Potential of Municipal Solid Waste for Renewable Energy Production and Reduction of Greenhouse Gas Emissions in South Korea

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1 TECHNICAL PAPER ISSN: J. Air & Waste Manage. Assoc. 60: DOI: / Copyright 2010 Air & Waste Management Association Potential of Municipal Solid Waste for Renewable Energy Production and Reduction of Greenhouse Gas Emissions in South Korea Changkook Ryu School of Mechanical Engineering, Sungkyunkwan University, Suwon, South Korea ABSTRACT Energy from waste (EfW) for nonrecyclable wastes is a suitable method of waste management and is important for renewable energy production. South Korea currently recycles 57% of household waste and landfills 26%. The remaining 17% is incinerated, mainly for heat production. In this study, the potential for energy production and reduction of corresponding greenhouse gas (GHG) emissions from municipal solid waste (MSW) in Korea was estimated without accounting for the lifecycle impact of waste management. The properties of the MSW were established from data available in national-scale waste surveys and reports. The potential of EfW for GHG emission reduction was calculated considering (1) the direct release of anthropogenic carbon, nitrous oxide (N 2 O), and methane (CH 4 ); and (2) the reduction in indirect GHG emissions by fossil fuel displacement. CH 4 emissions from landfilling were also estimated from biogenic carbon in waste. Applying the resulting emission factors to various EfW cases suggests that the current level of GHG emissions is significant but can be substantially reduced by increased use of EfW. A net reduction in GHG emissions can be achieved only by EfW with combined heat and power (CHP). INTRODUCTION Municipal solid waste (MSW) refers to household waste combined with a minor portion of commercial waste collected together. It is regarded as a source of renewable energy because it contains a high proportion of biomass materials such as paper/cardboard, wood, and food. From the perspective of sustainable waste management, the priority is on the reduction of waste generation followed by material recycling, both of which are highly beneficial in terms of greenhouse gas (GHG) emissions reduction 1,2 by saving resources otherwise required for manufacturing new products. However, some wastes are not suitable for recycling. For the nonrecyclable fractions, an energy recovery method becomes essential because it can reduce IMPLICATIONS This paper shows how to estimate the potential of wastes for renewable energy production and reduction of GHG emissions. Further detailed analysis of different waste management scenarios can be performed based on this approach. the use of fossil fuels. At the same time, it can also minimize the environmental and health problems of waste disposal, unlike the landfill alternative. The conventional technology for energy from waste (EfW) is direct combustion (incineration), but advanced technologies such refuse-derived fuel (RDF) production, gasification, and anaerobic digestion are also available. In using the energy produced from waste, combined heat and power (CHP) is the preferred option for maximizing overall energy efficiency. The potential of EfW and its impact on GHG emission reduction are significant. Estimates have shown that in the United Kingdom, the potential electricity yield from household, commercial, and industrial wastes will supply as much as 17% of the total electricity consumption in 2020 with the application of an advanced thermal conversion method that can also meet recycling targets. 3 Skovgaard et al. 4 estimated that GHG emissions from municipal waste management in European Union (EU) countries will decline from 47 Mt CO2,eq /yr in 2000 to 8 Mt CO2,eq /yr by 2020 with an increase in recycling and EfW rates of 43 and 23% in 2020, respectively. The main source of direct GHG emissions is methane (CH 4 ) released from landfill sites, whereas the main sources of GHG emission reduction are recycling and EfW. In the United States, electricity production from EfW for 7.7% of MSW was 13.5 TWh in 2002, which corresponds to 28% of the renewable power that year excluding hydropower. 5 The U.S. Environmental Protection Agency (EPA) 6 analyzed the GHG emission impact of 29 types of materials using a lifecycle approach and concluded that source reduction and recycling are the best ways to reduce GHG emissions, especially for metals. In addition, they showed that the combustion of mixed MSW emits less GHG than landfilling. South Korea has scarce natural resources but a huge energy demand; thus, EfW can play an important role in the production of renewable energy while reducing GHG emissions. The volume of South Korea s economy and energy consumption have more than doubled over the 16 years since Subsequent total emissions of GHGs have also doubled to Mt CO2,eq /yr in 2006, and its rate of increase is one of the fastest in the developed countries. Because of its significant contribution to world GHG emissions, 8 South Korea will be required to play an important role in the post-kyoto system starting in To achieve significant GHG emissions reduction, the country 176 Journal of the Air & Waste Management Association Volume 60 February 2010

2 Table 1. New and/or renewable energy production in South Korea in Sources of Energy Ktoe Percent Percent of TPES a Waste Waste gas Mixed wastes (incineration) Waste wood Waste burned in cement kilns Waste oil Landfill gas RDF/RPF b Hydro Biomass Wind Solar heat Photovoltaic Geothermal Fuel cell Total Notes: TPES total primary energy supply; b RPF refuse plastic fuel. needs to exploit all available resources for renewable energy production and endeavor to further increase its energy efficiency. South Korea consumed Mt of energy in 2006, in which the proportion of renewable energy was very low 2.24% in Table 1 gives the breakdown of energy production from the sources categorized as new and renewable; these categories are used in the national statistics. 9 According to the data, waste is the single most important source of new and renewable energy. The amount of energy from sources of waste was 4029 kilotons of oil equivalent (Ktoe) in 2006, comprising over three-quarters of the total national energy production. However, approximately 45% of this amount was obtained using waste gas at oil refineries, which is not considered renewable. Excluding the EfW gas, the country s energy production from renewables drops to less than 1.5% of the total energy production. The categories for waste feedstock that contain the biodegradable fractions are mixed wastes (incineration), waste wood, landfill gas (LFG), and RDF, which generated a total of 1526 Ktoe. The Korean government announced a new long-term National Energy Plan in 2008 that set ambitious national targets and introduced many new measures for sustainable development by The targets include an increase in renewable energy production, to 11%. To meet the target, detailed analyses and planning are required for each renewable source. This objective of this paper is to assess the potential of EfW for renewable energy production and GHG emissions reduction in South Korea. The current status of waste management and various statistical data on the national scale are reviewed to determine the total amount and the material properties of nonrecyclable MSW available for EfW. Then, energy production potential and subsequent GHG emissions are analyzed based on the chemical compositions and biogenic carbon fractions of wastes. The potential for GHG emission reduction are also calculated considering the displacement of fossil fuels and CH 4 emission from landfilling. The calculations do not include the lifecycle aspects of EfW such as GHG emissions during waste collection, pretreatment, and ash disposal. Finally, the role of EfW in future waste management is discussed. WASTE MANAGEMENT IN KOREA Table 2 presents the status of waste management in Korea in Over 116 Mt of waste was generated in the country, of which more than half was construction and demolition (C&D) waste. 11 The amount of household waste was Mt/yr. Although the proportion of household waste was only approximately 15% of the total amount of waste, its role as a renewable energy source is very important because it is largely organic and combustible. Fifty-seven percent (10.19 Mt) of household waste is currently being recycled, 17% (3.04 Mt) is incinerated, and 26% (4.60 Mt) is landfilled. The main technology applied for EfW is currently incineration, and large incineration plants (35 in 2007), mostly using grate-type furnaces, burn over 2.8 Mt/yr of household wastes. 12 RDF production is currently not significant only approximately 60 Kt/yr from a few facilities. No commercial facilities applying gasification or other thermal technologies are in operation. All of the large incineration plants convert the thermal energy in waste into steam, of which 19 plants are for CHP, and the rest are for district heating and other heat uses. Nineteen plants produced 195 GWh of electricity in 2007, which only represents approximately 6.5% of the heat in the steam produced and therefore is not substantial considering the parasitic electricity demand. C&D wastes are mostly incombustible and are recycled as base materials for construction sites and roads. The total amount of commercial and industrial (C&I) wastes, such as synthetic polymers, animal residues, and industrial and sewage sludge, is approximately 37 Mt, of which 74% is recycled. A significant portion of the sludge is disposed at sea, but such disposal will be banned in 2013 when the 1996 Protocol to the London Convention takes effect. Table 2. Status of waste management in South Korea in Waste (Mt/yr) Recycling Incineration Landfill Sea Disposal Total Household waste C&D waste C&I waste a Total Notes: a Includes industrial and sewage sludge. Volume 60 February 2010 Journal of the Air & Waste Management Association 177

3 Figure 1. Recent trend in household waste management and the amount of waste generated. Figure 1 illustrates the trend of household waste management since With the successful introduction of obligatory schemes for a volume-based waste fee system (enforced by requiring the purchase of dedicated bags for waste disposal) in 1995 and for source segregation of food waste in 2005, Korea has succeeded in maximizing the recycling rate of household waste while dramatically reducing the rate of landfilling. 11 The amount of waste generated was kept steady at approximately 1 kg/day/per capita, which is considered very low compared with 1.4 kg/day/per capita for the 27 EU countries in The main driving force behind this success in waste management was public awareness of environmental issues. On the other hand, this awareness acted as a barrier to the installation of EfW incineration facilities because the public became concerned about dioxin emissions from these facilities. In line with efforts to increase renewable energy production, the Korean government announced a Waste to Energy Strategic Plan in that aims to increase energy recovery and utilization for all available nonrecyclable wastes from the current level of 32% to 57% by 2012, and to 100% by To meet the targets, several EfW complexes will be established for cross-border centralization between local authorities and clustering of waste management facilities applying various technologies. RDF production for combustible wastes and anaerobic digestion for wet organic wastes were proposed as main EfW technologies in the plan, in addition to efforts to maximize utilization of energy produced from incineration plants. REFERENCE MSW PROPERTIES Material Breakdown Establishing representative waste properties is the first step in the estimation of energy and GHG reduction potentials of wastes. A detailed and consistent dataset is required for (1) material breakdown, (2) analysis of elemental composition of each material, and (3) evaluation of energy content. There are several surveys and statistics available in Korea, but none were readily available for this study because of their lack of comprehensiveness. Therefore, individual surveys with sufficient data sources and analysis periods were selected for evaluation, and consistent information was extracted to complete the waste property dataset. Table 3 presents the material breakdown of MSW. The data for the table were acquired from four recent national surveys carried out by different organizations. Although collected from a sufficient number of samples, the survey results showed significant differences in material composition. Dataset 1 gives the average values for source segregation residues in dedicated waste disposal bags collected from various source sites. 14 As part of the detailed surveys carried out every 5 yr, waste generated from different types of residential, commercial, and industrial sites nationwide (such as individual households, apartments, shops, restaurants, schools, offices, and factories) were analyzed during four seasons, from November 2006 to September There were a total of 7900 source sites. Despite the large number of sites, these data did not include waste collected from streets and open public places. In these data, the proportion of wastes classified as miscellaneous combustibles is very high (25.1%), which includes nappies, toilet tissues, and other household sanitary materials. 14 These miscellaneous combustibles are likely to be mostly biodegradable but with a high moisture content. Dataset 2 represents the downstream side collected from all (252) landfill sites in the same survey. 14 Dataset 3 represents another annual survey that accumulated the statistics of all (250) local authorities of waste management in 2006, 15 as required by regulation. However, this survey applied a very broad classification for plastics, rubbers, leathers, and other miscellaneous combustibles comprising about half of the total combustible materials. Dataset 4 gives the average values of monthly analyses from all (35) large incineration plants. 16 These data are generally similar to dataset 2, which is also a downstream-side survey. The proportions of the two main combustible materials (paper and plastics) and incombustibles in dataset 4 are similar to those in dataset 1. Table 3. Material breakdown (%) of MSW excluding source-segregated wastes. Dataset Source Types Food Paper Wood Plastics Fabric Rubber Leather Miscellaneous Combustibles Incombustibles 1 14 Source segregation residues Waste landfilled Source segregation residues Waste incinerated a Notes: a Mass-weighted average of monthly analyses in 35 large incineration plants. 178 Journal of the Air & Waste Management Association Volume 60 February 2010

4 Table 4. Elemental composition and heating value of nonrecyclable MSW. Food Paper Plastics Wood Textiles/Rubber/ Leather Miscellaneous Combustibles Incombustibles Average Weight fraction (%) Moisture (% wet) C (% wet) H (% wet) O (% wet) N (% wet) S (% wet) Cl (% wet) Ash (% wet) LHV (MJ/kg-wet) LHV contribution (%) Biogenic C (% of C) Biogenic C (%wet) Anthropogenic C (% wet) Such wide variation in the material breakdown in Table 3 clearly shows the difficulty associated with waste statistics because of the ambiguous nature of material classification and inconsistent analytical methods used among the bodies involved in the survey. However, each dataset has remarkable similarity to those from previous years. This suggests that the organizations involved in the survey are consistent in their method for material classification, and that the material composition did not change significantly over time. Chemical Composition of Reference MSW Considering the consistency required in the material classification and analysis of detailed material properties, reference waste properties were established using dataset 1 14 in Table 3. Except for miscellaneous combustibles, these data are comprehensive; that is, they provide the elemental composition and heating values of each material. Table 4 presents the elemental composition and heating value of the reference MSW. The following assumptions and calculations were introduced to complete the dataset using the raw data. Food, Paper, Plastics, and Wood. The moisture and ash contents were averaged for 10 categories of source sites. The chemical compositions (C, H, O, N, S, and Cl) on a wet basis were then recalculated from the values reported for a dry, ash-free basis. Textiles, Rubbers, and Leathers. The weight fraction is given as the weight sum of the three materials in the data source, and the elemental composition is presented for each material. Therefore, the three types of elemental composition data were averaged into a single component. The biogenic carbon fraction was assumed to be 50% for the GHG emission calculation. Miscellaneous Combustibles. These materials are likely to be very wet and mixed, as previously mentioned. This component was assumed to have 60% moisture, 12% ash content, and a combustible portion (38%) consisting of 90% paper and 10% plastics. Incombustibles. Thirty percent moisture content was assumed. Heating Value. The following correlation proposed by Channiwala and Parikh 16 was used for the higher heating value (HHV): HHV MJ/kg C H S N A (1) As shown in Table 4, the reference waste contained 30.29% moisture, 53.68% combustibles, and 16.03% ash. The lower heating value (LHV) was estimated to be MJ/kg. This relatively high LHV may be due to the reduced moisture content by the source segregation of food waste enforced since About half of the energy content in the waste is from plastics (53.6%), followed by paper (32.5%). Note that applying the material breakdown from dataset 4 in Table 3 to the chemical compositions in Table 4 resulted in an unreliably high-quality waste: 23.90% moisture content and 15.5 MJ/kg of LHV. This suggests that consistency in waste characterization is critical. The biogenic carbon fraction is essential in evaluating GHG emission. The carbon in food, paper, and wood was assumed to be fully biogenic, whereas that in plastics fully anthropogenic. The biogenic carbon fraction in the miscellaneous combustibles was calculated to be 84.5% using the proportion of paper on the basis of the third assumption described previously. The resultant biogenic carbon fraction for the reference MSW was 51% of the total carbon or 16.63% of the wet waste, as shown in Table 4. The reliability of the reference waste properties was checked using operation data from incineration plants. Table 5 shows the ash content and heating value extracted from the operation data of large household waste incineration plants in The 35 plants burned approximately 2758 Kt/yr of waste to produce GJ/yr of steam and 525 Kt/yr of ash. The hot ash generated from incineration was cooled by water and stored in an ash pit. Its moisture content typically ranged from 15 Volume 60 February 2010 Journal of the Air & Waste Management Association 179

5 Table 5. Data extracted from the large household waste incineration plants operation data 16 in Waste Incinerated (a) 2,758 Kt/yr Heat production as steam (b) 26,113,000 GJ/yr Heat recovery efficiency assumed (c) 80% LHV estimated (d b/ac) MJ/kg Ash generation (e) Kt/yr Typical moisture content of ash (f) 15 25% Ash content in waste (g ef/a) % Proximate analysis a Moisture 35.50%, combustible 54.23%, ash 10.27% LHV analyzed a MJ/kg Notes: a Mass-weighted average of monthly analysis data in 35 incineration plants. established for landfilling and combustion are then applied to various cases of waste management and fuel efficiencies to identify the potential for energy and reduction of GHG emissions. Landfill and Generation of CH 4 First, the amount of CH 4 generated from landfills was estimated, which can be emitted directly to the atmosphere, flared, or preferably used for energy production. The calculation was based on the mass balance method (Tier 1) proposed by the Revised 1996 Intergovernmental Panel on Climate Change (IPCC) Guidelines 21 and the 2000 IPCC Good Practice Guidance. 22 This method estimates the total amount of CH 4 generated from the degradable organic carbon (DOC) content of each waste material, independent of time, as follows: to 25% Excluding the moisture from the ash, the calculated ash content of the waste was %. This suggests that the value in Table 4 (16.03%) is reasonable. The previously mentioned data 16 also include a monthly analysis of waste properties for proximate analysis and the LHV for each plant. The mass-weighted average of the measured LHV values for all of the plants for the year 2007 was calculated to be MJ/kg. However, detailed assessment of individual data led to the conclusion that the reported LHVs for many plants were significantly underestimated, as shown in Figure 2. On the basis of the heat production and the reported LHV in the data, 10 of the 35 plants actually recovered more than 95% of the heat input, and such a recovery rate is thermodynamically impossible. Most of these plants reported 10.5 MJ/kg or lower LHV. Also, the ash content (10.27%) from monthly analysis was too low compared with the amount of ash actually generated. Therefore, estimating the LHV from the energy output can be more reliable. Assuming a heat recovery efficiency of 80%, the amount of steam production corresponded to MJ/kg of LHV for the input waste. This was 9.1% lower than the value (12.99 MJ/kg) in Table 4, which was considered acceptable for this study. CH 4 Emission ton CH4 /ton waste MSW F,i MCF DOC i DOC F,i F 16/12-R 1 OX (2) where MSW F, i is the fraction of municipal waste component i, as given in Table 5. MCF is the methane correction factor. Because most landfill sites in Korea are sanitary, the value of MCF was 1 in this study. DOC i is the DOC of municipal waste component i. This study used the carbon contents given in Table 4 because the DOC F values described below were based on the total carbon. DOC F, i is the fraction of DOC that can decompose for each material component i. This study used the values measured by the Sudokwon Landfill Site Management Corporation 23 for each material component based on total carbon content. The DOC F values are listed in Table 6. The value for the miscellaneous combustibles (0.470) was calculated based on the assumption made about its composition (90% paper and 10% plastics for the combustible content), as previously mentioned. F represents the fraction of CH 4 in LFG. The default value is 0.5, which has been confirmed by the Sudokwon Landfill Site Management Corporation. 23 ENERGY AND GHG EMISSION REDUCTION POTENTIALS For the reference waste, the amounts of energy and GHG emissions from landfill or thermal conversion into energy were estimated using various factors reported in the literature. When landfilled, the biodegradable portion of the waste releases CH 4 and carbon dioxide (CO 2 ). Part of the LFG is recovered, but the remainder diffuses into the atmosphere. Because of its high global warming potential (GWP), CH 4 can significantly contribute to GHG emissions. When waste is burned for energy by incineration or other thermal conversion, fossil carbon in the waste is released as CO 2 together with a small amount of other GHGs such as nitrous oxide (N 2 O) and CH 4. However, energy production indirectly reduces GHG emissions by displacing the use of fossil fuels. The amount of displaced fossil fuel depends on the LHV of the waste and the fuel efficiencies for heat and electricity. The emission factors Figure 2. Calculated fuel efficiencies for steam production vs. LHV analyzed in large incineration plants in Journal of the Air & Waste Management Association Volume 60 February 2010

6 Table 6. CH 4 emissions per ton of waste component when landfilled as baseline GHG emission. Food Paper Plastics Wood Textiles/Rubber/ Leather Miscellaneous Combustion Incombustion Total Weight fraction (%) DOC (as total C) (%) DOC F CH 4 emission (t CH4 /t waste ) to the atmosphere Equivalent GHG emission (t CO2,eq /t waste ) with a GWP of The conversion ratio of molecular weights between CH 4 and carbon is 16/12. R is the amount of recovered CH 4. The recent measurement by Environmental Management Corporation suggested that 23.3% of the total CH 4 generated was recovered. 24 The remainder was mainly diffused into the atmosphere through the surfaces of landfill sites. OX is the oxidation factor. A value of 0.1 was used in this study, which assumes that the sites are well managed. 25 Table 6 shows the calculation results. The quantity of CH 4 emission from landfills was estimated to be t CH4 /t waste, equivalent to 1.04 t CO2,eq /t waste with a GWP of 25 on the 100-yr horizon proposed in the IPCC Fourth Assessment Report. 26 With a recovery ratio of 23.3% in 2006, the amount of recovered CH 4 was t CH4 /t waste. Because the LHV of CH 4 is 50.5 MJ/ kg CH4, this figure corresponds to 0.64 MJ/kg waste, with only 4.9% of the LHV for the input waste (12.99 MJ/ kg waste ). Combustion and Subsequent GHG Emissions Combustion of waste converts chemical energy (LHV) into thermal energy of combustion gas at high efficiencies. Unlike CH 4 emissions from landfills, combustion releases the fossil carbon in the fuel into CO 2 and biogenic carbon. The combustion gas also includes trace amounts of N 2 O and CH 4. Therefore, the direct GHG emission from EfW is the sum of anthropogenic CO 2,N 2 O, and CH 4 emissions converted into an equivalent amount of CO 2 emission using the 100-yr GWP (298 for N 2 O and 25 for CH 4 ) 26 as follows: Direct GHG emission ton CO2,eq /ton waste 44/12 C anthropogenic CE 298 EF N20 25 EF CH4 (3) The anthropogenic carbon content was 15.97% wet, as given in Table 4. The conversion efficiency (CE) of carbon was assumed to be The emission factors for N 2 O (EF N2O ) and CH 4 (EF CH4 ) used in this study were taken from averages of the measured values in incineration plants in Korea 27 : kg N2O /t waste and kg CH4 / t waste. These values correspond to 16.7 kg N2O /TJ and 6.75 kg-ch 4 /TJ, which are within the ranges suggested by the IPCC 28 of kg N2O /TJ and kg CH4 /TJ, respectively. Using the preceding equation and input values, the direct GHG emission excluding biogenic CO 2 was calculated to be t CO2,eq /t waste. Reducing GHG Emissions by Fossil Fuel Displacement Energy production from waste in the form of heat and/or electricity displaces fossil fuel and hence reduces the emissions of GHGs. With the introduction of national emission factors for heat and electricity generation, the GHG emission reduction can be calculated for respective fuel efficiencies of EfW as follows: GHF emission reduction by fossil fuel displacement ton CO2,eq /ton waste LHV F elec EF elec F heat EF heat ) (4) This study used an emission factor for electricity (EF elec )of 0.8 t CO2,eq /MWh (0.226 t CO2,eq /GJ), which was proposed by the Korea Power Exchange 29 as a 3-yr average from 2005 to 2007 for thermal power plants, excluding nuclear plants. The factor for heat (EF heat ) was not readily available and was estimated from the fuel consumption for district heating. In 2006, 1358 Ktoe of liquid natural gas (LNG) and fuel oils were, in total, consumed for district heating, 7 which yielded an EF heat of t CO2,eq /toe ( t CO2,eq /GJ). The typical fuel efficiency of large modern incineration plants is approximately 20% for electricity only, and as high as 85% for CHP. 30 Therefore, the following three cases of energy production can be considered for GHG emission reduction by fossil fuel displacement: Electricity generation only: F elec 20%, F heat 0% : ton CO2,eq /ton waste, (5) Heat generation only: F elec 0%, F heat 80% : ton CO2,eq/ ton waste, (6) Efficient CHP plant: F elec 15%, F heat 70% : ton CO2,eq /ton waste. (7) Energy and GHG Emission Reduction Potentials of EfW Using the key factors established in the previous sections, the potentials of energy production and GHG emissions reduction were calculated on a per-ton-waste and annual basis for different EfW cases. The results are summarized in Table 7. The annual calculations are based on the total amounts of nonrecyclable MSW generation (7.637 Mt/yr) Volume 60 February 2010 Journal of the Air & Waste Management Association 181

7 Table 7. Energy potential and GHG emissions from different EfW cases. Category Parameter Units Case 1: Landfill, no EfW Case 2: Current Mix Case 3: Combustion for Electricity Only Case 4: Combustion for Heat Only Case 5: Combustion for CHP Conditions for landfill Proportion of waste % 100% 60% 0% 0% 0% CH 4 to the t CH4 /ton waste atmosphere CH 4 recovered t CH4 /ton waste F electricity GJ/GJ F heat GJ/GJ Conditions for Proportion of waste % 0% 40% 100% 100% 100% combustion F electricity GJ/GJ F heat GJ/GJ Output from landfill (per t waste basis) Output from combustion (per t waste basis) Energy potential GJ/t waste Direct GHG emission t CO2 /t waste GHG saving by FFD a t CO2 /t waste Energy potential GJ/t waste Direct GHG emission t CO2,eq /t waste GHG saving by FFD t CO2,eq /t waste Total Energy potential GJ/t waste Net GHG emission b t CO2,eq /t waste Annual basis Waste landfilled Mt/yr Waste burned Mt/yr Energy potential Mtoe/yr Electricity production Mtoe/yr Heat production Mtoe/yr Net GHG emission b Mt CO2,eq /yr Notes: a FFD fossil fuel displacement; b Net GHG emission direct GHG emission GHG saving by FFD. as shown in Table 2. If the nonrecyclable MSW is landfilled without energy production for the recovered CH 4 in case 1, its uncontrolled emission to the atmosphere could be as high as 8 Mt CO2,eq /yr. This quantity shows the importance of EfW activities for the reduction of GHG emissions. Case 2 is close to the current situation in Korea, in which 60% of the nonrecyclable MSW is landfilled and the remainder is incinerated, primarily for heat production. In 2006, electricity and heat generation using LFG were 38.6 and 15.2 Ktoe/yr, respectively, from landfill sites that treat MSW, C&I, and C&D wastes together. Because about half of the total amount landfilled was MSW, as shown in Table 2, it was assumed that the electricity and heat generation by the LFG from MSW was 19.8 and 7.6 Ktoe/yr, respectively. Then the fuel efficiencies of electricity and heat for the landfill were determined to obtain the corresponding energy outputs. The results show that GHG emissions are still significant (4.654 Mt CO2,eq /yr), mainly because of CH 4 emission from landfills. The total energy production was megatons of oil equivalent (Mtoe)/yr, which was mainly from burned waste. Cases 3 5 are for all of the waste burned with different fuel efficiencies: Case 3 for heat only, case 4 for electricity only, and case 5 for CHP. The net GHG emission was calculated from the direct GHG emission (0.641 t CO2,eq /t waste ) minus the GHG savings by fossil fuel displacement (see factors given in the previous section). The results suggest that achieving high energy efficiency is essential to negating direct GHG emissions from EfW by fossil fuel displacement. When compared with the baseline case (case 2) of emitting t CO2,eq /t waste of GHG, the use of EfW (cases 3 5) in reducing the proportion of landfill can contribute to a noticeable reduction in GHG emissions from the current level. However, a significant net reduction of GHG emissions can be accomplished only by efficient CHP (case 5, in which the amount was t CO2,eq /t waste ). If all of the nonrecyclable MSW is burned for CHP, annual GHG emissions can be reduced by Mt CO2,eq and energy production can be Mtoe in total. Note that national GHG emissions in 2006 were Mt CO2,eq and the total primary energy supply was Mtoe. CONCLUSIONS With scarce energy resources and heavy industrial activities, South Korea faces the difficult task of reducing GHG emissions. EfW can play an important role in the country s efforts for renewable energy production. The reference properties of nonrecyclable MSW were established using available analytical data, which had MJ/kg of LHV with a fossil carbon fraction of approximately 16% (wet). When landfilled, 1 t of waste could emit t CH4, equivalent to approximately 1 t CO2,eq. When burned for energy, the direct GHG emissions due to the fossil carbon fraction were t CO2,eq /t waste, but this could be reduced by saving the GHG emissions corresponding to the amount of fossil fuel displaced. To realize the energy and GHG reduction potentials, EfW should be maximized for nonrecyclable waste at high energy conversion efficiencies. Burning all of the nonrecyclable MSW for efficient CHP can contribute to a net reduction in GHG of approximately 2.7 Mt CO2,eq /yr whereas the current waste management scheme emits approximately 4.6 Mt CO2,eq /yr. This study can serve as the starting point for a 182 Journal of the Air & Waste Management Association Volume 60 February 2010

8 detailed analysis of waste management scenarios for energy production and its impact on GHG emissions. ACKNOWLEDGMENTS This work was supported by a National Research Foundation of Korea grant funded by the Korean government (KRF D00150). REFERENCES 1. Björklund, A.; Finnveden, G. Recycling Revisited Life Cycle Comparisons of Global Warming Impact and Total Energy Use of Waste Management Strategies; Res. Conserv. Recyc. 2005, 44, Waste Strategy for England; Department for Environment, Food, and Rural Affairs: London, U.K., 2007; p Lee, P.; Fitzsioms, D.; Parker, D. Quantification of the Potential Energy from Residuals (EfR) in the UK; Institute of Civil Engineers/Renewable Power Association: London, U.K., Skovgaard, M.; Hedal, N.; Villanueva, A.; Addersen, F.M.; Larsen, H. Municipal Waste Management and Greenhouse Gases; European Topic Centre (ETC)/Resource Waste Management (RWM) Working Paper 2008/1; ETC: Copenhagen, Denmark, Psomopoulos, C.S.; Bourka, A.; Themelis, N.J. 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In Proceedings of the 2005 Spring Meeting of the Korean Society of Environmental Engineers; Korean Society of Environmental Engineers: Suwon, South Korea, 2005; pp Revised 1996 Guidelines for National Greenhouse Gas Inventories; Intergovernmental Panel on Climate Change: Geneva, Switzerland, Good Practice Guidance and Uncertainty Management in National Greenhouse Gas Inventories; Intergovernmental Panel on Climate Change: Geneva, Switzerland Study on the Monitoring and Projection System of LFG and Leachate from Sudokwon Landfill Site (in Korean); Sudokwon Landfill Site Management Company: Incheon, South Korea, Development of GHG Emission Factors in Environmental Sectors Landfill (Final Report); Prepared by the Environmental Management Corporation for the Department of Environment, Korea: Incheon, South Korea, Kim, H.S.; Yi, S.M. Methane Emission Estimation from Landfills in Korea ( ): Quantitative Assessment of a New Approach; J. Air & Waste Manage. Assoc. 2009, 59, 70-77; doi: / Changes in Atmospheric Constituents and in Radiative Forcing. In IPCC Fourth Assessment Report; Intergovernmental Panel on Climate Change: Geneva, Switzerland, Lee, S.; Hong, J.; Kim, D.; Lee, S.; Song, H.; Cho, K.; Choi, S.; Lim, J. A Study on the Estimation of Emission Characteristics of Greenhouse Gases in the Waste Incineration. In Proceedings of the 45th Meeting of the Korean Society for Atmospheric Environment; Korean Society for Atmospheric Environment: Cheongwon, South Korea, 2007; pp IPCC Guidelines for National Greenhouse Gas Inventories; Intergovernmental Panel on Climate Change; National Greenhouse Gas Inventories Programme: Geneva, Switzerland, Development of Greenhouse Gas Emission Factor for Power; Korea Power Exchange: Seoul, South Korea, Energy from Waste Statistics, State-of-the-Art Report, 5th ed.; International Solid Waste Association: Vienna, Austria, About the Author Changkook Ryu is an assistant professor in the School of Mechanical Engineering at Sungkyunkwan University in South Korea. Please address correspondence to: Changkook Ryu, School of Mechanical Engineering, Sungkyunkwan University, Suwon , South Korea; phone: ; fax: ; cryu@me.skku.ac.kr. Volume 60 February 2010 Journal of the Air & Waste Management Association 183

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