ABSTRACT
The United Nations Framework Conventions on Climate Change (UNFCCC)
asks their Parties to submit a National Inventory Report (NIR) for
greenhouse gas (GHG) emissions on an annual basis. However, when many
countries are quickly growing their economy, resulting in substantial
GHG emissions, their inventory reporting systems either have not been
established or been able to be linked to planning of mitigation measures
at national administration levels. The present research was aimed to
quantify the GHG emissions from an environmental sector in Taiwan and
also to establish a linkage between the developed inventories and
development of mitigation plans. The "environmental sector"
consists of public service under jurisdiction of the Taiwan
Environmental Protection Administration: landfilling, composting, waste
transportation, wastewater treatment, night soil treatment, and solid
waste incineration. The preliminary results were compared with that of
the United States, Germany, Japan, United Kingdom, and Korea,
considering the gaps in the scopes of the sectors. The GHG emissions
from the Taiwanese environmental sector were mostly estimated by
following the default methodology in the Intergovernmental Panel on
Climate Change guideline, except that of night soil treatment and waste
transportation that were modified or newly developed. The GHG emissions
from the environmental sectors in 2004 were 10,225 kilotons of
C[O.sub.2] equivalent (kt C[O.sub.2] Eq.). Landfilling (48.86%), solid
waste incineration (27%), and wastewater treatment (21.5%) were the
major contributors. Methane was the most significant GHG (70.6%),
followed by carbon dioxide (27.8%) and nitrous oxide (1.6%). In summary,
the GHG emissions estimated for the environmental sector in Taiwan
provided reasonable preliminary results that were consistent and
comparable with the existing authorized data. On the basis of the
inventory results and the comparisons with the other countries,
recommendations of mitigation plans were made, including wastewater and
solid waste recycling, methane recovery for energy, and waste
reduction/sorting.
INTRODUCTION
Although the Republic of China (Taiwan) was not one of those
Parties that ratified the Kyoto Protocol, it has still spent the highest
efforts to comply with the international framework to confront the
global climate change. Since 1992, Executive Yuan, the highest
administration authority in Taiwan, has started to coordinate activities
related to United Nations Framework Convention on Climate Change
(UNFCCC) and other global environmental issues. In the meantime, the
Taiwan Environmental Protection Administration (TEPA) has been
continuously establishing greenhouse gas (GHG) mitigation policies. In
particular, the sectors of Industry, Transportation, and
Residential/Commercial were chosen by the TEPA for GHG inventorying,
registration, validation, and methodology establishment. (1-3)
In Taiwan, the sources of GHG emission are closely related to the
use of energy. (4) Despite abundant precipitation on an annual basis,
most of the precipitations occur in the rainy season associated with
typhoons. In addition, the rivers are very short, making them difficult
to use for hydropower production. Producing almost no energy resources
on its own, Taiwan relied on the supply of imported coal and petroleum
for approximately 80% of its energy in 1998. Under this situation, the
annual carbon dioxide (C[O.sub.2]) emissions per capita have increased
at an annual rate of 5.8% from 1990 to 2000, to 5.57 t and 9.83 t,
respectively. According to the statistics issued by TEPA, (5) the
C[O.sub.2] emissions in 2003 increased by 121% from the level in 1990.
The C[O.sub.2] emission estimation for 1990 ranked Taiwan 27th of 159
United Nations member countries, and Taiwan contributed approximately
0.5% to the global total. (6)
According to the Kyoto Protocol, adopted in 1997 at the Third
Conference of the Parties to the UNFCCC and enforced on February 16,
2005, the Annex I countries must reduce their overall GHG emissions by
at least 5% below 1990 levels in the commitment period 2008-2012. The
anticipated balance between economic growth and GHG mitigation became a
considerable challenge in Taiwan.
If Taiwan were one of the Annex I countries of the UNFCCC, the
corresponding GHG emissions would have to be reduced by 227% of the
projected value for 2010. (4) The amount to be reduced would be more
than 10-20 times that of many developed countries, (7) which would have
tremendous impact on an economy that has seen high growth in recent
years through export-oriented industrialization. For this reason, TEPA
considers Taiwan to be categorized as one of the Newly Industrialized
Countries. Although the economic performance has surpassed those of many
developing countries, Taiwan is not yet mature enough for making a
sustainable commitment following the Annex I countries.
According to the Intergovernmental Panel on Climate Change (IPCC)
guideline, (8) disposal and treatment of industrial and municipal wastes
can produce significant amount of GHG emissions. C[O.sub.2] is mainly
produced by waste incineration, methane (C[H.sub.4]) could be observed
from landfilling and waste transportation, and nitrous oxide
([N.sub.2]O) is produced from incineration and wastewater treatment. To
illustrate, C[H.sub.4] produced as a byproduct of the anaerobic
decomposition of waste can contribute approximately 5-20% of annual
global anthropogenic GHGs released to the atmosphere. (8) Also, in the
United States, it was claimed that landfills were the largest source of
anthropogenic C[H.sub.4] emissions, which accounted for 24% of total
U.S. C[H.sub.4] emissions. On the other hand, waste-related sectors
usually do not release other kinds of GHGs, such as perfluorocarbons
(PFCs), hydrofluorocarbons (HFCs), and sulfur hexafluoride ([SF.sub.6]).
However, none of the emission inventories from the waste-related
sectors had been developed in Taiwan. Therefore, the TEPA commissioned a
research project to investigate the GHG emissions from a so-called
"environmental sector," which is comprised of the waste
treatment activities that are under its administration. The activities
in the environmental sector include solid waste incineration, wastewater
treatment, landfilling, composting, night soil treatment, and waste
transportation. This paper summarizes the results from this project, in
particular, the latest information on Taiwanese anthropogenic GHG
emissions from the environmental sector in 1990, 1994, and 2000-2004, by
undertaking a preliminary investigation. Socioeconomic data from nine of
the 25 cities and counties in the Taiwan area were collected in a survey
for references, but all of the GHG calculation was completed based on
the activity data for the entire population. The nine cities and
counties cover 47% of the Taiwanese population (2004). To ensure the
inventories were comparable to other countries, the presented estimates
were calculated mostly using methodologies consistent with those
recommended in the IPCC guidelines, (8) but some methods were modified
or newly developed. In addition, a comparison with five developed
countries (United States, Germany, Japan, United Kingdom, and Korea)
were conducted and discussed. Finally, mitigation plans were discussed
based on the inventory results and comparison and recommendations were
made. Although the UNFCCC asks its Annex I parties to submit GHG
National Inventory Reports (NIRs) on an annual basis, not many populated
countries have either established their GHG inventory systems or linked
their inventory to planning of mitigation measures at national
administration levels.
METHODOLOGIES
The IPCC 1996 revised guidelines (8) was primarily followed in the
study to estimate the anthropogenic GHG emissions in the environmental
sectors. However, because the environment sector does not belong to a
formal IPCC source category, some methods followed the principle of the
IPCC guideline but modified with consideration of local conditions. The
overall calculations were conducted with the principle expressed in eq
1:
GHG emission [kg-C[O.sub.2] equivalent] = Activity Data [activity]
x Emission Factor [kg-GHG/activity] x Global Warming Potential
[kg-C[O.sub.2] equiv./kg-GHG] (1)
The global warming potential (GWP) values for each of the GHG were
defined in the IPCC Third Assessment Report. Note that instead of using
measurements with scientific instruments, the GHG emissions were
estimated by socioeconomic data. Officially published data were
collected to employ the IPCC Tier-1 (simple) method, so that a top-down
estimation was completed in the preliminary investigation. For example,
for quantifying emissions from solid waste incineration, the mass of
solid waste incinerated was used; for waste transportation, fuel
consumption was taken into account. The IPCC method excludes C[O.sub.2]
emissions from biomass (crops and forests) combustion, and definitively
states, "The present atmospheric C[O.sub.2] increase is caused by
anthropogenic C[O.sub.2] emissions." (10) However, the exclusion of
biomass was not carried out in the present study because of lack of data
for biomass content in the municipal solid waste (MSW) incineration. The
biomass delivered to the MSW treatments was difficult to quantify during
the study year because the MSW sorting policy enforced since 2006, in
which food waste was subject to sorting from general waste as well as
other recyclable materials, has changed the composition and amount of
biomass delivered to the waste incineration. The best available data
were carbon content and heat values, which were utilized in the GHG
calculation.
Table 1 describes how subsectors in the Taiwanese environmental
sector are similar to those under the waste sector, which is listed in
the NIRs and a national communication submitted to the UNFCCC. In Table
1, prescribed entries in the common report format (CRF) for the annual
NIR submitted to the UNFCCC are shown. CRF 6A is the category of managed
waste disposal on land, CRF 6B is wastewater handling, and CRF 6C is
solid waste disposal. In addition, NI and I indicate the subsector is
not included and included in the annual NIR of GHG, respectively. In
brief, although IPCC guidelines exist, coverage of the activities of
interest varies a great deal. Namely, wastewater treatment/handling and
landfilling were the only common subsectors reported by many countries.
Waste incineration was often discussed in the energy sector, and waste
transportation belonged to the end-user transportation sector if
discussed.
Waste Incineration
For waste incineration, the method of reporting GHG emission is
quite varied from country to country. This variance is due to two
different factors. The first factor is the difference in allocation of
GHG emission to the energy and the waste sectors. Some countries report
GHG emissions in the energy sector, even though not all of their
incinerators actually conduct energy recovery. The other countries
distinguish incinerators with and without energy recovery and report the
GHG emissions to the energy and the waste sectors, respectively.
Efficiency of thermal and chemical energy recovery tends to be lower
than that of conventional energy generators. Countries such as Japan
state that this could be a reason to discourage thermal and chemical
energy recovery on waste incineration and choose to only allocate
relevant GHG emissions to the waste sector. (11) The second factor is
the details of waste compositions. When estimating the GHG emitted from
waste incineration, biomass material such as paper and food waste should
not be considered as net anthropogenic C[O.sub.2] emissions in the IPCC
guidelines. (8) However, MSW sorting was not enforced until 2006 in
Taiwan. As a result, the entire amount of incinerated solid waste was
applied to the investigation. Thus, the estimated GHG emissions resulted
not only from plastics derived from fossil fuel but also possible
biomass burning. From the various data available, a different formula
was employed to calculate the GHG emissions from MSW incineration.
MSW Incineration GHG emission (kg-C[O.sub.2] equiv.) = MSW
incinerated [kg-waste] x GHG emission factor [kg-GHG/kg-waste] x GWP
[kg-C[O.sub.2] equiv./kg-GHG] (2)
MSW Incineration GHG emission (kg-C[O.sub.2] equiv.) = MSW
incinerated [kg-waste] x GHG emission factor [kg-GHG/cal] x heat value
[cal/kg-waste] x GWP [kg-C[O.sub.2] equiv./kg-GHG] (3)
MSW Incineration GHG emission (kg-C[O.sub.2] equiv.) = MSW
incinerated [kg-waste] x carbon content [kg-C/kg-waste] x (44/12)
[kg-C[O.sub.2]/kg-C] x (1-pollution control efficiency [-]) x combustion
efficiency [-] x GWP [kg-C[O.sub.2] equiv./kg-GHG] (4)
MSW Incineration GHG emission (kg-C[O.sub.2] equiv.) = MSW
incinerated [kg-waste] x (1-water content [kg-water/kg-waste]) x (44/12)
[kg-C[O.sub.2]/kg-C] x (1-pollution control efficiency [-]) x combustion
efficiency [-] x GWP [kg-C[O.sub.2] equiv./kg-GHG] (5)
where GHG is {C[O.sub.2], C[H.sub.4], [N.sub.2]O}.
The carbon contents in eq 4 were varied by cities and by years in
this study. According to the Yearbook of Environmental Protection
Statistics, (12) the carbon content ranged from 15.74 to 29.67% and
became the input for the corresponding GHG estimation. The GHG emissions
from MSW incinerators were broken down into stationary sources, mobile
sources, and fugitive sources in the IPCC guideline. In this study, only
the stationary sources were covered for incinerators. When the carbon
content of the wastes were available, eq 4 was used, otherwise, water
content was applied as the surrogate as in eq 5. The emission factors of
C[O.sub.2] and C[H.sub.4] were adopted from the energy sector, whereas
that of [N.sub.2]O was adopted from the waste sector in the IPCC
guideline. (8)
Wastewater Treatment
According to the IPCC Guideline, (8) C[H.sub.4] produced from
wastewater can be handled from two primary categories, domestic and
industrial treatments. Under each, C[H.sub.4] emissions should be
separately estimated from organic water and from sludge. Industrial
wastewater handling was estimated to be the major contributor, producing
10-20 times that of other domestic sources.
The GHG emissions estimated in this study focused on the emissions
from organic wastewater, whereas those from organic sludge were ignored.
This is because most of the sludge is sent for incineration, aerobic
treatment, or sun drying in Taiwan, and very little sludge was under
anaerobic treatment, which causes C[H.sub.4] emission. (13) In addition,
different from developed countries where human sewage systems cover most
of the population, in Taiwan, the human sewage system is still
underdeveloped. For the same reason, [N.sub.2]O from human sewage was
not estimated. Therefore, a modified approach for C[H.sub.4] emissions
that counted the sewage developing ratio was used, which assumed that
the treatment linked with human sewages will not cause C[H.sub.4]
production (eq 6). In Taiwan, the human sewage delivered through the
sewage system to the municipal wastewater treatments is treated with
aerobic digestion.
Domestic Wastewater C[H.sub.4] emission [kg-C[O.sub.2] equiv.] =
population [person] x (1 - Human Sewage System Coverage [-]) x
BO[D.sub.5] per capita per day [kg-BOD x perso[n.sup.-1] x [day.sup.-1]]
x 5-day BOD removal efficiency [-] x 365 [day] x C[H.sub.4] emission
factor [kg-C[H.sub.4]/kg-BOD] x GWP [kg-C[O.sub.2] equiv./kg-C[H.sub.4]]
(6)
The C[H.sub.4] emission factor (0.6 kg C[H.sub.4]/kg biological
oxygen demand [5-day BOD]) was used for domestic wastewater. The 5-day
BOD per capita per day is set at 0.04 kg, derived from the design
guideline of the sewage treatment system in Taiwan, which is consistent
with the IPCC guidelines. (8) The design guideline suggests the per
capita per day 5-day BOD concentration before and after the treatment be
160 mg/L and 80 mg/L, respectively; therefore, 5-day BOD removal
efficiency was set as 50%.
For the C[H.sub.4] emission from the industrial wastewater (eq 7),
the C[H.sub.4] emission factor was modified from the IPCC guideline so
that 0.25 kg C[H.sub.4]/kg chemical oxygen demand (COD) was used, and
300 working days were employed. The emission estimation was done
primarily for industrial parks regulated by TEPA, therefore, industries
such as livestock farming, restaurants, clothes cleaning, car washing,
car maintenance, hotels, and hospitals were excluded from industry and
accounted in the other source categories. For example, the wastewater
generated by these small businesses except for hospitals is either
treated in their septic tanks or in the sewage systems, which eventually
goes to the municipal wastewater treatment plants, so the corresponding
emissions were estimated in either the night soil subsector or domestic
wastewater treatment subsector in the study. Additionally, the United
Kingdom did not estimate the emissions from private wastewater treatment
plants operated by companies until it was discharged to the public
sewage system or rivers. (14)
Industrial Wastewater C[H.sub.4] emission [kg-C[O.sub.2] equiv.] =
(CO[D.sub.influent] [mg/liter] - CO[D.sub.effluent] [mg/liter]) x
Flo[w.sub.effluent] [liter/day] x 300 [day] x C[H.sub.4] emission factor
[kg-C[H.sub.4]/mg-COD] x GWP [kg-C[O.sub.2] equiv./kg-C[H.sub.4]] (7)
Landfilling
It was agreed that the C[H.sub.4] emissions occurred only during
the landfilling process, and the facilities with flares or C[H.sub.4]
used for energy purposes should also be taken into consideration. Also,
the method developed by the U.S. Environmental Protection Agency (EPA)
(15) does not count biomass to the calculation of the C[H.sub.4]
emission from landfilling. The first-order decay model (FOD or Tier 2)
developed by EPA (15) was applied with several parameters subject to
domestic conditions to estimate the C[H.sub.4] emissions from landfills
in Taiwan. Although the waste composition in Taiwan might cause a
different C[H.sub.4] generation factor from that adopted from the EPA,
given that there is no logical basis available to assume a reasonable
composition, using the C[H.sub.4] generation potential default value as
given by EPA would be the best decision at this moment. On the other
hand, parameters other than the C[H.sub.4] generation factor were set
according to Taiwanese circumstances.
The [N.sub.2]O emission was not modeled in the study because it was
considered negligible due to the nonconducive nitrification and
denitrification landfilling environment. The landfilling emission
diffusion model landGEM_v.302 (16) was employed. In the model,
C[H.sub.4] generation potential was adopted from the inventory value
(100 [m.sup.3]/Mg) listed in EPA AP42. (17) The rate constant 0.05/yr
was implemented by following the suggestion from EPA, stating that the
area with average annual rainfall greater than 635 mm should use
0.04/yr. (15)
Night Soil Treatment
[N.sub.2]O, a digestion product of human discharge, is the main GHG
emitted from night soil treatment. According to the Yearbook of
Environmental Protection Statistics, (12) night soil was mostly
delivered to night soil treatment plants, wastewater treatment plants,
MSW leachate treatment plants, and composting plants. The same report
indicates that in 2003, 102, 156 t of night soil (70.5% of the total
night soil delivered) was delivered to the night soil treatment plants.
Therefore, the scope in the study was defined only for municipal and
private night soil treatment plants. To avoid double counting, emission
beyond the scope was not modeled.
As indicated in Table 1, night soil treatment was not discussed in
the waste sector. Thus, the estimation was conducted by modifying the
formula used to calculate [N.sub.2]O emitted from human sewage. (8) Eq 8
explicates the modified approach.
[N.sub.2]O emission [kg-C[O.sub.2] equiv.] = annual per capita
protein intake [kg-protein/person] x fraction of nitrogen in protein [kg
N/g protein] x (population [person] x night soil regional delivering
rate [-]) x delivering rate to night soil treatment plants [-] x (44/28)
[kg-[N.sub.2]O/kg-[N.sub.2]] x emission factor [kg-[N.sub.2] to be
[N.sub.2]O/kg-[N.sub.2] in sewage] x GWP [kg-C[O.sub.2]
equiv./kg-[N.sub.2]O] (8)
On the basis of the statistics, (18) the protein intake rate for a
person 19-64 years of age and categorized by adult male and female in
Taiwan is 82.6 g/day and 61.6 g/day, from which the annual protein
intake rate for male and female is derived as 30.1 and 22.5 kg,
respectively. Both the fraction of nitrogen in protein (0.16 kg N/kg
protein) and the [N.sub.2]O emission factor (0.01 kg [N.sub.2]O-N/kg
sewage-N produced) were taken from the IPCC default values. (8) To
reflect the actual situation, the delivering rate to night soil
treatment plants was localized from the IPCC parameters. To illustrate,
the delivering rates in 2003 and 2004 were 70.5 and 77.5%, respectively.
However, the delivering data were not available until 2001, so the data
of 2001 (49.5%) were set as values for 1990-2000. Similarly, because the
entire population was not applicable for the night soil treatment, the
night soil regional delivering rate was multiplied by the total
population instead of using the original population. The regional
delivering rate varied from 23.7 to 42.9% during 1990-2004.
Composting
Estimation of GHG emissions from composting plants followed the
UNFCCC method, (19) so the boundary was defined to include the unit of
sorting, aerobic conversion, compost, on-site use of electricity, and
on-site use of fuels by dozers. [N.sub.2]O was identified as the primary
GHG emission, and the emissions produced during the composting period
were the focus. Although other factors affecting GHG emission rates may
exist, such as: (1) C[H.sub.4] emissions from anaerobic decomposition,
(2) long-term carbon storage in the form of undecomposed carbon
compounds, and (3) nonbiogenic C[O.sub.2] emissions from collection and
transportation of the organic materials to the central composting site
and from mechanical turning of the compost pile, they were not included
in this category. Namely, the decision to omit factor (1) was made
according to the analysis, (20) which showed that a properly managed
composting site does not generate C[H.sub.4] emissions. The [N.sub.2]O
emission from composting was modeled with the formula described in eq 9.
(19)
[N.sub.2]O emission [kg-C[O.sub.2] equiv.] = total quantity of
compost [kg-compost] x emission factor [kg-[N.sub.2]O/kg-compost] x GWP
[kg-C[O.sub.2] equiv./kg-[N.sub.2]O] (9)
The default emission factor of 0.043 kg [N.sub.2]O/t from the IPCC
guideline (8) was employed. The emission factor was reported with the
assumption that 42 mg [N.sub.2]O-N were generated from 650 kg dry
matter/t compost.
Waste Transportation
Because waste transportation is not included as an individual
sector in the IPCC source category, a new method was applied in the
study. The method to estimate the emission resulting from waste
transportation was designed with four actions: (1) scope definition, (2)
emission source identification, (3) parameter determination, and (4)
emission computation. Actions 1-3 are elaborated as below:
Scope Definition. Both the public and private transporters were
included in the scope of the study. In addition to the complete vehicle
list for public services owned by the central and local environmental
protection administration, the private vehicles that are used for
removing commercial/hazardous solid waste were surveyed.
Emission Source Identification. C[O.sub.2] emission from vehicle
engine ignition was identified as the relevant emission and the source.
C[H.sub.4] and [N.sub.2]O emissions were not assessed in the study, as
suggested in the GHG Protocol Initiatives, (21) although it was likely
that the emissions were actually occurring. Even so, C[H.sub.4] and
[N.sub.2]O emissions should have been decreased because control
technologies for those gases have been introduced. Because C[O.sub.2]
emission factors will differ for different types of vehicles and fuels,
such data were surveyed in detail to reflect the current situation in
Taiwan.
Parameter Determination. The emissions were calculated with eq 10.
GHG emission (C[O.sub.2] equivalent) = [m.summation over
(j=1)][n.summation over (i=1)][q.sub.ij][f.sub.ij] (10)
where [q.sub.ij] represents vehicle model i and fuel consumption j,
and [f.sub.ij] stands for the associated emission factor. Fuel
consumption data were chosen (instead of the vehicle miles traveled) for
the activity data because of the data availability. The fuel consumption
data were collected through a survey to the city and county
environmental protection administrations. Determination of the emission
factors for respective vehicle models and fuel types were completed by
following the IPCC methods. (22) The decision was made after exploring
possible existing local emission factors, relevant reports from EPA, and
the GHG Protocol Calculation Tool. (21) Table 2 shows the emission
factors ([f.sub.j]) taken from IPCC. (22)
RESULTS AND DISCUSSION
GHG Emission Inventory of the Taiwanese Environmental Sector
The GHG emissions by the subsectors for 1990, 1994, 2000-2004 are
shown in Figure 1. Figure 1 indicates that waste incineration,
wastewater, and landfilling, shown with filled symbols using the primary
axis on the left, made the major contribution. The highest emission
occurred at 5306.64 kt C[O.sub.2] Eq. from landfilling in 2000.
Transportation, night soil, and composting, shown with empty symbols on
the secondary axis, are the minor sources. The emission from composting
is negligible, compared with the other subsectors, which might explain
the exclusion of composting in the CRF or the GHG NIR by the IPCC
guidelines. Structural changes to the newly started municipal
incinerators have occurred since 2001, which might explain the obvious
increase in the resulting GHG emissions. These changes in priorities of
waste treatment methods could describe the increase in emissions from
the incineration and gradual decline in emissions from the landfilling.
The policy preference for incineration is largely driven by the national
circumstances, such as the nonavailability of land for constructing
landfilling sites. In addition, the decreasing trend in incineration
since 2003 could be inferred with the policy of food waste recycling,
aiming at enhancing the combustion efficiency of incinerators and
reducing the amount of MSW. Currently 30% of the MSW is food waste. The
emissions from wastewater treatment are relatively stable. Emissions
from the domestic wastewater contributed 80.5% in 2004, which was about
four times that from industrial wastewater (data not shown). However,
along with more sewage systems being constructed, the emissions from the
domestic wastewater decreased in ratio of the total GHG produced from
the wastewater handling from 95.8% (1990) to 80.5% (2004). Comparing
with the national total GHG emitted from the environmental sector, the
GHG from the domestic wastewater dramatically dropped from 40.4% (1990)
to 17.3% (2004).
[FIGURE 1 OMITTED]
[FIGURE 2 OMITTED]
Figure 2 shows the subsectoral distribution of the GHG emissions.
The total GHG emissions in the environmental sector from 1990 to 2004
increased by 108.9%, which is consistent with a previous study. (5)
According to the previous study, in 2000, the GHG emissions from the
environmental sector (10,243 kt C[O.sub.2] Eq.) were smaller than the
result calculated from the UNFCC national communication, (4) which
estimated the GHG emissions from industry (121,794 kt C[O.sub.2] Eq.),
transportation (34,470 kt C[O.sub.2] Eq.), and residential/commercial
(39,066 kt C[O.sub.2] Eq.). Although the annual growth rate from 1990 to
2000 for the three IPCC sectors was 5.5%, it was 7.7% for the
environmental sector estimated in this study.
Table 3 illustrates the distribution of gases in 2004 broken down
into the subsectors. It is shown that C[O.sub.2] was mainly produced
from waste incineration and transportation, C[H.sub.4] was mostly
observed from wastewater treatment and landfilling, and [N.sub.2]O was
primarily estimated from night soil. Compared with the GHG distribution
in 1990 (C[O.sub.2] [3.4%], C[H.sub.4] [94.6%], and [N.sub.2]O [2.1%]),
C[O.sub.2] emissions became more critical through the years. The fact
could be deduced by the increased number of incinerators, the closing of
landfilling sites, and an increased need for MSW transportation. The
increased need of MSW treatment can be explained by the population
growth from 20,400,000 (1990) to 22,700,000 persons (2004).
International Comparison
The GHG emissions from the waste sector in the United States,
Germany, Japan, United Kingdom, and Korea contributed only 1.67-3.29% to
their total emissions from 1997 to 2003, and also tend to be gradually
declining. (23) The preliminary investigation conducted in the study
made two types of comparison with the above countries. The first
comparison is based on the GHG emissions from the IPCC waste sectors
among these countries and those from the environmental sector in Taiwan.
Table 4 described those emissions on a per capita basis for the year
2001. The emission from Taiwan seemed to be higher than most of the
compared countries, although included subsectors do not match. The other
comparison was made for the subsectors that were calculated in common,
as shown in Table 5. Landfilling data in the Taiwanese environmental
sector were compared with the IPCC solid waste disposal subsector.
Wastewater treatment data in the Taiwanese environmental sector were
used in a wastewater handling evaluation. The best available data from
the solid waste disposal and wastewater handling in 2002 were discussed
(Table 5).
The result implied that the C[H.sub.4] per capita emitted from
landfilling (10.1 kg-C[H.sub.4]/capita) in Taiwan was relatively high,
which was only smaller than that of the United States (31.9
kg-C[H.sub.4]/capita). All of these countries (United States, Germany,
Japan, United Kingdom, and Korea) estimated their GHG from landfilling
with the recommended FOD method, except for Japan, which designed a
country-specific model on the basis of the FOD method. Landfills in the
United States received 61% of the total solid waste, because of the
simple land use on a relatively large geographic area. (9) Consequently,
approximately 1800 existing operational landfills were the largest
anthropogenic source of C[H.sub.4] emissions in the United States, and
they accounted for 24% of total U.S. C[H.sub.4]. On the other hand, from
1990 to 2003, with the increases in the amount of landfill gas collected
and combusted, a downtrend approximately 24% of the net C[H.sub.4]
emissions from 1990 to 2003 was observed. (9) In Germany, (24)
approximately 330 landfills for MSW are in operation. Strict legal
regulations require such landfills to have equipment for gas collection
and gas treatment. As a result of the regulations including landfill gas
collection, waste management, and waste separation for recycling, the
amount of municipal waste stored in landfills has decreased two-thirds
since 1990. Consequently, the resultant C[H.sub.4] emissions reduced by
more than 60% in comparison to the level in 1990. (24) In Japan, (25)
C[H.sub.4] emissions from this source only accounted for 0.3% of total
national emissions (2002), which also decreased by 8.4% between 1990 and
2002. The per capita emissions are the lowest among the reporting
parties, (11) because only 5% of MSW generated is disposed at solid
waste disposal sites for a population of 127 million. The data reflect
the fact that legislation is in favor of incineration instead of
landfilling because of limited land use. In the Japanese
country-specific method, waste was categorized into kitchen garbage,
waste papers or waste textiles, and waste wood, and emission factors
have been established for each type of waste respectively. Carbon
contents were specified for detailed categories such as kitchen garbage
and waste wood. (25) In the United Kingdom, (14) C[H.sub.4] was also
recovered for power generation. The 2002 data showed that 24% of
generated C[H.sub.4] was utilized and 45% was flared. In Taiwan,
landfilling was previously the major approach for waste management.
However, from 1990 to 2004, landfilling was gradually replaced by waste
incineration and the operation percentage has dropped from approximately
90 to 20%. At the same time, the incinerators have grown from a few
percentages to over 50%, whereas recycling and composting accounted for
the remaining measures. Particularly in 2002, the capacity of solid
waste treated by the incinerators was about two times that of the
landfills. (26) However, not all of the 263 landfill sites were
facilitated with gas recovery systems, and only 28% of them were
equipped with functional collection systems. (26) Recent changes in the
waste treatment systems in Taiwan could affect the composition of waste;
however, biomass content in the incinerated MSW is not analyzed in
Taiwan at this point. As a best effort, the default C[H.sub.4]
generation factor from the U.S. model was applied. Further detailed
analysis is needed to more accurately estimate emissions from this
category. (27)
The above discussion might help to preliminarily conclude the
factors that influence the C[H.sub.4] emissions produced from
landfilling in these discussed countries: (1) the popularity of
landfilling application, (2) efficiency of waste management, and (3)
accuracy of the emission estimation methods. The more landfilling sites
that exist in a country, the higher the resultant C[H.sub.4] emissions
tend to be. This hypothesis might be used to explain the enormous
emissions produced by the United States, which has almost six times as
many landfill sites as Germany and Taiwan. Germany and the United
Kingdom could be good examples of efficient waste management
implementation. The two countries, with comparable population and
landfilled waste amounts, produced similar amounts of C[H.sub.4]
emissions. In contrast to Germany, fewer gas collection systems and late
enforcement of the regulation for waste management might explain the
relatively high level of C[H.sub.4] emission in Taiwan. Japan emitted
even less C[H.sub.4] in 2002 than all of the above countries despite its
large population, the second largest in Table 5. This is due to the
smaller number of landfilling sites and a sophisticated method for
estimating C[H.sub.4] emissions.
The C[H.sub.4] per capita emitted from wastewater handling in
Taiwan (4.21 kg-C[H.sub.4]/capita) was also only smaller than that of
the United States (4.73 kg-C[H.sub.4]/capita), but greater than that of
Germany, Japan, and the United Kingdom (0.08-0.63 kg-C[H.sub.4]/capita).
Germany, for example (like Sweden and Denmark), uses aerobic procedures
in municipal wastewater treatments and it produces no C[H.sub.4]
emissions. (24) The small amount of C[H.sub.4] emissions estimated in
Table 5 was produced from treatment of human sewage not connected to
sewage networks, such as cesspools and septic tanks. In addition, since
1990 organic loads discharged into cesspools and septic tanks have been
drastically reduced due to the gradual increase in small wastewater
treatments, particularly in eastern Germany. (24) In Japan, no
C[H.sub.4] recovery system was mentioned in the wastewater treatments.
(25) However, sophisticated calculation was carried out for GHG
estimation. To illustrate, activity data (BOD) specific to categories of
manufacturing were used for the industrial wastewater handling. The
actual C[H.sub.4] volume specific to each of the treatment processes was
thoroughly estimated. Moreover, four different C[H.sub.4] emission
factors for domestic sewage treatment plants were designed for
corresponding purposes, such as community sewage treatment or on-site
treatment of human waste alone. (25) Country-specific methods and
emission factors based on the IPCC good practice guidance or relevant to
the national circumstances are generally used in Japan's case. (11)
The relatively low C[H.sub.4] emissions estimated in this subsector in
the United Kingdom could be the result of their C[H.sub.4] recovery
system, the subsequent utilization, and the flaring process. (14) In
Germany, the model analyzing the proportion of anaerobic digester
emissions actually accounted for the GHG emission recovery. (24) In
contrast, the largest C[H.sub.4] producer in this category, the United
States, mentioned no C[H.sub.4] recovery system in their national GHG
inventory report for wastewater handling. (9) Similarly in Taiwan, most
of the industry wastewater handlings proceed with anaerobic treatments,
and the majority of them lack of C[H.sub.4] recovery systems so that
they emit GHG directly into the atmosphere. In summary, in Taiwan and
the United States, no C[H.sub.4] recovery system was included in most of
the wastewater treatment; this is in contrast to the countries that
emitted relatively low GHG emissions. Also, because of the objective of
a preliminary investigation, the GHG estimation was completed with the
conventional Tier-1 method without dedicated evaluation of the
associated activity data and emission factor.
Mitigation Plans
Following the preliminary inventory results and the comparison with
the other countries, the mitigation plans were discussed using the
categories shown in Table 6. The candidates for recommended mitigation
plans were raised in a brainstorm meeting involving local environmental
protection administration officers and the university project members.
It should be noted that a plan that could reduce emissions from a
certain sector might not necessarily reduce overall emissions, because
it might simply move the emission from one sector to another. For such
kinds of plans, quantitative evaluation from life cycle points of view
has to be conducted to evaluate the effectiveness. Such studies are
demanding, so the preliminary study presented in this paper forms a
basis for such further studies.
From the inventory results and matrix shown in Table 6, a
recommendation of mitigation plan was made. Waste reduction, sorting,
and C[H.sub.4] recovery systems were recommended because they have the
highest potential to successfully reduce GHG emissions, and are commonly
useful for the three major emissions contributors (waste incineration,
wastewater treatment, and landfilling). Those recommendations are also
consistent with the results when comparing to other countries. In
addition, solid waste reuse and recycling and wastewater reuse were the
other recommended options.
Reuse and recycling of post consumer products that are otherwise
incinerated or landfilled will prolong the lifetime of a product and
reduce wastes that cause GHG emissions upon final treatment. Although
recycling also require activities (such as additional transportation and
cleaning) that entail GHG emissions as well, considering the current low
recycling rates in much of the environmental sector and relatively low
emission contribution from the transportation subsector, promoting waste
recycling may well be able to reduce the overall GHG emissions. Still,
to promote solid waste recycling in an efficient way, priorities have to
be set for enhancement of recycling via more detailed separation of
domestic wastes. Promotion of reuse will require changes in
citizens' mindset so that the acceptability of used product rises.
Wastewater reuse actually does not reduce GHG emission from the
environmental sector; however, it could reduce water consumption and
also the resultant GHG emissions related to freshwater treatment.
One-way analysis, starting from inventory results, would help
identifying mitigation plans that could possibly reduce emission in the
environmental sector but it could not identify plans that reduce
emissions in other sectors. Gaps in inventories and the administrative
sections should be recognized and overcome. On the other hand,
wastewater reuse could potentially increase GHG emissions from
transportation of water. In Taiwan, reused wastewater in some cities is
delivered by trucks and used for gardening. In such case, GHG emission
associated with the transportation (i.e. emission from truck, etc.)
would be occurring, and it could be more than the reduced GHG emission
anticipated by the wastewater recycling. In Taiwan, wastewater treatment
plants are remote from the downtown area, so it is possible that there
would be an increase in the GHG emission. The overall reduction has to
be approved through quantitative evaluations.
CONCLUSIONS
A preliminary investigation of GHG emissions for the environmental
sector in Taiwan was completed for the base years 1990, 1994, and
2000-2004. The methods described in the IPCC guideline (8) were followed
except for Night Soil Treatment and Waste Transportation. The estimated
GHG emissions were comparable and consistent with data from several
authorities. (1-4) In 2004, the total GHG emissions were 10,225 kt
C[O.sub.2] Eq. Landfilling (48.86%), waste incineration (27%), and
wastewater treatment (21.5%) were the major contributors. C[H.sub.4] was
the most significant GHG (70.6%), followed by C[O.sub.2] (27.8%) and
[N.sub.2]O (1.6%). International comparison was conducted based on
common sectors. The factors affecting the C[H.sub.4] emission from
landfilling include the number of landfill sites, the efficiency of
waste management, and the estimation method. The main cause affecting
the C[H.sub.4] emission from wastewater treatment was found to be the
C[H.sub.4] recovery system. Wastewater and solid waste recycling,
C[H.sub.4] recovery, and waste reduction were feasible mitigation plans
with higher priority at this time.
A quantification of parametric uncertainty is recommended to be
performed as subsequent research. Comprehensive and quantitative
evaluation of mitigation plans from life cycle viewpoint is desirable,
especially for those plans that could affect emissions not only from the
original sector but also from another sector. The Taiwanese case of
development of mitigation plans presented in this paper exhibits an
example of filling the gaps in inventories and the administrative
sections via a meeting with inventory analysts and administrative
officers as members.
ACKNOWLEDGMENTS
This study was conducted with funding support from the TEPA
(EPA-94-FA11-03-A210). The authors thank Wei-Kai Yang, Hsiu-Hsuan Li,
Yung-Chen Yao, and Jin-Tiao Liang for their contribution in data
collection and processing.
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