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The global threat caused by increasing surface temperature has led to negative climate changes. One of the greenhouse gases responsible for this global warming is methane. It is emitted naturally and anthropogenically from different sources and its concentration in the atmosphere has assumed alarming proportions. Its devastating consequences on climate change and atmospheric chemistry have made it to be a focus of intense scrutiny and study. The anthropogenic sources of its emissions are generally grouped under three sectors of agriculture, energy and waste. The past emission trends of methane from these sectors are investigated through their sources while mitigation and abatement strategies are suggested. It is observed that the agricultural sector emits the highest amount of methane, followed by the energy and waste sectors, respectively.
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Methane emission by sectors: A comprehensive review of emission
sources and mitigation methods
Rafiu O. Yusuf
, Zainura Z. Noor
, Ahmad H. Abba
, Mohd Ariffin Abu Hassan
Mohd Fadhil Mohd Din
Environmental Engineering Laboratory, Department of Chemical Engineering, Faculty of Chemical Engineering, Universiti Teknologi Malaysia, 81310 Skudai, Johor Bahru, Malaysia
Department of Environmental Engineering, Faculty of Civil Engineering, Universiti Teknologi Malaysia, 81310 Skudai, Johor Bahru, Malaysia
article info
Article history:
Received 28 February 2012
Accepted 6 April 2012
Climate change
Global warming
The global threat caused by increasing surface temperature has led to negative climate changes. One of
the greenhouse gases responsible for this global warming is methane. It is emitted naturally and
anthropogenically from different sources and its concentration in the atmosphere has assumed
alarming proportions. Its devastating consequences on climate change and atmospheric chemistry
have made it to be a focus of intense scrutiny and study. The anthropogenic sources of its emissions are
generally grouped under three sectors of agriculture, energy and waste. The past emission trends of
methane from these sectors are investigated through their sources while mitigation and abatement
strategies are suggested. It is observed that the agricultural sector emits the highest amount of
methane, followed by the energy and waste sectors, respectively.
&2012 Elsevier Ltd. All rights reserved.
1. Introduction .....................................................................................................5060
2. Agriculture ......................................................................................................5060
2.1. Source description ..........................................................................................5061
2.2. Mitigation measures for the agricultural sector . . .................................................................5062
2.2.1. Dietary supplementation ..............................................................................5062
2.2.2. Selection of high quality grasses . . . .....................................................................5062
2.2.3. Increase grain level ..................................................................................5062
2.2.4. Increasing feed conversion efficiency ....................................................................5062
2.2.5. Increasing animal productivity .........................................................................5062
2.2.6. Future options ......................................................................................5063
2.2.7. Methane emissions mitigation from manure management ...................................................5063
2.2.8. Biogas production....................................................................................5063
2.3. Mitigation for rice cultivation .................................................................................5063
3. Energy . . .......................................................................................................5063
3.1. Source description ..........................................................................................5064
3.1.1. Oil and gas . . .......................................................................................5064
3.1.2. Coal mining activities. . . ..............................................................................5064
3.1.3. Stationary and mobile sources..........................................................................5064
3.1.4. Biomass burning.....................................................................................5064
3.2. Mitigation options for the energy sector.........................................................................5064
3.2.1. Oil ................................................................................................5064
3.2.2. Natural gas . . .......................................................................................5065
3.2.3. Coal...............................................................................................5065
4. Waste . . . .......................................................................................................5066
Contents lists available at SciVerse ScienceDirect
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Renewable and Sustainable Energy Reviews
1364-0321/$ - see front matter &2012 Elsevier Ltd. All rights reserved.
Corresponding author. Tel.: þ60 177 470 315.
E-mail address: (Z.Z. Noor).
Renewable and Sustainable Energy Reviews 16 (2012) 5059–5070
4.1. Source description ..........................................................................................5066
4.1.1. Solid waste landfill...................................................................................5066
4.1.2. Wastewater ........................................................................................5066
4.1.3. Source Results ......................................................................................5067
4.2. Abatement options for lan dfills and wastewater plants .............................................................5067
4.2.1. Emissions reductions from landfills......................................................................5067
4.2.2. Wastewater methane emission abatement . . . .............................................................5067
5. Conclusions .....................................................................................................5067
References ......................................................................................................5067
1. Introduction
The emission of greenhouse gases from various sources has
resulted in climate change with the attendant increase in global
surface temperature [1,2]. Climate change, a resultant effect of
greenhouse gas emissions, is a worldwide concern because its
continuation is having significant and negative impacts on people,
natural resources, and economic conditions around the globe
[37]. The major greenhouse gases (GHGs) and their relative
quantities are water vapour, H
(36–70%), carbon dioxide,
(9–26%), methane, CH
(4–9%), and nitrous oxide N
O (3–7%)
plus other trace gases [8]. Of these greenhouse gases, CO
and CH
have been touted as being responsible for the rise in global
surface temperature [9]. The emissions of these gases are caused
by both natural and human (anthropogenic) actions.
Methane is only second to carbon dioxide in its contribution to
global warming [10]. It is the simplest alkane and is also the
principal component of natural gas with bond angles of 109.51
and is formed from the anaerobic decomposition of organic
matter in the environment. Methane is a much more powerful
greenhouse gas than CO
with a high global warming potential
(GWP) of 21–25 times more than CO
[1115]. The 100-year
GWPs of the greenhouse gases as given in the Second (SAR), Third
(TAR) and Fourth (AR4) Assessment Reports are shown in Table 1
[16,17]. Methane is said to be explosive when it is present in the
air in concentrations between 5–15% [18,19]. The yearly CH
emissions around the world are significantly smaller than CO
emissions, and CH
concentrations in the atmosphere are about
200 times lower than those of CO
[20], but methane accounts for
about 20% of global warming [21,22].
It is emitted naturally by wetlands [23,24], termites, wildfires
[20], grassland [25], coal beds [26,27] and lakes [28]. The human
(anthropogenic) sources of methane emissions include municipal
solid wastes (MSW) landfills [2931], rice paddies [3234], coal
mining [3537], oil and gas drilling and processing [38,39], cattle
ranching [4042], manure management [43,44], agricultural pro-
ducts [45,46], wastewater treatment plants [47], and rising main
sewers [48].
Methane concentration in the atmosphere remained stable for
thousands of years before it began to rise in the 19
(Fig. 1a). In 1750, the concentration of methane in the atmosphere
was 676–716 ppb. It rose to 1745 ppb in 1998 and 1800 ppb in
2008 [15,17,49]. The global anthropogenic emissions for methane
from all sectors in 2010 were estimated to be 6,875 million metric
tons CO
equivalent (MtCO
eq) [50,51].
This review examines the emissions of methane from 1990 to
2010 and provides explanation as to the trends observed. Anthro-
pogenic methane emissions pattern from all sources for 2010 are
presented in Fig. 1b. The major sources of methane emissions that
have been identified are grouped into three main sectors –
agriculture, waste, and energy. The sectorial emissions for 2010
are also presented in Fig. 1c while Fig. 1d shows the methane
emissions trends from 1990 to 2010. The overall emission pattern
indicated growths of 4%, 9%, 15% and 23.5%, respectively, for the
years 1995, 2000, 2005 and 2010 over the 1990 emission level.
These emissions are projected to grow by a further 32% and 41%
respectively by the years 2015 and 2020 [51]. Methane emissions
from the agricultural sector increased by 11% by the year 2000
and 24% by the end of 2010. The emissions from the energy sector
also increased by 8% in 2000 and 32% by 2010 while the waste
sector recorded increases of 4% and 12% by the end of the years
2000 and 2010 respectively. The raw data used in this review
were obtained from the report by the US Environmental Protec-
tion Agency (EPA).
The patterns of methane emissions from these sectors as well
as strategies for the mitigation of these methane emissions from
each sector are exhaustively discussed in the following sections.
2. Agriculture
The average global emissions of methane from the agricultural
sector through human (anthropogenic) activities were 3,520
eq which is 52.5% of the total methane emissions from
anthropogenic sources [51]. Of these agricultural emissions, those
from enteric fermentation (livestock rearing) alone was 53% [6]
while emissions from rice cultivation, other agricultural activities
and manure management were 18%, 18% and 11%, respectively
(Fig. 2a) [51]. Globally, methane emissions from ruminant live-
stock is 85 Tg of the 550 Tg released annually [52].
Methane emissions from enteric fermentation rose by only
1.5% between 1990 and 2000 but the increase rose to 17% by the
end of 2010 [53]. Rice cultivation resulted in a 6% increase in
methane emissions from 1990 to 2000 and this shot up to 18% by
2010. Methane emissions from manure management increased by
only 1% from 1990 to 2000 but the increase rose to 12% by the
year 2010 [53]. Emissions increase from other agricultural sources
has remained constant. The trends of methane emissions in the
agricultural sector from 1990 to 2010 are illustrated in Fig. 2b.
Table 1
Composition of 100-year GWP of the greenhouse gases.
21 23 25
O 310 296 298
HFC-23 11,700 12,000 14,800
HFC-32 650 550 675
HFC-125 2,800 3,400 3,500
HFC-134a 1,300 1,300 1,400
HFC-143a 3,800 4,300 4,470
HFC-152a 140 120 124
HFC-227ea 2,900 3,500 3,200
HFC-236fa 6,300 9,400 9,810
HFC-4310mee 1,300 1,500 1,640
6,500 5,700 7,390
9,200 11,900 12,200
7,000 8,600 8,860
7,400 9,000 9,300
23,900 22,200 22,800
R.O. Yusuf et al. / Renewable and Sustainable Energy Reviews 16 (2012) 5059 –50705060
The main reason for this upward increase in methane emis-
sions is the rising levels of agricultural production with the aim of
meeting the demands of rapidly-growing population centres in
China, South and East Asia, Latin America, and Africa. Consump-
tion of agricultural products is rising quickly due to increases in
both population and income in many areas of these regions.
Another factor that will cause increase in the demand for
agricultural products is changes in diet preferences, such as an
increase in per-capita meat consumption [51]. Overall, global
anthropogenic methane emissions from livestock alone is esti-
mated at 35–40% [54], 37% [55] and 25.5% [56].
2.1. Source description
The normal processes of digestion in animals result in methane
emissions. Enteric fermentation is a fermentation process in which
microbes in the animal’s digestive system cause the food to be
fermented [40,56,57]. This fermentation takes place in the rumen
of ruminant animals like cattle, buffalos, sheep, and goats and
result in relatively large methane emissions per unit of feed energy
consumed [56]. Methane emissions from enteric fermentation of
the domestic livestock contribute significantly to GHG inventories
[42,58,59]. Majority of methane emissions in this sector are from
domesticated ruminants such as cattle, buffalo, sheep, goats, and
camels. Methane emissions by other domesticated non-ruminants
such as swine and horses are relatively small [60]. Total emissions
are driven by the size of livestock populations and the type of
management practices, especially the feed regime used. Also
affecting methane emissions are the quantity, quality, and type
of feed [51]. The top five countries with respect to global methane
emissions from enteric fermentation are China, Brazil, India, the
U.S., and Russia [51].Table 2 shows the world and regional distri-
bution of domesticated ruminant population.
Aerobic decomposition of organic material during flooding of
the rice field gradually reduces the oxygen present in the soil and
water. This causes the development of anaerobic conditions in the
soil and methane is produced through anaerobic decomposition
18% Enteric fermentaion
Manure managemen
Rice cultivation
Other agric activities
1990 1995 2000 2005 2010
Emissions (MtCO2eq)
Enteric fermentation Rice cultivation
Manure mana
ement Other a
ricultural activities
Fig. 2. (a) Methane emissions from agriculture. (b) Methane emissions trend from
the agricultural sector (1990–2010).
1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000 2100
ppb of CH4
Antartica Greenland Tasmania
Fig. 1. (a) Methane concentration in the atmosphere. (b) Anthropogenic methane emissions by source in 2010. (c) Anthropogenic methane emission by sectors in 2010.
(d) Methane emission trends by sectors from 1990–2010.
R.O. Yusuf et al. / Renewable and Sustainable Energy Reviews 16 (2012) 5059–5070 5061
of soil organic matter by methanogenic bacteria [62,63]. The
amount of methane produced depends on water management
practices and the quantity of organic material available for
decomposition [64]. China and South and East Asian regions are
the largest sources of methane emissions from rice cultivation.
The single largest contributors in these regions are China, India,
Thailand, Indonesia, Vietnam, and Myanmar, which together emit
78% of all emissions from rice cultivation [51]. It is anticipated
that yield growth, as opposed to acreage growth, will continue to
be the main source of the production growth, with the continued
development and adoption of higher-yielding rice varieties in
many producing countries [65]. Thailand, Vietnam, and India are
projected to dominate global rice exports through the 2005 to
2015 projection period, with an estimated 60% or greater share of
the global export market [51]. China is expected to continue to be
a significant contributor, but at a lower rate of growth due to
decreases in production area [65].
Anaerobic decomposition of manure leads to the production of
methane [51]. Three primary factors affect the quantity of
methane emitted from manure management operations. These
are the type of treatment or storage facility, the ambient climate,
and the composition of the manure [43,66]. Storage and treat-
ment of manure in liquid systems such as lagoons, ponds or pits
leads to the development of anaerobic conditions which result in
methane emissions. Higher ambient temperature and moisture
content favour methane production. The composition of manure
is directly related to animal types and diets [67]. For example,
milk production in dairy cattle is associated with higher feed
intake, and therefore higher manure excretion rates than non-
dairy cattle. Also, supplemental feeds with higher energy content
generally result in a higher potential for methane generation per
unit of waste excreted than lower quality pasture diets. In some
instances, some higher energy feeds are more digestible than
lower quality forages, which can result in less overall waste
excreted. Consequently, a combination of all these factors will
affect the actual emissions from manure management systems
[51]. Methane emissions from manure management are largely
from the OECD (Fig. 2d). The top emitting countries are the U.S.,
Germany, India, China, France, Russia, Turkey, and Brazil [51].
Methane is produced from the open burning of biomass during
agricultural activities and from land use change [68,69]. The
sources included in this section are savannah burning, agricul-
tural residue burning, and open burning from forest clearing.
This category also includes minor amounts of country reported
emissions data on methane from agricultural soils [70]. However,
biomass burning constitutes the majority of emissions for this
source category. Latin America, Africa, and South and East Asia are
the largest emitters in this source category. These three regions
account for 85% of the methane emissions [51].
2.2. Mitigation measures for the agricultural sector
The mitigation of methane emissions from the agricultural
sector is briefly described.
2.2.1. Dietary supplementation
The use of long-chain fatty acids in the diet of the ruminants in
the form of processed oilseeds (like canola seed) will reduce
methane emissions without affecting diet digestibility [57,7173].
The use of lipids with ionosphores (such as monensin) in the diet
will also cause a reduction in methane emissions [74]. Monensin
causes a change in the bacterial species in the rumen resulting in
an increased proportion of propionate or could cause a decrease in
the numbers of rumen protozoa in the rumen [73]. Linseed fatty
acids reduce methane emission but have a negative effect on milk
production [75]. Sunflower oil in the diet will reduce methane
emission [76]. Incorporating fat in the diet as an energy source
lowers the carbohydrate content, which is the substrate for CH
formation while the numbers of protozoa in the rumen are also
lowered by the fats with many of them physically associated with
the methanogens [73]. A reduction in methane emission was
noticed when low protein diet was supplemented with amino
acids [77].
Effects of short term oral nitroethane administration on
methane emissions have been investigated and found to reduce
emissions and is an effective anti-methanogenic compound in
ruminants fed high forage diets [41]. Combining feed additives
like fermented mixed rations of whole–crop rice and rice bran
[78] and a mixture of lauric acid, myristic acid, linseed oil and
calcium fumarate [79] were found to lower methane emissions.
On the other hand a combination of diallyl disulphide, yucca
powder, calcium fumarate and linseed oil and another combina-
tion of capric acid and caprylic acid were found to have no
marked effect on methane emission reduction [80].
2.2.2. Selection of high quality grasses
High quality grasses with high concentration of water-soluble
carbohydrates, forage legumes containing secondary metabolites
(tannings) and fruits/plants containing saponins have been found
to reduce methane emissions [57,8184].
2.2.3. Increase grain level
Feeding grains and whole plant silages to the animals will
reduce methane emission [85,86]. Increasing the level of grain in
the diet reduces methane emission because the percentage of the
energy consumed that is converted to methane in the rumen is
typically reduced to about 3%, from the 6.5% or more that is
common for animals fed primarily forages [76]. However, the
grain must comprise more than 90% of the diet for any reduction
in methane emission to occur [87].
2.2.4. Increasing feed conversion efficiency
Enteric methane emissions could be reduced by improving the
efficiency of converting feed to meat and milk [88]. Less enteric
methane is generated when the amount of feed it takes to
produce animal products is reduced because methane emissions
are related to feed intake. This increased efficiency of production
can be achieved through animal breeding and improved nutrition
2.2.5. Increasing animal productivity
Increasing the productivity of individual animals so that fewer
animals are required to produce the same amount of product will
cause a reduction in methane emission. While the total amount of
methane produced per kilogram of milk or meat declines, methane
emissions per animal increase [88]. Overall, however, a reduction in
methane occurs because animal numbers decrease [89].Improved
feeding and animal genetics in the beef industry can reduce the time
cattle are on feed and this will impact on lifetime methane
emissions. Furthermore, improving reproductive performance of
Table 2
World and regional distribution of domesticated ruminants (10
World Africa North
Asia Europe Oceania
Cattle 1347 270 111 315 431 127 38
Buffalo 181 5 – 1 174 0.33 0.0002
Sheep 1078 288 7 73 452 134 113
Goat 862 291 3 21 516 18 1
R.O. Yusuf et al. / Renewable and Sustainable Energy Reviews 16 (2012) 5059 –50705062
cattle can reduce total methane emissions from the herd by
reducing the number of replacement heifers required [57,87,90].
2.2.6. Future options
Genetic selection of animals, vaccination, probiotics, prebiotics
and plant improvement have also been suggested as the most
promising future options for methane emissions mitigation [91].
A variety of emission reduction options that can be applied at
reasonable costs includes [92] (a) carbon sequestration on exten-
sively used grazing land, (b) reduction of methane emissions from
low-input ruminant production and (c) reduction of methane
emissions from animal waste through the recovery of energy and
waste management improvement.
2.2.7. Methane emissions mitigation from manure management
Methane emissions mitigation from manure management
dwells much more on slurry systems. There is a direct correlation
between methane emission and manure piling height. Lower
stacking or piling of the manure leads to lower methane emission
[43,93]. Dilution of animal manure before treatment reduces
methane emission (Su et al., 2003. Daily flushing and cooling of
the slurry will cause a substantial reduction in methane emission
[94]. Anaerobic digestion of the manure before outside treatment
will cause a reduction in methane emission [67,95]. A reduction
in methane emission from the manure of animals fed with low-
protein diet that is supplemented with synthetic amino acids has
been observed [77]. When compared to broadcasting, application
of manure by trail hose and injection reduces methane emission
by 0.7 and 3.2% respectively [96].
2.2.8. Biogas production
Studies have shown that production of biogas from manure, a
renewable form of energy, will reduce methane emissions
[3,97103]. This biogas could be channelled to industries and
improve overall eco-efficiency through the creation of industrial
symbiosis [104109]. With an annual biomass production of 220
billion tonnes [110] and studies carried out on household biogas
use [111], the importance of this form of energy with respect to
strategic and policy shift from fossil fuels cannot be overempha-
sised [112].
2.3. Mitigation for rice cultivation
Methane emission mitigation from rice production can be
achieved by the appropriate selection of rice cultivar, water
regime and fertilizers and has been shown that rice breeds with
heavier total weight emit less methane [113,114]. The incorpora-
tion of rice straw compost before transplanting and fresh rice
straw three months before transplanting, coupled with intermit-
tent irrigation, brought methane emissions down by 49% and 23%
respectively [115]. Drainage of the field during the flowering
period and the application of potassium lowered the emission of
methane [116,117].
3. Energy
The energy sector is second to agriculture in contribution to
global emissions of methane. Methane emissions trend from this
sector between 1990 and 2010 is shown in Fig. 3a. Emissions from
the oil and gas sector have been on the increase and this trend
will continue in view of the expanding economies of the ‘BRIC’
countries (Brazil, Russia, India, and China). The largest source of
methane emissions in the energy sector are fugitive emissions
from natural gas and oil systems [51]. They constitute approxi-
mately 17% of total man-made sources of global methane emis-
sions and in 2005 totalled approximately 82 billion m
(1165 MtCO
eq) [118]. About 28 Bcm (420 MtCO
eq) of methane
are released to the atmosphere annually from coal mining
activities around the world [119]. Approximately 88% of all
Fig. 3. (a) Methane emissions trends from the energy sector. (b) Global methane emissions from oil and natural gas operations. (c) Top five methane emitting countries
from oil and gas.
R.O. Yusuf et al. / Renewable and Sustainable Energy Reviews 16 (2012) 5059–5070 5063
methane emissions from coal mining originate from only ten
countries with the top five, in order of emissions, being China,
United States, India, Ukraine and Australia [37]. China is the
biggest coal producer in the world with an annual coal output of
2.79 billion tonnes in 2008 [120]. Chinese coal mines emitted up
to 18 billion m
(270 MtCO
eq) of methane into the atmosphere
in 2007 [121]. Decrease in methane emissions from coal mining is
envisaged because of a change in sources of energy from coal to
natural gas in several areas in Eastern Europe and the Former
Soviet Union (FSU) [51].
3.1. Source description
3.1.1. Oil and gas
Methane makes up about 95% of natural gas and is emitted
from natural gas production, processing, transmission and dis-
tribution. Significant quantities of methane are also emitted from
oil production and processing as natural gas is often found in
conjunction with petroleum deposits. Methane is a fugitive
emission in both oil and natural gas systems, from leaking
equipment, system upsets, and deliberate flaring and venting at
production fields, processing facilities, transmission lines, storage
facilities, and gas distribution lines. Global oil and gas methane
emissions increased by 3.6% in 2000 from the 1990 level and by
36% by 2010 (Fig. 3a). The three key factors that have affected the
overall trend in global emissions from 1990 to 2010 are the non-
EU FSU economic transition, the mild growth in production in
parts of the OECD, and the accelerated growth in energy produc-
tion and demand in all other regions, especially Asia [51].
Fig. 3b shows global oil and gas methane emissions from oil
and gas processing for the top twenty emitting countries [118]
with the leading emitters of being Russia, US, Ukraine, Mexico and
Iran (Fig. 3c). In 1990, the non-EU FSU and OECD countries
accounted for 75% of the global methane emissions. The percen-
tage of Russia’s contribution to the global emissions will fall from
33% in 1990 to 22% by 2020 [51]. The OECD countries experienced
only mild growth of 40% compared to the developing regions
because many of these countries have mature natural gas and
oil industries, hence oil and gas activities have stagnated.
This is in addition to the institution of air quality and safety rules
by many OECD countries that have the additional benefit of
reducing methane emissions. However, it is likely there will be
a continued and growing demand for natural gas in the OECD,
which may result in increased emissions in the distribution and
transmission sectors.
The Middle East, Latin American, and South and East Asian
regions are expected to increase global methane emissions from
22% in 1990 to 33% in 2010 [51]. Electricity production and
demand are expected to increase rapidly in the less developed
countries of these regions because of populations becoming more
urbanized and concentrated with industrial expansion. The
resulting increase in energy demands are will drive the rapid
growth in fuel production and consumption. Some of the largest
oil producing and exporting countries are located in the Middle
East and emissions are expected to increase there as a result of
increasing world demand for oil.
3.1.2. Coal mining activities
Methane is produced from coal during the process of coalifica-
tion, where vegetation is converted by geological and biological
forces into coal [122,123]. It is then stored within the coal seams
and the surrounding rock strata and is liberated when the
pressure above or surrounding the coal bed is reduced as a result
of natural erosions, faulting, or mining [27,36]. The quantity of gas
emitted from mining operations is a function of two primary
factors: coal rank and coal depth [51]. Four main sources are
responsible for methane emissions from the coal mining. These
are underground mines which account for the majority of global
methane emissions from coal mining, surface mines which gen-
erally emit considerably less methane than underground mines
because coal ranks are typically lower and there is less pressure to
trap methane in the coal, post-mining operations which refer to
the processing, storage, and transportation of the mined coal and
abandoned mines where methane emissions from coal mines
continue after operations have ceased [50].
There was significant decline in global coal mine methane
emissions 1990 to 2000, but increased steadily after 2000
(Fig. 3a). The changes in coal production in China, restructuring
of the energy industries in Europe and the non-EU FSU, and
industry changes in the U.S are the factors that will affect the
expected trend. China’s emissions are expected to increase 50% by
2020 due to increased coal production to meet expanding energy
needs [120]. Reduced coal production in England and Germany in
the 1990s contributed substantially to the reduction in OECD
emissions from 1990 to 2000. In Russia and Eastern European coal
producing countries, restructuring of the energy industries caused
many of the gassiest underground mines to close during the
1990s resulting in a decrease in emissions that has been sustained
in the projection years. In the US, decreased emissions from coal
mining activities are expected through 2020 because of shift in
production from underground to surface coal mines. Reductions
due to methane recovery and use of coal bed methane will cause a
reduction in methane emissions.
3.1.3. Stationary and mobile sources
Methane is emitted from stationary and mobile combustion as
a result of incomplete combustion. However, combustion is a
relatively minor contributor to overall methane emission.
Methane emissions increased from 199 MtCO
eq in 1990 to 218
and 235 MtCO
eq in 2000 and 2010 respectively (Fig. 3a) [51].
3.1.4. Biomass burning
Incomplete biomass combustion leads to the production of
methane. The major contributors to methane emissions within
this category are municipal waste combustion, charcoal, fuel
wood, agricultural residues, and agricultural waste. In the devel-
oping world biomass combustion often refers to the combustion
of biofuels in small-scale combustion devices for heating, cooking,
and lighting purposes. Estimates for this category are highly
uncertain and difficult to predict because of the wide variety in
the types and conditions under which these fuels are burned.
Methane emissions increased from 184 MtCO
e in 1990 to 206
and 226 MtCO
e in 2000 and 2010, respectively (Fig. 3a) [51].
3.2. Mitigation options for the energy sector
Methane is emitted in the oil and gas sector during normal
operations, system disruptions and routine maintenance. These
emissions can be cost-effectively reduced through the upgrade of
technologies or equipment and by operational improvement.
Some mitigation and abatement options for each unit are briefly
discussed. Mitigation options for coal methane are grouped
into four.
3.2.1. Oil
The mitigation and abatement options applicable to the oil sector
are vapour recovery units, flaring, direct use, and reinjection of gas
into oil fields for enhanced oil recovery [51,60,124,125].
R.O. Yusuf et al. / Renewable and Sustainable Energy Reviews 16 (2012) 5059 –50705064 Install vapour recovery units. Light hydrocarbons vaporise
out of solution during the storage of crude oil. These hydrocarbons
are then vented into the atmosphere. The vapour recovery unit will
capture these vapours for use as fuels or for sale. Flaring in place of venting for both offshore and onshore
gas wells. When flaring system is installed, an estimated 98%
reduction in fugitive emissions occurs through the burning of
vented gas where methane is converted to carbon dioxide. It is
more expensive to install a flare in an offshore environment due
to technical, environmental, and safety concerns. Direct use of methane. Another abatement option applies
primarily to offshore platforms with an estimated reduction
efficiency of 90%. This abatement option allows methane to be
used for consumption on oil platforms and/or converted to
liquefied natural gas. Reinjection of methane. An alternative to flaring or direct
use is reinjection of methane where the captured gas from
oil field operations is re-injected into the oil production field so
as to enhance future oil recovery. This method is estimated to
have a reduction efficiency of 95% with a technical lifetime of
15 years. Plunger lift system. A plunger lift can be used to effectively
push the fluids out of the well instead of ‘venting’ gas wells to the
3.2.2. Natural gas
The mitigation and abatement options for each segment of the
natural gas system are in the production, processing, transmission
and distribution stages [51,124,125]. Production abatement options. The production segment of
the natural gas sector consists of wells, compressors, dehydrators,
pneumatic devices, chemical injection pumps, heaters, meters,
pipeline, and central gathering facilities. Available abatement
technologies associated with this segment include
a. use catalytic converters in selected well field engines and
b. replace wet seals with dry seals in centrifugal compressors,
c. direct/enhanced inspection and maintenance at production
d. installation of flash tank separator in glycol dehydration
e. replace high-bleed pneumatic devices with low bleed devices
or with instrument air (compressed, dry air) systems, and
f. optimise glycol recirculation rates. Processing abatement options. The processing segment
consists of gas plant facilities that encompasses the use of
vessels, dehydrators, compressors, acid gas removal (AGR) units,
heaters, and pneumatic devices. The technologies for abatement
associated with the segment are
a. retrofit fuel gas for reciprocating compressors and blowdown
b. replace wet seals with dry seals in centrifugal compressors,
c. convert gas pneumatic controls to instrument air (compressed,
dry air), and
d. Direct inspection and maintenance (DI&M) at gas processing
plants. Transmission abatement options. The transmission segment
of a natural gas system comprises the transmission pipeline
networks, compressor stations, and meter and pressure-regulating
stations. The available abatement technologies include:
a. convert gas pneumatic controls to instrument air (compressed,
dry air),
b. use pipeline pumpdown techniques to lower gas line pressure
before maintenance,
c. DI&M at compressor stations and surface facilities for leak
d. replace wet seals with dry seals in centrifugal compressors,
e. replace compressor rod packing systems. Distribution abatement options. The distribution segment
is made up of the main and service pipeline networks, meter and
pressure regulating stations, pneumatic devices, and customer
meters. The abatement technologies in this segment include
a. use hot taps in service pipeline connections,
b. DI&M at gate stations,
c. use composite wrap for non-leaking pipeline defects, and
d. use a pipeline pumpdown technique to lower gas line pressure
before maintenance.
3.2.3. Coal
When fugitive methane gas from underground coal mines is
removed and used in profitable and practical ways, worker safety
will be improved, mine productivity will be enhanced, revenues
will increase, and greenhouse gas emissions will be reduced [50].
Four abatement options are currently available in the coal mining
sector. These are degasification and pipeline injection, enhanced
degasification, oxidation of ventilation air methane and flow
reversal. Degasification and pipeline injection. High-quality methane
is recovered from coal seams when one of the following
degasification methods is employed [50,119]: (1) vertical wells
(drilled from the surface into the coal seam months or years in
advance of mining), (2) gob wells (drilled from the surface into
the coal seam just prior to mining), and (3) in-mine boreholes
(drilled from inside the mine into the coal seam or the
surrounding strata prior to mining). The quality (purity) of the
gas that is recovered depends partially on the degasification
method employed, and determines how the gas can be used. For
example, only high quality gas (typically greater than 95%
methane) can be used for injection into natural gas pipelines.
Vertical wells and horizontal boreholes into the coal seam tend to
recover nearly pure methane (greater than 95% methane). High
quality methane can be recovered from very gassy mines, when
gob wells are drilled into the gob zone of mined-out coal seams,
especially during the first few months of production. This method
will cause a 28% emission reduction. Enhanced degasification. In enhanced degasification,
methane is recovered in the same way as in degasification,
using vertical wells, horizontal boreholes, and gob wells.
Furthermore, enrichment technologies such as nitrogen removal
units (NRUs) and dehydrators are used primarily to enhance
medium-quality gob well gas by removing impurities, thereby
allowing larger quantities of methane to be captured and used.
It is assumed in this option that well spacing will be tighter for
recovery to increase. This process improves recovery efficiency
R.O. Yusuf et al. / Renewable and Sustainable Energy Reviews 16 (2012) 5059–5070 5065
20% more than the degasification option [126]and causes a 10%
emission reduction. Oxidation of ventilation air methane (VAM). Methane
emitted from coal mine ventilation air can potentially be
utilised by oxidation technologies (both thermal and catalytic).
Extremely low methane concentration levels (typically below 1%)
render the sale of this gas to a pipeline not economically feasible.
However, CO
and heat could be generated from an oxidised
VAM which in turn may be used directly to heat water or to
generate electricity. Application of oxidiser technology to all mine
ventilation air with concentrations greater than 0.15% methane
will result in the mitigation of about 97% of the methane from the
ventilation air. This method will cause a 24% emission reduction.
Medium-to-low quality methane, with concentrations ranging
from 35 to 85% can also be used as an energy source in various
applications. Potential applications that have been demonstrated
in the U.S. and other countries for lower quality coal mine
methane (CMM) include [50].
a. Electricity generation with reciprocating engines, gas turbines
or steam turbines (the electricity can be used either on-site or
can be sold to utilities);
b. As a boiler or dryer fuel in on-site preparation plants or mine
vehicle fuel,
c. As a medium-BTU fuel for nearby industrial or institutional
facilities; and
d. Cutting-edge applications, such as in fuel cells and chemical
processes. Flow reversal. This involves the regenerative heat exchange
between a gas and a solid bed of heat exchange medium and
can utilise up to 100% of the methane from ventilation shafts. The
methane goes into and through the reactor in one direction while
temperature is increased until the oxidation of methane is
achieved. The hot products of oxidation then give up heat in
their movement towards the far side of the bed, and
the flow is reversed automatically. The application of heat
exchange technologies allows excess heat to be transferred for
local heating use, or for power production in gas or steam turbines.
It has been proved that the process is capable of sustaining
operation with ventilation air at low methane concentrations of
0.1% [126,127].
4. Waste
The waste sector is the third largest contributor to global
emissions of non-CO
GHGs with the two largest sources being
landfilling of solid waste and wastewater treatment. While the
sector as a whole accounts for only 15% of all non-CO
emissions, landfilling is the fourth largest individual source of
emissions (761 MtCO
eq), after agricultural soils (2,001 MtCO
enteric fermentation (1,772 MtCO
eq), and natural gas and oil
systems (993 MtCO
eq) [51]. Methane emissions from landfills
dropped from 761 MtCO
eq in 1990 to 730 MtCO
eq (4.1%) in
2000 and rose to 761 MtCO
eq in 2010 (Fig. 4a). It is projected to
reach 788 and 817 MtCO
eq by 2015 and 2020 respectively [51].
Emissions from wastewater, on the other hand, rose from 446
eq in 1990 to 523 MtCO
eq in 2000 (17.3%) and 594
eq in 2010, an increase of 33.2% (Fig. 4a). Methane emissions
from waste water are projected to be 630 and 665 MtCO
eq by
2015 and 2020 respectively [51].
4.1. Source description
4.1.1. Solid waste landfill
Methane is produced and emitted from the anaerobic decom-
position of organic material in landfills [128130]. The major
drivers of emissions are the amount of organic material deposited
in landfills, the extent of anaerobic decomposition, and the level
of landfill methane collection and combustion (e.g., energy use or
The OECD countries emitted nearly 49% of the global methane
from the landfilling of solid wastes in 1990. Other regions con-
tributed less than 15% of the methane emissions each for this source
category. The 170 MtCO
eq of methane emissions from U.S. were
46% and 23% of the OECD and global total, respectively [53].
Significant shifts in landfills contributions to methane emissions
are projected because countries with more steady-state economic
growth, and small or declining population growth rates, are
expected to experience minimalgrowthinlandllemissions[132].
The observed decline in emissions from 1990 to 1995 in the
OECD are attributed to the collection, flaring and use of landfill
methane as well as the non-climate regulatory programs that result
in mitigation of air emissions, collection of gas, or closure of facilities
[51]. In other regions where diversion of solid waste to managed
landfills as a means of improving overall waste management is
expected, an increase in methane emissions is envisaged. This will
be in addition to the combined effects of rapid economic change,
expansive growth policies, and population increase, particularly in
the urban centres of developing countries, changing consumption
patterns and increases in waste generation [132]. Areas with
projected high growth in emissions are Africa at 77% growth, S&E
Asia at 34% and Latin America at 52% growth [51].
4.1.2. Wastewater
Methane is emitted during the handling and treatment of
municipal and industrial wastewater [133]. Methane emissions
from wastewater increased by 17.3% and 33.2% in 2000 and 2010
respectively from the 1990 level of 446 MtCO
eq (Fig. 4a) [51].
The organic material in the wastewater produces methane when
it decomposes anaerobically. Most developed countries with
centralised aerobic wastewater treatment to handle their muni-
cipal wastewater, have low methane emissions are small and
incidental. However, in the developing countries, anaerobic sys-
tems such as latrines, open sewers, or lagoons with little or no
collection and treatment of wastewater are more prevalent.
Industrial wastewater can also be treated anaerobically, with
significant methane being emitted from those industries with
high organic loadings in their wastewater stream, such as food
processing and pulp and paper facilities [134].
1990 1995 2000 2005 2010
Methane emissions (MtCO2eq)
Landfilling Wastewater
Fig. 4. (a) Total emissions from the waste sector (1990–2010).
R.O. Yusuf et al. / Renewable and Sustainable Energy Reviews 16 (2012) 5059 –50705066
4.1.3. Source Results
South and East Asia and China accounted for 33% and 24%,
respectively, of global methane emissions from wastewater hand-
ling in 1990 while Africa, OECD, and Latin America accounted for
between 10–12% each [51]. The largest emitters in 1990 were
China (21%), India (18%), U.S. (6%), and Indonesia (4%). Waste-
water methane emissions in Africa and the Middle East is
expected to increase because of population growth, particularly
growth associated with countries that rely on less advanced,
anaerobic treatment and collection systems such as latrines,
septic tanks, open sewers, and lagoons [134]. Most developed
countries have an extensive infrastructure to collect and treat
urban wastewater, in which the majority of systems rely on
aerobic treatment with minimal methane production and thus
less effect on the emissions trend [134].
4.2. Abatement options for landfills and wastewater plants
Mitigation and abatement options that are available for land-
fills and wastewater plants are discussed in the sections.
4.2.1. Emissions reductions from landfills
Vertical wells and horizontal trenches are the methods used as
collection systems in most landfills to prevent migration of gas to
onsite structures or away from the landfill to adjacent property and
to prevent the release of non-methane organic compounds to the
atmosphere. Landfill gas (LFG) can be used to produce electricity
with engines, turbines, or other technologies, and can be refined and
injected into a natural gas pipeline. Using LFG in these ways can
yield substantial energy, economic, environmental, air quality, and
public health benefits [3,97,99,100,102,110,135141]. Collection and flaring. The presence of methane, if allowed
to build up, becomes a public health concern and a safety hazard
at landfills. Hence, methane has been removed from large landfills
and is combusted through flaring. Gas is collected through
vertical wells and a series of horizontal collectors typically
installed following the closing of a landfill cell. Vertical wells
are the most common type of well, while horizontal collectors are
used primarily for deeper landfills and landfill cells that are
actively being filled. Once captured, the gas is then channelled
through a series of gathering lines to a main collection header.
The USEPA recommends that the collection system be designed so
that an operator can monitor and adjust the gas flow. Electricity generation. Landfill gas that is extracted using a
series of vertical or horizontal wells and a blower (or vacuum)
system is collected in a central point, where it can be processed
and treated depending on the ultimate use of the gas. From here,
the gas can be flared, used to generate electricity, or be pumped to
an enduser for process heat. Direct utilisation of gas. Landfill gas can be directly used as
fuel to run leachate evaporators and liquid natural gas production.
In addition, landfill methane gas can be transported and used in
industrial processes, such as boilers, drying operations, kiln
operations, and cement and asphalt production. Gas collected from
the landfill can be piped directly to local industries where it is used
as a replacement or supplementary fuel. Change in waste management practice. Waste management
practices can be changed to reduce waste disposal (waste
minimisation) at landfills by adding composting and recycling-
and-reuse (waste diversion) programs. Incineration is another
possible consideration.
4.2.2. Wastewater methane emission abatement
Abatement options for the wastewater sector include the
incremental addition of methane mitigation equipment not
already included in the initial construction of a municipal waste-
water treatment plant, improve existing treatment practices and
use anaerobic digesters [47,134,142145]. Improved wastewater treatment practices. These treatment
practices for domestic and industrial wastewaters include reduc-
tion of the amount of organic waste anaerobically digested.
Storing and treating sludge under aerobic conditions is one of
the measures. Another option is through improved aeration and/
or the scaling back of the use of stagnant settling lagoons. Where
the treatment is carried out anaerobically, the methane generated
could be captured and used as a source of energy for the heating
of the wastewater and sludge digestion tank. Excess methane
could be used for electricity generation with flaring being the last
resort. Anaerobic digesters. Methane from anaerobic process can
be flared or used for cogeneration to reduce methane emissions
from biomass or liquid effluents with high organic content.
5. Conclusions
The study has reviewed the emission of methane from three
major sectors – agriculture, energy and waste. The dangers posed
by continued global warming have been highlighted through the
surface temperature profile over the years. The cause of this
global warming has been traced to anthropogenic activities
through the increased reliance on fossil fuels and forest degrada-
tion. Methane has been found to contribute about 20% to this
global warming. The review has also shown that the largest
sources of anthropogenic methane emissions are agriculture
(53%), energy (28%) and waste (19%). Population increase and
improved living standards, especially in developing economies,
will continue to push these emission values higher in the future.
The abatement and mitigation options that have been identified
and highlighted will go a long way in reducing these emissions or
rechanneling them to other uses and thus safeguard and protect
the environment.
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... Rising levels of greenhouse gasses (GHGs), aerosols, and changes in land-use land cover (LULC) types and extents have substantially altered atmospheric composition and energy balance. The increasing anthropogenic activities and exploitation of natural resources have increased their concentrations in the atmosphere (Yusuf et al. 2012). GHGs such as carbon dioxide (CO 2 ) have increased by 46% and methane (CH 4 ) by 157% over the period 1750 to 2018 globally (Bellouin et al. 2020). ...
... CH 4 (~ 10 years of atmospheric residence time) emissions have increased enormously to ~ 2.6 times greater than the concentrations in the preindustrial period of 1750 and have significantly affected the Earth's climate system (Sreenivas et al. 2016;Saunois et al. 2020). The increasing concentration of CH 4 (5-15%) in the air can be severely vulnerable to humanity and climate (Yusuf et al. 2012 and references therein). The global warming potential (GWP) of CH 4 is ~ 28 times more than that of CO 2 on a 100-year timescale (Myhre et al. 2014), and its relative radiative efficiencies are higher when compared to CO 2 (Stohl et al. 2015). ...
Full-text available
Methane (CH4), the second-largest greenhouse gas in terms of radiative forcing, is on the rise in the Eastern Himalayan region (EHR), as indicated by multiple datasets (CAMS ~ 0.087 Tg Yr−1, EDGAR v4.3.2 ~ 0.11 Tg Yr−1, and RCP8.5 ~ 0.16 Tg Yr−1). We found that the CH4 trend over the EHR is stronger than the global trend due to increased emissions from anthropogenic sources. From 1990 to 2016, CH4 emissions from anthropogenic activities and wetlands increased by 20% and 10% over the EHR. The land-use land-cover (LULC) change reveals a loss of ~ 0.42% of forest and an increase of 0.018% of urban built-up, 0.098% total wetland, and 0.033% of water-bodies coverage from 2001 to 2018. Future projections show a twofold (32.7 Tg CH4 Yr−1) increase in CH4 emissions by 2050 and up to a threefold (~ 48.2 Tg CH4 Yr−1) by the year 2100 from the base year level (14.6 Tg CH4 Yr−1) in 2000. Ambient concentrations of CH4 measured in Dibrugarh and the CAMS reanalysis data set from March 2014 to February 2015 show the maximum in December (~ 4485 and ~ 1981 ppb, respectively), while the minimum concentrations in July (~ 1155 ppb and ~ 976 ppb). The calculated global/EHR RF due to the CH4 for 2006–2100 is higher (0.0093 Wm−2 Yr−1/0.0095 Wm−2 Yr−1) than the historical (0.0038 Wm−2 Yr−1/0.0037 Wm−2 Yr−1) during 1851–2005. The resultant land surface temperature increase induced solely by CH4 is higher over the EHR (~ 0.0062 °C Yr−1) than the global (~ 0.0036 °C Yr−1).
... Therefore, METP could be an appropriate indirect selection criterion for FI and be applied to enhance the meat production efficiency of sheep (Paganoni et al., 2017). If proper management or breeding is not used to decrease METP, emissions will rise along with increasing the world's request for livestock products (Yusuf et al., 2012). Positive genetic associations between METP with CO 2 , METP + CO 2 , and METP METP + CO 2 emissions indicate that sheep with high methane emissions also emit more significant levels of CO 2 and consume more O 2 . ...
The objective of this study was to use a random-effects model of meta-analysis to merge various heritability estimates of different gas emission traits (methane yield [METY], methane production [METP], carbon dioxide production [CO2], the sum of carbon dioxide and methane production [METP + CO2], ratio, and oxygen consumption [O2]) and their genetic association with growth and partial efficiency traits in sheep. A total of 53 genetic correlations and 47 heritability estimates from 13 scientific articles were used in the meta-analysis. The included papers were published between 2010 and 2022. To measure heterogeneity, Chi-square (Q) test was performed, and the I2 statistic was determined. The average heritability estimates for the studied traits were low to moderate and ranged from 0.137 (for METY) to 0.250 (for METP + CO2). The heterogeneity test of heritability estimates indicated that heritability estimates for METY, O2 consumption, and had low Q values and non-significant heterogeneity (p > 0.10). However, the average heritability estimates for other traits experienced significant heterogeneities (p < 0.10). The genetic correlation estimate between METP with O2 was −0.597 (p < 0.05), but its genetic correlations with other gas traits ranged from 0.593 (with METP + CO2) to 0.653 (CO2; p < 0.05). Also, mean estimates of genetic correlation between METP with live weight (LW), feed intake (FI), and residual feed intake (RFI) were 0.719, 0.598, and 0.408, respectively. The genetic correlations of CO2 with performance traits varied from 0.641 (with RFI) to 0.833 (with FI; p < 0.05). This meta-analysis showed gas emission traits in sheep are under low-to-moderate genetic control. The average genetic parameter estimates obtained in this study could be considered in the genetic selection programmes for sheep, especially when there is no access to accurate phenotypic records or genetic parameter estimates for gas emission traits.
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Food consumption is a major source of greenhouse gas (GHG) emissions, and evaluating its future warming impact is crucial for guiding climate mitigation action. However, the lack of granularity in reporting food item emissions and the widespread use of oversimplified metrics such as CO2 equivalents have complicated interpretation. We resolve these challenges by developing a global food consumption GHG emissions inventory separated by individual gas species and employing a reduced-complexity climate model, evaluating the associated future warming contribution and potential benefits from certain mitigation measures. We find that global food consumption alone could add nearly 1 °C to warming by 2100. Seventy five percent of this warming is driven by foods that are high sources of methane (ruminant meat, dairy and rice). However, over 55% of anticipated warming can be avoided from simultaneous improvements to production practices, the universal adoption of a healthy diet and consumer- and retail-level food waste reductions.
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An increasing percentage of US waste methane (CH4) emissions come from wastewater treatment (10% in 1990 to 14% in 2019), although there are limited measurements across the sector, leading to large uncertainties in current inventories. We conducted the largest study of CH4 emissions from US wastewater treatment, measuring 63 plants with average daily flows ranging from 4.2 × 10-4 to 8.5 m3 s-1 (<0.1 to 193 MGD), totaling 2% of the 62.5 billion gallons treated, nationally. We employed Bayesian inference to quantify facility-integrated emission rates with a mobile laboratory approach (1165 cross-plume transects). The median plant-averaged emission rate was 1.1 g CH4 s-1 (0.1-21.6 g CH4 s-1; 10th/90th percentiles; mean 7.9 g CH4 s-1), and the median emission factor was 3.4 × 10-2 g CH4 (g influent 5 day biochemical oxygen demand; BOD5)-1 [0.6-9.9 × 10-2 g CH4 (g BOD5)-1; 10th/90th percentiles; mean 5.7 × 10-2 g CH4 (g BOD5)-1]. Using a Monte Carlo-based scaling of measured emission factors, emissions from US centrally treated domestic wastewater are 1.9 (95% CI: 1.5-2.4) times greater than the current US EPA inventory (bias of 5.4 MMT CO2-eq). With increasing urbanization and centralized treatment, efforts to identify and mitigate CH4 emissions are needed.
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Methane (CH4) emissions from streams are an important component of the global carbon budget of freshwater ecosystems, but these emissions are highly variable and uncertain at the temporal and spatial scales associated with watershed urbanization. In this study, we conducted investigations of dissolved CH4 concentrations and fluxes and related environmental parameters at high spatiotemporal resolution in three montanic streams that drain different landscapes in Southwest China. We found that the average CH4 concentrations and fluxes in the highly urbanized stream (2049 ± 2164 nmol L-1 and 11.95 ± 11.75 mmol·m-2·d-1) were much higher than those in the suburban stream (1021 ± 1183 nmol L-1 and 3.29 ± 3.66 mmol·m-2·d-1) and were approximately 12.3 and 27.8 times those in the rural stream, respectively. It provides powerful evidence that watershed urbanization strongly enhances riverine CH4 emission potential. Temporal patterns of CH4 concentrations and fluxes and their controls were not consistent among the three streams. Seasonal CH4 concentrations in the urbanized streams had negative exponential relationships with monthly precipitation and demonstrated greater sensitivity to rainfall dilution than to the temperature priming effect. Additionally, the CH4 concentrations in the urban and semiurban streams showed strong, but opposite, longitudinal patterns, which were closely related to urban distribution patterns and the HAILS (human activity intensity of the land surface) within the watersheds. High carbon and nitrogen loads from sewage discharge in urban areas and the spatial arrangement of the sewage drainage contributed to the different spatial patterns of the CH4 emissions in different urbanized streams. Moreover, CH4 concentrations in the rural stream were mainly controlled by pH and inorganic nitrogen (NH4+ and NO3-), while urban and semiurban streams were dominated by total organic carbon and nitrogen. We highlighted that rapid urban expansion in montanic small catchments will substantially enhance riverine CH4 concentrations and fluxes and dominate their spatiotemporal pattern and regulatory mechanisms. Future work should consider the spatiotemporal patterns of such urban-disturbed riverine CH4 emissions and focus on the relationship between urban activities with aquatic carbon emissions.
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The demand for agricultural goods is currently higher than it has ever been before due to the expansion of the world population. This has resulted in the conversion of grassland into agricultural areas, the development ofhigh-energy-intensive agriculture production systems, and the use of additional chemical and organic inputs inagricultural production systems. The output of greenhouse gases (GHGs) has also increased in the same way.Carbon dioxide (CO2), Nitrous Oxide (N2O), and Methane (CH4) is the most significant greenhouse gases (GHGS)that are producing a variety of disastrous consequences due to climate change. Despite the fact that CH4 and N2Oare released in smaller amounts than CO2, they have a larger Global Warming Potential than CO2. This analysisbegins with an examination of the variables that contribute to greenhouse gas emissions, which covers bothinorganic factors (such as nitrogen, phosphorus, and potassium fertilizers) and organic factors (Animal manure,composted manure, bio-solids, crop species). This study underlines the need for more research into the intricateinteractions of physical, chemical, and biological elements in the near future. Field crops other than cereals, suchas legumes, oilseeds, vegetables, and fruits, account for a significant amount of greenhouse gas (GHG) emissions.Precision agriculture may be a viable option for increasing agricultural efficiency. Optimal management prac-tices should be implemented in farm and field settings through methodical, site-specific approaches.
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Livestock manure is a major source of the greenhouse gases (GHGs) methane (CH4) and nitrous oxide (N2O). The emissions can be mitigated by production of biogas through anaerobic digestion (AD) of manure, mostly together with other biowastes, which can substitute fossil energy and thereby reduce CO2 emissions and postdigestion GHG emissions. This paper presents GHG balances for manure and biowaste management as affected by AD for five Danish biogas scenarios in which pig and cattle slurry were codigested with one or more of the following biomasses: deep litter, straw, energy crops, slaughterhouse waste, grass–clover green manure, and household waste. The calculated effects of AD on the GHG balance of each scenario included fossil fuel substitution, energy use for transport, leakage of CH4 from biogas production plants, CH4 emissions during storage of animal manure and biowaste, N2O emissions from stored and field applied biomass, N2O emissions related to nitrate (NO3−) leaching and ammonia (NH3) losses, N2O emissions from cultivation of energy crops, and soil C sequestration. All scenarios caused significant reductions in GHG emissions. Most of the reductions resulted from fossil fuel substitution and reduced emissions of CH4 during storage of codigestates. The total reductions in GHG emissions ranged from 65 to 105 kg CO2-eq ton−1 biomass. This wide range showed the importance of biomass composition. Reductions were highest when straw and grass–clover were used as codigestates, whereas reductions per unit energy produced were highest when deep litter or deep litter plus energy crops were used. Potential effects of iLUC were ignored but may have a negative impact on the GHG balance when using energy crops, and this may potentially exceed the calculated positive climate impacts of biogas production. The ammonia emission potential of digestate applied in the field is higher than that from cattle slurry and pig slurry because of the higher pH of the digestate. This effect, and the higher content of TAN in digestate, resulted in increasing ammonia emissions at 0.14 to 0.3 kg NH3-N ton−1 biomass. Nitrate leaching was reduced in all scenarios and ranged from 0.04 to 0.45 kg NO3-N ton−1 biomass. In the scenario in which maize silage was introduced, the maize production increased leaching and almost negated the effect of AD. Methane leakage caused a 7% reduction in the positive climate impact for each percentage point of leakage in a manure-based biogas scenario.
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A study was conducted to investigate the impact of an anti-methanogenic product supplementation on enteric methane emissions, whole rumen metagenome and ruminal fermentation in sheep. Twelve adult male sheep were randomly divided into two groups of six animals each. Animals were fed ad libitum on a total mixed ration either without (CON) or with an anti-methanogenic supplement (Harit Dhara-HD). The anti-methanogenic supplement contained 22.1% tannic acid in a 3: 1 ratio of condensed and hydrolysable tannins. The supplementation of product revealed a significant reduction in daily enteric methane emission (21.9 vs. 17.2 g/d) and methane yield (23.2 vs. 18.2) without affecting the nutrient intake and digestibility. However, the propionate concentration in the HD treatment group was significantly higher than in the CON group. On the contrary, the ammonia nitrogen concentration was lower. The anti-methanogenic supplement significantly decreased the ruminal protozoa in the HD treatment group. Whole rumen metagenome analysis revealed that the core bacterial (Bacteroidetes and Firmicutes) and archaeal communities (Methanobrevibacter and Methanosarcina) were comparable between the CON and HD treatment groups. However, the supplementation of anti-methanogenic product led to a considerable reduction in the abundance of Proteobacteria, whereas the abundance of Lentisphaerae was greater. The supplementation significantly decreased the abundance of Methanocaldococcus, Methanococcoides, Methanocella, and Methanoregula methanogens. A total of 36 KO related to methanogenesis were identified in this study. The activities of formate dehydrogenase (EC and tetrahydromethanopterin S-methyltransferase (EC were significantly lowered by the anti-methanogenic product supplementation in sheep. In conclusion, the anti-methanogenic supplement has the potential to decrease enteric methane emission (~22%) at the recommended level (5% of DM) of supplementation. The contribution of minor methanogens vulnerable to supplementation to rumen methanogenesis is not known; hence, the culturing of these archaea should be taken on priority for determining the impact on overall rumen methanogenesis.
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Recently it was discovered that over the Middle East during summer ozone mixing ratios can reach a pronounced maximum in the middle troposphere. Here we extend the analysis to the surface and show that especially in the Persian Gulf region conditions are highly favorable for ozone air pollution. Model results indicate that the region is a hot spot of photo-smog where air quality standards are violated throughout the year. Long-distance transports of air pollution from Europe, the Middle East, natural emissions and stratospheric ozone conspire to bring about high background ozone mixing ratios. This provides a hotbed to indigenous air pollution in the dry local weather conditions, which are likely to get worse in future.
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Methane, a potent greenhouse gas, is liberated from underground coal mines in large quantities. Emissions emanating from ventilation shafts represent the single largest source of coal mining emissions. U.S. Environmental Protection Agency (EPA) estimates 2000 global ventilation air methane emissions exceeded 16 billion cubic meters (570 Bcf), which is the equivalent of over 230 million tonnes of carbon dioxide equivalent. Of this total, Chinese mines emit 6.5 billion cubic meters (230 Bcf). The methane emitted from ventilation shafts is necessarily dilute, typically less than one percent. As such, conventional methane use options are technically unfeasible. Recent analyses by EPA and others have identified and validated the technical feasibility of a number of options to oxidize ventilation air methane. Prominent among these technologies is flow reversal reaction, where high temperatures in a reactor permit auto-ignition of dilute methane streams. This paper shall analyze flow reversal reaction=s applicability to cost-effectively reduce ventilation air methane emissions, discuss experiences to date, and further consider an array of technologies that EPA has identified that may optimize ventilation air methane control. The paper shall consider the specific comparative advantages of the technologies analyzed. It shall conclude by discussing the potential for developing this resource in China and provide recommendations on the steps necessary to realize this market. (PDF) Coal mine-ventilation air methane mitigation: Technologies to harnass an energy and environmental resource. Available from: [accessed Jul 02 2019].
Provide sustainable solutions to solid waste issues with help from this hands-on guide. Solid Waste Analysis and Minimization: A Systems Approach offers up-to-date technical details on current and potential solid waste minimization practices. This authoritative resource presents a framework for the proper application of solid waste analysis tools, and demonstrates the benefits in terms of environmental impact, process efficiencies, and financial enhancement. Twenty-one real-world case studies covering all industries, from manufacturing to service facilities, are included. Solid Waste Analysis and Minimization: A Systems Approach covers: U.S. and international waste generation rates Industrial ecology, solid waste exchanges, and recycling Environmental, economic, corporate image, personal, and social benefits of solid waste management and minimization Solid waste assessment strategies and launch plans The Six Sigma systems approach for deployment Metrics and performance measurement for solid waste management Documentation and development of the deployment plan Implementation and execution of the solid waste minimization plan Communicating and leveraging success Solid waste modeling, research, and data collection Characterization by business activities Estimation, prediction, and evaluation
Biomass is the first-ever fuel used by humankind and is also the fuel which was the mainstay of the global fuel economy till the middle of the 18th century. Then fossil fuels took over because fossil fuels were not only more abundant and denser in their energy content, but also generated less pollution when burnt, in comparison to biomass. In recent years there is a resurgence of interest in biomass energy because biomass is perceived as a carbon-neutral source of energy unlike net carbon-emitting fossil fuels of which copious use has led to global warming and ocean acidification.The paper takes stock of the various sources of biomass and the possible ways in which it can be utilized for generating energy. It then examines the environmental impacts, including impact vis a vis greenhouse gas emissions, of different biomass energy generation–utilization options.
Livestock producers face a number of challenges including pressure from the public to be good environmental stewards and adopt welfare-friendly practices. However, environmental stewardship and animal welfare may have excitingly conflicting objectives. Examples include pasture-based dairy and beef cattle production where high-fiber diets increase methane emissions compared with grain feeding practices in confinement. Livestock account for 35-40% of global anthropogenic emissions of methane, via enteric fermentation and manure, which together account for about 80% of the agricultural emissions. Recent estimates indicate that the methane emissions from African cattle, goats, and sheep are likely to increase from their current level of about 7.8 million tons of methane per year in 2000 to 11.1 million tons per year by 2003, largely driven by increase in livestock numbers. This paper therefore reviews certain areas of CH4 emissions from ruminants, highlights on how some novel feed additives can decrease CH4 emissions from ruminants; and how some plants secondary metabolites might act as a selective inhibitor of methanogens. An enteric methane emission (which is one of the greenhouse gases) represents an economic loss to the farmer where feed is converted to CH4 rather than to product output. As developing countries are now responsible for almost three-quarters of such emissions, this has important implications in terms of mitigation strategies, because these countries are presently outside the remit of the Kyoto Protocol.
This study was conducted to evaluate the effects of water management and the application of rice straw on methane emissions from paddy soil. Sixteen static chambers were installed in eight experimental plots. Methane emissions were monitored during the entire rice growing season in Suwon, Korea. Air samples, collected from the closed static chambers, were analyzed by using gas chromatography. Intermittent irrigation reduced methane emissions by 36% compared to flooding. The incorporation of well-decomposed rice straw (rice straw compost) before transplanting reduced methane emissions by as much as 49% relative to rice straw amendment. In addition, the incorporation of fresh rice straw three months before transplanting reduced methane emissions by 23%. Both intermittent irrigation and incorporation of decomposed rice straw, which are common practices for Korean farmers, proved to be effective in reducing methane emissions from rice fields in Korea.
Most previous optimization analyses for both short-term and long-term planning for solid waste management (SWM) overlooked global warming potential (GWP) impacts. This study integrates GWP and cost–benefit criteria to carry out optimal planning of a typical SWM system – the borough of Lewisburg, Pennsylvania. The GaBi® software package was used to estimate the possible greenhouse gas (GHG) emissions throughout the scenario-based design process. Five managerial scenarios were organized with and without the inclusion of GWP concern within such an optimization analysis for SWM. With the aid of LINGO® software package, the optimization models were solved sequentially to allocate different waste streams subject to the market demand and possible carbon regulation to maximize net benefit and minimize GWP, simultaneously or independently. The planning scenario with respect to a carbon-regulated environment particularly minimizes the large environmental gap in traditional cost–benefit analyses for SWM. Major finding in this study clearly indicates that simply using traditional cost-effectiveness principle or cost–benefit analysis with no GWP concern cannot compete with alternatives with GWP concerns especially in a carbon-regulated environment. The analysis eventually led to the prioritization of the Material Recovery Facilities (MRF) option before disposing of waste streams at the landfill site. Such a systems engineering approach is transferable to other SWM systems for a better planning, design, and operation in the future.