Scholarly article on topic 'Collaborative Emission Reduction of Greenhouse Gas Emissions and Municipal Solid Waste (msw) Management-Case Study of Tianjin'

Collaborative Emission Reduction of Greenhouse Gas Emissions and Municipal Solid Waste (msw) Management-Case Study of Tianjin Academic research paper on "Earth and related environmental sciences"

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Abstract of research paper on Earth and related environmental sciences, author of scientific article — Yuan Wang, Yu He, Beibei Yan, Wenchao Ma, Meng Han

Abstract There is a huge potential for reducing greenhouse gas emissions in the way of disposing municipal solid waste (MSW), and the important role of MSW in global greenhouse gas emissions has attracted much attention. Based on the composition of Tianjin MSW and its content, collaborative emission reduction of three main MSW disposal ways were analysis, including landfill without landfill gas (LFG) utilization (S1), landfill with LFG utilization (S2), and incineration (S3). Taking Tianjin Binhai municipal solid waste incineration power generation CDM project and Tianjin Shuangkou landfill gas recovery and electricity generation CDM project as examples, the calculation methods provided by Intergovernmental Panel on Climate Change (IPCC) Guidelines were used to calculate the greenhouse gas emissions and emission reductions, and then compared the collaborative emission reductions of the three scenarios. Results show that collaborative emission reductions of S1∼S3 respectively are 0.602 tCO2e/t MSW, 0.657 tCO2e/t MSW, and 0.871 tCO2e/t MSW, so the results of the comparison is S3>S2>S1.

Academic research paper on topic "Collaborative Emission Reduction of Greenhouse Gas Emissions and Municipal Solid Waste (msw) Management-Case Study of Tianjin"

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Environmental Sciences

Procedía Environmental Sciences 16 (2012) 75 - 84

The 7th International Conference on Waste Management and Technology

Collaborative emission reduction of greenhouse gas emissions and municipal solid waste (msw) management - case study of

rp • • •

Tianjin

Yuan Wanga'*, Yu Hea, Beibei Yana, Wenchao Maa, Meng Hanb

a School of Environmental Science and Engineering, Tianjin University, Tianjin 300072, China b Tianjin TEDA Environmental Protection Company Limited, Tianjin 300350, China

Abstract

There is a huge potential for reducing greenhouse gas emissions in the way of disposing municipal solid waste (MSW), and the important role of MSW in global greenhouse gas emissions has attracted much attention. Based on the composition of Tianjin MSW and its content, collaborative emission reduction of three main MSW disposal ways were analysis, including landfill without landfill gas (LFG) utilization (S1), landfill with LFG utilization (S2), and incineration (S3). Taking Tianjin Binhai municipal solid waste incineration power generation CDM project and Tianjin Shuangkou landfill gas recovery and electricity generation CDM project as examples, the calculation methods provided by Intergovernmental Panel on Climate Change (IPCC) Guidelines were used to calculate the greenhouse gas emissions and emission reductions, and then compared the collaborative emission reductions of the three scenarios. Results show that collaborative emission reductions of S1~S3 respectively are 0.602 tCO2e/t MSW, 0.657 tCO2e/t MSW, and 0.871 tCO2e/t MSW, so the results of the comparison is S3>S2>S1.

© 220122 Selection and/or peer-review under respons ibility of Basel Convention Coordinating Centre for Asia and the Pacific and National Center of Solid Waste Management, Ministry of Environmental Protection ofChina.

ELSEVIER

Keywords: greenhouse gas emission reduction; collaborative emission reduction; municipal solid waste

1. Introduction

According to the greenhouse gas (GHG) emissions data submitted to the UNFCCC by major economies during 1990-2007 (excluding countries in market transition and LULUCF), the EU-15 emissions data showed that although the emissions in the field of waste accounted for only 2.76% of total emissions in 2007, its total reduction are accounted for 29.7% of total reduction in the same year.

* Corresponding author

E-mail address: w_yuan77@163.com (Yuan Wang).

1878-0296 © 2012 Selection and/or peer-review under responsibility of Basel Convention Coordinating Centre for Asia and the Pacific and National Center of Solid Waste Management, Ministry of Environmental Protection of China doi: 10.1016/j.proenv.2012.10.011

Researching in the greenhouse gas emissions of Germany between 1990 and 2007, it could be found that the emissions in the field of waste accounted for only 3.33% of Germany's total emissions and the reduction in the same field accounted for 11.18% of total emission reductions. The emission reduction rate in the field of waste was 71.5% and 94.12% of which is achieved through the processing of municipal solid waste (MSW) [1]. The data above suggest that MSW has a huge potential for reducing greenhouse gas emissions. China has made strengthening the MSW management as a priority area of reducing greenhouse gas emissions by compiling "China's National Climate Change Programme" in 2007. Thus, the important role of MSW in global greenhouse gas emission reduction has been attracted much attention.

Current annual emission of MSW is very high in China, as shown in fig. 1, Garbage clean-up and transport volume became bigger during 1979 to 2010, and the harmless treatment ratio was also increasing [2]. In 2010, the MSW clean-up and transport volume was 158.05 Mt (million tons) in China, 77.9% for harmless treatment. Among the MSW of harmless treatment, 77.9% was processed by the way of landfill, only 18.8% was processed by the way of incineration and 1.5% was processed by the way of compost. Selecting the appropriate processing mode can not only reduce the impact of MSW on local environment, but also reduce greenhouse gas emissions and save fossil fuels and mitigate of global climate wanning.

Fig. 1 Chinese MSW collection volume and harmless treatment volume during 1979-2010

"Collaborative" first appeared in the Third Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) in 2001, refers to "the profit gained by the implementation of relevant policies for various reasons at the same time". Collaborative emission reduction in this paper is more specific and refers to the effects of greenhouse gas reduction while controlling the discharge process of local pollutants. This paper is concerning the three main ways of MSW disposal: incineration, landfill without landfill gas (LFG) utilization and landfill with LFG utilization. It makes accounts of collaborative emission reduction of GHG and MSW disposal while taking Tianjin as an example.

2. Calculation Methods of GHG Emission Reduction

So far the calculation methods of GHG emissions of MSW are mainly based on the methods provided by IPCC Guidelines for National Greenhouse Gas Inventories and LCA methods, and the calculation methods of greenhouse gas emission reduction of MSW disposal project are mainly based on CDM projects methodology. Although the LCA method takes into account the carbon emissions of packing,

transportation, landfill and other processes during the all landfill process, because of the amount of dissipation of greenhouse gases during transportation and other processes are very limited, the main greenhouse gas emissions are concentrated in the disposing process. Zhao et al (2010) [3] had made a comparative analysis between IPCC inventory methods and the LCA method, the carbon emissions trends calculated by the two accounting methods of different MSW disposal methods are basically the same. In view of the IPCC inventory method is more standardized than the LCA method, this paper mainly uses IPCC inventory methods combine with CDM projects methodology to calculate the GHG emission reductions. As approximately 50% of LFG generated in the MSW landfill is methane, LFG is a kind of good energy that can be collected and utilized, LFG recovery and utilization is a good MSW disposal approach. However, due to the amount of MSW collection is small and the lack of land used for landfill in many areas of China, the size of landfills there are small. And they don't have the conditions for LFG recovery and utilization, or cannot achieve their economic benefits, so sanitary landfill is still the main way of MSW disposal. In this paper, the sanitary landfill with LFG flaring emptying is a scenario to consider.

Scenarios set as follows:

• S0 Baseline: Landfill without LFG utilization is the disposal approach, the LFG directly be emptied

without any treatment [4].

• S1 LFG without utilization: Compared to S0, the LFG is emptied after flaring.

• S2 LFG utilization: Compared to S0, the landfill plant in this scenario is equipped with LFG collection,

upgrade, and conversion system. LFG is assumed to produce electricity and the LFG that cannot be collected is emptied after flaring.

• S3 Incineration: All of the MSW is assumed to be treated in the MSW incineration power plant. This

scenario can get benefit from incineration with energy recovery instead of LFG utilization.

2.1. S0 Baseline Scenario - Calculation of GHG Emissions of Landfill

After the landfill of MSW, due to microbial activities, biodegradable organic ingredients in MSW are gradually broken down; this process can be divided into five stages: hydrolysis/aerobic degradation stage, hydrolysis/fermentation stage, acidification stage, production methane stage, oxidation stage [5]. Methane production from MSW degradation is a dynamic biological conversion process using microorganism as intermediary and affected by many factors, the main influencing factors as follows:

• MSW features. Biodegradable organic matter content, as well as the composition of cellulose , protein,

and fat in MSW, plays a decisive role in the production of landfill gas and affects the total LFG generated. The easily degradable organic matter (such as kitchen waste) makes the most direct contribution to the production of LFG, and provided the conditions for the degradation of other organic matter [6].

• Moisture. Moisture content of MSW depends mainly on the water content of MSW itself, rainfall in

the landfill, seepage control measures of surface water and groundwater. Appropriate supplementary water is propitious to degradation. The movement of water inside MSW can also transport the microorganisms and nutrients to everywhere and at the same time take away degradation products, thus speeding up the degradation. But excessive moisture content will be a cooling effect, and block the flow of gas , resulting in the reduction of gas production. Studies have shown that the initial moisture content of MSW for 60% -80% is more suitable for degradation [7].

• Temperature. The generation of LFG has related to the activity of methane bacteria. There are two

active methane bacteria during methanogenic stage, one is medium temperature methane bacteria and the optimum temperature for 30~35 °C, another is thermophilic methane bacteria and the

optimum temperature for 45~65°C [8]. So the suitable temperature for methane bacteria is between 30~65 °C, too low or too high a temperature will cause the decreasing of LFG generation.

These are important factors that can affect the GHG emissions, in addition, pH and the landfill site characterization would affect the GHG emissions [9]. MSW features mainly affects the total emissions, while moisture, temperature, etc. mainly affect degradation half-life (ti/2), that is to say, affect the LFG production rate.

The main components of landfill gas are CH4 and CO2, each accounting for about 50% of total LFG. The content of other gases such as O2, N2, H2S, hydrocarbons and aromatics is extremely low. Because the CO2 emissions of this part are carbon emissions from biomass, they are not included in its GHG emissions [10]. The baseline scenario is mainly used to measure the amount of landfill methane and then convert it into a global warming potential (GWP). Use the first order decay (FOD) method to calculate.

The FOD calculation formula is as follows:

Dch4 = [(A xk X Mx XCmx XF X 16/12) X e-k(t-x)] X GCH4 (1)

where DCH4 is methane generated in sanitary landfill, t; A is the normalization factor to fix the total, A = (1 - e-k )/k; k is methane production rate constant, k = In (2) /11/2; Mx is total amount of MSW which were landfilled in xth year, t; Cmx is decomposable DOC amount per MSW in xth year, t/t; F is volume ratio of CH4 in LFG; 16/12 is molecular weight ratio of CH4/C; GCH4 is the multiple compared greenhouse effect produced by CH4 to CO2, as 21.

CH4 is the result of the degradation of organic matter under anaerobic conditions. Part of CH4 is oxidized in landfill cover layer, and can be recovered to use as energy or be flared. Therefore, the landfill actual emission of CH4 is less than the amount of production. The calculation formula of CH4 emissions is as follows:

Eso = (Dch4 - R) • (1 - OX) (2)

where ES0 is CH4 release by the sanitary landfill, t; R is the amount of recycled CH4, t; OX is oxidation factor, %.

2.2. Calculation of GHG Emission Reductions of Two Landfill Disposal Methods-S1, S2

S1 is the scene of the general MSW sanitary landfill, LFG was collected through the airway equipment

and then burned into C02: tiare

Cfi* + 2QZ =* CQZ -H 2

This part of CO2 is also from biomass (as methane comes from the decomposition of organic waste, CO2 conversed from thus part of methane does not belong to fossil carbon sources), they are not included in its GHG emissions. So the baseline of this Scenario is: in the absence of LFG utilization projects, MSW landfill emissions of CH4.

Compared to baseline S0, the CO2 emission reduction amount of LFG without utilization is the GHG emission amount of S0.

The CO2 emission reduction amount of S1 is defined as ES1:

Esi — Esq

The baselines of S2 LFG utilization are:

In the absence of LFG utilization projects, MSW landfill emissions of CH4;

In the absence of LFG utilization projects, the average CO2 emissions of the local power plant.

The CO2 emission reduction amount of S1 is defined as ES2:

Es2 = Eso + Eelec (4)

where Eelec is the emission reduction amount of power generation to replace the normal electricity, calculation formula as formula 5.

Eelec ET • CEFelec (5)

where ET is external power output after the disposal of MSW by landfill, MW*h; CEFelec is the average CO2 emission factor from local power generation, tCO2e/MW^h.

2.3. Calculation of GHG Emission Reductions of Incineration - S3

The baselines of S3 incineration are:

• In the absence of MSW incineration projects, MSW landfill emissions of CH4, calculation formula as

formula 1;

• In the absence of MSW incineration projects, the average CO2 emissions of the local power plant;

• In the absence of MSW incineration projects, the average CO2 emissions of the local boiler heating

plant.

In the calculation of CO2 emission reductions of MSW incineration power generation projects, due to the original source of the carbon contained in animals, plants, kitchen waste, paper and any other MSW contents is biomass, from the perspective of the carbon balance, the whole process above is zero carbon emission and not included in the calculation. While the original source of the carbon contained in plastic and other MSW contents is fossil, they should be deducted in the calculation of emission reductions. Due to the low calorific value of MSW in current Chinese cities, it often need to add coal, heavy oil, natural gas and other auxiliary fossil fuels in the incineration of MSW. So the amount of CO2 of this part should be deducted in the calculation of emission reductions [11]. The calculation formula is as follows:

Es3 = Eso' + Een - Eghg - Efud - El (6)

where ES3 is the emission reduction amount of S3, tCO2e; ES0' is CH4 release by the sanitary landfill according to the situation of S3, calculated as formula 7; Een is alternative energy sources emission reduction amount (including the substitution of electricity and heat), calculated as formula 8; EGHG is the emission amount by burning of MSW source of fossil carbon, calculated as formula 9 [10]; Efud is the emission amount by combustion of auxiliary fuel, tCO2e; El is the leakage emissions remaining after incineration of waste, tCO2e.

As incineration eliminates all the possibility of producing methane one-time, this paper uses the mass balance method to calculate the baseline emission amount:

Eso' = M• C • r • (16/12) • F • Gch4 (7)

where M is total amount of MSW which were landfilled, t; C is the percentage of biodegradable organic carbon contained in MSW, identified by the components of MSW; r is the decomposition rate of degradable organic carbon (DOC) in MSW, IPCC recommended as 50% (as constant ).

Een — ETe • CEFelec + ETt • CEFt (8)

where ETe is external power output after the disposal of MSW by incineration, MW'h; ETt is external heat output after the disposal of MSW by incineration, GJ; CEFt is the average CO2 emission factor of local industrial boiler, tCO2e/GJ.

EghG — EcO2 + EN2O (9)

where ECO2 is the amount of CO2 emissions from fossil source in the incineration of MSW, t; EN2O is the amount of N2O emissions in the incineration of MSW, tCO2e.

When specific accounting of the project emission reductions, the baseline emissions as well as the characteristics of the disposal project itself need to be consider. Accounting of the landfill is superimposed dynamic first-order decay, unlike the static accounting, the result is related to the accounting year and the annual amount of waste disposal. After the operation period, due to the decline of LFG amount and utilization efficiency, as well as a lack of management that make the LFG direct emission without treatment, resulting in the reduction of the emission reductions. While incineration eliminates all the possibility of producing methane one-time, thus reducing the emissions of the baseline completely.

3. Analysis of Collaborative Emission Reduction of Three Disposal Methods in Tianjin

3.1. Tianjin MSW Characteristics and Model Parameter Selection

In 2010, 2.07 Mt MSW was generated in Tianjin (the daily per capita MSW was about 0.9 kg), 1.93Mt of which for harmless treatment, the harmless treatment rate was 77.9%. Among the MSW of harmless treatment, 1.35 Mt was processed by sanitary landfill, accounting for 69.8%; 0.58 Mt was processed by S3 incineration, accounting for 30.2%. Among the MSW of sanitary landfill, 0.75 Mt was processed in S1, accounting for 38.9%; 0.60 Mt was processed in S2, accounting for 30.9% [12].

Based on the composition of Tianjin MSW in 2006 [13] (table 1), it can be obtained that DOC content is 0.134t/tMSW and fossil carbon content is 0.106t t/t MSW.

From Table 1 that the kitchen waste composition is 57%, and is conducive to degradation. At the same time the degradation rate of paper is the center is medium, and its proportion is relatively small, for 8.7%. Practice has proved that 20~30 C/N ratio is most favorable to anaerobic fermentation. MSW C/N is 42 in Tianjin (Table 1), and that is not conducive for degradation. The MSW average moisture content was 44.4% according to Table 1, the moisture content was small, lower than the optimum range for gas production.

In Tianjin, the average temperature is 13 °C, the annual precipitation is 600 mm, while the evaporation rate is 1032 mm. It belongs to the drier areas (annual precipitation / evaporation < 1) of the North Temperate Zone (temperature < 20 °C). Using the default half-life values of the MSW components provided by the IPCC in the conditions of Tianjin, it can be obtained by the weighted average that the MSW degradation half-life (t1/2) is 9.4 years, and the methane generation rate (k) is 0.074.

Table 1. Fraction composition of MSW in Tianjin

Fraction Fraction (%) Moisture (%) C (%) DOC (%) N (%)

Kitchen waste 56.9 70 48a 48 2.6

Slag & ceramics 16.2 20 24.3 0 0.5

Metals 0.4 2 4.5 0 0.1

Glass 1.3 2 0.5 0 0.1

Paper 8.7 10.2 43.4 43.4 0.3

Plastics 12.1 1.2 60 0 0

Textiles 2.5 10 48 38.4 2.2

Wood 1.9 1.3 49.6 49.6 0.2

a Elementary composition of MSW is analyzed based on dry weight.

3.2. Introduce Instance Projects

Clean development mechanism (CDM) projects are chosen as instance Projects: Hangu MSW incineration power generation project in Binhai New Area in Tianjin (Hangu for short) [14] and Shuangkou MSW landfill gas power generation project in Tianjin (Shuangkou for short) [15]. These two projects accounted for 56.81% of the amount of MSW disposal in Tianjin. Shuangkou is the only LFG utilization project that has been put into use in Tianjin. In 2010, it disposed of 5.96 Mt MSW, accounting for 100% of the S2 processing capacity and 30.88% of the total MSW. Hangu was put into use in 2011 and if put into use in 2010, it would account for 85.78% of S3 processing capacity and 25.93% of the total MSW. The two waste disposal projects are representative in Tianjin, and therefore they are selected as the instances on behalf of S2 and S3.

• S1: As common sanitary landfill standard data are difficult to obtain, calculate in accordance with

Shuangkou data. Assuming that all LFG is emptied after flaring, other conditions are the same as S2.

• S2: According to the design of Shuangkou, LFG is collected from landfills for power generation. Both

the excess LFG and the gas generated when electricity is not generated would be discharged through on-site combustion system after flaring. The collection rate of LFG generated by MSW landfill is 45~60%, and the average collection rate is 55.5%. 95% of power generated by LFG is sent into the grid and 5% is consumed on site. The prior period for landfilling is four years, the project life cycle is from 2008 to 2028 for a total of 21 years. The total MSW capacity is 6.64 Mt, the daily processing capacity is 1300 tons. The landfilling period is from 2008 to 2018, total 11 years.

• S3: Hangu has a two-year construction period and a twenty-year life cycle. This program will treat 0.5

Mt MSW per year, total 10 Mt MSW during its operation period. The power generated by this program is up to 85,900 MW*h per year, and heat supply is up to 1,084,000GJ. On-site power consumption is 200MW^h per year.

3.3. Collaborative Emission Reduction of Three Disposal Methods

For landfill without LFG utilization (S1), all LFG is emptied through on-site combustion systems after flaring without power generation. The emission reductions are equivalent to the methane emissions of landfill. Use formula 1 and formula 2 to calculate the S0 baseline emissions, and then though formula 3 to obtain the total emission reductions of S1 as 4.00 Mt CO2e. The average GHG emission reduction of MSW processing by S1 is 0.602 t CO2e/t MSW.

For landfill with LFG utilization (S2), calculate the average CO2 emissions of the local power plant without the LFG utilization projects in Tianjin at first. The CEFelec is measured by the weighted average

of both grid margin emission factor (EFgrid, OM, y) and capacity margin emission factor (EFgrid, BM, y), which is also called margin CM, and the weight defaults of both wOM and wBM are 50% [16]. Tianjin is in North China, its CEFelect is 0.87 tCO2/MW^h, based on the data of power grid in North China. 1t methane from landfill can generate electricity of 1.986MW^h, the average net generating capacity is 60.3 kW^h/t MSW. According to formula 5, the emission reduction for substitution of electricity is 0.055 t CO2e/t MSW. Use formula 4 to obtain the total emission reductions of S2 as 4.36 Mt CO2e. The average GHG emission reduction of MSW processing by S2 is 0.657 t CO2e/t MSW.

For incineration (S3), use formula 7 to obtain the emission reductions of avoiding methane emissions by mass balance method as 0.936 t CO2e/tMSW. The average generating capacity of combusting 1t MSW is 171.4 kW^h, and heat productivity is 2.168GJ. According to formula 8, the emission reduction for substitution of energy is 0.354 t CO2e/t MSW. According to formula 9, the GHG emissions caused by burning fossil carbon can be calculated, and the result is that the total emission of CO2 and N2O is 0.403 t CO2e/tMSW. Based on the monitoring result of a MSW incineration power plant in Shanghai [17], the emissions caused by auxiliary material and accelerant in incineration process is 6.7-7.7kg CO2 eq./t, that is Efri. The leakage emissions remaining after incineration (E) is 9.63 kg CO2e/t MSW. Use formula 6 to obtain the total emission reductions of S3 as 8.71 MtCO2e. The average GHG emission reduction of MSW processing by S3 is 0.871 t CO2e/t MSW.

Fig. 2 Collaborative emission reduction composition of processing unit MSW in S1~S3 three scenarios

In summary, the collaborative emission reductions of S1~S3 respectively are 0.602 tCO2e/t MSW, 0.657 tCO2e/t MSW, and 0.871 tCO2e/t MSW. Contrast the collaborative emission reduction composition of processing unit MSW in S1~S3 three scenarios, as shown in Fig. 2. The GHG emission reduction amount of S1 all comes from eliminating the GHG emission amount of S0. Most emission reduction of S2 comes from eliminating the GHG emission amount of S0, accounting for 91.6%. And there is 8.4% of emission reduction for substitution of energy. Most emission reduction of S3 also comes from eliminating the GHG emission amount of S0. As incineration eliminates all the possibility of producing methane onetime, the emission reduction of this part above is bigger than S1 and S2 during its operation period. And the alternative energy sources emission reduction of S3 including the substitution of electricity and heat, it is much larger than that of S2. But the releases of fossil carbon in MSW incineration process and emission from auxiliary fuel are additional emission, which offset part of the emission reductions.

4. Conclusions and Discussion

4.1. Conclusions

Contrast the three scenarios of S1~S3, they have their advantages and disadvantages.

• Collaborative emission reduction: S3>S2>S1. Unlike S2, S1 did not have the steps of the LFG power

generation, so the collaborative emission reduction of S1 is less than S2 without the reduction for substitution of energy. The reduction for substitution of energy of S3 is much larger than that of S2, and the methane emission reduction of S3 for the baseline is more thorough than others. Although the releases of fossil carbon in MSW incineration process and emission from auxiliary fuel offset part of the emission reductions, the collaborative emission reduction of S3 is still larger.

• Power generation efficiency: S3>S2. The efficiency of incineration power generation is higher than

that of LFG power generation. The power generation of the former is about 205~268 kW^h /t MSW, while that of the latter is only 168 kW^h /t MSW.

• The collaborative emission reduction of incineration is larger than the other two ways of landfill, and

due to its low occupation of land and easiness to select the location, the incineration utilization is adequate for the city with a shortage of land. But incineration can emit GHG itself, based on He et al

[17], and the GHG emissions of incineration process is still unable to offset the emission reductions of alternative fossil fuel power generation, that is to say, the GHG emissions of per unit MSW incineration is higher than that of fossil fuel incineration. Though it mitigates CH4 emissions caused by landfill, the incineration efficiency itself is needed to rise.

• The collaborative emission reduction of S1 sanitary landfill is only slightly less than that of S2 LFG

utilization, and the result of S1 accounting for 91.6% of S2. There is no power generation equipment in S1, so the construction cost of S1 is much less than S2. According to China's actual situation in the township, building small and medium - sized sanitary landfill is still an important method for processing of MSW.

4.2. Discussion

• Incineration power generation projects can also supply heat, the waste heat after incineration can also

be utilized through cogeneration technology. But some existing incineration plants are small scale, geographically isolated, inhabitants around are of small number and sparse, they don't have the conditions of heating or don't have heating design. On this paper, the reduction for substitution of heating of incineration accounts for 40.7% of its total emission reduction. So no heating makes the emission reduction down to 0.516 t CO2e/tMSW, less than the emission reduction of S2.

• The landfill unit is open during landfill operations in MSW landfill, the LFG is not easy to be

controlled and collected. The methane generated during operation of the landfill operating steps which is not handled or collected for utilization accounting for 50% of the total capacity in theory

[18]. But because of methodological considerations and lacking of data, this part of methane was not considered in this paper. Therefore, the actual methane consumption should be less than the calculated emission of the baseline.

These issues need to be concretely analyzed in actual MSW processing projects, and the LFG production process need further study.

Acknowledgements

This work was supported in part by the project in the National Science & Technology Pillar Program "integration research and demonstration of low-carbon technologies in MSW disposal system". No. 2011BAJ07B04.

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