Preliminary investigation of greenhouse gas emissions from the environmental sector in Taiwan.

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