencies. Information about mineral concentrations in the soil can also be
useful information. The cost of these assessments is generally small for commercial ranching
operations.
Availability
Various combinations of mineral and protein supplements are currently available commercially
in regions with significant commercial ranching operations. However, assessments of the
seasonal deficiencies remain to be performed in many cases. Additionally, commercially
available supplementation packages often do not precisely match the supplementation
requirements.
Applicability
Mineral and/or protein supplementation is applicable when mineral and/or protein deficiencies
are limiting production. Animals with otherwise adequate feed resources (i.e., diets with
adequate amounts of feed energy) and adequate disease control are the principal candidates.
These supplementation strategies are also applicable only to situations in which animal
productivity is important. Therefore, its application is limited to situations in which the sale
of animal products (e.g., calves) is the primary purpose for keeping the animals.
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RUMINANT LIVESTOCK 6 - 27
Barriers
The primary barriers to increased use of protein and mineral supplements include:
1) insufficient data describing the existence and severity of deficiencies in many areas;
2) supplementation products tailored to specific regional and local deficiencies are needed.
In some areas (e.g., in parts of the U.S.), the structure of the beef production industry also
limits the use of productivity enhancing agents such as mineral and protein supplements. In
some cases, contractual arrangements between pasture/rangeland owners and cattle owners
must be modified to provide incentives for the adoption of productivity enhancing techniques.
Benefits
In addition to the reduction of methane emissions per unit product, it is anticipated that the
use of targeted supplements will result in other benefits:
Animal productivity will be increased. Supplements will provide improvements in the
productive efficiency of animals already raised in relatively efficient operations.
Targeted Protein/Mineral Supplements
methane reductions remain to be quantified, but
may be on the order of 5-10% per unit product
expected productivity increases
technology currently available
cost effective
6.3.5 BlOENGINEERING OF RUMEN MICROBES
The efficiency of feed utilization and hence methane production in ruminant animals is
principally controlled by the microbes in the rumen. Over the long term, it may be possible
to select or bioengineer specific microbes that improve feed utilization (thereby reducing
methane production indirectly) or suppress methanogenesis directly.
Some microbial feed additives that improve rumen fermentation are becoming commercially
available. These products currently contain naturally-occurring microbes. In the future,
specially engineered microbes may further enhance efficiency.
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6 - 28 RUMINANT LIVESTOCK
Present knowledge of the rumen environment indicates that the level of rumen
methanogenesis can be altered. Significant research remains to be done in order to develop
microbes that will enhance feed efficiency and reduce methane production directly or
indirectly. For example, areas of research needed to reduce methane production directly
include:
Determination of the key methanogenic species in animals on different diets;
Correlation of methanogenic species and other rumen environmental factors with levels
of methane production; and
Identification of techniques to inhibit specifically-targeted methanogens without
adversely affecting animal performance. A variety of pathways for inhibiting
methanogens could be examined, including developing hydrogen-using microbes that
can out-compete the methanogens or developing microbes that produce an antibiotic
that selectively inhibits the growth of methanogens.
Given that genetic research on rumen microbes has only recently begun, there is considerable
potential for successful development of useful products. At this time, however, it is
premature to assess the costs and emissions reduction potential of this strategy.
6.4 Production Enhancing Agents
There are a variety of agents that enhance production in ruminant animals directly by
regulating various body functions. Animal growth is a complex physiological process that is
regulated by hormones produced by the endocrine system (Leung, 1988). To enhance growth
and improve feed efficiency, scientists have identified both naturally-occurring hormones and
synthetic compounds with similar chemical compositions that achieve production-enhancing
effects.
Growth hormone is generally considered to be the most important hormone affecting growth
and development. Through the use of recombinant DMA techniques, growth hormone can
now be produced in sufficient quantities to make its use in animal production possible. The
administration of other hormones has also been found to have commercially valuable effects
on growth and quality of beef animals.
By improving animal productivity and/or feed efficiency, these production enhancing agents
reduce methane emissions per unit product produced. This section reviews the major
production enhancing agents that are in use or near final development, including bovine
somatotropin (the bovine growth hormone), and anabolic steroid agents. This section
concludes with a summary of research that is continuing on other agents that may be
available in the future.
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RUMINANT LIVESTOCK 6 - 29
6.4.1 BOVINE SOMATOTROPIN (BST)
Bovine somatotropin (bST) is a growth hormone that occurs naturally in cows, and plays a
major role in the initiation and maintenance of lactation. This hormone can be synthesized
using recombinant DNA techniques; bST produced in this manner is often referred to as rbST.
Injecting rbST in dairy cows has been shown to increase milk production per lactation by
about 10 to 20 percent or more (Blayney & Fallert, 1990). The use of rbST reduces the feed
input per unit product (despite an increase in feed input per cow), and therefore reduces the
methane emissions per unit product. rbST is also expected to be effective in promoting feed
efficiency and lean tissue production in growing beef animals. Less research has been
performed in this area, so the following discussion focuses solely on rbST use in lactating
cows.
Reduction Technology Description
Growth hormones are proteins, secreted by the pituitary gland in all vertebrate animals.
Growth hormones are naturally occurring compounds that are vital for the regulation of
growth in young animals, and for lactation in mature animals. These hormones are species-
specific, and the hormone occurring in cows is known as "bovine growth hormone" (BGH) or
"bovine somatotropin" (bST).
The secretion of bST stimulates a secondary hormone (also known as a "mediator"), an
insulin-like growth factor-l (IGF-I), which helps coordinate the growth process of young cows.
The hormone bST itself is extremely effective at maintaining lactation in dairy cows. Milk
from untreated cows always contains certain levels of both bST and IGF-I.
Commercial application of recombinant DNA techniques has made possible the large scale
synthesis of bovine growth hormone. In extensive field testing, rbST has been found to be
effective in increasing milk production. The synthetic hormone, rbST, while sometimes
different from bST (that is produced naturally in cows) in overall structure by one or more
amino acids, always contains the same biologically active structure, and stimulates the same
growth and lactation processes.
Concern over the use of a synthetic drug that alters growth patterns has prompted extensive
study and review of the potential health effects for both humans and cows. Currently, the
scientific consensus overwhelmingly supports the safety and effectiveness of rbST (NIH,
1990). Both bST and IGF-I are digested like any protein when taken orally by humans, and
are biologically inactive in humans even when injected. The nutritional content of milk and
meat are unaffected by rbST treatments.
In the United States, the Food and Drug Administration (FDA) has already found the use of
rbST to be safe for humans; the FDA is currently considering the health and safety of animals
and of the environment, and is expected to reach a final decision within the next year. The
hormone rbST has currently been approved for use in 8 countries: Brazil, Mexico, Namibia,
Zimbabwe, South Africa, Bulgaria, Czechoslovakia, and the former Soviet Union (DeGraff,
personal communication, 1991).
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6 - 30 RUMINANT LIVESTOCK
Productivity studies have demonstrated an average increase in milk production of 10 percent
or more. The increase for a particular herd will vary depending on environmental and farm
management conditions. The productivity increase is also correlated to dose size, although
there is an upper limit beyond which there is no further growth effect. This hormone is
administered by daily injection (because it is digested if taken orally), although sustained-
release formulas have been developed that allow fewer injections. Typical dose sizes range
from 12.5 to 50 mg of rbST per day, with the optimum dose size around 40 mg (Fallert et al.,
1987). Feed intake rises when rbST is used because cows require more energy to produce
more milk, and feed supplies must be increased to maintain milk production levels.
The commercial price of bST has not yet been determined. The U.S. Department of
Agriculture (USDA) has estimated that rbST will cost $0.24 per cow per day, which will give
an expected $2 return on every $1 invested (Blayney & Fallert, 1990; Fallert et al., 1987).
Because most countries actively support their dairy industries, the expected return on
investment of rbST treatment depends to a large extent on the level of dairy price supports.
Milk production increases within several days of treatment, resulting in a short payback period
(Blayney & Fallert, 1990; Fallert et al., 1987).
Availability
The synthesis of rbST is well developed, and several U.S. companies are prepared to begin
its manufacture if FDA approves commercial application. Field trials in the U.S. have also
provided experience in the application of this drug to production animals. Where application
is approved, rbST is expected to be available in the near-term (before 1995).
Applicability
This strategy is likely to be cost effective for herds that are currently intensively managed,
that receive high quality feed, and that have a high genetic potential (i.e., where other
strategies are already in use) (OTA, 1991). In particular, effective use of rbST requires that
animal diets are controlled to provide the necessary additional energy for increased milk
production. In many regions of the world the necessary feed resources and management
techniques are not available.
Barriers
Government health and safety regulations currently control the application of rbST. There are
concerns that must be investigated before commercial application begins. However, as
indicated above, the preponderance of information currently available indicates that rbST is
effective and safe, and is therefore likely to be approved by additional countries.
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RUMINANT LIVESTOCK 6-31
Benefits
In addition to reducing methane emissions (OTA, 1991), the use of rbST improves the
productivity in lactating cows by over 10 percent.
Bovine Somatotropin
methane reduced by up to 10% or more per unit
product
increase productivity by 10% or more
technology currently available
cost effective
* suitable for intensive operations
6.4.2 ANABOLIC STEROIDS
Anabolic steroids have been demonstrated to be effective in increasing the rate of weight gain
and improving feed conversion efficiency among beef cattle. These effects are achieved by
redirecting the energy used to deposit fat in the animal to the deposition of protein. As a
consequence, the animal adds protein more quickly and efficiently. Additionally, the use of
anabolic steroids also results in a leaner beef product at slaughter.
Reduction Technology Description
Several hormones have been approved for use in food producing cattle including the following:
progesterone, used in steers and intact males grown for beef;
testosterone, used in heifers and in some cases steers;
zeranol, used in heifers and steers;
trenbolone, used in heifers and steers; and
estradiol benzoate, used in combination with testosterone or progesterone in heifers
and steers.
The preferred method for introducing the hormones into the animal is by placing or
"implanting" a small pellet under the skin of the animal's ear. The pellet releases a defined
dose of hormone into the animal's bloodstream. Via the bloodstream, the hormone reaches
its appropriate and effective sites throughout the body. Implanting is preferred to previously
used injection methods of delivery because the dose can be controlled carefully, thereby
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6 - 32 RUMINANT LIVESTOCK
preventing concentrations of the hormone from building up in tissues used for human
consumption.
The hormones will typically increase daily rates of gain by 5 to 15 percent and improve feed
efficiency by 5 to 10 percent (USDA, 1987; Ensminger, 1983). Hormone implants are not
used in milk producing animals, replacement heifers, or beef cows.
Costs
Hormone implants are extremely cost effective. The value of the increased rate of weight
gain and the feed efficiency exceeds the cost of the implant and the cost of administering it
to the animal.
Availability
Hormones are widely available and can be obtained commercially for use in producing beef
animals. However, hormones have been banned recently from human food production in the
European Community (EC). Additionally, food cannot be imported that was produced with
hormone implants.
Applicability
Hormone implants are applicable to commercial beef production. The principal limitation on
the use of hormones is inaccessibility to the cattle being raised. Because the pellets must be
implanted in each animal, implants may not be applicable to extensive ranch conditions where
contact with the animals is infrequent.
Barriers
Currently, the principal barrier to wider implementation of implants is regulatory. As
mentioned above, the EC has recently banned the use of implants due to consumer concerns
regarding safety. Consequently, the use of hormones is officially restricted in farm animals
in the EC, and effectively eliminated from farm animals in other countries whose products are
intended for import to the EC. Despite consumer safety concerns, all safety reviews of the
above mentioned hormones, including the review conducted by the EC, have indicated that
the implants pose no risk to animals, humans, or the environment.
Benefits
The benefits of the hormone implants are improved rate of weight gain and improved feed
efficiency. Additionally, by redirecting energy away from fat deposition in favor of protein
accretion, a leaner beef product is produced. Methane emissions are reduced via two
mechanisms: 1) improving feed efficiency to directly reduce methane emissions per unit
product, and 2) promoting faster weight gain, thus reducing the time to slaughter and
reducing total methane emissions.
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RUMINANT LIVESTOCK 6 - 33
Anabolic Steroid Implants
methane reduced 5-10% or more per unit product
technology currently available
* cost effective
improves animal productivity
6.4.3 OTHER AGENTS
Additional production enhancing agents are being developed that are expected to have
commercially-valuable effects on growth, feed efficiency, and carcass characteristics.
Examples of compounds under investigation include isoproterenol, clenbuterol, and cimaterol
(Muir, 1988). To date, these and similar compounds have been demonstrated to improve
growth rates and feed efficiency by up to 20 percent. Additionally, carcass characteristics
are improved, including increases in protein and decreases in fat.
Other mechanisms are also being investigated to improve animal productivity. For example,
it has been determined that somatostatin (SS) inhibits somatotropin (ST) release. If the
inhibitory effects of SS could be prevented, additional growth could be achieved using the
animal's own supply of ST. One mechanism being explored is the development of a vaccine
that would cause antibody binding to SS, thereby reducing its inhibitory effect on ST release.
Considerable research remains to be done in this area.
Efforts are currently under way to review the safety characteristics of the candidate
compounds and strategies for improving productivity. Additionally, potential impacts on beef
palatability are being examined.
6.5 Improved Genetic Characteristics
Methods for improving the genetic characteristics of large ruminant animals through breeding
are well established. Genetic potential is an important characteristic in virtually all animal
production systems. In the tropics and subtropics, certain strains of cattle and buffalo have
increased resistance to parasites and heat stress. In all environments, genetic potential in
terms of milk production, growth rates, and ease of reproduction are important.
Significant strides have been made throughout the world to improve the genetic
characteristics of cattle. Record keeping and evaluation systems are in place in the many of
-------
6 - 34 RUMINANT LIVESTOCK
the major dairy countries (in both developing and developed countries) to provide scientifically-
based data on animal potentials. Additionally, genetic material from high-producing cows has
been systematically introduced in many developing countries.
When management conditions are adequate, improved genetic characteristics have the
potential to improve production levels and decrease methane emissions per unit product. For
example, improved management and feeding must accompany improved genetics in order for
benefits to be realized. Insufficient feed, inadequate disease control, and other environmental
stresses (e.g., heat, drought) will prevent genetically improved animals from realizing their
potentials.
Examples of improved genetic potential are described in this section. However, opportunities
for accelerating genetic improvement so that methane emissions are reduced have not yet
been fully evaluated.
6.5.1 CROSSBREEDING IN DEVELOPING COUNTRIES
Crossbreeding to improve genetic characteristics has been systematically performed in
selected dairy herds in developing countries. For example, India has imported thousands of
Holstein, Friesian, and Jersey bulls and cows for its crossbreeding program. Similarly, China
is importing Holstein, Friesian, and Simmental animals for its emerging milk industry
(Jasiorowski, 1988; Sollod, 1992).
Imported cows, bulls, and frozen semen have all been used in crossbreeding programs to
produce animals with the increased production qualities of the exotic parents and the
environmental fitness of the indigenous parents. Numerous evaluations of the performance
of crossbreeds have been conducted and have produced mixed results. Some village-based
studies have shown that poor farmers often fail at raising crossbreeds because they are
unable to provide the animals with adequate nutrition, while wealthier farmers with better feed
resources are more successful. Therefore, although crossbreeding programs are successful
in certain situations, improving the conditions under which animals are managed in general
will increase the applicability of this strategy. Additionally, with crossbred animals raised in
harsh environments, it appears to be important to retain a larger portion of the indigenous
genes, because indigenous animals are better adapted to withstand extreme climatic
conditions, variations in feed quality and availability, and disease and parasites.
While improving genetic potential in developing countries through crossbreeding may
contribute to methane emissions reductions, the full potential of this strategy will only be
realized when the strategies for improving the nutrition of the animals are also implemented.
Although it is not as effective as crossbreeding, selective breeding among indigenous animals
is simple and inexpensive, but it has been largely neglected.
6.5.2 CONTINUED GENETIC IMPROVEMENT IN DAIRY CATTLE
The major dairy countries have well established breeding programs that will lead to continued
genetic improvement in dairy cattle. This has primarily occurred in developed countries, but
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RUMINANT LIVESTOCK 6 - 35
can be adapted to developing countries and expanded in these regions. The breeding
programs generally lead to the selection of sires and cows with economically important
heritable traits, such as: milk composition (depending on milk pricing and marketing in the
individual countries); milk production; stature; udder support; legs and feet; milking speed;
birth weight; temperament; and fertility (Ensminger, 1980).
For example, artificial insemination (Al) techniques have enabled improved genetic material
from proven sires to be spread quickly throughout dairy herds. However, the availability of
semen from the best bulls is limited, which effectively restricts the rate of improvement of
genetic potential. In the future, embryo cloning and transplanting techniques may enable the
genetic material from superior producing cows to also be made available more widely.
Currently, embryo cloning and transplanting are not used commercially. Similarly, research
is underway to develop methods of significantly increasing the semen that can be obtained
from bulls (Senger, 1992). These methods, once developed, could help to increase the rate
of improvement of genetic potential, and consequently reduce methane emissions.
Continued genetic improvement will reduce methane emissions per unit product. The extent
of these reductions has not been estimated at this time. The rate of improvement (and hence
emissions reductions) will be influenced, in part, by dairy pricing and production policies.
6.5.3 TRANSGENIC MANIPULATION
In the long term, transgenic manipulation, the transfer of genetic material from one species
to another, holds promise as a method for dramatically improving the productivity of domestic
livestock, including large ruminant animals. Transgenesis research is largely aimed at
developing new genomes through the manipulation of genetic material using recombinant
DNA, embryo manipulation, and embryo transfer techniques (Leng, 1991b).
To date, emphasis has been placed on developing techniques for introducing DNA that will
promote the expression of growth hormone. Growth has already been accelerated in
transgenic mice carrying genes that lead to the production of growth hormone or the
expression of growth hormone releasing factor (Allen, 1988). These characteristics have been
shown to be transmittable to subsequent generations. Considerable research remains,
however, before transgenic manipulation is used commercially in food producing animals.
6.6 Improved Reproduction
Many ruminant animals are maintained for purposes of producing offspring. For example, in
the United States and Australia, tens of millions of cows are maintained for the production
of calves for beef production. Similarly, in India, millions of cows and she-buffalo are
maintained for producing bullocks for use as draft animals.
By improving the reproductive efficiency of the relevant populations of cows, methane
emissions per unit product can be substantially reduced. In many cases, there is substantial
opportunity for improving reproductive efficiency. Three strategies are being pursued for
improving reproduction directly and are described in this section: twinning; embryo
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6 - 36 RUMINANT LIVESTOCK
transplant; and artificial insemination and estrus synchronization. In many cases, the full
costs and emissions reduction benefits of these strategies have not been assessed at this
time.
Additionally, several strategies discussed previously will improve reproduction as a side
benefit. For example, improved animal nutrition due to feed processing and/or strategic
supplementation can reduce age at first calving and inter-calving intervals substantially (Leng,
1991 a). Similarly, targeted supplementation to eliminate key mineral deficiencies has been
demonstrated to improve reproductive efficiencies in the U.S.
6.6.1 TWINNING
Twinning holds tremendous promise of reducing the number of cows required to produce a
given number of calves. Because cows account for a significant portion of total emissions
in some regions, emissions reductions can be sizable as a result of twinning.
To date, selection for natural twinning has not held much promise because the heritability of
twinning is low (Ensminger, 1987). Additionally, under current management conditions
twinning has not been a desired characteristic among brood cows because:
heifers born twin with a bull are often sterile;
twin calves are generally lighter than single-birth calves; and
cows that produce twins are more difficult to re-breed the following season.
Strategies for improving the productivity of twin births are being developed. Techniques to
inhibit the hormones that suppress twinning have been developed, enabling twinning to be
promoted or prevented as appropriate. For example, in years with excellent pasture conditions
twinning may be promoted because adequate nutrition is available. In years of poor pasture
conditions, single births would be desirable.
Options for improving the nutrition of cows carrying twins and of the twin calves are also
being developed to reduce the rate of stillbirths associated with twinning and to help ensure
that the calves grow and mature quickly.
At this time, twinning is not practical for commercial operations. Cost-effective
commercialized techniques for twinning are likely to be available in the mid-term (after 1995).
The techniques will likely be applicable to commercial beef production situations in which
there is reasonably good contact with the animals and for which conditions are not too harsh.
6.6.2 EMBRYO TRANSPLANTS
There is great opportunity for increasing the efficiency of production through technological
advances in reproductive physiology. If successfully applied, recently developed techniques
for super-ovulation and the transfer of embryos can produce offspring that are uniform in
productive capacity, growth characteristics and quality. As artificial insemination has provided
the means to multiply the value of genetically superior males, embryo transfer will do the
-------
RUMINANT LIVESTOCK 6 - 37
same for females. Advantages are that calves with outstanding genetic merit can be
produced by foster cows of lesser quality, and superior cows are relieved of the burden of
long pregnancies. Because of it's technological complexity, the applicability of embryo
transfers at this time is mainly limited to highly managed dairy and beef operations in
developed countries.
6.6.3 ARTIFICIAL INSEMINATION AND ESTRUS SYNCHRONIZATION
Artificial insemination (Al) and estrus synchronization (ES) are well-known and established
techniques used in many regions to improve the reproductive performance of cows. Al has
been widely adopted in dairying in the major dairy countries. The advantages of Al include
(Ensminger, 1987):
Al eliminates the need to maintain many sires, thereby reducing costs;
Al enables the superior genetic potential of a single sire to be spread among many
progeny;
Al eliminates loss of reproduction efficiency due to sterile sires; and
Al helps reduce the spread of diseases associated with mating activities.
Estrus Synchronization has also become widely used. The benefits of ES include:
ES enables embryo transplants to be performed;
ES improves the cost-effectiveness and simplifies Al administration; and
ES facilitates pregnancy testing, thereby reducing the maintenance of cows that have
been unable to become pregnant.
A range of products are currently available for promoting ES reliably. The effectiveness of the
products has been demonstrated, although results will depend on individual herd
characteristics, such as nutrition and disease control. Expanded use of Al and ES can reduce
methane emissions. However, the extent of the emissions reduction has not been evaluated
to date.
6.7 Other Strategies
A variety of other strategies have been identified for reducing methane emissions from
ruminant animals. Further analysis is required to quantify their potential costs and emissions
reduction benefits. Several are summarized below.
Milk Marketing in Surplus-Producing Countries
Several regions routinely produce more milk than is sold, including the EC, U.S., New Zealand
and Australia. Excess quantities are generally stored, in some cases for long periods of time.
These dairy surpluses are largely a consequence of the farm policies implemented in these
regions. Considerable discussion has been and is taking place to identify options for reducing
this over-supply.
-------
6 - 38 RUMINANT LIVESTOCK
Reductions in the production of dairy products in these regions can reduce methane emissions
from dairy animals. If productivity per cow is maintained while total regional production is
reduced, total methane emissions will decline by an amount equal to the reduction in
production. If, however, total reductions in production are accomplished principally by
reducing production per cow, methane emissions may only decline slightly.
One strategy for reducing the dairy surplus is to decrease the priority given to the production
of milk fat, and increase the importance of non-fat milk solids. The basis for this approach
is that in the U.S., for example, the existing surplus is principally in milk fat production. By
changing the milk pricing system to de-emphasize fat production, farmers will take steps to
produce milk with less fat and more non-fat solids.
Such a milk pricing policy change is compatible with reducing methane emissions because the
animal diets that promote fat production are also relatively high in roughage. Reduced
roughage diets will decrease fat production, and are also expected to reduce methane
emissions. Consequently, a policy change that is desirable for purposes of reducing the fat
surplus may also help to reduce methane emissions.
Disease Control
Morbidity is an important limiting factor in many animal production systems. In many areas,
veterinary care is not available, and animal production and profitability suffer as a
consequence. Improved disease control through the development of vaccines will help to
reduce morbidity and improve animal production.
Various programs are in place to improve animal disease control in most regions of the world.
These programs will reduce methane emissions per unit of product as a side benefit.
Beef Marketing: U.S.A.
The U.S. beef industry is re-orienting its marketing toward a system called "Value Based
Marketing." The current beef marketing system has been accused of harboring inefficiencies
due to the historical working relationships that exist among livestock producers, meat packers,
and retailers. As a consequence, the industry does not produce meat as efficiently as possible
given consumer tastes. For example, the industry appears to produce more fat than is desired
by consumers.
In promoting Value Based Marketing, the industry plans to tie the production system closer
to the consumer. Improved communication among retailers, packers, and producers is one
goal. Additionally, objective meat grading instruments are under development.
Value Based Marketing should help to make the U.S. beef industry more efficient. It has been
estimated, for instance, that about 2 billion pounds of excess trimmable fat are produced
annually, and that the industry can save at least $2 billion annually through its elimination
(NCA et al., 1990). With the proper Value Based incentives in place, this fat will be
eliminated, and methane emissions will be reduced. Additional efficiency improvements are
expected that will also reduce emissions.
-------
RUMINANT LIVESTOCK 6 - 39
6.8 References
Contributions were made by:
R. Bowman, AT International, U.S.A.
P.M. Byers, Professor, College of Agriculture and Life Sciences, Texas A & M University,
U.S.A.
Gary Evans, USDA Global Change Program, U.S.A.
Michael Gibbs, Livestock Expert, ICF Consulting Associates, Inc., U.S.A.
R.A. Leng, Director, Institute of Biotechnology, University of New England, Australia
Additional information may be found in the following:
Allen, Ronald (1988), "Muscle Cell Growth and Development," in Designing Foods, National
Research Council, National Academy Press, Washington, D.C., pp. 142-162.
Blayney, D.P. and R.F. Fallert (1990), Biotechnology and Agriculture: Emergence of Bovine
Somatotropin (bST), U.S. Dept. of Agriculture, Washington, D.C., Staff Report AGES 9037.
DeGraff D.L. (1991), Monsanto Agricultural Company, personal communication, October
1991.
Ensminger, M.E. (1980), Dairy Cattle Science. The Interstate Printers & Publishers, Danville,
Illinois.
Ensminger, M.E. (1983), The Stockman's Handbook. The Interstate Printers & Publishers,
Danville, Illinois.
Ensminger, M.E. (1987), Beef Cattle Science. The Interstate Printers & Publishers, Danville,
Illinois.
Fallert, R.F.,T. McGuckin, C. Betts, G. Bruner (1987). bST and the Dairy Industry: A National.
Regional, and Farm-level Analysis. Economic Research Service, U.S. Dept. of Agriculture,
Washington, D.C., AER #579.
Fleming, Euan (1991), Improving the Feed Value of Straw Fed to Cattle and Buffalo,
Australian Center for International Agricultural Research, Canberra, Australia.
Habib, G., S. Basit Ali Shah, Wahidullah, G.Jabbar, Ghufranullah (1991), Importance of Urea
Molasses Blocks on Animal Production (Pakistan), International Atomic Energy Agency,
International Symposium on Nuclear and Related Techniques in Animal Production and Health,
Vienna, Austria, 15-19 April 1991.
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6 - 40 RUMINANT LIVESTOCK
Hendratno, C., J.V. Nolan and R.A. Leng (1991), Importance of Urea Molasses Multinutrient
Blocks for Ruminant Production in Indonesia, International Atomic Energy Agency,
International Symposium on Nuclear and Related Techniques in Animal Production and Health,
Vienna, Austria, 15-19 April 1991,
Jasiorowski, H.A., M. Stolzman, and Z. Reklewski (1988), The International Friesian Strain
Comparison Trial: A World Perspective, Food and Agriculture Organization of the United
Nations, Rome, Italy.
Leng, R.A. (1991 a). Improving Ruminant Production and Reducing Methane Emissions from
Ruminants by Strategic Supplementation. U.S. Environmental Protection Agency, Washington,
D.C., EPA/400/1-91/004.
Leng, R.A. (1991b), Application of biotechnology to nutrition of animals in developing
countries. FAO Animal Production and Health Paper 90, Food and Agriculture Organization of
the United Nations, Rome, Italy.
Leung, F.C. (1988), "Hormonal Regulation of Growth," in Designing Foods, National Research
Council, National Academy Press, Washington, D.C., pp. 135-141.
Muir, Larry A. (1988), "Effects of Beta-Adrenergic Agonists on Growth and Carcass
Characteristics of Animals," in Designing Foods, National Research Council, National Academy
Press, Washington, D.C., pp. 184-193.
NCA et al. (National Cattlemen's Association, Beef Industry Council, and Beef Promotion and
Research Board) (1990), "The War on Fat!" A Report from the Value Based Marketing Task
Force, August.
National Institutes of Health (NIH) (1990), Bovine Somatotropin: Technology Assessment
Conference Statement, December 5-7, 1990.
Nour, A.M. (1987), "Rice Straw and Rice Hulls in Feeding Ruminants in Egypt," in Utilization
of Agricultural Bv-Products as Livestock Feeds in Africa. International Livestock Center for
Africa, Addis Ababa, Ethiopia, pp. 53-61.
Office of Technology Assessment (1991), U.S. Dairy Industry at a Crossroad: Biotechnology
and Policy Choices - Special Report, Washington, D.C., OTA-F-470.
Owen E., and M.C.N Jayasuriya (1989), "Recent Developments on Chemical Treatment of
Roughages and their Relevance to Animal Production in Developing Countries," in Feeding
Strategies for Improving Productivity of Ruminant Livestock in Developing Countries,
International Atomic Energy Agency, Vienna, Austria, pp. 205-230.
Perdok, H.B. et al. (1988), "Improving livestock production from straw-based diets," in
Increasing Small Ruminant Productivity in Semi-arid Areas. E.F. Thomson and F.S. Thomson,
eds., ICARDA, pp. 81-91.
M. Saadullah (1991), Importance of Urea Molasses Block Lick and Bypass Protein on Animal
Production (Bangladesh), International Atomic Energy Agency, International Symposium on
-------
RUMINANT LIVESTOCK 6 - 41
Nuclear and Related Techniques in Animal Production and Health, Vienna, Austria, 15-19 April
1991.
Senger, Phil (1992), "Sperm production doubled in rats - are bulls next?," Hoard's Dairyman,
Vol. 137, No. 1, January 10, 1992.
USDA (U.S. Department of Agriculture) (1987), Economic Impacts of the European Economic
Community's Ban on Anabolic Implants. Appendices A-D, Food Safety and Inspection Service,
October 1987.
USEPA (United States Environmental Protection Agency) (1989). Reducing Methane Emissions
from Livestock: Opportunities and Issues. EPA/OAR, Washington, D.C., EPA/400/1-89/002.
Van Soest, Peter J., (1987), Nutritional Ecology of the Ruminant. Comstock Publishing
Associates, Ithaca, New York.
-------
CHAPTER SEVEN
LIVESTOCK MANURE
7.1 Background
Methane Production and Emissions
Methane is produced during anaerobic decay of the organic material in livestock manure. The
organic component of livestock manure contains carbohydrates, proteins, and lipids that can
supply the energy needs of microorganisms. An empirical measure of the organic component
is the volatile solids (VS) content. Methane may be produced when bacterial decomposition
of volatile solids is allowed to occur in an oxygen-free (anaerobic) environment (see Exhibit
7-1). The end products of the complete anaerobic process are methane gas (CH4), carbon
dioxide gas (CO2), other trace gases, and a slurry containing bacterial mass and undigested
solids.
The quantity of methane generated depends on certain physical, chemical and environmental
factors. Physical and chemical factors which directly affect potential methane production
include the quantity of manure, the proportion of the manure that is available for
decomposition (i.e., %VS), and the biodegradability of the manure. These factors will vary
by animal species and diet. For example, cattle fed a high energy grain diet produce a highly
biodegradable manure with a high %VS, whereas cattle fed a roughage diet will produce a
less biodegradable manure containing more complex organics such as cellulose, hemicellulose,
and lignin. Under similar conditions, the manure of cattle fed the high energy corn-based diet
will produce about twice as much methane as the manure of the cattle fed a roughage diet
(USEPA, 1992). Also, manure produced by ruminants (e.g., cattle) will, in general, have a
lower methane producing capacity than the manure produced by monogastrics (e.g., swine).
Manure management practices and climatic variables are environmental factors which
influence methane production in two important ways. First, the management system
determines whether anaerobic conditions will exist. For example, long term pit storage
promotes anaerobic conditions, whereas uncollected manure from grazing livestock will likely
decompose in the presence of oxygen, and thus without significant methane production.
Second, management systems determine the water content of the manure. Moisture content
is critical because water provides a reaction medium and is required for the biological
decomposition of the volatile solids. Liquid/slurry systems handle manure with less than 20
percent total solids, and have the highest methane potentials. Solid systems handle manure
with total solids above 20 percent. The percent total solids (%TS) of current management
practices is an important factor in choosing an appropriate methane recovery strategy. The
effects of manure management systems on potential methane emissions are summarized in
Exhibit 7-2.
The most important climatic variables are temperature and moisture. Bacteria are greatly
affected by temperature, and this is particularly true of methanogenic bacteria. Methane
production is maximized between 40 and 60 °C, but can occur between 4 and 75 °C (Safley,
1990). Moisture is important to the degree that it affects the water content of the manure
and the percent TS (described above).
-------
7 -2
LIVESTOCK MANURE
Exhibit 7-1
Phases of Anaerobic Digestion
. STAGE 1 .
Fermentative
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organisms
Cellulose-decomposing
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Protein-decomposing
organism
Fats + Cellulose + Protein = VS
__ STAGE 2
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Methanogenic
Exhibit 7-2
Impact on Methane Potential by Manure
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-------
LIVESTOCK MANURE 7 - 3
In addition to producing methane, livestock manure can be harmful to humans and the
environment. Manure run-off from confined livestock operations degrades both ground and
surface water quality, contaminating drinking water and leading to eutrophication of rivers and
lakes. Noxious odors associated with livestock manure impair air quality. Furthermore,
livestock manure can be a breeding ground for human pathogens and disease vectors.
Improving the management of livestock manure can greatly reduce these problems.
Methane Recovery Strategies
Methane emissions constitute a wasted energy resource which can be recovered by adapting
manure management and treatment practices to facilitate methane collection. This methane
can be used directly for on-farm energy, or to generate electricity for on-farm use or for sale.
The other products of anaerobic digestion, contained in the slurry effluent, can also be utilized
in a number of ways, depending on local needs and resources. Successful applications include
use as animal feed and aquaculture supplements, in fish farming, and as a crop fertilizer.
Additionally, managed anaerobic decomposition is a very effective method of reducing the
environmental and human health problems associated with manure management. The
controlled bacterial decomposition of the volatile solids in manure reduces the potential for
contamination and eutrophication due to runoff (Safley, 1991). The organic nitrogen content
of the manure is largely converted to ammonia, which is readily utilized by plants and is the
primary constituent of commercial fertilizers (Loehr, 1988). Anaerobic decomposition also
significantly reduces pathogens (Edgar and Hashimoto, 1991), and methanogenesis eliminates
most noxious odors. Thus, there are significant incentives for improving livestock manure
management practices.
Successful methane recovery strategies have been demonstrated under a variety of
conditions. In each case, methane recovery strategies improving anaerobic decomposition
were tailored to recognize important regional factors. For example, the ambient temperature
and climate -- e.g., tropical, temperate -- will greatly affect the performance of certain
designs. Additional important factors include economic, technical and material resources;
existing manure management practices; regulatory requirements; and the specific benefits of
developing an energy resource (biogas) and a source of high quality fertilizer. Choosing an
appropriate strategy is vital to meeting the varied needs and gaining the acceptance of
livestock farmers.
The following strategies are described in this report:
Covered Lagoons: The treatment of manure in lagoons is associated with relatively large
scale intensive farm operations. Manure solids are washed out of the livestock housing
facilities with large quantities of water, and the resulting slurry, containing a low percent
total solids, flows into lagoons. The anaerobic conditions treat manure and usually result
in significant methane emissions, provided temperatures remain high enough. Placing an
impermeable floating cover over the lagoon and applying negative pressure effectively
recovers methane which can be utilized for electricity generation, farm heating, and
refrigeration. Lagoons are most common rural North America, Europe, and less populated
regions of Asia and Australia.
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7 - 4 LIVESTOCK MANURE
Small Scale Digesters: Digesters are designed to enhance the anaerobic decomposition
of organic material and to maximize methane production and recovery. Small scale
digesters typically require a small amount of manure and are relatively simple to build and
operate. As such, they are an appropriate strategy for regions with technical, capital, and
material resource constraints. Due to the rising cost of commercial fertilizers, the recovery
of high quality fertilizer from digesters can be an even more important benefit than the
energy supplied from biogas. A number of different digester designs have been developed.
These designs are not heated, and while they can operate in colder regions, they are more
appropriate for temperate and tropical regions.
Larger Scale Digesters: The larger, often more technologically advanced digesters
described in this section are usually heated, have larger capacities, require greater capital
investment, and in general are more complex to build and operate. However, advanced
designs can greatly improve the performance of livestock manure digesters, and can
operate in colder regions. This strategy integrates the operation of a digester with current
manure management practices at large animal farms, typically in more developed regions.
The two primary digester designs are Complete Mix and Plug Flow digesters. Manure
quantity and the percent total solids of the manure are important criteria for determining
the appropriate technology.
Exhibit 7-3 summarizes these strategies for reducing methane emissions from livestock
manure, which are described in more detail in the individual assessments. Each technical
assessment contains the following sections:
Recovery Technology Description;
Costs;
Availability;
Applicability;
Barriers; and
Benefits.
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7 - 6 LIVESTOCK MANURE
7.2 Covered Lagoons
A common method of removing manure from confined livestock facilities involves flushing the
floors with large quantities of water. The resulting liquid manure is stored in a large lagoon
where anaerobic conditions promote decomposition of the volatile solids. Although this
method effectively treats the manure, it also produces large quantities of biogas (methane and
carbon dioxide) which is usually released into the atmosphere. The strategy presented here
recovers this potentially useful gas by placing an impermeable cover over the manure lagoon.
Successful applications of this strategy have yielded sufficient methane to satisfy the energy
needs of a farm without disrupting existing manure management procedures. Methane
recovery efficiencies exceeding 80 percent have been achieved.
Recovery Technology Description
Flush water manure management systems are common on animal farms where large numbers
of livestock are confined, and spend significant periods of time inside (e.g., dairy feedstalls
and milking parlors, and intensive swine operations). In these systems, animal manure is
removed from the building by periodic flushing with large quantities of water (as opposed to
scrape systems). The advantages of flush systems over alternative techniques are better
cleanliness, less wear on barn equipment, and lower labor requirements. However, the use
of large volumes of water significantly increases the total volume of slurry that must be
handled and reduces the percent total solids in the resulting waste stream.
Percent total solids from flush systems are typically less than 1 percent, which is too low for
effective use in a conventional digester. Instead, these liquid wastes are often stored in large
lagoons which provide a simple and cost-effective treatment system. Under the anaerobic
conditions that often occur in the lagoons, bacteria reduce the biologically active component
(volatile solids) of the manure; the remaining liquid can be drawn off for application as a
fertilizer. However, because the decomposition in the lagoons is anaerobic, methane and
carbon dioxide (biogas) are released. This gas can be a valuable energy resource.
Methane Recovery: The biogas is captured by placing a floating, impermeable cover over
the lagoon, or the portion of the lagoon with the highest methane flux. This cover must
not only be impermeable, but must also be sealed at the edges to prevent any influx of air
and subsequent dilution of the biogas (Safley and Westerman, 1990). The cover is
constructed of a rubber-like material (e.g., hypalon) which rests directly on solid floats laid
on the surface of the lagoon (see Exhibit 7-4). The cover is anchored along the edge of
the lagoon with a concrete footing, and is held in position with ropes. Where the cover
attaches to the edge of the lagoon, an air tight seal is constructed by placing a sheet of
the impermeable cover material over the lagoon bank and several meters into the lagoon,
and clamping the cover (with the footing) onto the sealed bank. Seals are formed on the
remaining edges using a two meter deep "curtain" of material hanging vertically from the
edge of the cover into the lagoon.
Selective sizing and placement of the cover can greatly improve cost effectiveness by
reducing capital costs without reducing recovery efficiency. In most cases, the manure
solids will be concentrated nearest the flush-water inflow and will not be evenly
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LIVESTOCK MANURE
7 -7
distributed across the entire lagoon. Methane production per unit area of the lagoon
surface area will be higher where the solids are concentrated, and often a significant
proportion of the total methane emissions can be recovered with a relatively small cover
area. The design of the cover naturally lends itself to easy modular expansion. Mapping
the sludge depth along the lagoon bottom or floating small (several m2) biogas test units
can help in determining the optimal cover size and location.
Exhibit 7-4
Schematic of a Covered Lagoon Digester System
Source: Chandler et al., 1983.
When the cover is in place, biogas produced in the covered area of the lagoon is trapped.
A collection device, such as a long perforated pipe, is placed under the cover along the
sealed edge of the lagoon, and the gas is removed by connecting a suction blower to the
end of the pipe. The blower draws the collected gas out of the cover and delivers it to the
engine generator (or other utilization option). The blower and collection pipes are sized
according to the quantity of gas and the distance from the lagoon to the engine.
Utilization Options: The recovered gas is typically 60 to 80 percent methane, with a
heating value of approximately 600 to 800 Btu/cf (22 to 29,000 kJ/m3) (DOE, 1988).
The gas can be used in an internal combustion engine generator, a boiler or space heater,
in refrigeration equipment, or directly combusted as a cooking and lighting fuel. The gas
usually must be cleaned to some degree, depending upon the specifications of the end use
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7 - 8 LIVESTOCK MANURE
equipment. This processing typically involves the removal of water and moisture in a
water trap, and the removal of particulates with a filter. Processing may also be used to
remove CO2 and any trace corrosive chemicals.
Significant quantities of medium quality gas can be recovered from livestock manure
lagoons. Techniques and materials for recovering the gas have been developed and
successfully implemented. Recovered gas can be used in a variety of options to satisfy
the energy requirements of the farm operation.
Internal Combustion Engines. Electricity generation with an internal combustion engine
is the most convenient option for large, industrialized farms. These engines are readily
available in a variety of sizes, are reliable, and can easily be connected to an electricity
generator. Electricity generated in this manner can replace energy purchased from the
local grid, or can be sold directly to the local electricity supply system. In addition,
waste heat from these engines can provide heating or warm water for farm use (DOE,
1988).
For example, a 75 kW generator was powered by 700 to 1000 m3/day (25 to 36,000
cf/day) of biogas, with an actual electricity output of 40 to 70 kW (Chandler et al.,
1983). This quantity of gas was produced from a one acre lagoon, 6 meters (20 feet)
deep at a 1000 head swine farm; the lagoon was 1 /3 covered. Typical energy demand
at a 1000 head swine farm ranges from 50 to 110 kW.
Boilers. Boilers and space heaters fired with biogas produce heat for use in the farm
operations. Although this may be an efficient use of the gas, it is generally not as
convenient an energy source as electricity. Nevertheless, in some situations it may be
a viable option (DOE, 1988).
Chilling/Refrigeration. Dairy farms use considerable amounts of energy for refrigerating
milk. Gas-fired chillers are commercially available and can be used for milk
refrigeration (DOE, 1988). For some farms in the U.S. this may be the most profitable
option for methane utilization (Roos, 1992).
Overall project economics will depend on a number of site specific factors, such as the details
of the manure management system, farm energy needs, energy costs, and regulatory
requirements. In particular, the potential amount and quality of recoverable methane will vary
greatly and will have a large effect on the revenue (or savings) realized. Recognizing these
variable factors, this section presents ranges for component costs, and some representative
economic analyses.
Lagoon Covers: Installation costs for the impermeable lagoon covers range from US $15
to 30/m2 (approx. $1.3 to 2.7/ft2). Once installed the maintenance costs are minimal
(Chandler et al., 1983).
Biogas Handling Equipment: Capital costs for suction blowers, plastic piping, and
purification equipment are approximately $0.1 6 to $0.33 per kW of capacity (or $4-8 per
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LIVESTOCK MANURE 7 - 9
kWh of electricity generated daily). However, this figure should be taken as a rough guide,
as actual cost will depend upon many factors including the distance the gas is transported,
and specifications of the purification system.
Utilization Options: Capital costs for internal combustion engine generators are typically
$400 to 800/kW (e.g., $40-50,000 for a 75 KW engine) (Chandler et al., 1983; Anderson,
personal communication; Moser, personal communication). Operation and maintenance
costs are estimated at 1.5 to 20 per kWh.
Boiler costs can be estimated for a given boiler capacity as follows: (BTU's available per
hour)*(boiler efficiency)*(cost per BTU). For example, a typical 150,000 BTU/hr boiler
with an efficiency of 80 percent, and a cost per BTU of $0.01, would cost $1,200 to
install (Woodbury, personal communication).
Chillers will cost from $700 to $1,100 per ton of cooling capacity, depending upon the
efficiency of the system. A typical cooling requirement would be 0.0165 ton/hour/milking
cow (Woodbury J, personal communication).
Costs and savings for complete projects have been developed by USEPA and the Tarleton
Research Institute for biogas recovery at Texas dairy farms. At these farms, the manure from
milking parlors is collected using flush systems and the liquid wastes are stored in anaerobic
lagoons. Even though this manure accounts for only 10-20 percent of the total manure
produced, the recovery of biogas is economically attractive for larger dairies (e.g., with over
500 cows) when used to fire absorption chillers to refrigerate milk. Using manure from
parlors as well as feed lanes to generate electricity increases profitability for larger herd sizes.
Typical payback periods for these dairies are two to five years, with initial investments of
approximately $75 to $90 per head (Roos, 1992).
Cost-effectiveness of biogas recovery has also been demonstrated for swine facilities. For
example, a case study of a successful project at a California swine farm with 1000 sows
farrow to finish produced the figures shown in Exhibit 7-5. Initial capital costs (in 1981) for
the entire system were $89,000 (Chandler et al., 1983).
Availability
The technology for recovering methane (biogas) from covered lagoons uses materials and
equipment that are commercially available. Similarly, utilization options use equipment that
is readily available.
Applicability
The storage of livestock manure in lagoons is most common at large farms with confined
rearing practices, and this strategy is designed to be appropriate for these farms. The volume
of methane generated in the lagoon must satisfy a large enough portion of the farm's energy
needs to make the project attractive when offsetting electricity or other energy costs, or
replacing other fuels.
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7- 10
LIVESTOCK MANURE
Additional factors that encourage the adoption of this strategy include:
Increasing prices for commercial fertilizers. The liquid fertilizer byproduct of lagoon
storage is cheap, convenient, and high quality.
Environmental regulations controlling livestock manure runoff may result in increased
anaerobic storage and larger regulatory compliance costs at large farm operations (e.g.,
in the U.S.).
Currently, anaerobic lagoons are most common in rural North America, Europe, and to some
extent in Asia and Australia (USEPA, 1992). However, this strategy will become increasingly
applicable as the degree of industrialization and the use of confined rearing practices increases
in other regions of the world.
Exhibit 7-5
Covered Lagoon Biogas Recovery System
Capital Investment
Lagoon Cover
1C Engine and Generator
Biogas Handling
Utility Interconnect
Building
Total Revenue (1st Year)
Total Operation and Maintenance Costs (1st Year)
Expected Payback Period
Internal Rate of Return
$89,000
$37,380
$40,940
$7,120
$1,780
$1,780
$36,530
$8,623
2.9 Years
34%
Source: Chandler et al., 1983.
Barriers
Any change in current manure management practices must be accepted by farmers if it is to
be successful; natural resistance to adopting new techniques is a significant barrier.
Therefore, this strategy must prove that it is compatible with existing practices and levels of
labor intensity, that it is economically sound, and technically reliable. The continued success
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LIVESTOCK MANURE 7-11
of technically sustainable demonstration projects will be important in overcoming the barrier
of acceptance.
Benefits
In addition to reducing methane emissions, the recovery of biogas from covered lagoons can
result in the following benefits:
Effective treatment of livestock manure. The treatment of manure in anaerobic
lagoons reduces runoff problems, and reduces pathogen levels (Loehr, 1984).
High quality fertilizer production. Anaerobic treatment of manure produces a liquid
fertilizer with a high inorganic nitrogen (NH3 ammonia) content (UNEP, 1984).
Improved energy use. Biogas is a cleaner burning fuel than most of the fossil fuels it
replaces (i.e., coal and oil). This reduces the emissions of particulates, nitrogen
oxides, and sulfur oxides. Furthermore, biogas is a renewable and a less carbon
intensive than coal or oil, reducing net carbon dioxide (a greenhouse gas) emissions
into the atmosphere.
Improved aesthetic quality. Covering lagoons improves control over flies and odors.
Covered Lagoons
methane reductions of up to 80 percent
medium quality gas (60-80%)
moderate capital investment
reduced energy costs
technology currently available
* minimum maintenance requirements
clean energy source
7.3 Small Scale Digesters
Appropriately designed anaerobic digesters can provide significant benefits for developing
countries. The anaerobic digestion of livestock manure reduces human and environmental
health problems associated with pathogens and disease vectors, produces cheap fertilizer and
other valuable products (e.g., animal and fish feed), and creates a renewable and convenient
energy source (biogas) (U.N. Guidebook, 1984). Small scale digesters are typically up to 100
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7- 12
LIVESTOCK MANURE
m3 (3,600 cubic feet) in total capacity, or a daily capacity of 3.5 m3 (130 cubic feet) capable
of handling about 1,800 kg of manure per day. Digesters can be successfully integrated with
existing agricultural practices, while improving sustainability by returning nitrogen and trace
minerals to the land, improving soil quality, and reducing erosion (Pimental, 1975). This
assessment describes the variety of existing designs, and how design and implementation can
best be tailored to important local factors such as climate and resource availability. These
systems are usually not heated and have the best success in the tropics.
Recovery Technology Descriptions
Anaerobic digesters utilize the ability of certain bacteria to digest the biologically active
component of livestock manure. Therefore, digesters must maintain suitable conditions for
the bacteria if they are to be effective. Exhibit 7-6 illustrates the basic components of a
digester, including a mixing pit, the digester, a gas holder (typically integral to the reactor),
and effluent handling. The design of these components must strike a balance between using
regionally appropriate materials and technical skills and maximizing the performance of the
digester, since it is not beneficial to build an inexpensive and simple digester if it is not
technically reliable over time, or to "over-design" a system that is not practical to build and
operate with local resources. Several designs are available to fit local variables while
maintaining digestion efficiency (Gunnerson & Stuckey, 1986).
Exhibit 7-6
Components of an Anaerobic Digester
Manure Handling
Manure
Collection
Mixing
Pit
Displacerrjent
Tank
Gas Holder
Fish
Note: In most designs, the gas holder is a part of the digester vessel.
This section classifies the types of digester systems available, outlines important operational
factors and their effect on efficiency, and describes the utilization of the digestion products.
The digesters described here are similar in concept to those described in the next section.
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LIVESTOCK MANURE 7-13
"Larger Scale Digesters," although the designs are typically simpler to build and operate.
Digesters can be classified by the arrangement of their components, with the distinguishing
characteristic being the method of storing the biogas produced in the reactor chamber
(digester):
Floating Gas Holders: These systems collect biogas by building a steel, fiberglass, or
ferrocement "floating" holder to form the roof of the digester chamber. This cover is able
to move vertically along internal or external guides. As gas is produced the holder rises
to accommodate the increased volume ("floating" on the pressurized gas); when gas is
drawn off, the holder falls, maintaining a constant gas pressure. An air tight water or
manure seal is formed around the bottom of the holder (see Exhibit 7-7). These systems
are commonly known as Mexican, Brazilian, Indian or KVIC, and Taiwan designs (UN,
1984).
Floating gas holder systems have been installed in several countries, especially India.
Experience indicates that corrosion often reduces the effective lifetime of steel floating
covers. Furthermore, the construction of the steel holder and guides is a relatively
complicated and expensive process (compared to other systems described below), and will
at best only be feasible in regions with manufacturing capability.
Exhibit 7-7
Floating Gas Holder System
Mixing Pit
Displacement Pit
Storage
Flexible Bag Holders: These systems are perhaps the simplest to construct and operate.
A large rubber bag both contains the decomposing manure and collects the biogas. As
biogas is produced and consumed, the flexible bag expands and contracts according to the
volume of gas it contains. (The basic design is similar to Plug Flow systems described in
"Larger Scale Digesters.")
The rubber bags, typically made from a residual manure of the bauxite industry known as
"red mud plastic," originated in Taiwan and have potential for application in certain
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7 - 14
LIVESTOCK MANURE
conditions by virtue of their low cost, ease of production, transport, and having virtually
no on-site construction requirements. Some projects have reported that the rubber
degrades when exposed to sunlight for long periods, and in general is more likely to be
damaged through normal wear and tear, although this may be true only in some cases.
Fixed Dome: Fixed dome systems combine the digester and gas storage components in
a single, fixed unit. This allows the entire unit to be constructed from masonry (e.g.,
brick, cement hollow blocks, ferrocement) and with no moving parts. This greatly reduces
the complexity and cost of the system. A reliable, gas tight dome can be achieved with
a paraffin wax application, making this system extremely reliable overall (Roos, 1988).
As gas is produced it exerts a pressure of up to one meter water column (0-2
pounds/square inch) on the digester contents; this pressure forces some slurry into the
displacement pit, eventually balancing the gas pressure (see Exhibit 7-8). The simplicity
of construction and operation make this system extremely promising. The main drawback
of this system is the variable gas pressure.
Exhibit 7-8
Fixed Dome Digester System
Mixing Pit
Displacement Pit
Storage
These types of digesters can be built in a variety of sizes; the capacity can be tailored to
fit the application. Typical sizes range from a 4 to 5 m3 design, suitable for a single family
running a small farm, up to 75 to 100 m3 and larger (Roos, 1988). Basic digester systems
will produce about 0.5 to 1 m3 of biogas per m3 of digester volume. (Although larger
capacities are feasible, in practice the initial investment is only justified if more advanced
design features are included; see "Larger Scale Digesters").
For example, a small family farm might be expected to own 4 to 6 pigs, and may use one
hectare for crop production. The biogas produced in a 4.5 m3 digester, run on the
livestock manure, would provide sufficient biogas for domestic cooking, lighting, or
refrigeration, in addition to fertilizer and animal feed supplements from the slurry effluent
(Roos, 1988).
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LIVESTOCK MANURE 7-15
Although the exact details of operation will depend upon the system size and design, the
common goal of each system is to manage the natural anaerobic digestion to promote
efficient decomposition of the livestock manure. The important factors controlling
digestion efficiency, and the ability of these systems to affect them, are discussed below.
Manure Handling and Composition. The water content of the manure entering the
digester must be controlled to maintain 7 to 9 percent total solids, ideal for ease of
handling and for digestion efficiency (gas production). In practice, this requires a 1:1
dilution of the raw manure with water. This dilution can be done in the mixing pit,
from which the manure is transferred to the digester. The logistics of handling the
manure must also be considered. Gathering manure in extensive operations (e.g.,
pasture grazing) may be impractical; intensive operations where livestock are confined
in smaller areas facilitate manure handling (Roos, 1992).
Temperature. The systems described here work in the mesophilic range (i.e., 30 to 35
°C; 60 to 90 °F). Thus, the temperature in the digester should not drop below 30 °C,
or methanogenesis will decrease markedly. The designs here usually do not involve
any active heating of the digester vessel (to the thermophilic range), so maintaining the
temperature depends upon the ambient temperature and the insulating properties of
the system; fixed dome systems, with mortar construction, are better insulators than
other designs. Additionally, tropical regions are more suited for simple unheated
anaerobic digesters. (Thermophilic designs are more complicated, and are more
sensitive to small temperature fluctuations) (Chen and Hashimoto, 1978).
Utilization of Biogas and Other Products: Anaerobic digestion yields biogas and a slurry
effluent. With minimal treatment, these two products are both valuable resources for
developing countries. Furthermore, they can be utilized to maximum effect for local
residential or agricultural purposes. This allows the operator (e.g., the participating farmer)
to directly benefit from the digester, without relying on the sale of products in a cash
market.
Biogas is typically 60 to 80 percent methane, with a heating value of 600 to 800 Btu/cf
(22,000 to 29,000 kj/m3). The gas can be used directly for domestic cooking and
lighting, or can be used in stationary engines to drive machinery (e.g., water pumps,
threshers) or generate electricity. These end uses require specialized or modified
equipment, but many practical designs currently exist. Typical gas requirements for some
end uses are given below in Exhibit 7-9. These values can be compared to the following
approximations: per capita gas consumption is 0.34 to 0.41 m3 per day; a typical family
of six will use 2.9 m3 per day (Roos, 1988).
Digester effluent is typically a 2 to 12 percent total solids slurry. The daily volume of
effluent is roughly equal to twice the daily manure production, because the manure is
usually diluted with water. The effluent contains valuable nitrogen, minerals, and other
organic material that improves soil conditions. The slurry can be treated in a variety of
ways -- separation into solids and liquids, drying, unseparated. The exact treatment and
use can be designed to meet particular local needs (see Exhibit 7-10).
Unseparated effluent can be used directly as a fertilizer, replacing expensive commercial
fertilizers. Additionally, separated solids (dried or undried) can be used. If the effluent is
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7 - 16
LIVESTOCK MANURE
separated, the liquid portion can be used for irrigation. Alternatively, dried solids have
been used as a feed supplement for livestock. The nitrogen contained in the solids is a
crude protein source, improving digestion efficiency (microbial growth) in cattle, and the
process enhances vitamin B12 as well (Maramba, 1983). The nutrient content of slurry,
or the liquid portion, can be used to promote algae growth in fish ponds (Maramba, 1983).
Exhibit 7-9
Gas Requirements of End Use Technologies
Cooking:
small burner
medium burner
large burner
Domestic:
mantle lamp (60W)
refrigerator
Engines:
motive power
electric power
8 ft3/hr
1 0 ft3/hr
1 5 ft3/hr
4-5.5 ft3/hr
.6-1.2 ft3/ft3 volume
16-19 ft3/bhp
21-25 ft3/kWh
.22 m3/hr
.28 m3/hr
.42 m3/hr
,
.11-.15 m3/hr
.6-1.2 m3/m3
.45-.54 m3/bhp
.6-.7 m3/kWh
Source: Maramba, 1983.
Exhibit 7-10
Treatment and Utilization of Digester Effluent
Fertilizer
Irrigation
Feed Supplement
Fish Ponds
Unseparated Effluent
X
X
Solids
X
X
Liquid
X
X
X
Source: Maramba, 1983
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LIVESTOCK MANURE
7- 17
As a rough approximation, anaerobic digesters will reduce the potential for methane
production by two thirds or more, leaving the remaining one third of the compounds that
can decompose anaerobically in the effluent. If the effluent is handled under anaerobic
conditions, such as in a treatment lagoon or tank, then methane may be generated from
the effluent. Therefore, where livestock manure is currently managed anaerobically and
generates methane, efficient digesters with gas recovery systems may reduce methane
emissions by up to 70 percent, with larger reductions achievable at longer retention times.
Costs
The initial costs and economic viability of digester systems will vary greatly with the size,
design, and the local availability of resources. As an example of the economies of scale and
relative differences between various designs and construction techniques, Exhibit 7-11 shows
initial costs for projects carried out in Jamaica.
Exhibit 7-1 1
Digester Construction Costs ($/cubic meter volume)
Digester Type
Fixed Dome - Ferrocement
Fixed Dome - Poured Concrete
Floating Cover
Digester Volume (m3)
4.5
154
178
240
7
110
132
210
20
60
82
130
50
34
68
104
Source: Roos, 1988.
Availability
The digester systems described in this assessment have been used extensively, and the basic
components of each design are well understood. The information necessary to construct and
operate digesters exists, and can be made available through a combination of government and
private sector technology transfer.
Applicability
The basic anaerobic digester systems described in this assessment are designed for regions
where resource constraints limit the application of more advanced technologies. These
resource constraints include technical and material resources necessary for construction and
long term operation, and also economic resources. Thus, these systems are most appropriate
for rural, agricultural regions in tropical developing countries.
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7-18 LIVESTOCK MANURE
More specifically, these systems are appropriate for agricultural areas where there are
economic and socio-economic benefits to be gained from the improved treatment of livestock
manure and from the products of anaerobic digestion. A necessary condition for applicability
is the availability of manure from agricultural activity. Integrated livestock and crop
production are ideal systems, especially where livestock are kept penned near the farm.
Whether considered at a regional or individual level, an important factor is the benefit derived
from the products of digestion. Biogas provides a renewable and convenient energy source,
making digesters suitable for countries that are net importers of fossil fuels, or where energy
costs are rising significantly. In many regions the value of fertilizer supplies is an even more
significant incentive for implementation. The price of commercial fertilizers has been rising,
and is projected to rise further in the future. This has strained the ability of small and medium
size farmers to maintain viable production levels, and also hampers national economic
performance. Anaerobic digesters can help to make these farmers more self-sufficient,, and
reduce the cost of importing fertilizers. Similarly, alternative uses of digester effluent such
as cattle feed and in fish ponds improve these conditions further.
In addition to the tangible benefits of energy and fertilizer supplies, the improved soil condition
and reduced health and environmental problems (e.g., pathogens, air and water quality) should
be accounted for when considering regional and national plans for implementation. This is
important because many bacteria have become resistant to anti-biotic treatments (WHO,
1980).
Barriers
Technical reliability and effective system management is essential for successful programs.
Historically, some implementation programs have not ensured that designs are appropriate,
construction is of sufficient quality, or that technical support is available. As a result, projects
have not been successful over time, and have therefore failed to gain acceptance. However,
the experience gained through these projects combined with successful dissemination of this
experience will enable future projects to avoid these barriers to successful implementation.
Initial costs can often pose a significant barrier, since the cash resources of small and medium
farmers in many regions is often limited. As construction methods have been refined,, and
made more appropriate for local resources, construction costs have fallen significantly (e.g.,
the use of ferrocement fixed dome construction). However, financing arrangements may be
necessary to promote these systems.
An additional barrier may be government policies that act to reduce the perceived benefits of
livestock manure digesters. For example, fossil fuel energy and fertilizer import subsidies will
have the effect of reducing the replacement value of biogas and digester effluent. Such
policies may need to be examined when implementing national policies, particularly in lesser
developed countries.
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LIVESTOCK MANURE 7-19
Benefits
In addition to reducing methane emissions from livestock manure, basic anaerobic digesters
have the following benefits:
Reduced fossil fuel use. Biogas is a renewable and convenient fuel that can replace
conventional fossil fuels in many applications. This replacement will result in reduced
fuel costs and/or imports.
Reduced demand for commercial fertilizers. By returning nutrients and minerals to the
land, the need for expensive commercial fertilizers can be reduced, saving scarce
foreign exchange.
Improved environmental and human health. Anaerobic digestion effectively treats
livestock manure, reducing the danger from human pathogens and manure runoff into
surface and groundwater. Additionally, using effluent as fertilizer improves soil quality,
reducing soil erosion (and improving agricultural productivity).
Increased self sufficiency of farms. By reducing expenditures and energy demands,
increasing productivity, small and medium size farms can be made more self sufficient.
Improved indoor air quality. Using gas as a domestic fuel, in place of relatively dirty
fuels such as coal or wood, can greatly improve the quality of indoor air (Hamburg,
1987).
Small Scale Digester Systems
methane reductions of up to 70 percent
appropriate technology
reduced energy costs
reduced fertilizer costs
technology currently available
minimum maintenance requirements
7.4 Larger Scale Digesters
Large and medium scale biogas digesters promote the anaerobic digestion of livestock manure
and collect the methane (biogas) that is produced. The recovered biogas can be used to
power a variety of end uses which provide electricity, heat or cooling to the farm. In addition
to effectively treating livestock manure and providing a low-cost and clean energy source, this
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7 - 20
LIVESTOCK MANURE
strategy can yield high quality fertilizer as a byproduct of the digestion process. The systems
described here are plug flow digesters and complete mix digesters (see Exhibit 7-12).
Because of the size, materials, and relative complexity of these technologies, they are most
appropriate for more industrialized regions.
Recovery Technology Descriptions
Because manure management systems vary among farms, the percent total solids (TS) of the
manure also differs widely. Correspondingly, the two technologies discussed here are
appropriate for a range of manure compositions. Complete mix digesters typically use manure
with 2-10 percent total solids; plug flow digesters use manure with 8-15 percent total solids.
Both systems range in size and are capable of handling the manure output of operations with
a few hundred to several thousand head or more, or roughly 0.5 million poultry. Both designs
are compatible with existing management practices.
Exhibit 7-12
Schematic Diagrams of Anaerobic Digesters
SLURRY .
IN
EFFLUENT
OUT
PLUG-FLOW DIGESTER
SLURRY
IN
EFFLUENT
OUT
Source: Koelsch et al., 1989.
Plug Flow Digesters: Plug flow digesters use manure that is undiluted, or has had only
small quantities bf water added. This type of digester has been implemented successfully
at many farms with scraper manure systems, or at farms that use front-end loaders to
remove manure. The basic digester design is a long trough, often built below ground level,
with an air tight but expandable cover (see Exhibit 7-13). The manure is collected daily
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LIVESTOCK MANURE
7 -21
and added at one end of the trough. Each day, a new "plug" of manure is added, slowly
pushing the manure down the trough. The size of the system is determined by the size
of the daily "plug" and the retention time -- the total time that manure spends inside the
digester as it flows from one end to the other, as indicated in the following equation:
Working Digester Volume Daily Waste Volume X Retention Time (in days)
The overall dimensions of the digester are designed to allow a retention time of 20 to 30
days at 30 to 35 "C; lower temperatures will slow the rate of digestion and necessitate
a longer retention time. (At a given temperature, longer retention times allow more
complete digestion, but will increase construction costs.) The depth of the trough is
usually 2 to 5 meters (8 to 16 feet); the length and width are designed in a 5:1 ratio. For
example, a 25 feet wide trough would be 125 feet long (7.5 by 40 meters), with a total
volume of 40,000 to 45,000 cubic feet (1100 to 1300 m3). With a retention time of 20
days, this system could handle 2,100 ft3 (60 m3) of manure per day -- sufficient for
several hundred cows. The cover would have a maximum capacity of approximately
30,000 cubic feet (800 m3). These calculations are based on a rectangular trough;
however, the designs are often U- or V-shaped, which increases the structural strength
but decreases total volume by up to 50 percent (Koelsch, 1989; Treleven, 1989).
Exhibit 7-13
Plug Flow Digester
Bypass
Manure Entrance
J Om LJA***
, Chamber
5
; Digester
> (
Gas Bag Collection
Cover
C-"V
Exit v
Control
Chamber f
f I
* r
Manure Exit
Lagoon Storage
for
Agricultural Fertilizer
The air tight cover prevents gas leaks and helps maintain anaerobic conditions inside the
trough. As the manure moves through the digester it decomposes, producing biogas
which is trapped in the expandable cover. The gas is collected through a perforated pipe
supported above the surface of the manure, and is transported to the end use (e.g., the
engine generator).
-------
7 - 22 LIVESTOCK MANURE
There are several components of the system in addition to the digester vessel itself.
These include the manure delivery system, mixing pit equipment (holding/pre-heating
tank), a removal and collection system for the effluent, and other design features that
improve the ease of operation and overall performance. Where possible, digester systems
use a gravity-feed design. The pre-heating tank, the digester, and the collection system
are built on a gentle slope to facilitate transfer and movement of the manure. Otherwise,
pumps must be installed to move the manure from one area to the next.
Mixing Pit. Many systems use a mixing pit with a volume roughly equal to one day's
manure output to store manure before it is added to the digester. This is a convenient
method for easily adjusting the percent total solids of the manure (by dilution with
water), and for adding the manure to the digester (Koelsch, 1989). The tank is
connected to the digester by a pipe (usually underground) that is below the surface
level of the manure, which effectively prevents air from flowing into the digester.
There must also be a digester bypass route for maintenance periods and undesirable
batches of manure.
Mixing pits facilitate pre-heating the manure - raising the temperature of the manure
to promote decomposition and methanogenesis. A second important method of
promoting methanogenesis is to warm the contents of the digester itself. Maintaining
a temperature of above 30 °C is crucial to achieve high rates of digestion. The energy
for pre-heating and digester heating is often derived from waste heat from the cooling
system of an internal combustion engine generator. In both cases, hot water pipes
from the engine coolant system run through the containers, transferring heat to the
manure.
Effluent Collection. As the digested manure reaches the end of the digester trough it
must be removed and stored before use (e.g., as fertilizer). In gravity-feed systems
the material is simply displaced as new manure is added. Removing the manure
without allowing air to enter the system is usually achieved with a trap mechanism.
Manure can be applied directly, or can be further processed (e.g., separated with a
centrifuge into liquid and solid components to ease handling).
In order to protect the flexible cover, and to maintain optimal temperatures, some
digesters are enclosed in simple structures. Also, the digester vessel can be built with
an insulating layer to retain heat, and the cover can also be insulated with fiberglass.
Complete Mix Digesters: Complete mix digesters typically handle manure with a lower
percent total solids than plug flow digesters (i.e., dilute liquid/slurry), and in general they
handle larger volumes of manure. The significant difference between the plug flow and
complete mix technologies is the design of the digester vessel, and thus the processing
of the manure. However, the basic system components are similar (i.e., mixing pit,
reactor (digester), removal and storage, heating).
As with plug flow digesters, the manure is collected in a mixing pit where the dilution can
be adjusted and the manure can be pre-heated, and from here it is pumped (or flows) into
the digester vessel. (Clarifiers can be used if the manure is too dilute, or to reduce
volume). The digester vessel is simply a large, vertical, poured concrete or steel container
(similar to a liquid/slurry storage container). The vessels are typically circular, this design
-------
LIVESTOCK MANURE
7 - 23
being the strongest and most economical (see Exhibit 7-14). Both the digester and holding
tank are heated (with engine cooling system waste heat).
When manure is added to a complete mix digester it is deliberately mixed within the
digester vessel. This creates a homogeneous substrate, preventing stratification and the
formation of a surface crust, and keeping solids in suspension. However, it also means
that manure is not processed sequentially (i.e., there is not a fixed retention time).
Therefore, although the average retention time can be controlled, the actual retention time
of a particular batch of solids will vary considerably; volatile solids may spend too short
or too long a period of time in the digester. This potential inefficiency is generally
balanced by the improved digestion efficiency due to mixing, heating, and other
management techniques. (This is in contrast to plug flow digesters, where the elongated
design prevents mixing of manure; however, maintaining a homogeneous substrate is not
a problem with the more solid manure used in plug flow designs.)
Digester volumes range considerably, from around 100 m3 (3,500 ft3; 25,000 gal.) to
several thousand m3 (e.g., 5000 m3; 180,000 ft3; 1.3 M gal.) Improved efficiency of
digestion, due to heating and mixing, often result in an average retention time from 10 to
20 days. Thus, these capacities represent daily capacities of approximately 1,500 gallons
to 100,000 gallons per digester (210 to 14,000ft3) (Waybright, 1991). Larger volumes
are usually handled in multiple digester systems. (These figures indicate the flexibility of
digesters; they do not represent definite size limits.) For example, flush systems at dairy
operations produce upwards of 20 to 30 gal/day/cow.
Exhibit 7-14
Complete Mix Digester
Bypass
Racirculasng
Pump
Lagoon Storage
tor Agricultural Fertlizst
A fixed expandable cover maintains anaerobic conditions and traps the methane that is
produced. The methane is removed from the digester with a suction blower, processed.
-------
7 - 24 LIVESTOCK MANURE
and transported to the end-use site. Adequate space must be maintained between the
surface of the manure and the cover for gas to collect.
In this process, manure pumped from the holding tank displaces a portion of the contents
of the digester vessel. The displaced material can be further treated for use as a fertilizer,
or used directly. Alternatively, in some systems it is pumped into the next of a series of
digesters, thereby increasing the extent of anaerobic decomposition and the quantity of
methane produced.
Utilization Options: The utilization options for the recovered biogas have been described
above in "Covered Lagoons." The options include electricity generation with gas fired
engine generator; gas fired boilers and space heaters; and chilling equipment. A well
maintained digester will produce as much as 0.25 to 0.6 m3 of biogas (50 to 65% CH4)
per kg of VS, operating at 30 to 35 °C, and more at higher temperatures (Safley &
Westerman, 1988).
As a rough approximation, anaerobic digesters will reduce the potential for methane
production by two thirds or more, leaving the remaining one third of the compounds that can
decompose anaerobically in the effluent. If the effluent is handled under anaerobic conditions,
such as in a treatment lagoon or tank, then methane may be generated from the effluent.
Therefore, where livestock manure is currently managed anaerobically and generates methane,
efficient digesters with gas recovery systems may reduce methane emissions by up to 70
percent, with larger reductions achievable at longer retention times.
Choosing between the available options involves an assessment of the size and type of
current manure management practices (i.e., volume and %TS), the technical and economic
resources available, and the demand for energy and fertilizer products.
Costs
The initial capital costs and subsequent operating costs of anaerobic digesters will vary
considerably with size, and also with the particular design of the various system components.
Using conservative assumptions (e.g., only considering revenue from energy sales or cost
savings from use, and not from other products of digestion), one study for the U.S. estimated
that installed costs for economically viable projects may range as high as $3,000/kW; this
assumes that the payback period will be 5 years or less (Quok & Chandler, 1984). These
results are summarized in Exhibit 7-15.
These figures provide a valuable first estimate for project costs. However, actual installed
costs and overall economic viability will vary with site specific factors. For example, specific
projects include:
A 400 head dairy farm which installed a $124,000 plug flow digester (to handle
manure from an existing scraper system). The digester had a total volume of 150,000
gallons. Operating costs were $2,000/yr. The 45 kW generator saves $22,000/yr in
electricity costs. Additional savings from waste heat and fertilizer use are estimated
to be $10,000/yr (Ferchak, 1988).
-------
LIVESTOCK MANURE
7 - 25
A 500 head dairy installed a $200,000 plug flow system, with a maximum generating
capacity of 85 kW. The average output of 40 kW creates savings of approximately
$4,000/month in electricity and heating fuel (Treleven, 1989).
A 2,700 head dairy farm installed 3 complete mix digesters, with a daily capacity of
30,000 gallons, at a cost of $250,000 (in 1991 dollars). Estimated net annual income
has been $90,000. In 1990, over 1 million kWh of electricity was produced for on-
farm use and sale to a local utility company (Waybright, 1991).
Availability
Considerable experience exists in the planning, de~ ^n, and operation of biogas digesters.
Anaerobic digesters are a viable technology that can .^iprove existing manure treatment
practices while providing energy and other valuable by-prouucts.
Exhibit 7-1 5
Estimates of Economically Feasible Projects
cw\n
13UUU
1 10000-
I
5000
COST OF BIOGAS SYSTEMS
FOR SCRAPE AND FLUSH SYSTEMS
CURRENTLY AVAILABLE SYSTEMS
i
\ .ŤŤŤ. Complete mix, flush system
ť Complete mix, scrape system
\\ Plug flow, scrape system
V
V XX
\ N **^
\S:"-"~-::: ..._
Economically Feasible
1 1 1 1 1 1 1 1 1 1 1 1 1 1
20 40 60 80 100 120 140
Capacity (Kilowatts)
Source: Quok and Chandler, 1 984
Applicability
The technologies described in this assessment are applicable for a wide variety of manure
management systems. However, it is important to identify the most appropriate digester
-------
7 - 26
LIVESTOCK MANURE
design for existing management practices, available resources, and to ensure economic
viability.
Plug flow digesters do not mix the manure as it is being decomposed, and therefore are more
suited to homogeneous manure (e.g., from dairy and beef operations). Furthermore, the
manure must be relatively concentrated. Complete mix digesters, on the other hand, are also
capable of operating with more dilute and less homogeneous manure. These considerations
are summarized in Exhibit 7-16.
A second factor is the availability of labor and technical support to maintain the digester.
Anaerobic digesters usually require minimal maintenance. However, it is important that the
time, personnel, and expertise are available when operating problems occur. This is especially
true of complete mix digesters, which are typically larger and contain more mechanical
components (Koelsch, 1989).
Exhibit 7-16
Digester Design/Manure System Compatibility
Plug Flow
Complete
Mix
Scrape System
Dairy
X
X
Beef
X
X
Layer
(X)1
X
Swine
(X)2
X
Flush System (dilute)
Dairy
X
Beef
X
Layer
X
Swine
X
1 Poultry manure must be very dilute because of high ammonia levels Source: Quok and Chandler, 1984.
2 Less common; pig farms typically use flush systems.
In addition to these technical and operational considerations, it is important to analyze
potential economic scenarios. Revenues flow primarily from energy sales (or the savings that
result from reducing the amount of energy purchased by the farm). Therefore, the potential
gas volume and local energy rates must be favorable. As with covered lagoons, larger farms
are more likely to produce significant quantities of biogas. Revenue can also be obtained from
fertilizer sales (or improved fertilizer quality). Installing an anaerobic digester can also reduce
pollution, odor, and other less quantifiable problems.
Currently, the type and size of manure systems that are compatible with these designs, and
the material, economic, and technical resources necessary to build and operate them, make
this strategy applicable to relatively industrialized countries, or large, highly-managed farms.
Barriers
As with any change in farm operations, anaerobic digesters must gain the acceptance of
animal farmers by demonstrating compatibility, economic viability, and technical reliability.
-------
LIVESTOCK MANURE , 7-27
In the past, many expensive and unreliable demonstration projects have hindered acceptance.
Technical reliability is a particularly important factor because of the relatively complex
technologies (compared to covered lagoons and small scale digesters). Digester systems can
require high initial costs. Farmers may lack sufficient capital to undertake projects
independently.
Benefits
In addition to reducing methane emissions from livestock manure, anaerobic digesters can
result in the following benefits:
Effective treatment of livestock manure. The treatment of manure in anaerobic
digesters reduces runoff problems, and reduces pathogen levels. Improved treatment
may better comply with applicable regulations.
High quality fertilizer production. Anaerobic treatment of manure produces a fertilizer
with a high ammonia content.
Improved energy use. Biogas is a cleaner burning fuel than most of the fossil fuels it
replaces. This reduces the emissions of particulates, nitrogen oxides, and sulfur
oxides. Furthermore, biogas is a renewable and a less carbon intensive than coal or
oil, reducing net carbon dioxide (a greenhouse gas) emissions into the atmosphere.
Improved aesthetic quality. Processing manure in (anaerobic) sealed containers
improves control over dust, flies, and odors. Furthermore, manure effluent from
digesters will have less odor than untreated manure.
Larger Scale Digesters
ť methane reductions of up to 70 percent
Ť medium quality gas (60-80% CH4)
moderate capital investment
reduced energy costs
technology currently available
compatible with a range of waste
management systems
clean energy source
ť regulatory compliance
-------
7 - 28 LIVESTOCK MANURE
7.5 References
Contributions were made by:
Andrew G. Hashimoto, Head, Department of Bioresource Engineering, Oregon State
University, USA
Mark Moser, President, RCM Digesters, USA
Kurt F. Roos, USEPA, USA
L.M. Safley, Department of Biological and Agricultural Engineering, North Carolina State
University, USA
John M. Sweeten, Associate Department Head, Texas A&M University, USA
Jonathan Woodbury, ICF, USA
Additional information may be found in the following:
Anderson, C., Waste Management of North America, personal communication, 10/91.
Chandler, J.A., S.J. Hermes, and K.D. Smith (1983), A Low Cost 75 KW Lagoon Biogas
System, presented at "Energy from Biomass and Wastes VII," Lake Buena Vista, Florida,
January 25, 1983.
Chen Y.R. and A.G. Hashimoto (1987), "Kinetics of Methane Fermentation," in Biotechnology
and Bioengineering Symposium No.8, pp.269-282.
Edgar, T.G. and A.G. Hashimoto (1991). Feasibility Study for a Tillamook County Dairy Waste
Treatment and Methane Generation Facility. Department of Bioresource Engineering, Oregon
State University.
Ferchak, J. (1988), "Biogas Installation at the Oregon Dairy Farm," University of Pennsylvania,
Energy Management and Policy, PA, June/July 1988.
Hamburg, R.A. (1987), "Household Biomass, Biogas and Coal Combustion in Henan Province,
People's Republic of China: A Preliminary View of the Resultant Indoor Air Pollution," prepared
by Omega-Alpha Recycling Systems, Orma, West Virginia.
Gunnerson C.G. and D.C. Stuckey (1986), Anaerobic Digestion: Principles and Practices for
Biogas Systems, World Bank, Washington, D.C.
IPCC (Intergovernmental Panel on Climate Change) (1990), Greenhouse Gas Emissions from
Agricultural Systems, U.S. Environmental Protection Agency, Washington, D.C.,
EPA/20P/2005.
-------
LIVESTOCK MANURE 7 - 29
IPCC (1990), Methane Emissions and Opportunities for Control: Workshop Results of the
Intergovernmental Panel on Climate Change, U.S. Environmental Protection Agency,
Washington, D.C., EPA/400/9-90/007.
Koelsch, R.K., E.E. Fabian, R.W. Guest, J.K. Campbell (1989), "Anaerobic Digesters for Dairy
Farms," in Agricultural and Biological Engineering, Department of Agricultural and Biological
Engineering, New York State College of Agriculture and Life Sciences, Ithaca, New York,
Extension Bulletin 458.
Loehr, R.C., Pollution Control for Agriculture, Academic Press, 1984.
Maramba, F.D., A. Judan, E. Obias, "Fuel, Feed, and Fertilizer from Farm Wastes - The
Philippine Experience," in Third International Symposium on Anaerobic Digestion. Boston,
1983.
Moser, Mark, and Kurt Roos, (draft in preparation), Opportunities for Profitably Reducing
Methane Emissions from Livestock Waste: A Texas Dairy Industry Case Study. U.S.
Environmental Protection Agency, Washington, D.C.
Pimental D. (1975), "World Food, Energy, Man and Environment," in Energy, Agriculture and
Waste Management, ed. Jewell, W.J., Ann Arbor Science Publishers, Inc., Ann Arbor,
Michigan.
Quok, L. and J.A. Chandler (1984), Potential of Biogas Systems for California Farms with
Confined Animals, presented at "Energy from Biomass and Wastes VIII," Lake Buena Vista,
Florida, January 31, 1984.
Roos, K.F. (1988), Issues in Anaerobic Digestion: Economics. Technology, and Transfer, M.S.
Thesis in Energy Management and Policy, University of Pennsylvania, Pennsylvania.
Roos, K.F. (1992), "Profitable Alternatives for Regulatory Impacts on Livestock Waste
Management," in National Livestock. Poultry, and Aguacuiture Waste Management.
proceedings of the American Society of Agricultural Engineers national workshop, 29-31 July
1991.
Safley, L.M., P.W. Westerman (1990), "Psychrophilic Anaerobic Digestion of Dairy Cattle
Manure," in Agriculture and Food Processing Waste. ASAE 1990.
Safley, L.M. & P.W. Westerman (1988), "Biogas Production from Anaerobic Lagoons," in
Biological Wastes, No.23, pp.181-193, 1988.
Treleven, Mike (1989), "Black Gold," in California Farmer, June 3, 1989.
UN (United Nations), Updated United Nations Guidebook on Biogas Development. New York,
1984.
UNEP (United Nations Environmental Program), Biogas Fertilizer System. Nairobi, 1984.
-------
7 - 30 LIVESTOCK MANURE
US DOE (U.S. Department of Energy) (1988), Handbook of Bioqas Utilization, 1988.
USEPA (United States Environmental Protection Agency) (1992), Global Methane Emissions
from Livestock and Poultry Manure. GCD/OAR, U.S. Environmental Protection Agency,
Washington, D.C., EPA/400/1-91/048.
Waybright, Richard C. (1991), On-Farm Utilization of Animal Wastes, Philadelphia Society for
Promoting Agriculture, April 4, 1991.
World Health Organization (WHO) (1980), A Challenge to Developing Countries: The
International Drinkinq-Water Supply and Sanitation Decade. 1981-1990. WHO Chronicle
no.34, pp. 327-331, 1980.
-------
CHAPTER EIGHT
WASTEWATER MANAGEMENT
8.1 Background
Methane Production and Emissions
Wastewater and its residual solids byproduct (sludge) have the potential to produce globally
significant methane emissions. Wastewater, often referred to as sewage, includes residential,
commercial and industrial liquid and water-carried wastes. Methane emissions result if the
wastewater and sludge are stored or treated under anaerobic conditions (in the absence of
oxygen), and if the gases produced are allowed to reach the atmosphere. Although data are
very limited, global emissions from this source are estimated to be 20 to 25 teragrams per
year (USEPA, 1990).
Highly organic waste streams, such as domestic wastes and effluent (discharge) from food
processing facilities, likely contribute most of the methane from this source. These waste
streams are characterized by high biochemical oxygen demand (BOD) and quickly deplete
available oxygen as their organic matter decomposes. Untreated domestic waste streams,
for example, typically range from 100 to 400 milligrams of BOD per liter. Food processing
plants, which include fruit and sugar processing plants, meat packing plants, creameries, and
breweries, can produce untreated wastewater with BOD as high as 100,000 milligrams per
liter.
Wastewater in most developed countries usually undergoes treatment to reduce or eliminate
harmful constituents in facilities run by municipalities or by industrial production plants.
Although there are some methane emissions from this source, wastewater in developed
countries is not considered a major source of emissions. This is because treatment often
takes place under aerobic conditions and, when anaerobic processes are used (e.g., in some
wastewater treatment and most sludge treatment facilities), the generated methane is
collected and utilized or burned off. Wastewater treatment systems and their methane
production potential are described in more detail in Exhibit 8-1.
The largest potential for methane emissions from wastewater exists in developing countries,
where waste streams are often unmanaged or maintained under anaerobic conditions without
control of the methane. For example, less than 40 percent of municipal wastewater in most
developing countries is collected in sewage systems, and only a fraction of this collected
waste undergoes treatment (Bartone, 1992). The untreated waste is often flushed along with
its sludge into waste lagoons, rivers or the ocean, or is buried. Releasing the waste into rivers
can cause anoxic conditions with potential for methane emissions, while also creating health
risks associated with the spread of pathogens, heavy metals, and toxic compounds.
Methane Emission Reduction Strategies
A number of strategies exist for reducing methane emissions from wastewater and sludge.
Wastewater management techniques can greatly reduce the production of methane, or
alternately, generated methane can be captured and used as a fuel or flared. Such
-------
8-2
WASTEWATER MANAGEMENT
Exhibit 8-1
Wastewater Treatment Systems and Methane Production
. . k Commercial
ReSldences | Bui|dmgs
-s ^
Primary
Treatment
Sedimentation/
separation,
partial
decomposition:
pretreatment
(by industry)
oxidation/
primary
treatment pond
Raw primary 1
sludge 1
^^_
Dewatering/
drying
^n
i i
"r"*.38 II Incineration 1 Ť .
"^^
1 |Ml)Of nmMlK praauctlon pdUM
: PoŤi>ť nign nmnan. producMn .
If 1 Minor nWMn* production phuŤ *
(Industry 1
Institutior
"
Effluent,
wastes
Secondary
Treatment
Biologica
Treatment:
trickling filter
RBC
land treatment
1 i
Raw secondary 1
^r^~^^^
jr.
, i
;herrŤcal k Compos
Vealment i Landfill
T T
ingA 1 Anae
ng j iDiga
Land application (landfilling
Agriculture
Silviculture
Construction materials
Ocean disposal
1 (around/ L
surface I
Use/disposal of
treated
water
t
Advanced
Treatment
_^ filtration
C adsorption
ion exchange
sedimentation
disinfection
land treatment
'
Raw tertiary 1
sludge 1
^^
. .
robic|| Land |
jJonJ^TreamjenJ
, soil reclamation) L
Waste
Genei
1
Waste
Treat
Slu
Rcm
i
Slu
Treat
i
SIlH
Use/DI
nwater
ration
water
ment
ige
oval
dge
ment
dge
Bposal
-------
WASTEWATER MANAGEMENT 8 - 3
Exhibit 8-1 (cont.)
Wastewater Treatment Systems and Methane Production
The extent to which wastewater is treated depends on its degree of contamination and
the requirements placed on its intended destination (e.g. discharge to surface or ground-
water, use in industrial processes, irrigation), and on available infrastructure, technology
and funding.
In most developed countries and other regions where the technology is available,
industrial waste streams which are to be discharged into municipal treatment systems
often undergo bacterial pretreatment or chemical disinfection to reduce contaminants
to acceptable levels. After pretreatment, if it is necessary, the possible levels of
wastewater treatment consist of: primary treatment, which refers to the removal of
suspended solids by sedimentation or flotation; secondary treatment, usually involving
aerobic biological stabilization; and advanced mechanical or chemical treatment. Natural
systems such as land treatment are also used in providing secondary and advanced
treatment.
Each stage of wastewater treatment results in the production of sludge, a byproduct
which generally contains high concentrations of organic matter and thus has potential
to produce significant methane emissions. After sludge is thickened by gravity or
mechanical means to concentrations of 5-10 percent solids, one or a combination of the
following types of treatment is used to prevent its putrescence and/or reduce its
volume; land treatment; aerobic or anaerobic digestion; chemical treatment; and
incineration. Stabilized sludge can be safely reused or disposed of by composting,
incineration or landfilling. The ash, compost, and slag endproducts are suitable for use
as organic fertilizers and soil amendments in agriculture, forestry and land reclamation,
and sometimes in the production of construction materials.
Sources: Escritt, 1984; Hammer, 1986; and Loehr, 1984
technologies and practices are common in many developed countries, and can be adapted for
use in other regions where wastewater and sludge may currently produce significant methane
emissions. Application of these strategies would also greatly improve human health
conditions and other environmental problems. These practices include:
Prevention of methane production during wastewater treatment:
Aerobic Primary Wastewater Treatment;
Aerobic Secondary Wastewater Treatment;
Land Treatment;
-------
8 - 4 WASTEWATER MANAGEMENT
Recovery and utilization/flaring of methane from anaerobic digestion of wastewater or
sludge:
Utilization;
Flaring;
Minimization of methane emissions during sludge treatment and disposal:
Aerobic Digestion;
Land Application;
Chemical Stabilization;
Incineration;
Landfilling with Methane Recovery;
Aerobic Composting; and
Experimental Uses for Sludge.
Assessments include descriptions of the following:
Reduction/Utilization Technologies;
Costs;
Availability;
Applicability;
Barriers; and
Benefits.
In general, the implementation of these strategies will be as a result of a country's goals to
reduce the quantities of unmanaged wastes and to reduce related risks to human health and
the local environment. In many cases, these strategies represent large capital investments
which are justifiable only to the extent that these local benefits are achieved. Therefore, the
available strategies are generally described here as options which will increasingly be used in
developing regions of the world, and not as options that can be promoted based on their sole
ability to limit methane emissions. The strategies are described in the technical assessments
which follow, and are summarized in Exhibit 3-2.
-------
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-------
8 - 6 WASTEWATER MANAGEMENT
8.2 Prevention of Methane Production During Wastewater Treatment
One method of reducing wastewater-related methane emissions is to prevent methane
production by maintaining the wastes under aerobic conditions (generally 0.2 to 0.6 mg or
greater levels of oxygen per liter of wastewater) (Loehr, 1984). The maintenance of aerobic
conditions ensures the complete metabolization of the organic matter in the wastewater either
by aerobic bacteria or by facultative organisms which can be aerobic or anaerobic depending
on the level of available oxygen. Managing wastewater aerobically also prevents the release
of odorous gases (e.g. hydrogen sulfide, mercaptans, disulfides), which accompanies
anaerobic decomposition. Aerobic conditions can be maintained through a variety of
wastewater management techniques during both primary and secondary treatment.
Aerobic Primary Wastewater Treatment: This strategy involves maintaining sufficient
oxygen levels during the primary phase of wastewater treatment. The level of oxygen can
be sustained by using proper organic loading techniques (controlling waste levels and
organic concentrations) or by providing oxygen to the wastes through mechanical aeration.
Aerobic Secondary Wastewater Treatment: A variety of aerobic secondary wastewater
treatment strategies exist which can be used after primary treatment, including activated
sludge processes, trickling filters, and rotating biological contactors (RBCs). In each case,
stabilization is accomplished through the prolonged exposure of wastewater to aero Die
microorganisms which are either floating (due to mechanical aeration) or attached to fixed
or rotating media.
Land Treatment: Applying raw or partially stabilized wastewater to soil is another method
of breaking down the organic constituents in the wastewater while preventing methane
production. During land application, wastewater is either added to the soil surface or
mixed with the upper layer of soil, which acts as a natural filter for the wastes. This
treatment method is not appropriate for wastes containing heavy metals, which pose
health risks.
8.2.1 AEROBIC PRIMARY TREATMENT
Primary treatment refers to the sedimentation and separation of large particles from
wastewater, along with partial decomposition of the organic matter. These processes can
occur naturally or as a result of human effort wherever raw wastewater is collected.
Wastewater ponds can be aerobic, anaerobic, or facultative (anaerobic only in the lower
layers), depending on their depths, loading rates, and levels of sludge build-up. A variety of
health and environmental objectives can be met by maintaining sufficient oxygen to minimize
methane production.
Primary wastewater treatment can occur aerobically in aerobic oxidation ponds and primary
treatment ponds (i.e., first pond in a multiple pond system) if sufficient oxygen levels eire
sustained in the waste stream. The term "oxidation ponds" generally describes those ponds
in which raw wastewater undergoes primary treatment without the aid of mechanical aeration,
and often receives no further treatment; this is frequently the case in countries where
wastewater is not intensively managed. Primary treatment ponds are used in the first of
-------
WASTEWATER MANAGEMENT 8 - 7
several treatment phases which wastewater receives in municipal or industrial treatment
plants. These ponds in many areas become anaerobic due to overloading, and little effort is
made to control the methane which is produced (Maber, pers. comm.). This section describes
management methods that can help to maintain aerobic or facultative conditions in ponds
which may otherwise be at least partly anaerobic.
Reduction Technology Description
Primary wastewater treatment ponds can be maintained under aerobic conditions if loaded
with the proper types and volumes of wastes, or if oxygen is provided to the wastes through
aeration practices.
Proper loading: this strategy is possible in all primary treatment ponds and is especially
suitable for oxidation ponds. Proper loading involves limiting the depths and the BOD
loading rates of the ponds and allowing adequate detention times for the wastes.
Constructing additional ponds and promptly removing sludge may also be necessary for
maintaining proper waste loads. These techniques can be used for both aerobic and
facultative ponds.
Aerobic ponds, also called high-rate aerobic ponds, maintain dissolved oxygen throughout
their entire depth. They are usually 30 to 45 cm deep, allowing light to penetrate the full
depth. Oxygen is provided by surface aeration and photosynthesis (mixing helps to
expose all algae to sunlight), and aerobic bacteria stabilize the waste. High-rate aerobic
ponds are most successful when allowed a 3 to 5 day waste detention time, and may
require paving the bottom to prevent weed growth. They can achieve a high degree of
BOD removal in areas where land is limited, but are only feasible in warm, sunny climates.
Facultative ponds operate anaerobically in the lower depths and aerobically in the upper
layers, with oxygen provided by photosynthetic algae and surface reaeration. These types
of ponds are more common and easier to operate and maintain than aerobic ponds, and
are often used to treat raw municipal wastewater, and primary and secondary effluent.
Facultative ponds can operate with negligible methane emissions if their depths do not
exceed 2 meters and if the bottom layers are maintained at relatively cool temperatures.
Under these conditions, the amount of methane generated should be small enough to be
naturally absorbed or oxidized as it moves toward the surface through aerobic levels.
Facultative ponds can require large areas of land and detention times of up to 30 days to
stabilize wastes (Loehr, 1984; USEPA, 1983).
Aeration: This strategy involves aerating primary wastewater treatment ponds to ensure
continuous oxygen transfer and encourage the growth and activity of the aerobic
microorganisms that decompose waste. This can be accomplished by pushing air into the
wastewater with rapidly-moving mechanical impellers or injecting air or pure oxygen below
the surface and using mixers to entrain the air in the wastewater. Aerated ponds are
significantly more efficient than non-aerated oxidation ponds, requiring an average of only
1 to 10 days retention time (Loehr, 1984).
-------
8 - 8 WASTEWATER MANAGEMENT
Costs
In areas where wastewater is currently unmanaged, there will be start-up costs for the
construction and maintenance of diversion, collection and treatment facilities; the magnitude
of these costs will depend on the level of technology required for each treatment option.
Proper loading: Oxidation ponds are the least costly wastewater treatment option, because
operating costs are extremely low.
Aeration: The equipment needed for this strategy and the energy required to operate the
aerators can be costly. Depending on the volume of wastewater flow into the pond, well-
constructed aerated oxidation ponds are estimated to cost from $150,000 to $3 million
for construction, assuming a range of 0.05 to 10 million gallons of wastewater flow per
day (Mgal/d). Annual operation and maintenance costs are estimated to range from
$20,000 to $500,000, based on the same volume assumptions (USEPA, 1950).
However, these costs may be offset to some extent by the improved performance and
capacity of aerated primary ponds; one aerated pond may stabilize as much wastewater
as several non-aerated oxidation ponds.
Availability
Primary treatment ponds and aeration technologies are available in most countries. Building
facilities in areas without existing wastewater management infrastructures, and properly
maintaining them in all countries, may necessitate some management training.
Applicability
The applicability of each aerobic primary treatment method depends on the amount of waste
to be treated and its concentration of organic matter. Wastes with fairly low organic content
or waste streams that have been diluted with storm water are suitable for treatment in aerobic
or facultative ponds; large volumes of waste and highly organic wastes, such as effluent from
food processing plants or strong domestic sewage, generally require aeration to ensure a
sufficient oxygen supply.
Several other factors limit the applicability of this technique. Aerobic ponds are not suitable
where cold climates discourage bacterial activity. Both aerobic and facultative ponds, which
can produce odors, may not be acceptable in densely-populated areas. Finally, wastewater
which receives primary treatment in aerobic and facultative ponds is only partially stabilized
and not suitable for all uses. For example, effluent from aerobic ponds may contain high
coliform levels, effluent from facultative ponds can contain significant amounts of algae, and
both types of ponds can produce effluent with high levels of suspended solids (USEPA, 1983).
Barriers
The additional labor required for the proper construction and maintenance of primary treatment
ponds may create a barrier in areas where wastes are currently unmanaged.
-------
WASTEWATER MANAGEMENT 8 - 9
Proper loading: Due to the amount of wastes which pass through primary ponds in
treatment plants, relying on proper loading techniques to maintain aerobic conditions in
these ponds may not be feasible. This is especially true because the constant sludge
removal which is necessary for maintaining aerobic conditions interferes with the
thickening of the sludge required for further processing. In such cases, aeration may be
more suitable.
Aeration: The initial equipment costs and the operating costs can pose barriers to the use
of aeration in wastewater management.
Benefits
In addition to preventing the production and emission of methane from wastewater, the
containment and control of wastewater by the means described above can result in several
other benefits:
The containment and control of wastewater by these means reduces health risks such
as the spread of diseases often carried in wastewater. Common waterborne diseases
include viruses (hepatitis), protozoa (giardiasis), and bacteria (cholera).
These methods can also prevent concentrations of phosphorous and/or nitrogen from
increasing in lakes and rivers. These nutrients can be carried by waste streams into
receiving waters in large amounts, and can cause eutrophication, or deterioration in
water quality.
The maintenance of aerobic conditions in primary ponds can reduce or eliminate the
odors which result from anaerobic processes. In the case of aerated ponds, odors can
be reduced to an even greater extent by covering the ponds and funneling any
generated gases back into their aeration systems (Lagnese, 1992).
Aerating primary ponds enhances their efficiency: the BOD in aerated ponds is reduced
by 50 to 90 percent compared to about 35 percent in non-aerated ponds (Loehr,
1984). Because the efficiency of the pond is improved, larger volumes of wastewater
can be stabilized each day.
Aerobic Primary Treatment
technologies widely available
low-cost strategies
reduced health risks and odors
methane reductions of up to 100% if
aerobic conditions are maintained
-------
8- 10
WASTEWATER MANAGEMENT
8.2.2 AEROBIC SECONDARY WASTEWATER TREATMENT
Wastewater treatment in some regions consists only of primary treatment, after which most
waste streams still contain high concentrations of organic matter and nutrients. Improper
management of these partially stabilized waste streams can create large methane emissions
as well as other environmental problems and health hazards. Further stabilization is possible,
however, through secondary wastewater treatment, which usually consists of a closely
managed aerobic biological procedure resulting in the removal of up to 95 percent of the
organic matter in the waste (Loehr, 1984).
Reduction Technology Description
Three common methods of aerobic secondary wastewater treatment are activated sludge
wastewater treatment, trickling filters, and rotating biological contactors (Exhibits 8-3 through
8-5). These strategies are discussed below.
Activated sludge wastewater treatment: This is a suspended growth process, utilizing
aerators (bubble diffusers or impellers) to suspend aerobic microorganisms in liquid wastes
and supply them with oxygen until the organic matter is metabolized and stabilized. The
sludge is then separated in sedimentation tanks, and part of the sludge that is still
biologically active is returned to the aeration tank to treat incoming water. The remainder
of the sludge is washed for sludge treatment and disposal. This stabilization process
requires relatively little space, and the waste detention times range from several hours to
several days.
Exhibit 8-3
Conventional Activated Sludge Wastewater Treatment Process
Scum scraper
Influent
Effluent
Clarifier
Recycle sludge
-------
WASTEWATER MANAGEMENT
8- 11
Trickling filters: This method is similar to the activated sludge technique, except that the
microorganisms working to stabilize the organic material are attached to a fixed bed.
Rotary nozzles apply the wastewater to the surface of the beds, and the organic matter
in the liquid is stabilized as it trickles down over beds filled with stone or plastic media.
Microorganisms attached to the media stabilize the wastewater. Trickling filters are
generally preceded by primary treatment to reduce suspended solids, as high
concentrations of solids can result in clogging or reduced equipment efficiency. Most
trickling filters can be operated by hydraulic head and require no electrical energy.
Exhibit 8-4
Trickling Filters Wastewater Treatment Process
Incoming
Effluent
Distributor
Sprinklers
Slope 1°/a
Effluent
collecting
trough
Effluent discharge
1 1/2" to 2 1/2" Stones
Rotating Biological Contactors (RBCs): This process operates under the same principle as
the other secondary treatment processes. Large diameter plastic disks are rotated slowly
(2 to 5 rotations per minute) in a wastewater tank; as the wastewater trickles over the
surface, the attached microorganisms metabolize the organic matter in the liquid. RBCs
have relatively low power costs because the energy required to rotate the disks is
minimized by the buoyancy of the disks.
-------
8- 12
WASTEWATER MANAGEMENT
Exhibit 8-5
Rotating Biological Contactors Wastewater Treatment Process
Rotation
Radial passages
Air cups
Costs
The costs of these types of secondary wastewater treatment can be moderately high because
of the equipment and energy requirements, and depend to a great extent on the daily volume
of wastewater flowing into the facility. Activated sludge wastewater treatment systems are
estimated to cost from $70,000 to $10 million for construction, assuming a flow of 0.1 to
80 Mgal/d. Annual operation and maintenance costs are estimated to range from $4,000 to
$600,000, assuming 0.1 to 100 Mgal/d (USEPA, 1980).
High rate trickling filters are estimated to cost from $250,000 to $ 10 million for construction,
and from $3000 to $45,000 per year for operation and maintenance, assuming flows of 1 to
100 Mgal/d. Costs for trickling filters with plastic media are estimated to be in the same
range, but with assumed flows of 0.1 to 100 Mgal/day (USEPA, 1980). These costs may be
lower when trickling filters are operated by hydraulic head, as these systems have no energy
demand.
RBCs are estimated to cost from $100,000 to $5.5 million for construction, assuming a flow
of 0.15 to 100 Mgal/d. Annual operation and maintenance costs are estimated to range from
$9,000 to $100,000, assuming 0.1 to 100 Mgal/d (USEPA, 1980).
-------
WASTEWATER MANAGEMENT 8-13
Availability
Aerobic secondary wastewater treatment technologies are common in Europe, the U.S., and
Japan, but may not be widely available in other regions. Technology transfer and funding
programs may be necessary to stimulate the adoption of these techniques worldwide.
Applicability
Secondary wastewater treatment is applicable for most wastes, and is considered in many
countries to be the minimum treatment level necessary for any waste stream destined for
release into receiving waters or for eventual human use (e.g. irrigation, groundwater). Each
of the strategies described above applies to different types of waste loads: the activated
sludge process is suitable for large amounts of highly organic wastes; trickling filters are
better suited for smaller volumes of waste or wastes with moderate organic concentrations;
and the RBC can be used to treat almost any waste stream.
Barriers
The high energy requirements of many types of suspended growth secondary wastewater
treatment, especially the activated sludge process, may pose a significant barrier to the spread
of this treatment method.
Benefits
In addition to preventing methane production, aerobic secondary wastewater treatment has
several other possible benefits:
These secondary treatment processes remove 75 to 95 percent of the organic matter
which remains in wastewater after primary treatment (Loehr, 1984).
The stabilization of wastewater through aerobic secondary treatment reduces the
health risks associated with the improper management and disposal of insufficiently-
treated wastewater.
Aerobic Secondary Treatment
moderate capital investment
technology available in many regions
health benefits
prevention of odors
ť methane emissions can be eliminated if
aerobic conditions are maintained
-------
8-14 WASTEWATER MANAGEMENT
8.2.3 LAND TREATMENT
An alternative method of stabilizing wastevvater while preventing methane production is
applying the wastewater to soil, which acts as a "living filter" for the wastes (Loehr, 1984).
Reduction Technology Description
Wastewater can be land treated by applying it to the soil surface or mixing it with the upper
layer of soil, which results in the biological degradation of the organic constituents ol the
waste and the eventual immobilization of the inorganics. Properly-managed land treatment
operations produce no methane, as aerobic conditions are necessary for optimal performance.
Aerobic conditions can be maintained by allowing sufficient time between wastewater
applications and through proper loading of organic matter.
Depending on the concentration of pollutants in the water and the stabilizing ability of the soil,
wastewater may require preliminary treatment before land application. The rate of
wastewater application will also be determined by the characteristics of the wastes and the
land application site. A slow rate of wastewater application to vegetated soil surfaces such
as cropland or forests results in the most successful removal of pollutants. Other land
treatment strategies involve applying wastewater to highly permeable soils, whereby the
wastewater is filtered and recharges groundwater (rapid infiltration systems), or to relatively
impermeable soils (overland flow systems). This last technique involves applying wastewater
to gently sloped, vegetated sites where it is stabilized as it filters through the surface soil and
plant litter, and is retrieved in collection ditches for surface recharge (Loehr, 1984).
Costs
Land treatment is generally a low-cost option, compared to other treatment options, as it
requires limited equipment and energy use. Final costs can be highly variable, however,
depending on the volume of wastewater flow and on external factors such as the
transportation distance to the treatment site and the cost of purchasing or renting the land
used for treatment.
Slow rate land treatment is estimated to have from $100,000 to $30 million capital costs,
assuming a flow of 0.1 to 100 Mgal/d. Annual operation and maintenance costs are
estimated to range from $4,000 to $1 million, assuming 0.1 to 80 Mgal/d (USEPA, 1980).
Rapid infiltration systems are estimated to have from $30,000 to $3 million capital costs and
$3000 to $200,000 annual operation and maintenance costs, assuming a wastewater flow
of about 0.1 to 25 Mgal/d (USEPA, 1980).
Overland flow systems are estimated to have from $80,000 to $10 million capital costs and
$5000 to $200,000 annual operation and maintenance costs, assuming a wastewater flow
of about 0.1 to 30 Mgal/d (USEPA, 1980).
-------
WASTEWATER MANAGEMENT 8-15
Availability
The application of waste water to land is used as a treatment practice in many countries, and
is widely available as it requires a minimum of technology. The spread of information may
need to be facilitated, however, to ensure that proper techniques are used to prevent the
production of methane and to avoid contaminating vegetation or groundwater.
Applicability
Land treatment is a suitable method for stabilizing both untreated and partially treated
wastewater with any amount of organic content, and is most often used to treat wastes from
food processing plants. Because of its low cost, there is growing interest in using this method
to stabilize municipal wastewater (Loehr, 1984).
Barriers
Possible barriers to the land treatment of wastewater include land cost and availability,
ownership, and the difficulties of transporting wastewater over long distances. In addition,
misapplication of raw or partially treated wastewater to crops and other areas could result in
health hazards and risks to nearby habitats.
Benefits
Some benefits of land treatment, in addition to the prevention of methane emissions, are listed
below.
Land treatment prevents odors.
Land treated water can serve several useful purposes during and after its treatment
(e.g. recharging ground water, irrigation).
Land Treatment
* no advanced technology required
* generally low-cost strategy
reduced odors
* suitable for a wide range of waste
streams
useful purposes for land-treated water
* methane emissions can be eliminated if
aerobic conditions are maintained
-------
8-16 WASTEWATER MANAGEMENT
8.3 Recovery and Utilization/Flaring of Methane from Anaerobic
Digestion of Wastewater and Sludge
An alternative to preventing methane production in wastewater and sludge is to encourage
anaerobic conditions in the wastes through anaerobic treatment (digestion). The resulting
emissions of methane and other gases can be recovered and utilized as an energy source or
flared (burned) off.
Utilization: Methane generated during anaerobic digestion can be captured and used as
a source of fuel to heat the treatment facilities or sludge digestion tank, produce power
for other parts of the plant, or for sale to nearby homes, industrial plants or utilities.
Flaring: Flaring involves the recovery and diversion of the generated methane to a burner,
where its combustion prevents its release to the atmosphere. Flaring can be used to
dispose of all of the methane or excess methane which cannot be utilized.
8.3.1 ANAEROBIC DIGESTION WITH METHANE UTILIZATION
Anaerobic digestion involves placing wastes in an enclosed tank (digester) at temperatures of
around 35°C (95°F) for an average of 10 to 60 days. During this time, organic matter is
degraded in the absence of oxygen by microorganisms such as fermentative bacteria and
methanogenic bacteria, and converted to biogas (about 60 to 70 percent methane and 30 to
40 percent carbon dioxide, with traces of hydrogen sulfide, hydrogen and carbon monoxide).
The necessary microorganisms grow naturally, but can be encouraged by recycling portions
of the bacteria-laden sludge back into the digester vessel. For especially highly-concentrated
organic wastes, additional bacteria may be needed and can be purchased or grown on-site in
side-stream bioreactors (Strauss, 1992).
Several processes exist for digesting wastewater from municipal systems or industrial plants
before the sludge is removed. One such method is the Upflow Anaerobic Sludge Blanket
(UASB): wastes enter through the bottom of the digester, travel through an anaerobic layer
of sludge, and exit from the top (Loehr, 1984; De Santo, pers. comm.). Another example is
the one-step wastewater treatment process used in Brazil (Bartone, pers. comim.). More
commonly, however, anaerobic digestion is used to treat only the sludge which is removed
from liquid wastes during primary, secondary, and/or advanced wastewater treatment (see
Exhibit 8-1). This is the most common method of stabilizing sludge in many countries (e.g.,
60 percent of the sludge produced in the U.S. and Europe; almost half of the sludge in Japan)
(Murakami, 1988).
Utilization Technology Description
The "biogas" generated during the digestion of either wastewater or sludge is composed
mostly of methane, and can be captured and utilized as a fuel source. Methane generated
from municipal and industrial treatment plants can be used to heat the buildings at the
wastewater treatment plant or the sludge digestion tank. In some cases, the methane is used
to produce power for use in other parts of the plant, and the cooling water from the engine-
-------
WASTEWATER MANAGEMENT 8-17
driven generators is used to heat the digestion tank. Methane or the energy which it creates
can also be sold to nearby industrial plants, utilities, or homes.
Costs
Anaerobic digestion systems are estimated to cost from $100,000 to $3 million for
construction, and about $10,000 to $100,000 per year for operation and maintenance,
assuming a wastewater flow of about 0.1 to 100 Mgal/d (USEPA, 1980).
Although the costs of digestion and methane utilization facilities are high, the energy value
of methane often makes its recovery and use cost-effective. This is especially true at sites
with high strength organic waste streams and where primary (undigested) sludge is used. In
food processing plants, for example, it is estimated that replacing oil with the generated gas
as fuel for the plant could show a capital return in about five years (IPCC, 1991). Treatment
plants in Japan have found electricity generation from sludge-generated methane to be cost-
effective at large plants. With the addition of heat recovery technologies, these plants have
recorded over 80 percent thermal efficiencies for gas engine systems, and have achieved
energy production levels of 2 kilowatt hours (kWh) for every cubic meter of digester gas
(Sato, 1984).
Availability
Anaerobic digestion technologies are widely available and used in most of Europe and in the
U.S. and Japan, and less commonly in some developing countries. These techniques are
feasible in most areas where an adequate amount of raw sludge is consistently available.
Other factors, however, may affect the suitability of this option for certain areas; these
factors are discussed in the following sections.
Applicability
Anaerobic treatment systems with methane recovery and utilization are suitable in large
operations that have both high strength organic wastes and large energy demands, such as
food processing plants. Although methane production rates from waste streams vary
significantly, estimates indicate that waste from food processing plants can produce up to 0.9
cubic meters of methane per kilogram of volatile solids destroyed (Loehr, 1984). Methane
utilization may not be as cost-effective at small municipal treatment plants due to the small
amounts of sludge generated.
Levels of methane production from digestion are not always suitable for the energy needs of
each plant, which may differ based on climate and fluctuations in waste loads. When the
methane produced is not sufficient to supply fuel for all of the plant's needs, auxiliary power
sources such as natural gas and fuel oil are often needed as supplements.
Methane utilization technologies can also be applied to small operations and domestic waste
streams. In parts of India, methane generated from simple digestion tanks attached to
communal latrines provides heat and light for local communities (Escritt, 1984).
-------
8-18 WASTEWATER MANAGEMENT
Barriers
The advanced technologies and high capital costs of these technologies can pose barriers to
their spread and use. Anaerobic digesters and methane utilization facilities also require
continuous and careful operation.
Another potential barrier is the impurity of the generated methane: digester methane contains
corrosive elements such as hydrogen sulfide (H2S) and mercaptans. Plants which utilize the
methane can either use it directly in engines designed to burn low quality gas as a fuel, or can
install equipment to scrub the H2S to acceptable levels for use as a higher grade gas fuel
source. The costs of the specialized machinery or scrubbing equipment, or the maintenance
costs for machinery using unscrubbed gas, can lower the possible profit margin from methane
utilization. The generated methane also has a low energy value compared with conventional
fuels (600 BTU per cubic foot compared to 900 BTU per cubic foot for natural gas). These
two factors, coupled with low conventional fuel prices (such as the currently low natural gas
prices in the U.S.), may make flaring a more cost-effective option.
Benefits
Anaerobic digestion of sludge has many benefits:
This stabilization process requires less space than aerobic processes and can reduce
sludge volume more quickly, depending on the type of sludge.
Anaerobic digestion removes up to 95 percent of the organics in the sludge and
effectively inactivates pathogens (Loehr, 1984).
This treatment method produces valuable methane.
The utilization of methane from anaerobic digestion not only prevents the release of methane
to the atmosphere, but can also provide enough energy to make the digestion process cost-
efficient or profitable.
Anaerobic Digestion with Methane
Utilization
* technologies available
* methane emission prevented
Ť valuable fuel source produced
Ť cost-effective when methane utilized
-------
WASTEWATER MANAGEMENT 8-19
8.3.2 FLARING
Reduction Technology Description
Where utilization technologies are not available or are not economically feasible, flaring is an
effective method of disposing of methane generated from wastes. Flaring involves the
recovery of methane from the digester tank and its diversion to a flame, where it is burned.
Efficient flaring operations, such as most operations in the United States, can reach
efficiencies of 98 to 100 percent (Farrell, 1992), thus preventing the release of methane to
the atmosphere.
Costs
Anaerobic digestion systems are estimated to cost from $100,000 to $3 million for
construction, and about $10,000 to $100,000 per year for operation and maintenance,
assuming a wastewater flow of about 0.1 to 100 Mgal/d (USEPA, 1980).
The costs of flaring equipment and operation are low, relative to methane utilization
equipment costs. Flaring methane, however, prevents its utilization and thus cannot offset
the costs of the digester construction and operation.
Availability
Flaring technologies are widely available. Flaring methane should be feasible in any region
where anaerobic sludge digestion is practiced, due to its minimal technological requirements
and low operational costs.
Applicability
Flaring is the primary means of methane control in plants that do not recover and utilize
generated gas, and is a common method of eliminating excess gas in plants which do use
recovery techniques.
Flaring is also a suitable way to eliminate methane emissions from anaerobic water treatment
ponds, which are used increasingly in Brazil and other regions for treating wastewater and
sludge in a one-step process; rates of methane release from such systems may be too low to
merit utilization.
Barriers
Because methane which is flared cannot be utilized for other purposes (e.g., heating digesters
in the treatment plant), the cost of powering the treatment plant may prove prohibitive in
flaring operations.
-------
8 - 20 WASTEWATER MANAGEMENT
Benefits
Anaerobic digestion has many advantages (see Utilization section). Flaring the generated
methane also provides the following benefits:
Flaring prevents methane emissions.
Flaring helps to eliminate odors which result from anaerobic processes, and avoids the
hazards associated with free-floating combustible gases.
Anaerobic Digestion with Raring
* technology available
* reduce risks of free-floating gases
ť reduce odors
* prevent methane emissions
Ť suitablewhengas-scrubbing equipment
not available
8.4 Minimization of Methane Emissions During Treatment. Utilization.
and Disposal of Sludge
Just as methane emissions can be avoided during wastewater treatment, methane production
can be minimized during sludge stabilization. Stabilization processes are important for
reducing potential environmental and health problems which may be caused by high
concentrations of organic matter and pathogens in raw sludge. Various means also exist to
safely utilize or dispose of stabilized sludge. These stabilization and disposal options include
aerobic digestion, land application, chemical stabilization, incineration, landfilling, aerobic
composting, and some experimental uses for sludge.
Aerobic Digestion
Aerobic digestion of sludge is similar to anaerobic digestion, but no methane is generated
because the process takes place in the presence of oxygen. Pretreated or raw sludge is
placed in a tank, and mechanical aerators or diffusers provide oxygen to the waste in order
to stimulate aerobic bacteria to break down the volatile organic matter in the sludge. Because
these results can also be achieved under facultative conditions, it is sometimes possible to
aerate only the top several feet of a tank, leaving gases from the bottom portions of the tank
to be absorbed or metabolized as they rise.
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WASTEWATER MANAGEMENT 8-21
The technology for this type of sludge digestion is relatively simple and requires only enough
energy to operate the aerators, as the aerobic microorganisms in the tanks create their own
heat. These systems are estimated to cost from $30,000 to $3 million for construction, and
about $2,000 to $500,000 per year for operation and maintenance, assuming a wastewater
flow of about 0.1 to 100 Mgal/d (USEPA, 1980). Because it is relatively inexpensive and
produces few odors, aerobic digestion is suitable for small operations and densely populated
areas.
Land Application
Land application of sludge is similar to land treatment of wastewater, and does not result in
methane production if sufficient time is allowed between sludge applications. After sludge
has been properly stabilized, it can be applied to the soil surface or mixed with the upper layer
of soil in liquid, dewatered, or dried form. Liquid sludge can also be injected below the soil
surface. The rate of application will depend on the quality of the sludge and crop nutrient
requirements.
The application of sludge to agricultural areas and forests both stabilizes the sludge solids and
utilizes the available moisture, organic matter, and nutrients. Land application of sludge also
helps improve soil structure, water holding capacity, and organic matter content. Care must
be taken, however, to avoid potential health problems that could result from the application
of unstabilized sludge to crop production or animal grazing areas.
Land application costs are generally low, but can vary greatly depending on the volume of the
wastewater flow and on the distances necessary to transport the sludge to application sites.
These systems are estimated to cost from $10,000 to $700,000 for land preparation, and
about $1000 to $100,000 per year for materials and labor, assuming a wastewater flow of
about 0.1 to 100 Mgal/d (USEPA, 1980).
Chemical Stabilization
The use of chemicals can be a relatively inexpensive and simple method of stabilizing sludge.
Because the chemicals that are added prevent fermentation, no methane is produced during
this process. Adding chemicals can be used as the sole method of stabilizing sludge or in
combination with other methods. The most common chemicals used for stabilization are lime
and other alkaline chemicals, such as cement kiln dust and fly ash, which raise the pH of
sludge. Other chemicals that have been used to effectively stabilize sludge include chlorine
and ozone.
Chemically treated sludge can be safely land applied or landfilled, and in some cases it can be
incinerated. Sludge treated with lime or other alkaline materials can be used directly to
condition and correct the acidity of soil, or as a daily or final landfill cover material. Various
other uses have been found for chemically treated sludge after subsequent incineration (see
Incineration section).
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8 - 22 WASTEWATER MANAGEMENT
Incineration
Incineration involves burning dewatered or dried sludge solids at high temperatures in
specially-designed furnaces. This method of disposing of raw or digested sludge is commonly
used in many developed countries (about 15 to 20 percent of the sludge in the U.S. and 55
percent of the sludge in Japan is incinerated) (Farrell, pers. comm.; Murakami, 1988).
Incineration can reduce the sludge solids to 10 to 20 percent of their original volume and
virtually eliminate volatile materials, although products of incomplete combustion can create
emissions problems.
The economic feasibility of incineration depends on the moisture and volatile solids content
of the waste, emission control requirements, and conventional fuel prices. Incineration can
often be cost effective when dewatered, primary (undigested) sludge is burned, since this type
of sludge often contains sufficient energy value to meet the needs of the incineration facilities.
Burning mixtures of primary and secondary sludge can also be cost-effective. Incineration of
secondary sludges, sludges with high moisture levels, or highly-contaminated sludge,
however, may require auxiliary fuels to burn off excess moisture or toxic organic compounds
to levels that meet air emissions requirements. Depending on these variables and the type of
system used, incineration is estimated to cost: from $200,000 to $500,000 for construction
with a wastewater flow of less than 0.7 Mgal/d, and to cost up to $2.5 to 5.5 million for
wastewater flows of up to 100 Mgal/day. Anuual operating and maintenance costs are
estimated to range from $10,000 to $1 million, assuming a wastewater flow of about 0.1 to
50 Mgal/d (USEPA, 1980).
The main limitation to this technology may be concern over air emissions, which may make
it difficult to site incinerators near the urban centers where much sludge is generated.
Incinerating sludge can also create ash disposal problems, as the ash which remains after
combustion often contains concentrated levels of heavy metals and thus has limited use
options. In some cases, incinerated ash may be considered a hazardous waste, potentially
causing problems if disposed of in a poorly designed landfill. Some use and disposal
possibilities being tested include using these materials as ingredients for bricks and pavement
subbases, and as fluxing agents in smelters. Incinerated ash from limed sludge is less
hazardous, and in Japan it is substituted for lime in some soil conditioning processes and used
as a cover at sanitary landfill sites and as top soil (Murakami, 1988).
An extreme form of incineration, sometimes called "melting," involves heating sludge to
temperatures of around 1300 to 1500 °C. At these temperatures, the inorganic materials
(silica, iron, aluminum, calcium, magnesium, potassium and sodium) are transformed into a
relatively safe substance termed slag. Cooled slag has been approved in Japan for use as a
subbase for bicycle roads and footpaths, and as a concrete aggregate. It may also be possible
to mold slag into usable plates or blocks for construction (Murakami, 1988).
Landfillinq with Methane Recovery
About 25 to 30 percent of the sludge produced during wastewater treatment in the U.S. and
Europe is co-disposed with municipal solid waste in landfills, where it appears that the sludge
may stimulate methane production (Farrell, pers. comm.). While this disposal method has
potential to cause greater methane emissions at open landfills, the landfilling of sludge is an
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WASTEWATER MANAGEMENT 8-23
excellent option at sites where methane is recovered and utilized (see Landfill chapter).
Sludge landfills in operation have incurred costs of about $220 per dry metric ton of sludge,
including the costs for dewatering and hauling the sludge, landfill capital, and operation and
maintenance (USEPA, 1989).
A related method of sludge disposal is sometimes called anaerobic composting. This strategy
involves placing primary sludge in sludge-only landfills, where it is stabilized by anaerobic
bacteria over a period of about ten years. In some cases, plans have been made to recover
this material for land application (Howe and Coker, 1992). Methane emissions from this type
of sludge management can be eliminated if the gas produced in the landfill is recovered and
utilized.
Aerobic Composting
Aerobic composting is a relatively quick method of transforming sludge into a useful resource.
This process involves placing raw or digested sludge into aerated pikes, vessels, or open
windrows (stacks of raw composting material), and allowing the organic material to
decompose aerobically. The presence of oxygen is ensured by mechanical aeration, or turning
in the case of windrows. The complete composting process generally lasts 20 to 60 days
(Biocycle, 1991).
While sludge can be composted alone, there is growing interest in co-composting sludge with
bulking agents such as sawdust, wood chips, yard litter and agricultural wastes. Although
yard and agricultural wastes can be difficult to manage, they are valued for their ability to
enhance the composting process and add organic nitrogen and nutrients to the final product.
Because aerobic composting naturally takes place at relatively high temperatures, pathogens
are destroyed as a result of the process. The final product therefore has many possible
beneficial uses. These include: soil enrichment of gardens, plant nurseries, and croplands;
production of potting mixes and topsoil; turf production and maintenance; and reclamation of
disturbed lands. The market for composted sludge in the U.S. is promising (Biocycle, 1991).
Aerobic sludge composting in windrows is estimated to cost from $30,000 to $2 million for
construction, and about $10,000 to $400,000 per year for operation and maintenance,
assuming a wastewater flow of about 0.1 to 100 Mgal/d. Static pile composting may cost
about $300,000 for construction and $30 to 40 per dry ton (USEPA, 1980).
Experimental Uses for Sludge
Other options for stabilizing sludge for use as a fuel are in the experimental stage. These
include the conversion of sludge into oil by pyrolysis (heating to bring about chemical change)
or direct thermal liquefaction, and secondary dewatering and direct use of sludge as a fuel
(Murakami, 1988). These appear to be promising, although expensive, options for sludge
stabilization and disposal.
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8-24
WASTEWATER MANAGEMENT
Minimize Methane During Sludge
Treatment and Disposal
many technologies available; others
under research and development
reduce health risks by stabilizing
organics
reduce odors
reduce methane emissions
substantially reduce sludge volume
treated sludge useful for land
reclamation
cost-effective in many cases
produce energy
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WASTEWATER MANAGEMENT 8 - 25
8.5 References
Contributions were made by:
Carl Bartone, Urban Development Division, World Bank, U.S.A.
Robert Bastian, Office of Wastewater Enforcement and Compliance, USEPA, U.S.A.
Nadine DeSanto, Marketing Coordinator, Biothane Corporation, U.S.A.
Dr. Joseph Farrell, Water and Hazardous Waste Treatment Research, EPA/ORD, Risk
Reduction Engineering Laboratory, U.S.A.
Joseph Lagnese, environmental engineer, U.S.A.
Steve Maber, Water and Sanitation Division, World Bank, U.S.A.
Marvin Rubin, Office of Water, USEPA, U.S.A.
Katsuya Sato, Japan Environment Agency, Japan
John L. Strauss, Biosphere Corporation S.A., Switzerland
James Wheeler, Operations Branch, USEPA, U.S.A.
Additional information may be found in the following:
Biocycle Staff, eds. (1991), The Biocvcle Guide to The Art and Science of Composting,
Biocycle, Journal of Waste Recycling. Emmaus, Pennsylvania: The JG Press, Inc.
Escritt, Leonard B. (1984), Sewerage and Sewage Treatment:lnternational Practice. William
D. Haworth, ed. Chichester: John Wiley and Sons Limited.
Hammer, Mark J. (1986), Water and Wastewater Technology, second edition, New York:
John Wiley and Sons.
Howe and Coker (1992), "Residuals Recycling at Alcosan- Two New Approaches," in WEF
1992, Proceedings of "The Future Direction of Municipal Sludge (Biosolids) Management:
Where We Are and Where We Are Going" Specialty Workshop in Portland, OR, July 16-30,
1992, pp 713-730.
IPCC (Intergovernmental Panel on Climate Change) (1990), Climate Change: The IPCC
Response Strategies, prepared by the Response Strategies Working Group, with WMO and
UNEP. Geneva, June 9, 1990.
Loehr, Raymond C. (1984), Pollution Control for Agriculture, second edition, Orlando:
Academic Press, Inc. (Harcourt Brace Jovanovich, Publishers).
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8 - 26 WASTEWATER MANAGEMENT
Murakami, Ken, and Yoshio Oshima (1988), "Treatment, Disposal and Utilization of Sewage
Sludge in Japan- Current Practice and Future Direction," Proc. 3rd WPCF/JSWA Joint
Technical Seminar on Sewage Treatment Technology.
Sato, Kazuaki (1984), "Digester Gas Use in Wastewater Treatment Plants in Japan,"
presented at 3rd International Symposium on Environmental Techniques Development,
October 1984, Posan, Korea.
USEPA (United States Environmental Protection Agency) (1980), "Innovative and Alternative
Technology Assessment Manual," (CD-53), U.S. Environmental Protection Agency/Office of
Research and Development, and EPA/Water Program Operations, EPA 430/9-78-009,
February, 1980.
USEPA (1983), "Design Manual: Municipal Wastewater Stabilization Ponds," U.S.
Environmental Protection Agency, EPA 625/1-83-015, October, 1983.
USEPA (1989), "Environmental Regulations and Technology: Use and Disposal of Municipal
Wastewater Sludge," (WH-595), U.S. Environmental Protection Agency/Office of Water,
EPA 625/10-84-003, March, 1989.
USEPA (1990), Methane Emissions and Opportunities for Control: Workshop Results of
Intergovernmental Panel on Climate Change. Response Strategies Working Group, coordinated
by EPA/OAR and Japan Environment Agency, September, 1990.
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CHAPTER NINE
BIOMASS BURNING
9.1 Background
Methane Emissions
Biomass burning is a major source of global methane emissions. Methane, along with carbon
dioxide (CO2). carbon monoxide (CO) and other trace substances, is one of the forms in which
carbon is released into the atmosphere when biomass is burned. Although typically more than
95 percent of the carbon burned as biomass is released in the form of C02 and CO, a small
but significant component is released as methane (0.5-1.6% by weight) (Norse, 1991). While
the lack of comprehensive data and consistent measurement techniques make it difficult to
determine global methane emissions from this source, estimates range from 20 to 80 Tg per
year, or 5 to 15 percent of total annual methane emissions from all sources. Emission rates
are expected to increase along with rates of deforestation and landscape degradation.
Most major sources of biomass burning are anthropogenic and fall into two general categories:
1) large open fires associated with land management practices, common in forest, savanna
and crop ecosystems, and 2) small-scale fires in which biomass is burned for fuel in
households or industry.
In response to declining agricultural yields and population pressures, farmers in many regions
regularly convert forests to cropping and pasture land. Many of their land management
techniques involve the burning of standing vegetation. Shifting cultivation in the tropics, for
example, requires that forests be cut, logging debris and unwanted vegetation burned, and
the land farmed for several years and left fallow to re-vegetate. Large-scale fires in temperate
and boreal forest ecosystems are also common. Estimates indicate that about 1000 Tg of
woody biomass (Norse, 1991) are burned annually on 1 to 5 percent of the world's land
(USEPA, 1990).
Savanna and rangeland biomass is often burned to improve the quantity and quality of
livestock forage, and in some regions to eliminate parasites (Menault, 1991). Agricultural
residues are also burned in the field to return nutrients to the soil or reduce shrubs on
rotational fallow lands. Such agriculture-related burning may account for up to 50 percent of
the biomass burned annually (Ahuja, 1990).
Finally, a large amount of global biomass burning falls under the second general category:
biomass fuel burning in households or industry. While industrial biomass combustion may be
increasing in importance, studies to date have focused on emissions from small-scale
combustion. Firewood, charcoal, crop residues and animal dung are burned for fuel in small-
scale cooking and heating stoves in nearly half of the world's households. Pilot studies have
indicated that emission rates for methane and other non-CO2 greenhouse gases from this
source are high (8-9 g methane/kg dry fuel wood), resulting in potentially significant total
emissions. The combustion of firewood, for instance, may be responsible for 10 to 45
percent of the methane released from all global biomass combustion. Firewood combustion
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9-2 BIOMASS BURNING
in developing countries alone may generate 20 to 50 percent of total global carbon emissions
from biomass combustion (Smith et al., 1992).
The exact nature and composition of the products of combustion vary according to the
following factors:
Fuel size, composition and distribution;
Fuel chemistry; and
Moisture content of fuel.
These fuel characteristics affect the duration of the different phases of combustion (flaming,
smoldering and glowing), each of which is associated with a different level of combustion
efficiency (CE). The percentage of C02 in the combustion products increases as the CE
increases, while the release of methane, non-methane hydrocarbons (NMOCs) and particulates
is enhanced during incomplete combustion phases. Studies show that methane emission rates
from smoldering fires (with CEs of 50 to 80%) are often 2 to 3 times higher than those from
80 to 98 percent efficient flaming fires (Norse, 1991).
In addition to instantaneous emissions, research indicates that enhanced biogenic soil
emissions following open fires may result in continued emissions of methane, N2O and NO for
several years.
Methane Emissions Reduction Strategies
Ongoing work has identified a number of options that could potentially reduce methane
emissions from biomass burning. These options include:
Reducing the frequency, area and amount of biomass burned:
Forests:
- Increase productivity of existing agricultural lands;
- Lengthen rotation times of shifting agriculture;
- Enhance forest resource utilization;
- Apply alternative silvicultural practices in forest systems;
- Implement fire management programs;
- Incorporate charcoal into the soil after burning;
- Clear-fell forest before or instead of burning;
Grasslands:
- Increase grassland management;
- Substitute game ranching for domestic livestock;
- Develop fodder trees to feed livestock;
Croplands:
- Compost or incorporate crop residues into soil;
- Increase use of crop residues as household fuel;
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BIOMASS BURNING 9 - 3
- Replace annual or seasonal crops with tree crops;
- Minimize soil disturbance;
Improving efficiency of biomass used as fuel:
Increase efficiency of biomass cook stoves;
Develop high-efficiency gasifiers for crop residues; and
Switch to alternative fuels.
The feasibility of some of these options has been demonstrated in many regions of the world.
The potential for reducing methane emissions from biomass burning has received some
attention, but further work is need to fully quantify management impacts. Substantial
research efforts are required to determine the quantity and types of emissions released and
the potential for reducing these emissions. Since strategies that focus on reducing or
modifying biomass burning will affect other greenhouse gases as well, assessing response
options will require a comprehensive accounting of the greenhouse gas balance. Research is
also needed to identify the reduction options which are culturally, economically and
ecologically appropriate for each region, and which will not threaten food security.
Other collateral benefits will result from reducing biomass burning. These include
maintenance of forest and agricultural resources, reduced soil erosion, and the protection of
human health, life and property. Several strategies have already gained international
acceptance for their potential to protect species diversity and reduce rates of deforestation.
For example, implementation of one hectare of agroforestry in tropical latitudes can offset 5
to 20 hectares of deforestation (Dixon, 1992). The multiple crops and sustained nature of
agroforestry offer other benefits. These and other areas of possible research are discussed
on the following pages.
9.2 Opportunities for Reducing Methane Emissions
Research to date shows that the burning of crop lands, grasslands and forests may be
reduced through sustained land management programs and the promotion of different land use
practices. Emissions from biomass burned as fuel may be reduced through the use of more
efficient stoves, other combustion devices and fuels.
Reducing the Frequency. Area and Amount of Biomass Burned
Forests
Increase productivity of existing agricultural lands. The conversion of forest and
savanna to agricultural land could be reduced by the widespread use of sustainable
agricultural practices which optimize yields and intensive practices which increase
productivity. Possible practices include the use of chemical and organic fertilizers,
biotechnology, improved cultivar species and/or appropriate management systems
which minimize soil disturbance. Reclaiming degraded agricultural lands may also be
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9 - 4 BIOMASS BURNING
an option. These efforts could be aided by educational programs designed to provide
an understanding of organic residue management and the consequences of soil
degradation (Norse, 1991).
Lengthen rotation times and improve productivity of shifting agriculture. Increasing
the length of the fallow period and improving crop yields would allow abandoned land
to reforest, slowing forest conversion and reducing emissions of greenhouse gases
(Andrasko et al., 1991). A number of integrated or agroforest systems can be
employed to achieve this goal.
Enhance forest resource use. Making the harvesting of forest resources an
economically viable alternative to agriculture could decrease forest burning. Possible
options include developing uses for forest products and establishing forest and
agroforest cropping systems (Norse, 1991). Research is necessary to determine
appropriate tree species and agroforestry cultivation methods in different regions, and
the effects of these trees on regional soils and crops.
Apply alternative silvicultural practices in forest systems. Routine removal of interim
crops can significantly reduce fuel load and improve forest productivity. Forest-
thinning is a well-developed management option which could be an alternative to
burning.
Implement fire management programs. Fire management programs are designed to
prevent, detect and suppress natural and accidental fires. The most common fire
management tool is prescribed burning, which involves burning excess forest biomass
under confined and monitored conditions in order to reduce available combustible fuels.
This practice has been shown to reduce the intensity and size of wildfires.
Fire management programs have been successfully utilized in Canada, the United
States and Australia for many years, and could have significant benefits in developing
countries where large areas burn annually; potential for reducing greenhouse gas
emissions must be explored through study of the ecologies of candidate forests, and
optimal fire sizes and frequencies.
Incorporate charcoal into the soil after burning. Plowing charcoal into forest soil,
although a labor-intensive process, could prevent it from burning again in subsequent
fires (Andrasko et al., 1991).
Clear-fell forest before or instead of burning. Clear-felling trees and selling them for
lumber or other wood products instead of burning them could reduce the amount of
biomass burned in many regions (Andrasko et al., 1991). The feasibility of this option
depends on available transportation and markets.
Grasslands
Increase grassland management. Wildfire prevention similar to forest practices may
be possible in grasslands. The greatest potential, however, may lie in intensifying land
management in order to reduce the frequency and area of fires which are intentionally
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BIOMASS BURNING 9 - 5
set to improve forage. This strategy would require significant research on regional
vegetation, climate, and cultural practices.
Substitute game ranching for domestic livestock. Unlike domestic livestock, which
require the highly-nutritional young forage which grows after grasslands are burned,
animals native to a region are adapted to naturally occurring vegetation. Raising native
game instead of livestock where feasible may therefore reduce burning needs, increase
forage yield per field, reduce costs, and reduce animal-related methane emissions.
Stall-feeding domestic livestock may also be possible, but would be constrained by
local technology and pastoralist lifestyles (Andrasko et al., 1991).
Develop fodder trees to feed livestock. Fodder-producing tree plantations could replace
pasture as food for stall-fed livestock. This option would require capital and time for
phasing in fodder trees. Several thousand multi-purpose tree species which produce
food, fuel, and fodder have been identified and tested worldwide.
Croplands
Incorporate crop residues into soils instead of burning. Many common agricultural
systems, such as shrub-fallow systems and high-yield grain crops, depend on burning
to remove biomass from fields and increase soil fertility. Incorporating crop residues
into the soil, although a labor-intensive process, could increase soil fertility while
reducing methane emissions.
Increase use of crop residues as household fuel. Removing field wastes and using
them as fuel in household stoves or gasifiers could reduce agricultural burning.
Programs to increase cropland productivity could increase the mass of field wastes
available for use as fuel, further reducing the need to burn other types of biomass for
energy.
Replace annual or seasonal crops with tree crops. Tree crops, which do not require
periodic burning, may be a suitable alternative,to some annual or seasonal crops.
Integrated and/or agroforest systems have been employed by farmers in some regions
for centuries. Such a transition in new areas, however, would require consideration
of time and capital investments, farmer education and market development.
Minimize soil disturbance. Soil-site disturbance generally increases biogenic methane
emissions. Alternative management options, such as no-till or reduced-tilling
techniques, are available for implementation in many regions. Soil biology, chemistry
and structure can also be managed to reduce emissions.
Improving Efficiency of Biomass used as Fuel
Increase efficiency of biomass cookstoves: Research has shown that it is possible to
double the efficiency of cookstoves (now typically 10 to 12 percent), thus reducing the
amount of fuel required for cooking and cost-effectively reducing greenhouse gas
emissions by one half (Ahuja, 1990). This process may involve a trade-off: improving the
stove's heat transfer efficiency reduces its combustion efficiency, thus increasing the
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9 - 6 BIOMASS BURNING
proportion of methane produced. Improved stove models still show reductions in methane
emissions, however, because of dramatically decreased fuel requirements. Accurate
measurements of thermal efficiencies and emissions from different types of stoves are
needed.
Develop high-efficiency gasifiers for crop residues: High-efficiency combustion systems
such as gasifiers could be used to burn crop residues. Biomass Degeneration systems
have also been suggested as an efficient option. Demonstration and feasibility projects
would be necessary for the development of these devices.
Switching to alternate fuels: Switching from the use of biomass fuels to the use of
commercial fuels such as kerosene or liquid petroleum gas (LPG) could reduce total
resulting greenhouse gas emissions from cookstoves. Such reductions are especially likely
in areas where biomass fuel is harvested on a non-renewable basis, resulting in net
deforestation. In these areas all of the CO2 released from biomass burning results in a net
atmospheric CO2 increase.
This strategy may even be beneficial in areas where there is no net deforestation.
Although CO2 from stoves does not appear to contribute to the greenhouse effect in such
areas (Ahuja, 1990), the greenhouse impact of emissions of methane and other
greenhouse gases may exceed those from CO2, especially in the short term (Smith et al.,
1992; Smith and Thorneloe, 1992). Fuel switching may thus be justified for its potential
to reduce these other gases. Implementation of this strategy would be constrained by
availability and fuel costs.
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BIOMASS BURNING 9 - 7
9.3 References
Contributions were made by:
Kenneth J. Andrasko, U.S. Environmental Protection Agency, U.S.A.
Bob Dixon, U.S. Environmental Protection Agency, U.S.A.
David Norse, Food and Agriculture Organization of the United Nations, Italy
Kirk R. Smith, Environment and Policy Institute, East-West Center, U.S.A.
Darold Ward and Wei Min Hao, Intermountain Research Station, U.S.A.
Additional information may be found in the following:
Ahuja, Dilip (1990), "Research Needs for Improving Biofuel Burning Cookstove Technologies:
Incorporating Environmental Concerns," in Natural Resources Forum. May.
Andrasko, Kenneth J., Dilip R. Ahuja, Steven M. Winnettand Dennis A. TirpaM 1991), "Policy
Options for Managing Biomass Burning to Mitigate Global Climate Change," in Global Biomass
Burning: Atmospheric. Climatic and Biospheric Implications. Joel S. Levine, ed., Cambridge,
Massachusetts: MIT Press.
Burke, Lauretta and Daniel Lashof (1989), "Greenhouse Gas Emissions Related to Agriculture
and Land-Use Practices," February, 1989.
Dixon, Bob (1992), USEPA, personal communication.
Lashof, D.A. and D.A. Tirpak (1990), Policy Potions for Stabilizing Global Climate: Report to
Congress. USEPA, Washington, D.C., EPA/21P-2003.1.
Menaut, J.C., L. Abbadie, F. Lavenu. Ph. Loudjani and A. Podaire (1991), "Biomass Burning
in West African Savannas," (draft, for J. Levine, ed.. Global Biomass Burning. Cambridge, MIT
Press).
Norse, D. (1991) "Biomass Burning," Food and Agriculture Organization of the United Nations,
November (draft).
Smith, Kirk R., R.A. Rasmussen, Ferdinand Manegdeg, and Michael Apte (1992), Greenhouse
Gases from Small-Scale Combustion in Developing Countries: A Pilot Study in Manila.
Prepared by Air and Energy Engineering Research Laboratory, Research Triangle Park, N.C.,
for EPA/OAR and EPA/OPPE
Smith, Kirk R. and Susan A. Thorneloe (1992), "Household Fuels in Developing Countries:
Global Warming, Health, and Energy Implications," for presentation at EPA Symposium on
Greenhouse Gas Emissions and Mitigation Research, August 20, 1992, Washington, D.C.
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9 - 8 BIOMASS BURNING
USEPA (United States Environmental Protection Agency) (1990), Methane Emissions and
Opportunities for Control: Workshop Results of Intergovernmental Panel on Climate Change.
USEPA, Washington, D.C., EPA/400/9-90/007.
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CHAPTER TEN
RICE CULTIVATION
10.1 Background
Methane Production. Transport and Emissions
Methane released during flooded rice cultivation is a major source of global methane
emissions. Methane,is produced in the soils of flooded rice fields, largely from the anaerobic
decomposition of organic material by methanogenic bacteria. These organic materials include
carbon sources such as root exudates, soil organic matter, and floodwater biomass (i.e.
algae), as well as organic fertilizers.
An estimated 60 to 80 percent of the methane which is produced is oxidized in the upper
layer of the soil by aerobic methanotrophic bacteria, and inside the plant, and leached away
with the percolating water as dissolved methane. The remaining, non-oxidized methane is
transported from the submerged soil into the atmosphere primarily through the intercellular
gas space system of the rice plant; most of this methane is released into the atmosphere from
the plant's culm (an aggregation of leaf sheaths). Methane is also transported by diffusion
through the floodwater and ebullition (bubbling up of gas). Exhibit 10-1 illustrates emissions
of methane from flooded rice fields as the net result of methane production, oxidation, and
transport to the atmosphere.
The quantity of methane emitted by a rice field depends upon several important factors.
These include:
Soil factors;
Nutrient management;
Water regimes; and
Cultivation practices.
Methane Mitigation Strategies
Recent research has begun to identify various management practices that could potentially
reduce methane emissions from rice cultivation. Recognizing that increasing rice productivity
and satisfying other social and cultural constraints are fundamental objectives, experts in the
area generally believe that 10 to 30 percent reductions in methane emissions from rice
cultivation, relative to current levels, may be possible over the long term (Braatz and Hogan,
1991). However, much additional research is needed to establish and demonstrate practices
that will maintain or increase rice productivity while reducing methane emissions from rice
cultivation. Present knowledge indicates that modifications in the following practices have
the potential to reduce methane emissions:
Cultivar selection;
Nutrient management;
Water management; and
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10-2
RICE CULTIVATION
Cultivation practices.
Substantial research efforts are required to identify the most feasible and regionally
appropriate and feasible methane mitigation opportunities. Since long periods of time are
required for evaluation of mitigation options and subsequent demonstration, promotion, and
adoption of those options found to be effective, it is necessary that comprehensive and
coordinated research take place over the next several years. This may best be achieved
through the formation of a research consortium of the major rice-growing countries, to
facilitate regional and international collaboration and research on methane emission issues.
Different avenues of research which should be pursued under such a program are outlined
below.
Exhibit 10-1
Methane Production and Emission from Flooded Rice Held*
CH4
Emission
CH4
Oxidation
CH4
Production
Leaching - CH4
Dissolved in Water
anoxic
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RICE CULTIVATION 10-3
10.2 International Research Plan
A comprehensive approach including management of water regimes, development of cultivars,
efficient use of fertilizers, and other management practices can be formulated to achieve
reductions in methane emissions. However, current knowledge is insufficient in the areas of
the complex interaction between methane production and oxidation, as well as the exchange
of methane between the atmosphere and rice fields. The following sections briefly describe
the current understanding of and the types of research needed in each of these areas.
Cultivar Selection
Rice cultivars appear to produce differing amounts of methane over the growing season.
Studies show two or three peaks in emissions occurring during the season, believed to be
times when high concentrations of organic root exudates or root litter are available to soil
bacteria. Methane production is thought to be positively linked to the amount of root
exudates on the rice variety. Development and use of varieties that minimize root exudation
may, therefore, reduce the quantity of organic matter available for decomposition, thereby
reducing methane emissions.
Certain rice cultivars may also affect the rate of oxygen and methane transport through the
plant (Figure 1). Downward oxygen transport and associated oxidation of methane in the soil
rhizosphere, as well as upward methane transport, may vary among cultivars, providing
opportunity for additional methane reduction through cultivar selection.
Cultivar selection would be easy to implement compared to other methane mitigation
strategies, and would be practical if rice productivity was maintained. Comprehensive studies
of rice varieties are needed to determine the relationship between rice variety and methane
emission, and whether gas transport and loss of organic material from roots affect yields.
Nutrient Management
Several nutrient management techniques are used in rice cultivation, including the application
of raw or composted organic material, and the addition of nitrogen fertilizers (e.g., ammonium
sulfate and urea). The application of nitrogen fertilizers appears to reduce methane emissions
relative to unfertilized fields and fields fertilized with organic material, particularly if the
fertilizer is deeply incorporated into the soil. This reduction is believed to occur because the
C:N ratio of the soil is decreased so that more organic carbon remains in the soil biomass.
In contrast, the application of raw organic material such as rice straw to rice fields, whether
or not in combination with mineral fertilizers, appears to enhance methane emissions.
Composted organic material also enhances emissions, but to a much lesser extent. Thus the
use of nitrogen fertilizers and/or the replacement of raw with composted organic materials
may be options for mitigating methane emissions.
Nitrification inhibitors also have the potential to limit methane production in rice fields. These
chemicals restrict the bacterial oxidation of nitrogen, thus decreasing nitrogen loss in flooded
soils. Encapsulated calcium carbide (ECC), a nitrification inhibitor used in conjunction with
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10-4 RICE; CULTIVATION
ammonium sulfate or urea, releases acetylene (C2H2), which has been shown to reduce
methane emissions.
Nitrogen fertilizers are already the major sources of N for flooded rice, a primary necessity to
sustaining or increasing rice production in Asia. However, strategies based on using these
fertilizers and other additives such as nitrification inhibitors must be integrated with existing
nutrient management techniques, and their technical and socioeconomic feasibility explored.
Research efforts are needed to determine the potential of different types of fertilizers to
reduce methane emissions, the effects of amount, timing and application on emissions, and
the relationships of soil properties with additions of different nutrients.
Water Management
Methane emissions may be influenced by the type of water regime (e.g., inundation period and
drainage schedule) used during rice cultivation. Draining the rice field during the growing
season or between crops seems to decrease methane production by increasing the state of
oxidation of the paddy soil. Studies show, however, that in order to avoid a decrease in
productivity, soil water contents must be kept above 70 percent of saturation during the
second half of the vegetative stage and before flowering, when the rice plants are most
susceptible to drought.
Methane emissions may also significantly decrease with increasing rates of water percolation
because organic substances can be leached away with the percolating water, reducing the
available substrate for methanogens. In addition, the infiltrating water may introduce fresh
dissolved oxygen into the reduced layer in flooded soils, thus increasing the redox potential
of the soil and inhibiting methane production.
Water management as a possible mitigation practice depends on the physical characteristics
of a region, and is only feasible in certain areas. The most suitable areas for this strategy are
those with lowland and flatland irrigated rice fields, which have highly secure and controllable
water supplies. These techniques are not suitable on terraced hillsides, where drainage may
cause physical damage to fields (e.g. collapse of terrace construction) and reduced yields.
Drainage may also be less feasible in rainfed areas, where rice cultivators depend on the water
stored in the fields.
Research efforts should focus on the relative effects of different water management schemes
on methane emissions, and on determining which rice ecologies, climatic regions and
socioeconomic conditions are most suitable for altered water management schemes. The
effects of different water management schemes on nitrous oxide emissions is also an
important research issue.
Cultivation Practices
The adaptation of some tillage, seeding, and weeding techniques in order to minimize water
use and mechanical soil disturbance may have potential for decreasing methane emissions
from rice cultivation. The substitution of wet tillage and transplanting of rice seedlings with
dryland tillage and dry seeding, for example, appears to reduce methane emissions. This is
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RICE CULTIVATION 10-5
believed to be the result of shortening the anaerobic phase of the growing season, which may
raise the soil redox potential and result in delayed and lower methane production. Minimum
or zero tillage should have similar effects.
Avoiding the mechanical disturbance of soil during weeding may also reduce methane
emissions by minimizing the release of gases trapped in the soil. In addition, refraining from
weeding reduces the amount of organic substrate (i.e., uprooted weeds) available to
methanogens, which may also contribute to the reduction of methane.
Many cultural practices that enhance methane emissions have been developed to suit the
physical, biological, and socioeconomic conditions of different regions, and many reduction
strategies may not be applicable. For this reason, revising these practices in order to reduce
methane emissions will not be appropriate or acceptable unless other rice cultivation changes
make these revisions practical. Assessing how and to what extent land preparation
techniques, seeding and transplanting techniques affect methane emissions should therefore
be a low research priority.
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10-6
RICE CULTIVATION
10.3
References
Contributions to this set of technological assessments were made by:
Kathleen Hogan, Chief, Methane Programs, Global Change Division, USEPA
Heinz-Ulrich Neue, International Rice Research Institute
Katsu Minami, Japan National Institute of Agro-Environmental Sciences
The following also contributed to the EPA's Rice Research Plan:
Lex Bouwman
National Institute of Public Health
and Environmental Protection, RIVM
Netherlands
Barbara Braatz
ICF Incorporated
U.S.A.
Bernard Byrnes
International Fertilizer Development
Center
U.S.A.
Ralph Cicerone
University of California at Irvine
U.S.A.
Alex Guenther
National Center for Atmospheric Research
U.S.A.
Alan Hills
National Center for Atmospheric Research
U.S.A.
Kathleen Hogan
USEPA
U.S.A.
Lee Klinger
National Center for Atmospheric Research
U.S.A.
Victor Law
Tulane University
U.S.A.
Charles Lindau
Louisiana State University
U.S.A
Katsu Minami
Japan National Institute of
Agro-Environmental Sciences
Japan
Arvin Mosier
U.S. Department of Agriculture
U.S.A.
Heinz-Ulrich Neue
International Rice Research Institute
Philippines
David Olszyk
USEPA
U.S.A.
William Patrick
Louisiana State University
U.S.A.
Heinz Rennenberg
Fraunhofer Institute for Atmospheric
Environmental Research
Germany
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RICE CULTIVATION 10-7
Kurt Roos William Steen
USEPA USEPA
U.S.A. U.S.A.
John Rogers Patrick Zimmerman
USEPA National Center for Atmospheric Research
U.S.A. U.S.A.
Ronald Sass
Rice University
U.S.A.
Additional information may be found in the following:
Braatz, Barbara and Kathleen Hogan, eds. (1991), "Sustainable Rice Productivity and Methane
Reduction-Research Plan," USEPA, Office of Air and Radiation, September.
Neue, Heinz-Ulrich and P.A. Roger (1991), "Methane Formation and Fluxes in Rice Fields,
Principles and Prospects," presented at NATO Advanced Research Workshop on Atmospheric
Methane Cycle: Sources, Sinks, Distributions and Role in Global Change, October 6-11,1991,
Portland, Oregon, U.S.A. (abstract).
USEPA (United States Environmental Protection Agency) (1990), "Methane Emissions and
Opportunities for Control: Workshop Results of Intergovernmental Panel on Climate Change,"
September. (EPA/400/9-90/007)
USEPA (1990), "Workshop on Rice Research and Methane Reduction: Summary Report,"
September, Washington, D.C
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