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Environmental performance of municipal solid waste strategies based on LCA method: a case study of Macau
Journal of Cleaner Production 57 (2013) 92e100
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Journal of Cleaner Production journal homepage: www.elsevier.com/locate/jclepro
Environmental performance of municipal solid waste strategies based on LCA method: a case study of Macau Qingbin Song a, Zhishi Wang a, *, Jinhui Li b a b
Faculty of Science and Technology, University of Macau, Macau, China School of Environment, Tsinghua University, Beijing 100084, China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 8 November 2012 Received in revised form 8 April 2013 Accepted 22 April 2013 Available online 15 June 2013
Increasing public attention has been brought to bear on the environmental impacts of municipal solid waste (MSW) management in Macau, due to the continually increasing amount of MSW being generated and the limited space and capacity of waste treatment facilities. This study evaluates the current and potential patterns of MSW management with regard to environmental impacts in Macau, using the life cycle assessment (LCA) method. We also assess the baseline scenario, reflecting the existing MSW management system, as well as five other scenarios, exploring waste treatment innovations, to quantitatively predict potential environmental impact mitigation for Macau. Additionally, a sensitivity analysis is used to investigate the influence of the different assessment methods and recycling rates of valuable resources in the source separation process. The results show that the current management system of MSW in Macau can treat and dispose of the MSW well, and at the same time can generate some environmental benefits. Compared with Scenario 0 (the current MSW management system), Scenario 4 (source separation and incineration) shows the highest potential to increase the environmental benefits. Scenario 5 (integrated waste management) is also a good option, with higher benefits (85.96%) than Scenario 0. The analysis shows that, in each scenario (except Scenario 1, the past process of landfill only), the waste treatment processes, including source separation and incineration, dominate the environmental impacts; while processes such as collection and transportation, composting, and landfill, have a relatively small influence. The sensitivity analysis of recycling rate shows an approximately linear relation of inverse proportion between recycling rate and total environmental impact. Considering the limited financial resources and the current waste management practices in Macau, Scenario 4 would be the preferred choice. Ó 2013 Elsevier Ltd. All rights reserved.
Keywords: Life cycle assessment Municipal solid waste Environmental impacts Macau
1. Introduction The management of municipal solid waste (MSW) continues to be a major challenge in urban areas throughout the world, particularly in the rapidly growing cities and towns of the developing world (Jing et al., 2009; Guerrero et al., 2013). With the rapid economic development in Macau, along with population growth, increased prosperity and tourism in recent years, the amount of waste generated in Macau has also been increasing, exerting great pressure on waste management systems within Macau’s limited land area (Jin et al., 2006). The amount of MSW generated in Macau has increased steadily over the last decade (DSEC et al., 2012; DSPA, 2012), from
* Corresponding author. Tel.: þ86 83974470; fax: þ86 28838314. E-mail address: [email protected] (Z. Wang). 0959-6526/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jclepro.2013.04.042
232,726 tons in 2001 to 321,752 tons in 2010dan average annual increase of 3.70%. The daily mean quantity per capita of solid waste generated was 1.46 kg/day in 2001 and 1.59 kg/day in 2010dan average annual increase rate of 1.05%. This rapid growth could be attributed to increases in both population and economic development (Fig. 1). The composition of MSW depends on a wide range of factors such as food habits, cultural traditions, lifestyles, climate and income, etc. The changing physical composition of MSW over time in Macau is shown in Table 1. Food waste, paper, plastics, and the others contributed the most to the MSW. It can be seen that a considerable quantity of MSW, including paper and cardboard, plastics, metal and glass, can be recycled, recovered or reused. From Table 1, it can be also seen that the composition of MSW has fluctuated enormously, especially in the categories of “Other” and “Food.” There are two possible reasons. One possible reason is that when sampling the solid waste, because many substances were
450000
2.00
400000
1.80
350000
1.60 1.40
300000
1.20
250000
1.00 200000
0.80
150000
0.60
100000
0.40
50000
0.20
0
0.00 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 MSW
Daily mean quantigy per capita of MSW (kg)
The generation amount of MSW (tons)
Q. Song et al. / Journal of Cleaner Production 57 (2013) 92e100
Daily mean quantity
Fig. 1. MSW generation amounts and daily mean quantities per capita, 2001 to 2010.
difficult to be classified, especially for the substances less than 2 cm in diameter, many composition of the solid waste was considered as the “Others”. Another reason is because Macau was only a small tourist city (about 30 km2 and 557 thousand populations) and owned a small capacity of solid waste, the composition of solid waste will be influenced by the tourists and the economic environment. The separation and recycling of valuable resources has been practiced in Macau for nearly 10 years. Prior to 2009, in addition to 208 public sites equipped with recyclable waste separation facilities, a number of waste collection stations with recyclable waste separation containers were installed, facilitating residential recyclable waste disposal. Altogether, 289 high-rise buildings participated in the “Domestic Waste Separation and Recycling Program” in 2009, and 307 entities, including schools, government departments and associations, took part in the related waste recycling program. Collected resources consisted primarily of three typesdpaper, plastics and metals, as shown in Table 2. It can be seen that there was a steady increase in recovered resources, especially paper and plastics. Prior to 1992, the Macau Government was responsible for waste collection and transport. Currently, however, the collection and transport of solid waste has been contracted to Macau Residue System Company, Ltd (CSR). In recent years, some additional measures have been implemented to improve public hygiene and to continue to optimize the facilities for waste collection and separation. In 2008, Macau’s first “Automatic Urban Waste Collection System”, which collected the waste through the underground pipe system, and was driven by the negative pressure, was put into operation in the reclamation zone of Areia Preta. It has a daily treatment capacity of 50 tons, accounting for about 7% of the total solid waste generated in Macau, and treating the waste of about 19,000 dwelling units and nearly 60,000 residents. In addition, a
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total of 121 waste collection stations were constructed by the Civic and Municipal Affairs Bureau (IACM); 104 of them were equipped with recyclable waste separation containers. Solid waste in Macau is incinerated, with the residue sent to landfills. Because of Macau’s small geographic area and the concomitant high cost of land, solid waste incineration has been given a top priority over other waste disposal methods in Macau. Before the 1990s, all the MSW in Macau was sent to landfills. Landfill is now the lowest-priority management option, and in principle is reserved for wastes that are not suitable for thermal treatment or for those that have low calorific power. Only construction and demolition waste, and by-products from incineration, are sent to landfills for disposal. At present, there are two landfill sitesdone for construction waste and one for fly ash. Since its inception in 1992, the incineration plant has been used to treat waste generated in Macau. In 2006, as the volume of MSW in Macau increased and the refuse incineration plant approached its treatment capacity, the MSAR Government decided to expand the plant, constructing three new incinerators. This expansion increased the daily treatment capacity of the incineration plant from 864 tons to 1728 tons. The new Macau Incineration Plant (MIP) was equipped with pollution control systems, as well as with electricity-generation and scrap metal recovery facilities. The exhaust emission of the incinerators in the plant meets the latest emission standard of Directive 2000/76/EC issued by the European Union (EU). The electricity generation capability, in addition to supplying electricity for the plant itself, transmitted approximately 94 million kwh to the public power grid in 2010 (see Table 3)d enough to supply about 33,000 households in Macau. In the MIP, the by-products from incineration are fly ash, bottom ash and iron-containing metals. The fly ash is solidified with cement, collected in impervious containers and transported to the landfill for fly ash. The Municipal Laboratory of the Macau SAR Government conducts routine analysis on the fly ash content to make sure that it contains no toxic substances. The bottom ash is sent to the landfill for construction waste. The iron-containing metals are recovered through a magnetic separation process. Table 3 shows the amount of by-products from incineration over time. European Union has proposed a four-point hierarchical system of waste management regulation: (EU, 2006): (1) reduction of solid waste production, (2) recovery of material, (3) recovery of energy and (4) landfill disposal, but this proposal has not been developed in sufficient detail to be applied in specific situations. When developing the most appropriate solid waste management system for a given territory, decision makers have to take into account not only the technical aspects and implementation costs, but also the environmental impacts produced by the treatment and disposal processes, as well as attitudes within local communities (De Feo and Malvano, 2009). In fact, co-operation of the residents is a prerequisite for the successful implementation of any solid waste
Table 1 Typical composition of MSW in Macau (%), 2001 to 2010. Composition
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
Food Paper and cardboard Plastics Glass and stone Metals Textiles Wood Othera
32.93 15.01 15.20 10.51 2.72 3.20 2.25 18.20
22.70 10.56 16.67 5.03 2.80 6.11 2.01 34.20
14.08 12.86 16.53 4.18 0.51 5.10 6.53 40.20
14.50 16.90 22.20 5.10 7.80 5.30 2.40 25.70
11.11 12.16 20.00 5.60 2.70 6.15 7.30 34.98
6.28 13.15 11.51 5.83 4.04 7.78 3.44 47.98
4.33 3.63 24.38 3.81 1.21 13.67 2.77 46.20
20.9 15.8 40.9 5.4 2.3 5.6 5.9 3.2
54.2 19.9 9.4 6.3 2.4 0.3 1.2 6.3
45.65 16.30 14.13 5.43 3.26 2.17 8.70 4.35
a
Includes unclassified matter less than 2 cm in diameter.
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Table 2 Recovered resources in Macau (tons), 2001 to 2010. Categories
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
Paper Plastics Metallic materials
59.99 3.05 e
53.78 3.18 e
60.30 3.61 11.50
56.17 5.49 9.87
46.01 8.37 11.39
82.01 9.61 19.77
106.68 17.24 21.45
281.17 39.26 22.59
236.60 37.17 24.58
278.99 47.01 16.67
management plan (Rahardyan et al., 2004; De Feo et al., 2005; Özeler et al., 2006). In general, a local community would tend to support a management system that minimizes environmental impacts (De Feo et al., 2005). This paper, therefore, will focus mainly on studying the environmental impact produced by several municipal solid waste management systems (the current system and five assumed scenarios) in Macau. Selecting the best treatment and disposal options for solid waste from an environmental point of view would be a very difficult task. To provide an improved basis for waste management, coherent evaluations of benefits and drawbacks related to the wide range of treatment and disposal options available are necessary. In the last 30 years, the systematic Life Cycle Assessment (LCA) method has been widely employed to assess the potential environmental impact of a product or system over its entire life cycle, including resource extraction, transportation, manufacturing, utilization, consumption, recycling and waste management. The LCA method has been found to be a useful methodological tool in undertaking a quantitative environmental analysis of the entire process (Fruergaard et al., 2010; Carlsson Reich, 2005; Cleary, 2009). The LCA (ISO 14040-44, 2006) method provides an excellent framework for evaluating municipal solid waste (MSW) management strategies. Many of its applications in this field have been focused on its use as a decision support tool in the selection of the best MSW management strategy (from an environmental point of view). It has been applied in a wide range of countries, including Italy (Buttol et al., 2007; Brambilla Pisoni et al., 2009; Scipioni et al., 2009; Cherubini et al., 2009; de Feo and Malvano, 2009; Giugliano et al., 2011), Spain (Bovea and Powell, 2006; Guereca et al., 2006; Bovea et al., 2010), Sweden (Eriksson et al., 2005), Germany (Wittmaier et al., 2009), UK (Emery et al., 2007), USA (Contreras et al., 2008), Singapore (Khoo, 2009) and China (Zhao et al., 2009a, 2009b; Jing et al., 2009; Song et al., 2012), among others. The main objective of this study was to apply the LCA methodology as an analysis tool to compare the environmental impacts of the 6 MSW management scenarios, including the current MSW management system. The research results can help decision makers evaluate strategies for the treatment of solid waste from an environmental impact point of view.
influence MSW generation, the same amounts and composition of MSW are disposed of in all 6 scenarios.
2. Materials and methods
2.1.6. Scenario 5dintegrated waste management (source separation, composting, and incineration) This scenario investigates the potential to minimize environmental impacts through an integrated MSW management system. Metals, paper, and plastics are recycled at a 30% rate, and food waste is separated at the source and collected to be treated by
2.1. MSW management scenarios This study compares 6 scenarios, reflecting different MSW management systems. Since the scenarios are assumed not to
2.1.1. Scenario 0 (current system) Scenario 0 corresponds to the current MSW management system in Macau. As discussed above, except for resources recovered at source, the MSW is treated in the Macau Incineration Plant. Fly ash and bottom ash are transported to landfills for disposal, ironcontaining metals are recovered, and electricity is generated as a by-product of incineration. 2.1.2. Scenario 1dlandfill only Landfill was the past technology choice in Macau, and at present landfill is the lowest-priority management option, being reserved in principle for wastes that are not suitable for thermal treatment or which have low calorific power. In this study, Scenario 1dall the MSW is sent to the landfilldwill be evaluated to determine its environmental impacts. 2.1.3. Scenario 2dsource separation, composting, and landfill This scenario explores the potential to reduce the environmental impacts of MSW disposal by materials recycling and composting. Metals, glass, paper, and plastics are assumed to be recovered at a 30% recycling rate in the source separation process. All the food waste will be treated by composting, and the rest will be transported to the landfill for disposal. 2.1.4. Scenario 3dincineration and composting The high moisture content of food waste results in a lower heat value of MSW (especially in mainland China), which reduces the combustion efficiency of MSW. Therefore this scenario introduced the composting of food waste, while using incineration for the remainder of the waste. 2.1.5. Scenario 4dsource separation and incineration This scenario is similar to the current MSW management system in Macau, except that in this scenario the source separation process is further improved, metals, paper, and plastics are assumed at a 30% recycling rate.
Table 3 By-products from MSW incineration (tons), 2001 to 2010. Category
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
Fly ash Bottom ash Iron Electricity (106kwh)
4230 44,868 36 56
4986 44,655 12 59
5616 46,353 39 60
5519 49,576 164 62
5562 58,644 168 63
6115 59,619 152 62
5970 53,102 56 66
8376 52,692 96 61
11,256 62,602 82 77
11,700 56,900 83 94
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composting; the other MSW is transported to the MIP for incineration. Finally, the waste generated in the composting and incineration processes will end up in the landfill for construction waste. 2.2. Life cycle assessment 2.2.1. Goals, functional unit, and system boundary (1) The goal The goal of this study is two-fold: to evaluate the environmental impacts of the existing MSW management system in Macau from a life-cycle perspective, and to investigate the potential of reducing the environmental impacts with other MSW management strategies, through scenario studies. (2) Functional unit The functional unit in this study is defined as “the disposal of the MSW collected in Macau in 2010.” The total amount was 321,752 tons, which have been grouped into the components shown in Table 1. (3) System boundary The relevant processes are included within the boundary of the MSW management system, as shown in Fig. 2. MSW is the input to the MSW management system. Upstream processes related to the manufacture and use stages of products entering the waste stage are excluded. 2.2.2. Life cycle inventory The life cycle inventory (LCI) aims at identifying and quantifying the environmental interventions related to the system, and results in a list of environmental inputs and outputs. So far, no relevant life cycle inventory (LCI) database is available. In addition, little public data with regard to MSW management system are available. As in many other cases, the achievement of adequate LCI data in our study turned out to be very difficult. The data used in this study were derived from on-site investigations, references, and the database Ecoinvent 2.2 data. In the LCI phase, key assumptions of this study were: ➢ The compost plant was located at the edge of the Landfill for Construction Waste of Macau. The average collection and
transport distance to the compost plant was assumed to be 18 km; ➢ The emissions to air, water and soil, and the input materials to incineration, were uniform across all the scenarios, except for the amount of electricity generated. Through the field survey, we can know that the CO2 emission (only 165 kg/ton MSW) in Macau Incineration Plant was relatively lower than that of other researches (Chen and Lin, 2010). In addition, through the calculation, it can be estimated that the change of the MSW composition had little influence (less than 1%) on the total environmental impacts. ➢ The source separation of solid waste was assumed to consume no materials, and to depend only on residents’ activities. In order to obtain a quantitative model, the data sources, processes and destinations described in Tables 4 and 5 were used in this study for the various scenarios of solid waste management in Macau. For Scenarios 3, 4 and 5, the heat value of solid waste treated in the MIP would vary, depending on the volume incinerated; this variation would in turn affect the amount of electricity generated. It was assumed, however, that the thermal efficiency would not change; hence the amount of electricity generated would be influenced by the heat value of the solid waste. In our study, the heat value was estimated by the method used in the national standard “Sampling and Analysis Methods for Domestic Waste” (CJ/ T 313-2009). 2.2.3. Allocation The allocation procedure in a multi-functional process is a critical issue in LCA studies, especially in those on waste management systems. Waste treatment systems are becoming increasingly complex and multi-functional, as technical innovation progresses. The ISO standard for LCA (ISO, 2006) describes acceptable allocation procedures in the following order of preference: (1) avoiding allocation by dividing processes into sub-processes; (2) avoiding allocation by expanding the system; (3) applying principles of physical causality for allocation burdens; and (4) applying other principles of causalitydfor instance, economic value. The system expansion or substitution option dominates LCA studies of waste management systems (Zhao et al., 2009a). As the allocation method has a large influence on results, the robustness and the usefulness of LCA results for decision support could be limited by the choice of method. In this study, the substitution approach was adopted to solve the allocation problems (Chen et al., 2006; Bjorklund and Finnveden, 2007).
Municipal solid waste
Waste management system
Resource recycling
Source separation
Energy
95
Collection and Transportation Materials
Electricity and irons
Incineration
Composting
Fertilizer
Emissions to environment Landfill
Fig. 2. System boundary of waste management system.
96
Q. Song et al. / Journal of Cleaner Production 57 (2013) 92e100
Table 4 Input, processing and destinations for the 6 scenarios of solid waste management. Categories
Scenario 0
Source separation
Paper 278.99 tons; 0 Plastic 47.01 tons; Metal 16.67 tons 321,409 tons 0 0 0 0 321,752 tons 15 km (to MIP); 18 km (to compost plant); 4 km (MIP to landfill for construction waste); 10 km: (MIP to landfill for fly ash) Transport, municipal waste collection, lorry 21 t
Incineration Compost Landfill Transportation
Scenario 1
Scenario 2
Scenario 3
Scenario 4
Scenario 5
Paper 35,251 tons; Plastic 14,160 tons; Metal 5241 tons 0 146,880 tons 120,220 tons
0
Paper 35,251 tons; Plastic 14,160 tons; Metal 5241 tons 267,100 tons 0 0
Paper 35,251 tons; Plastic 14,160 tons; Metal 5241 tons 120,220 tons 146,880 tons 0
174,872 tons 146,880 tons 0
The starting point for the substitution method is that the system delivers co-products in addition to its main service, waste treatment. This approach thereby avoids the need to produce these coproducts separately by the “normal means of production,” and these avoided processes can therefore be subtracted from the MSW management system. In this case, Chinese electricity production in 2010 was chosen as the avoided process for the electricity recovered from MSW treatment in Macau, since 73% of the total electric power consumed in Macau is imported from mainland China. Further choices have to be made regarding avoided processes when recycled materials are assumed to replace virgin materials. Although many recycled materials are equivalent in amount to virgin materials, the replacement ratioddefined as recycled material: virgin materialdis in some cases less than 1:1 (Bjorklund and Finnveden, 2007), as shown in Table 6. Because the recycled materials may be converted into many other products, it is impossible that we know the detail ratio of different products, especially for the recycled papers and plastics. In Macau, the recycled materials will be transported into mainland China, and we
didn’t know the detail ratio of different products produced by the recycled materials. Therefore, we used the main replacement materials to represent the avoided processes (Zhao et al., 2009a).
Table 5 Main input flows to waste management options; amounts normalized per ton of waste.
3.1. Environmental impacts of the five scenarios
Category Emissions to air (kg)
Emissions to water (kg) Materials and energy input
Materials output
Biological CO2 Fossil CO2 SO2 HCl NOx NH3 H2S CO Total nitrogen TOC COD Electricity (MJ) Diesel (MJ) Gasoline (MJ) Activated carbon (kg) Aqueous ammonia (kg) Slaked lime (kg) Cement (kg) Compost (kg) Electricity (MJ) Iron (kg) Wastewater (ton) Fly ash (ton) Bottom ash (ton) Other materials (kg)
Data source
Composting
Incineration
261.31 42.33 0.0012 0.002 e 0.023 0.00017 1.78 0.011 0.046 0.14 140.4 8.27 e e e e e 476.2 (N: 0.83%; P: 0.2%; K: 0.99%) e e e e e 80 Razza et al., 2009
e 165.02 0.01 0.0089 0.24 0.011 e 0.030 e e e 311.22 15.69 18.61 0.21 0.73 7.86 1.51 e 1964.79 0.26 0.085 0.036 0.18 e Field survey
2.2.4. Life cycle impact assessment and sensitivity analysis In this study, the life cycle assessment was constructed using SimaPro software version 7.2 and expressed with the Eco-indicator ’99 (H) method. The Eco-Indicator ’99 method is an example of a multi-step, fully aggregating method, leading to a result of a single number. The overall method is an example of the damage-oriented or end-point approach. Through this method, it will be very easy to make the comparison between the different waste management scenarios. The sensitivity analysis identifies sensitive parameters: i.e. whether a small change in an input parameter would induce a large change in the impact category. Here, the input parameters for sensitivity analysis focus on the recycling rate. 3. Results and discussion
3.1.1. Scenario 0dcurrent system The results of the impact assessment of Scenario 0 (the actual solid waste management system in Macau) are shown in Table 7. The total environmental impact is 4145.2 Pt, and negative value means that environmental benefit can be realized. Under this current processing technology, incineration generates significantly more environmental benefits than other three MSW treatment technologies, while transportation causes the most environmental impacts. Because of the low volume of resource recycling in the source separation, however, only small environmental benefits are obtained. On the other hand, since only the byproducts (fly ash and bottom ash) of incineration are sent to the landfill, environmental impacts are low. From Table 7, it can be seen that the environmental benefits on human health are the most important, accounting for 74.32%, followed by resources and ecosystem quality. These results of Scenario 0 are shown in more detail in Table 8, which lists the main contributors to the environmental impacts. Here, in the incineration process, the highest benefits came mainly from the avoided SO2 and PM2.5 emissions to air, together accounting for about 45.12% of the benefit, a direct result of the use of coal as the primary fuel in Chinese thermal power plants. The source separation’s main benefit was avoiding the production of paper, plastics and metals; hence its benefits show up as a reduction in resource consumption. For the transportation process, the environmental impacts of oil consumption were of the most importance, followed by NOx production; these can be attributed to
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Table 6 Substitution options for various outputs. Item
Recycling process
Avoid processes
Replacement ratio
Electricity Compost matter
Incineration Composting
1:1 1:1
Paper Metals
Source separation Source separation and Incineration Source separation
Chinese electricity (coal thermal power plant) N: ammonium nitrate, as N, at regional storehouse P: diammonium phosphate, as P2O5, at regional storehouse K: Potassium chloride, as K2O, at regional storehouse Paper, newsprint, 0% DIP, at plant Iron and steel, production mix Polyethylene terephthalate, granulate, bottle grade, at plant
1:0.9
Plastics
the fuel consumption of garbage lorries. In the landfill process, the emissions to water (Arsenic, ion) contributed the largest environmental impact. For Scenario 0 as a whole, the environmental benefits were realized primarily by avoiding SO2 and PM2.5 emissions to air, together accounting for about 50.53%, similar to the benefits of the incineration process. The current management system of MSW in Macau can treat and dispose of MSW well, and at the same time can generate large environmental benefits by recycling the valuable recovered resources (paper, plastics, and metals) and by generating electricity. 3.1.2. Scenario 1dlandfill (prior system) This scenario tests the environmental impacts of the MSW landfill disposal. As shown in Table 7, compared to the transportation process, the landfill process caused more environmental impacts. Because there were no recovered resources in Scenario 1, no environmental benefits were generated. It can be also seen that the impacts on human health were of more importance, similar to Scenario 0. As can be seen in Table 9, for the transportation process, the consumption of resources (oil) contributed the largest environmental impact, while in the landfill process, the emissions to water were of the highest environmental importance, especially Cadmium ion and Copper ion, accounting for 49.86% and 31.51% of the total environmental impacts, respectively. The environmental impacts of Scenario 1 as a whole were 14875.69 Eco-indicator ’99 points, similar to the landfill process. Compared to Scenario 0, the environmental impacts were more serious: scenario 0 shows a benefit whereas scenario 1 a net impact. Therefore it would not be appropriate to apply this scenario in the future.
1:0.8 1:1
3.1.3. Scenario 2dsource separation, composting, and landfill Table 7 presents the environmental impacts of Scenario 2, which mainly tested the potential of reducing the environmental impacts by source separation and composting. In Scenario 2, large environmental benefits would be generated by source separation, due to the recovery of resources, and this contribution was more important than the other three treatment processes. On the whole, the composting process brought some benefits, but because of smaller environmental benefits per kg of compost materials, compared to resources recovered (paper, plastics, and metals) in the source separation process, the benefits were much lower for composting than for source separation. In this scenario, the main environmental impacts were caused by the transportation process, followed by the landfill process. Table 10 presents the main contributors to the environmental impacts in Scenario 2. The contributions from the transportation and landfill processes were similar to those of Scenario 0, the main difference being that the environmental impacts of Scenario 0 were higher than those of this scenario. The source separation process can avoid the resource extraction of the manufacturing phase; therefore the main contributors to the benefits of source separation were the resource consumptions (especially the oil and natural gas) avoided. In the composting process, the main benefits were due to the natural gas consumptions avoided, and its impacts were mainly from the CO2 emissions to air. The environmental benefits of Scenario 2 as a whole were 5405.20 Eco-indicator ’99 points, caused by the avoided oil and natural gas consumption, similar to the results from source separation. Compared to Scenario 0, a 30.35% environmental benefit increase can be achieved by enhancing the source separation process and adding composting. However, due to the small benefits of
Table 7 Environmental impacts of different Scenarios (Pt). Scenarios Scenario 0
Scenario 1
Scenario 2
Scenario 3
Scenario 4
Scenario 5
Human health Ecosystem quality Resources Human health Ecosystem quality Resources Human health Ecosystem quality Resources Human health Ecosystem quality Resources Human health Ecosystem quality Resources Human health Ecosystem quality Resources
Source separation
Transportation
Incineration
Compost
Landfill
2015.70 678.64 3017.38 e e e e e e 2015.70 678.64 3017.39 e e e 2015.70 678.64 3017.38
214.12 30.72 293.51 207.25 29.73 284.10 345.41 49.56 473.50 114.71 16.46 157.25 236.66 33.95 324.41 201.67 28.93 276.45
2174.55 195.47 176.18 207.25 29.73 284.10 e e e e e e 3398.78 305.91 293.75 3400.14 305.83 250.24
51.54 4.20 107.68 e e e e e e 51.54 4.20 107.68 51.54 4.20 107.68 e e e
46.04 2.96 19.91 104.10 6.68 45.02 8151.51 5547.05 308.67 38.75 6.22 32.11 59.52 4.11 26.91 93.56 6.01 40.46
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Table 8 Main contributors to environmental impacts for Scenario 0 (Pt). Category Resources
Emissions to air
Emissions to water Others Total
Coal, hard, unspecified, in ground Gas, natural, in ground Oil, crude, in ground Occupation, dump site Nitrogen oxides Carbon dioxide, fossil Particulates, <2.5 um Particulates, >2.5 um, and <10 um Sulfur dioxide Methane, fossil Arsenic, ion
Source separation
Transportation
Incineration
Landfill
Total
0.30 0.10 6.94 0.03 1.69 1.96 1.04 0.18 1.91 0.08 2.12 23.75 40.10
0.23 0.07 265.78 0.03 103.53 32.11 55.55 5.00 9.15 0.70 2.47 46.45 521.08
172.66 58.88 60.53 43.62 899.15 472.55 1057.35 67.83 1100.17 70.35 577.07 201.84 4781.98
0.07 0.02 40.44 2.81 11.69 0.89 0.22 0.06 0.98 0.14 68.72 29.76 155.80
172.66 58.89 238.75 40.81 785.62 441.51 1002.62 62.95 1091.95 69.59 508.00 149.38 4145.2
composting, the environmental improvement was mainly due to improvements in source separation. 3.1.4. Scenario 3dincineration and composting Scenario 3 attempted to reduce environmental impacts and achieve the most environmental benefits by a combination of incineration and composting. As shown in Table 7, the environmental benefits of the incineration process accounted for the largest proportion in this scenario, and the main environmental impacts were caused by the transportation process. Compared to scenario 0, it can be seen that the weight of the MSW, which ended in the incineration plant, decreased by 45.65% in scenario 3, but the environmental benefits decreased by only about 16%. This proves that the separation of food waste will be useful for improving the heat value of solid waste. However, due to the low environmental benefits of composting, the overall benefits of this scenario were smaller than for Scenario 0. For the four processes, their contributions to the environmental impacts or benefits were similar to those of some of the other scenarios, the differences being the actual values of environmental impacts or benefits. The overall environmental benefits of Scenario 3 were 3379.06 Eco-indicator ’99 points, similar to the incineration process. Compared to Scenario 0, there was an 18.51% reduction of the benefit in this scenario. It can therefore be concluded that the introduction of composting alone cannot improve the environmental impact of solid waste management in Macau. 3.1.5. Scenario 4dsource separation and incineration The goal of Scenario 4 was to investigate the potential to improve the current MSW management system through further enhancing the source separation process. It can be seen from Table 7 that when the recycling proportion of source separation was increased to 30%, the environmental benefits were significantly increased, and source separation became the most important
Table 9 Main contributors to environmental impacts for Scenario 1 (Pt). Category Resources Emissions to air Emissions to water
Others Total
Oil, crude, in ground Nitrogen oxides Methane, biogenic Arsenic, ion Cadmium, ion Copper, ion Nickel, ion Zinc, ion
Transportation
Landfill
Total
442.97 168.3456 0.0005 3.29 1.29 0.11 0.35 0.13 251.98 868.46
264.20 15.77 650.60 338.87 6984.45 4413.70 380.68 437.06 521.89 14007.23
707.17 184.1156 650.6005 342.16 6985.74 4413.81 381.03 437.19 773.87 14875.69
contributor to the benefits. It can be concluded that the improvement of source separation will be beneficial to the management of MSW in Macau. The distribution of contributions to the environmental impacts or benefits in the scenario 4 was similar to those some of the other scenarios. The environmental benefits for Scenario 4 as a whole were 9020.83 Eco-indicator ’99 points, caused by avoiding both the oil and natural gas consumption, and the SO2 and PM2.5 emissions to air, together accounting for 52.69% of the environmental benefits. Compared to Scenario 0, Scenario 4 shows the highest potential (117.55%) for increasing the benefits. The major environmental improvement was realized from source separation. 3.1.6. Scenario 5dintegrated waste management (source separation, composting, and incineration) In order to test a combination of options in an integrated MSW management system, life cycle assessment was performed for Scenario 5. As shown in Table 7, the source separation and incineration processes contributed the most environmental benefits of the integrated management system, and the main impacts were from the transportation process. Composting and landfill contributed very little to either the impacts or benefits. For the four processes, their contributions to the environmental impacts or benefits were similar to that of some of the other scenarios. The environmental benefits of Scenario 5 as a whole were 7710.96 Eco-indicator ’99 points, mainly caused by avoiding both the oil and natural gas consumption, together accounting for 35.75% of the environmental benefits. Compared to Scenario 0, Scenario 5 is also a good option, with higher benefits (85.96%). 3.1.7. Comparison of scenarios For the Eco-indicator ’99 method, it can be seen that among the 6 scenarios, only Scenario 1 generated more environmental impacts, while all the other 5 scenarios can bring environmental benefits. Of the five scenarios, Scenario 4 was of most importance, accounting for about 30.41% of all the benefits, followed by Scenario 5 (26.00%), Scenario 2 (18.22%), Scenario 0 (13.98%), and Scenario 3 (11.39%). As discussed above, source separation and incineration could generate larger influences on the environmental impacts or benefits than other treatment processes, and are the more important recycling technologies. For the current management system of MSW in Macau, in order to achieve more environmental benefits in the future, improvement of the source separation process will be the most important (as in Scenario 4, for example). Although it was expected that Scenario 5 (integrated management system) would be the best MSW management system (Zhao et al., 2009), actually Scenario 4 performed better than Scenario 5
Q. Song et al. / Journal of Cleaner Production 57 (2013) 92e100
99
Table 10 Main contributors to environmental impacts for Scenario 2 (Pt). Category Resources
Emissions to air
Emissions to water
Gas, natural, in ground Oil, crude, in ground Occupation, forest, intensive Carbon dioxide Nickel Sulfur dioxide Nitrogen oxides Particulates, <2.5 um Benzopyrene Arsenic, ion Cadmium, ion
Others Total
Source separation
Transportation
Compost
Landfill
Total
1360.00 1540.00 314.00 243.00 58.90 208.00 77.40 97.20 596.00 220.00 94.30 903.4 5710.00
9.71 147.00 0.0024 17.80 0.24 5.06 3.99 1.93 0.00 1.09 0.43 100.99 288.00
84.70 31.00 0.01 18.20 1.83 47.20 2.96 8.31 0.00 7.79 7.24 18.12 60.30
2.22 29.60 0.00014 0.82 0.06 1.36 0.78 0.61 0.00 0.55 0.13 40.90 77.10
1432.77 1394.4 314.01 206.18 60.43 154.38 75.59 102.97 596.00 226.15 100.98 743.39 5405.20
in our study. This result could be attributed mainly to two aspects: 1) the assumption, in our study, that the electricity avoided was from mainland China (the coal thermal power plant); 2) the high heat and treatment efficiency of the incineration plant in Macau.
4. Conclusions
3.2. Sensitivity analysis to recycling rates This section discusses the results of a sensitivity analysis based on different recycling rates in the source separation process, ranging from 10% to 90%, on the basis of Scenario 5. That analysis indicates that as the recycling proportions of paper, metals and plastics range from 10% to 90%, the solid waste for the incineration plant will vary from 44% to 24% of all the MSW, while the solid waste proportion of the compost will stay the same (45.65% of all the MSW). It is appropriate to test the influence of the recycling rate within these ranges, because the recycling potential of paper, metals and plastics in Macau’s MSW cannot be exactly assessed, due to the fluctuating compositions of MSW. Fig. 3 illustrates the sensitivity of the environmental impacts to the recycling rate in Scenario 5. It is obvious that total environmental benefits from Scenario 5 will increase as the recycling rate increases. There is an approximately linear relation of inverse proportion between the recycling rate and environmental benefit, with a coefficient of determination R2 ¼ 0.9999. This linear relation allows the conclusion that, when implementing the integrated MSW management strategy, a 20% change in the overall recycling rates would induce about the same change (3349 Pt) in total environmental benefits in the opposite direction. Resource recycling in the source separation process makes a considerable contribution to environmental benefits, proving that source
0 10% Recycling
30% Recycling
50% Recycling
70% Recycling
90% Recycling
Eco-indicator'99 points (Pt)
-2000 -4000 -6000 -8000 -10000 -12000 -14000 -16000
separation will be more and more important to improving the environmental benefits of the MSW management system in the future.
Resources Ecosystem Quality Human Health
-18000 Fig. 3. Sensitivity analysis of Scenario 5 to recycling rate.
With the recent rapid economic development in Macau, along with population growth, increased prosperity and tourism in recent years, the amount of waste generated in Macau has also been increasing, exerting great pressure on waste management in Macau’s limited land area. In this study, from a life-cycle perspective, the current Macau MSW management system and five other potential scenarios were evaluated to explore the potential for reducing the environmental impacts of different MSW management strategies in Macau. The results for Scenario 0 show that the current management system of MSW in Macau can treat and dispose of the MSW well and at the same time can generate large environmental benefits by recycling the valuable recovered resources (paper, plastics, and metals) and generating electricity. In Scenario 1, the environmental impacts would become more serious; hence it is not appropriate to apply this scenario in the future. Compared with Scenario 0, a 30.35% environmental benefits increase can be achieved by enhancing the source separation process and adding composting (Scenario 2). In Scenario 3, there would be an 18.51% environmental benefit reduction, compared to Scenario 0. Scenario 4 showed the highest potential (117.55%) for increasing the environmental benefits. Scenario 5 is also a good option, with higher benefits (85.96%) than Scenario 0. The analysis shows that, in each scenario (expect Scenario 1), the waste treatment processes, including source separation and incineration, dominate the environmental impacts; while processes such as collection and transportation, composting, and landfill, have a relatively small influence. The sensitivity analysis for the recycling rate reveals an approximately linear relation of inverse proportion between the recycling rate and the environmental impacts from the waste management system. Recycling of valuable resources makes a significant contribution to environmental impact reduction, compared to the other treatment processes. Based on our findings, the preferable MSW management systems are Scenarios 4 and 5. However, given the limited financial support and current waste management practices, the first priority for achieving environmental impacts mitigation would be Scenario 4, because this scenario is basically an enhancement of the current MSW management systemdimprovements in the source separation process. The present analysis focuses only on environmental impacts, which is only one environmental consideration related to waste
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management. In order to build a more complete picture of MSW management, further research should include analysis of the economic performance of the system. Since there are at present no research studies focusing on life cycle assessment of MSW in Macau, the LCA research on MSW in our study can provide some useful data on the environmental impacts of MSW, thereby helping governors and managers better understand the environmental pollution situation and put forward the appropriate management policies to deal with the serious MSW issues in Macau. Acknowledgment This study was funded by the National High Technology Research and Development Program of China (863 program, 2009AA06Z304), and the University of Macau. References Bjorklund, A.E., Finnveden, G., 2007. Life cycle assessment of a national policy proposaldthe case of a Swedish waste incineration tax. Waste Manage. 27, 1046e1058. Bovea, M.D., Powell, J.C., 2006. Alternative scenarios to meet the demands of sustainable waste management. J. Environ. Manage. 79, 115e132. Bovea, M.D., Ibáñez-Forés, V., Gallardo, A., Colomer-Mendoza, F.J., 2010. Environmental assessment of alternative municipal solid waste management strategies. A Spanish case study. Waste Manage. 30, 2383e2395. Brambilla Pisoni, E., Raccanelli, R., Dotelli, G., Botta, D., Melià, P., 2009. Accounting for transportation impacts in the environmental assessment of waste management plans. Int. J. Life Cycle Assess. 14, 248e256. Buttol, P., Masoni, P., Bonoli, A., Goldoni, S., Belladonna, V., Cavazzuti, C., 2007. LCA of integrated MSW management systems: case study of the Bologna District. Waste Manage. 27, 1059e1070. Carlsson Reich, M., 2005. Economic assessment of municipal waste management systemsdcase studies using a combination of life cycle assessment (LCA) and life cycle costing (LCC). J. Clean Prod. 13, 253e263. Chen, T., Lin, C., 2010. CO2 emission from municipal solid waste incinerator: IPCC formula estimation and flue gas measurement. J. Environ. Eng. Manage. 20 (1), 9e17. Chen, W.J., Nie, Z.R., Wang, Z.H., 2006. Life cycle inventory and characterization of flat glass in China. China Building Mater. Sci. Technol. 3, 54e58 (in Chinese). Cherubini, F., Bargigli, S., Ulgiati, S., 2009. Life cycle assessment (LCA) of waste management strategies: landfilling, sorting plant and incineration. Energy 34 (12), 2116e2123. Cleary, J., 2009. Life cycle assessments of municipal solid waste management systems: a comparative analysis of selected peer-reviewed literature. Environ. Int. 35, 1256e1266. Contreras, F., Hanaki, K., Aramaki, T., Connors, S., 2008. Application of analytical hierarchy process to analyze stakeholders preferences for municipal solid waste management plans, Boston, USA. Resour. Conserv Recycl. 52, 979e991. De Feo, G., Malvano, C., 2009. The use of LCA in selecting the best MSW management system. Waste Manage. 29, 1901e1915.
De Feo, G., Panza, D., Belgiorno, V., 2005. Public opinion and residents concerns, perception and attitudes toward MSW treatment and disposal plants. In: Proceedings of Sardinia 2005, Tenth International Waste Management and Landfill Symposium. CISA, Cagliari, Sardinia, Italy. DSEC (Statistics and Census Service Macao SAR Government), 2012. Environmental Statistics 2001e2010. Available at: http://www.dsec.gov.mo/Statistic.aspx. DSPA (Environmental Protection Bureau of Macao SAR Government), 2012. Report of Environmental Status in Macao 2001e2009. Available at: http://www.dspa. gov.mo/Default.aspx?alias¼www.dspa.gov.mo/zhcn. Emery, A., Davies, A., Griffiths, A., Williams, K., 2007. Environmental and economic modelling: a case study of municipal solid waste management scenarios in Wales. Resour. Conserv Recycl. 49, 244e263. Eriksson, O., Carlsson, M., Frostell, B., Björklund, A., Assefa, G., Sundqvist, J.O., Granath, J., Baky, A., Thyselius, L., 2005. Municipal solid waste management from a systems perspective. J. Clean Prod. 13, 241e252. EU (European Union), 27.4.2006. Directive 2006/12/EC of the European parliament and of the council of 5 April 2006 on waste. Off. J. Eur. Union. L114/9-L114/21. Fruergaard, T., Hyks, J., Astrup, T., 2010. Life-cycle assessment of selected management options for air pollution control residues from waste incineration. Sci. Total Environ. 408, 4672e4680. Giugliano, M., Cernuschi, S., Grosso, M., Rigamonti, L., 2011. Material and energy recovery in integrated waste management system. An evaluation based on life cycle assessment. Waste Manage. 31, 2092e2101. Guereca, L.P., Gasso, S., Baldasano, J.M., Jiménez-Guerrero, P., 2006. Life cycle assessment of two biowaste management systems for Barcelona, Spain. Resour. Conserv Recycl. 49 (1), 32e48. Guerrero, L.A., Maas, G., Hogland, W., 2013. Solid waste management challenges for cities in developing countries. Waste Manage. 33 (1), 220e232. ISO 14040, 2006. Environmental Management. Life Cycle Assessment. Principles and Framework. Jin, J., Wang, Z., Ran, S., 2006. Solid waste management in Macao: practices and challenges. Waste Manage. 26, 1045e1051. Jing, S., Huang, G.H., Xi, B.D., Li, Y.P., Qin, X.S., Huo, S.L., Jiang, Y., 2009. A hybrid inexact optimization approach for solid waste management in the city of Foshan. China J. Environ. Manage. 91, 389e402. Khoo, H.H., 2009. Life cycle impact assessment of various waste conversion technologies. Waste Manage. 29, 1892e1900. Özeler, D., Yetis, Ü., Demirer, G.N., 2006. Life cycle assessment of municipal solid waste management methods: Ankara case study. Environ. Int. 32, 405e411. Rahardyan, B., Matsuto, T., Kakuta, Y., Tanaka, N., 2004. Residents’s concerns and attitudes towards solid waste management facilities. Waste Manage. 24, 437e451. Razza, F., Fieschi, M., Innocenti, F.D., Bastioli, C., 2009. Compostable cutlery and waste management: an LCA approach. Waste Manage. 29, 1424e1433. Scipioni, A., Mazzi, A., Niero, M., Boatto, T., 2009. LCA to choose among alternative design solutions: the case of a new incineration line. Waste Manage. 29 (9), 2426e2474. Song, Q., Wang, Z., Li, J., Zeng, X., 2012. Life cycle assessment of TV sets in China: a case study of the impacts of CRT monitors. Waste Manage 32 (10), 1926e1936. Wittmaier, M., Langer, S., Sawilla, B., 2009. Possibilities and limitations of life cycle assessment (LCA) in the development of waste utilization systems. Applied examples for a region in Northern Germany. Waste Manage. 29, 1732e1738. Zhao, W., Voet, E., Zhang, Y., Huppes, G., 2009a. Life cycle assessment of municipal solid waste management with regard to greenhouse gas emissions: case study of Tianjin, China. Sci. Total Environ. 407, 1517e1526. Zhao, Y., Wang, H.T., Lu, W.J., Damgaard, A., Christensen, T.H., 2009b. Life cycle assessment of the municipal solid waste management system in Hangzhou, China. Waste Manage. Res. 27, 399e406.
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Journal of Cleaner Production journal homepage: www.elsevier.com/locate/jclepro
Environmental performance of municipal solid waste strategies based on LCA method: a case study of Macau Qingbin Song a, Zhishi Wang a, *, Jinhui Li b a b
Faculty of Science and Technology, University of Macau, Macau, China School of Environment, Tsinghua University, Beijing 100084, China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 8 November 2012 Received in revised form 8 April 2013 Accepted 22 April 2013 Available online 15 June 2013
Increasing public attention has been brought to bear on the environmental impacts of municipal solid waste (MSW) management in Macau, due to the continually increasing amount of MSW being generated and the limited space and capacity of waste treatment facilities. This study evaluates the current and potential patterns of MSW management with regard to environmental impacts in Macau, using the life cycle assessment (LCA) method. We also assess the baseline scenario, reflecting the existing MSW management system, as well as five other scenarios, exploring waste treatment innovations, to quantitatively predict potential environmental impact mitigation for Macau. Additionally, a sensitivity analysis is used to investigate the influence of the different assessment methods and recycling rates of valuable resources in the source separation process. The results show that the current management system of MSW in Macau can treat and dispose of the MSW well, and at the same time can generate some environmental benefits. Compared with Scenario 0 (the current MSW management system), Scenario 4 (source separation and incineration) shows the highest potential to increase the environmental benefits. Scenario 5 (integrated waste management) is also a good option, with higher benefits (85.96%) than Scenario 0. The analysis shows that, in each scenario (except Scenario 1, the past process of landfill only), the waste treatment processes, including source separation and incineration, dominate the environmental impacts; while processes such as collection and transportation, composting, and landfill, have a relatively small influence. The sensitivity analysis of recycling rate shows an approximately linear relation of inverse proportion between recycling rate and total environmental impact. Considering the limited financial resources and the current waste management practices in Macau, Scenario 4 would be the preferred choice. Ó 2013 Elsevier Ltd. All rights reserved.
Keywords: Life cycle assessment Municipal solid waste Environmental impacts Macau
1. Introduction The management of municipal solid waste (MSW) continues to be a major challenge in urban areas throughout the world, particularly in the rapidly growing cities and towns of the developing world (Jing et al., 2009; Guerrero et al., 2013). With the rapid economic development in Macau, along with population growth, increased prosperity and tourism in recent years, the amount of waste generated in Macau has also been increasing, exerting great pressure on waste management systems within Macau’s limited land area (Jin et al., 2006). The amount of MSW generated in Macau has increased steadily over the last decade (DSEC et al., 2012; DSPA, 2012), from
* Corresponding author. Tel.: þ86 83974470; fax: þ86 28838314. E-mail address: [email protected] (Z. Wang). 0959-6526/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jclepro.2013.04.042
232,726 tons in 2001 to 321,752 tons in 2010dan average annual increase of 3.70%. The daily mean quantity per capita of solid waste generated was 1.46 kg/day in 2001 and 1.59 kg/day in 2010dan average annual increase rate of 1.05%. This rapid growth could be attributed to increases in both population and economic development (Fig. 1). The composition of MSW depends on a wide range of factors such as food habits, cultural traditions, lifestyles, climate and income, etc. The changing physical composition of MSW over time in Macau is shown in Table 1. Food waste, paper, plastics, and the others contributed the most to the MSW. It can be seen that a considerable quantity of MSW, including paper and cardboard, plastics, metal and glass, can be recycled, recovered or reused. From Table 1, it can be also seen that the composition of MSW has fluctuated enormously, especially in the categories of “Other” and “Food.” There are two possible reasons. One possible reason is that when sampling the solid waste, because many substances were
450000
2.00
400000
1.80
350000
1.60 1.40
300000
1.20
250000
1.00 200000
0.80
150000
0.60
100000
0.40
50000
0.20
0
0.00 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 MSW
Daily mean quantigy per capita of MSW (kg)
The generation amount of MSW (tons)
Q. Song et al. / Journal of Cleaner Production 57 (2013) 92e100
Daily mean quantity
Fig. 1. MSW generation amounts and daily mean quantities per capita, 2001 to 2010.
difficult to be classified, especially for the substances less than 2 cm in diameter, many composition of the solid waste was considered as the “Others”. Another reason is because Macau was only a small tourist city (about 30 km2 and 557 thousand populations) and owned a small capacity of solid waste, the composition of solid waste will be influenced by the tourists and the economic environment. The separation and recycling of valuable resources has been practiced in Macau for nearly 10 years. Prior to 2009, in addition to 208 public sites equipped with recyclable waste separation facilities, a number of waste collection stations with recyclable waste separation containers were installed, facilitating residential recyclable waste disposal. Altogether, 289 high-rise buildings participated in the “Domestic Waste Separation and Recycling Program” in 2009, and 307 entities, including schools, government departments and associations, took part in the related waste recycling program. Collected resources consisted primarily of three typesdpaper, plastics and metals, as shown in Table 2. It can be seen that there was a steady increase in recovered resources, especially paper and plastics. Prior to 1992, the Macau Government was responsible for waste collection and transport. Currently, however, the collection and transport of solid waste has been contracted to Macau Residue System Company, Ltd (CSR). In recent years, some additional measures have been implemented to improve public hygiene and to continue to optimize the facilities for waste collection and separation. In 2008, Macau’s first “Automatic Urban Waste Collection System”, which collected the waste through the underground pipe system, and was driven by the negative pressure, was put into operation in the reclamation zone of Areia Preta. It has a daily treatment capacity of 50 tons, accounting for about 7% of the total solid waste generated in Macau, and treating the waste of about 19,000 dwelling units and nearly 60,000 residents. In addition, a
93
total of 121 waste collection stations were constructed by the Civic and Municipal Affairs Bureau (IACM); 104 of them were equipped with recyclable waste separation containers. Solid waste in Macau is incinerated, with the residue sent to landfills. Because of Macau’s small geographic area and the concomitant high cost of land, solid waste incineration has been given a top priority over other waste disposal methods in Macau. Before the 1990s, all the MSW in Macau was sent to landfills. Landfill is now the lowest-priority management option, and in principle is reserved for wastes that are not suitable for thermal treatment or for those that have low calorific power. Only construction and demolition waste, and by-products from incineration, are sent to landfills for disposal. At present, there are two landfill sitesdone for construction waste and one for fly ash. Since its inception in 1992, the incineration plant has been used to treat waste generated in Macau. In 2006, as the volume of MSW in Macau increased and the refuse incineration plant approached its treatment capacity, the MSAR Government decided to expand the plant, constructing three new incinerators. This expansion increased the daily treatment capacity of the incineration plant from 864 tons to 1728 tons. The new Macau Incineration Plant (MIP) was equipped with pollution control systems, as well as with electricity-generation and scrap metal recovery facilities. The exhaust emission of the incinerators in the plant meets the latest emission standard of Directive 2000/76/EC issued by the European Union (EU). The electricity generation capability, in addition to supplying electricity for the plant itself, transmitted approximately 94 million kwh to the public power grid in 2010 (see Table 3)d enough to supply about 33,000 households in Macau. In the MIP, the by-products from incineration are fly ash, bottom ash and iron-containing metals. The fly ash is solidified with cement, collected in impervious containers and transported to the landfill for fly ash. The Municipal Laboratory of the Macau SAR Government conducts routine analysis on the fly ash content to make sure that it contains no toxic substances. The bottom ash is sent to the landfill for construction waste. The iron-containing metals are recovered through a magnetic separation process. Table 3 shows the amount of by-products from incineration over time. European Union has proposed a four-point hierarchical system of waste management regulation: (EU, 2006): (1) reduction of solid waste production, (2) recovery of material, (3) recovery of energy and (4) landfill disposal, but this proposal has not been developed in sufficient detail to be applied in specific situations. When developing the most appropriate solid waste management system for a given territory, decision makers have to take into account not only the technical aspects and implementation costs, but also the environmental impacts produced by the treatment and disposal processes, as well as attitudes within local communities (De Feo and Malvano, 2009). In fact, co-operation of the residents is a prerequisite for the successful implementation of any solid waste
Table 1 Typical composition of MSW in Macau (%), 2001 to 2010. Composition
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
Food Paper and cardboard Plastics Glass and stone Metals Textiles Wood Othera
32.93 15.01 15.20 10.51 2.72 3.20 2.25 18.20
22.70 10.56 16.67 5.03 2.80 6.11 2.01 34.20
14.08 12.86 16.53 4.18 0.51 5.10 6.53 40.20
14.50 16.90 22.20 5.10 7.80 5.30 2.40 25.70
11.11 12.16 20.00 5.60 2.70 6.15 7.30 34.98
6.28 13.15 11.51 5.83 4.04 7.78 3.44 47.98
4.33 3.63 24.38 3.81 1.21 13.67 2.77 46.20
20.9 15.8 40.9 5.4 2.3 5.6 5.9 3.2
54.2 19.9 9.4 6.3 2.4 0.3 1.2 6.3
45.65 16.30 14.13 5.43 3.26 2.17 8.70 4.35
a
Includes unclassified matter less than 2 cm in diameter.
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Q. Song et al. / Journal of Cleaner Production 57 (2013) 92e100
Table 2 Recovered resources in Macau (tons), 2001 to 2010. Categories
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
Paper Plastics Metallic materials
59.99 3.05 e
53.78 3.18 e
60.30 3.61 11.50
56.17 5.49 9.87
46.01 8.37 11.39
82.01 9.61 19.77
106.68 17.24 21.45
281.17 39.26 22.59
236.60 37.17 24.58
278.99 47.01 16.67
management plan (Rahardyan et al., 2004; De Feo et al., 2005; Özeler et al., 2006). In general, a local community would tend to support a management system that minimizes environmental impacts (De Feo et al., 2005). This paper, therefore, will focus mainly on studying the environmental impact produced by several municipal solid waste management systems (the current system and five assumed scenarios) in Macau. Selecting the best treatment and disposal options for solid waste from an environmental point of view would be a very difficult task. To provide an improved basis for waste management, coherent evaluations of benefits and drawbacks related to the wide range of treatment and disposal options available are necessary. In the last 30 years, the systematic Life Cycle Assessment (LCA) method has been widely employed to assess the potential environmental impact of a product or system over its entire life cycle, including resource extraction, transportation, manufacturing, utilization, consumption, recycling and waste management. The LCA method has been found to be a useful methodological tool in undertaking a quantitative environmental analysis of the entire process (Fruergaard et al., 2010; Carlsson Reich, 2005; Cleary, 2009). The LCA (ISO 14040-44, 2006) method provides an excellent framework for evaluating municipal solid waste (MSW) management strategies. Many of its applications in this field have been focused on its use as a decision support tool in the selection of the best MSW management strategy (from an environmental point of view). It has been applied in a wide range of countries, including Italy (Buttol et al., 2007; Brambilla Pisoni et al., 2009; Scipioni et al., 2009; Cherubini et al., 2009; de Feo and Malvano, 2009; Giugliano et al., 2011), Spain (Bovea and Powell, 2006; Guereca et al., 2006; Bovea et al., 2010), Sweden (Eriksson et al., 2005), Germany (Wittmaier et al., 2009), UK (Emery et al., 2007), USA (Contreras et al., 2008), Singapore (Khoo, 2009) and China (Zhao et al., 2009a, 2009b; Jing et al., 2009; Song et al., 2012), among others. The main objective of this study was to apply the LCA methodology as an analysis tool to compare the environmental impacts of the 6 MSW management scenarios, including the current MSW management system. The research results can help decision makers evaluate strategies for the treatment of solid waste from an environmental impact point of view.
influence MSW generation, the same amounts and composition of MSW are disposed of in all 6 scenarios.
2. Materials and methods
2.1.6. Scenario 5dintegrated waste management (source separation, composting, and incineration) This scenario investigates the potential to minimize environmental impacts through an integrated MSW management system. Metals, paper, and plastics are recycled at a 30% rate, and food waste is separated at the source and collected to be treated by
2.1. MSW management scenarios This study compares 6 scenarios, reflecting different MSW management systems. Since the scenarios are assumed not to
2.1.1. Scenario 0 (current system) Scenario 0 corresponds to the current MSW management system in Macau. As discussed above, except for resources recovered at source, the MSW is treated in the Macau Incineration Plant. Fly ash and bottom ash are transported to landfills for disposal, ironcontaining metals are recovered, and electricity is generated as a by-product of incineration. 2.1.2. Scenario 1dlandfill only Landfill was the past technology choice in Macau, and at present landfill is the lowest-priority management option, being reserved in principle for wastes that are not suitable for thermal treatment or which have low calorific power. In this study, Scenario 1dall the MSW is sent to the landfilldwill be evaluated to determine its environmental impacts. 2.1.3. Scenario 2dsource separation, composting, and landfill This scenario explores the potential to reduce the environmental impacts of MSW disposal by materials recycling and composting. Metals, glass, paper, and plastics are assumed to be recovered at a 30% recycling rate in the source separation process. All the food waste will be treated by composting, and the rest will be transported to the landfill for disposal. 2.1.4. Scenario 3dincineration and composting The high moisture content of food waste results in a lower heat value of MSW (especially in mainland China), which reduces the combustion efficiency of MSW. Therefore this scenario introduced the composting of food waste, while using incineration for the remainder of the waste. 2.1.5. Scenario 4dsource separation and incineration This scenario is similar to the current MSW management system in Macau, except that in this scenario the source separation process is further improved, metals, paper, and plastics are assumed at a 30% recycling rate.
Table 3 By-products from MSW incineration (tons), 2001 to 2010. Category
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
Fly ash Bottom ash Iron Electricity (106kwh)
4230 44,868 36 56
4986 44,655 12 59
5616 46,353 39 60
5519 49,576 164 62
5562 58,644 168 63
6115 59,619 152 62
5970 53,102 56 66
8376 52,692 96 61
11,256 62,602 82 77
11,700 56,900 83 94
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composting; the other MSW is transported to the MIP for incineration. Finally, the waste generated in the composting and incineration processes will end up in the landfill for construction waste. 2.2. Life cycle assessment 2.2.1. Goals, functional unit, and system boundary (1) The goal The goal of this study is two-fold: to evaluate the environmental impacts of the existing MSW management system in Macau from a life-cycle perspective, and to investigate the potential of reducing the environmental impacts with other MSW management strategies, through scenario studies. (2) Functional unit The functional unit in this study is defined as “the disposal of the MSW collected in Macau in 2010.” The total amount was 321,752 tons, which have been grouped into the components shown in Table 1. (3) System boundary The relevant processes are included within the boundary of the MSW management system, as shown in Fig. 2. MSW is the input to the MSW management system. Upstream processes related to the manufacture and use stages of products entering the waste stage are excluded. 2.2.2. Life cycle inventory The life cycle inventory (LCI) aims at identifying and quantifying the environmental interventions related to the system, and results in a list of environmental inputs and outputs. So far, no relevant life cycle inventory (LCI) database is available. In addition, little public data with regard to MSW management system are available. As in many other cases, the achievement of adequate LCI data in our study turned out to be very difficult. The data used in this study were derived from on-site investigations, references, and the database Ecoinvent 2.2 data. In the LCI phase, key assumptions of this study were: ➢ The compost plant was located at the edge of the Landfill for Construction Waste of Macau. The average collection and
transport distance to the compost plant was assumed to be 18 km; ➢ The emissions to air, water and soil, and the input materials to incineration, were uniform across all the scenarios, except for the amount of electricity generated. Through the field survey, we can know that the CO2 emission (only 165 kg/ton MSW) in Macau Incineration Plant was relatively lower than that of other researches (Chen and Lin, 2010). In addition, through the calculation, it can be estimated that the change of the MSW composition had little influence (less than 1%) on the total environmental impacts. ➢ The source separation of solid waste was assumed to consume no materials, and to depend only on residents’ activities. In order to obtain a quantitative model, the data sources, processes and destinations described in Tables 4 and 5 were used in this study for the various scenarios of solid waste management in Macau. For Scenarios 3, 4 and 5, the heat value of solid waste treated in the MIP would vary, depending on the volume incinerated; this variation would in turn affect the amount of electricity generated. It was assumed, however, that the thermal efficiency would not change; hence the amount of electricity generated would be influenced by the heat value of the solid waste. In our study, the heat value was estimated by the method used in the national standard “Sampling and Analysis Methods for Domestic Waste” (CJ/ T 313-2009). 2.2.3. Allocation The allocation procedure in a multi-functional process is a critical issue in LCA studies, especially in those on waste management systems. Waste treatment systems are becoming increasingly complex and multi-functional, as technical innovation progresses. The ISO standard for LCA (ISO, 2006) describes acceptable allocation procedures in the following order of preference: (1) avoiding allocation by dividing processes into sub-processes; (2) avoiding allocation by expanding the system; (3) applying principles of physical causality for allocation burdens; and (4) applying other principles of causalitydfor instance, economic value. The system expansion or substitution option dominates LCA studies of waste management systems (Zhao et al., 2009a). As the allocation method has a large influence on results, the robustness and the usefulness of LCA results for decision support could be limited by the choice of method. In this study, the substitution approach was adopted to solve the allocation problems (Chen et al., 2006; Bjorklund and Finnveden, 2007).
Municipal solid waste
Waste management system
Resource recycling
Source separation
Energy
95
Collection and Transportation Materials
Electricity and irons
Incineration
Composting
Fertilizer
Emissions to environment Landfill
Fig. 2. System boundary of waste management system.
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Table 4 Input, processing and destinations for the 6 scenarios of solid waste management. Categories
Scenario 0
Source separation
Paper 278.99 tons; 0 Plastic 47.01 tons; Metal 16.67 tons 321,409 tons 0 0 0 0 321,752 tons 15 km (to MIP); 18 km (to compost plant); 4 km (MIP to landfill for construction waste); 10 km: (MIP to landfill for fly ash) Transport, municipal waste collection, lorry 21 t
Incineration Compost Landfill Transportation
Scenario 1
Scenario 2
Scenario 3
Scenario 4
Scenario 5
Paper 35,251 tons; Plastic 14,160 tons; Metal 5241 tons 0 146,880 tons 120,220 tons
0
Paper 35,251 tons; Plastic 14,160 tons; Metal 5241 tons 267,100 tons 0 0
Paper 35,251 tons; Plastic 14,160 tons; Metal 5241 tons 120,220 tons 146,880 tons 0
174,872 tons 146,880 tons 0
The starting point for the substitution method is that the system delivers co-products in addition to its main service, waste treatment. This approach thereby avoids the need to produce these coproducts separately by the “normal means of production,” and these avoided processes can therefore be subtracted from the MSW management system. In this case, Chinese electricity production in 2010 was chosen as the avoided process for the electricity recovered from MSW treatment in Macau, since 73% of the total electric power consumed in Macau is imported from mainland China. Further choices have to be made regarding avoided processes when recycled materials are assumed to replace virgin materials. Although many recycled materials are equivalent in amount to virgin materials, the replacement ratioddefined as recycled material: virgin materialdis in some cases less than 1:1 (Bjorklund and Finnveden, 2007), as shown in Table 6. Because the recycled materials may be converted into many other products, it is impossible that we know the detail ratio of different products, especially for the recycled papers and plastics. In Macau, the recycled materials will be transported into mainland China, and we
didn’t know the detail ratio of different products produced by the recycled materials. Therefore, we used the main replacement materials to represent the avoided processes (Zhao et al., 2009a).
Table 5 Main input flows to waste management options; amounts normalized per ton of waste.
3.1. Environmental impacts of the five scenarios
Category Emissions to air (kg)
Emissions to water (kg) Materials and energy input
Materials output
Biological CO2 Fossil CO2 SO2 HCl NOx NH3 H2S CO Total nitrogen TOC COD Electricity (MJ) Diesel (MJ) Gasoline (MJ) Activated carbon (kg) Aqueous ammonia (kg) Slaked lime (kg) Cement (kg) Compost (kg) Electricity (MJ) Iron (kg) Wastewater (ton) Fly ash (ton) Bottom ash (ton) Other materials (kg)
Data source
Composting
Incineration
261.31 42.33 0.0012 0.002 e 0.023 0.00017 1.78 0.011 0.046 0.14 140.4 8.27 e e e e e 476.2 (N: 0.83%; P: 0.2%; K: 0.99%) e e e e e 80 Razza et al., 2009
e 165.02 0.01 0.0089 0.24 0.011 e 0.030 e e e 311.22 15.69 18.61 0.21 0.73 7.86 1.51 e 1964.79 0.26 0.085 0.036 0.18 e Field survey
2.2.4. Life cycle impact assessment and sensitivity analysis In this study, the life cycle assessment was constructed using SimaPro software version 7.2 and expressed with the Eco-indicator ’99 (H) method. The Eco-Indicator ’99 method is an example of a multi-step, fully aggregating method, leading to a result of a single number. The overall method is an example of the damage-oriented or end-point approach. Through this method, it will be very easy to make the comparison between the different waste management scenarios. The sensitivity analysis identifies sensitive parameters: i.e. whether a small change in an input parameter would induce a large change in the impact category. Here, the input parameters for sensitivity analysis focus on the recycling rate. 3. Results and discussion
3.1.1. Scenario 0dcurrent system The results of the impact assessment of Scenario 0 (the actual solid waste management system in Macau) are shown in Table 7. The total environmental impact is 4145.2 Pt, and negative value means that environmental benefit can be realized. Under this current processing technology, incineration generates significantly more environmental benefits than other three MSW treatment technologies, while transportation causes the most environmental impacts. Because of the low volume of resource recycling in the source separation, however, only small environmental benefits are obtained. On the other hand, since only the byproducts (fly ash and bottom ash) of incineration are sent to the landfill, environmental impacts are low. From Table 7, it can be seen that the environmental benefits on human health are the most important, accounting for 74.32%, followed by resources and ecosystem quality. These results of Scenario 0 are shown in more detail in Table 8, which lists the main contributors to the environmental impacts. Here, in the incineration process, the highest benefits came mainly from the avoided SO2 and PM2.5 emissions to air, together accounting for about 45.12% of the benefit, a direct result of the use of coal as the primary fuel in Chinese thermal power plants. The source separation’s main benefit was avoiding the production of paper, plastics and metals; hence its benefits show up as a reduction in resource consumption. For the transportation process, the environmental impacts of oil consumption were of the most importance, followed by NOx production; these can be attributed to
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Table 6 Substitution options for various outputs. Item
Recycling process
Avoid processes
Replacement ratio
Electricity Compost matter
Incineration Composting
1:1 1:1
Paper Metals
Source separation Source separation and Incineration Source separation
Chinese electricity (coal thermal power plant) N: ammonium nitrate, as N, at regional storehouse P: diammonium phosphate, as P2O5, at regional storehouse K: Potassium chloride, as K2O, at regional storehouse Paper, newsprint, 0% DIP, at plant Iron and steel, production mix Polyethylene terephthalate, granulate, bottle grade, at plant
1:0.9
Plastics
the fuel consumption of garbage lorries. In the landfill process, the emissions to water (Arsenic, ion) contributed the largest environmental impact. For Scenario 0 as a whole, the environmental benefits were realized primarily by avoiding SO2 and PM2.5 emissions to air, together accounting for about 50.53%, similar to the benefits of the incineration process. The current management system of MSW in Macau can treat and dispose of MSW well, and at the same time can generate large environmental benefits by recycling the valuable recovered resources (paper, plastics, and metals) and by generating electricity. 3.1.2. Scenario 1dlandfill (prior system) This scenario tests the environmental impacts of the MSW landfill disposal. As shown in Table 7, compared to the transportation process, the landfill process caused more environmental impacts. Because there were no recovered resources in Scenario 1, no environmental benefits were generated. It can be also seen that the impacts on human health were of more importance, similar to Scenario 0. As can be seen in Table 9, for the transportation process, the consumption of resources (oil) contributed the largest environmental impact, while in the landfill process, the emissions to water were of the highest environmental importance, especially Cadmium ion and Copper ion, accounting for 49.86% and 31.51% of the total environmental impacts, respectively. The environmental impacts of Scenario 1 as a whole were 14875.69 Eco-indicator ’99 points, similar to the landfill process. Compared to Scenario 0, the environmental impacts were more serious: scenario 0 shows a benefit whereas scenario 1 a net impact. Therefore it would not be appropriate to apply this scenario in the future.
1:0.8 1:1
3.1.3. Scenario 2dsource separation, composting, and landfill Table 7 presents the environmental impacts of Scenario 2, which mainly tested the potential of reducing the environmental impacts by source separation and composting. In Scenario 2, large environmental benefits would be generated by source separation, due to the recovery of resources, and this contribution was more important than the other three treatment processes. On the whole, the composting process brought some benefits, but because of smaller environmental benefits per kg of compost materials, compared to resources recovered (paper, plastics, and metals) in the source separation process, the benefits were much lower for composting than for source separation. In this scenario, the main environmental impacts were caused by the transportation process, followed by the landfill process. Table 10 presents the main contributors to the environmental impacts in Scenario 2. The contributions from the transportation and landfill processes were similar to those of Scenario 0, the main difference being that the environmental impacts of Scenario 0 were higher than those of this scenario. The source separation process can avoid the resource extraction of the manufacturing phase; therefore the main contributors to the benefits of source separation were the resource consumptions (especially the oil and natural gas) avoided. In the composting process, the main benefits were due to the natural gas consumptions avoided, and its impacts were mainly from the CO2 emissions to air. The environmental benefits of Scenario 2 as a whole were 5405.20 Eco-indicator ’99 points, caused by the avoided oil and natural gas consumption, similar to the results from source separation. Compared to Scenario 0, a 30.35% environmental benefit increase can be achieved by enhancing the source separation process and adding composting. However, due to the small benefits of
Table 7 Environmental impacts of different Scenarios (Pt). Scenarios Scenario 0
Scenario 1
Scenario 2
Scenario 3
Scenario 4
Scenario 5
Human health Ecosystem quality Resources Human health Ecosystem quality Resources Human health Ecosystem quality Resources Human health Ecosystem quality Resources Human health Ecosystem quality Resources Human health Ecosystem quality Resources
Source separation
Transportation
Incineration
Compost
Landfill
2015.70 678.64 3017.38 e e e e e e 2015.70 678.64 3017.39 e e e 2015.70 678.64 3017.38
214.12 30.72 293.51 207.25 29.73 284.10 345.41 49.56 473.50 114.71 16.46 157.25 236.66 33.95 324.41 201.67 28.93 276.45
2174.55 195.47 176.18 207.25 29.73 284.10 e e e e e e 3398.78 305.91 293.75 3400.14 305.83 250.24
51.54 4.20 107.68 e e e e e e 51.54 4.20 107.68 51.54 4.20 107.68 e e e
46.04 2.96 19.91 104.10 6.68 45.02 8151.51 5547.05 308.67 38.75 6.22 32.11 59.52 4.11 26.91 93.56 6.01 40.46
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Table 8 Main contributors to environmental impacts for Scenario 0 (Pt). Category Resources
Emissions to air
Emissions to water Others Total
Coal, hard, unspecified, in ground Gas, natural, in ground Oil, crude, in ground Occupation, dump site Nitrogen oxides Carbon dioxide, fossil Particulates, <2.5 um Particulates, >2.5 um, and <10 um Sulfur dioxide Methane, fossil Arsenic, ion
Source separation
Transportation
Incineration
Landfill
Total
0.30 0.10 6.94 0.03 1.69 1.96 1.04 0.18 1.91 0.08 2.12 23.75 40.10
0.23 0.07 265.78 0.03 103.53 32.11 55.55 5.00 9.15 0.70 2.47 46.45 521.08
172.66 58.88 60.53 43.62 899.15 472.55 1057.35 67.83 1100.17 70.35 577.07 201.84 4781.98
0.07 0.02 40.44 2.81 11.69 0.89 0.22 0.06 0.98 0.14 68.72 29.76 155.80
172.66 58.89 238.75 40.81 785.62 441.51 1002.62 62.95 1091.95 69.59 508.00 149.38 4145.2
composting, the environmental improvement was mainly due to improvements in source separation. 3.1.4. Scenario 3dincineration and composting Scenario 3 attempted to reduce environmental impacts and achieve the most environmental benefits by a combination of incineration and composting. As shown in Table 7, the environmental benefits of the incineration process accounted for the largest proportion in this scenario, and the main environmental impacts were caused by the transportation process. Compared to scenario 0, it can be seen that the weight of the MSW, which ended in the incineration plant, decreased by 45.65% in scenario 3, but the environmental benefits decreased by only about 16%. This proves that the separation of food waste will be useful for improving the heat value of solid waste. However, due to the low environmental benefits of composting, the overall benefits of this scenario were smaller than for Scenario 0. For the four processes, their contributions to the environmental impacts or benefits were similar to those of some of the other scenarios, the differences being the actual values of environmental impacts or benefits. The overall environmental benefits of Scenario 3 were 3379.06 Eco-indicator ’99 points, similar to the incineration process. Compared to Scenario 0, there was an 18.51% reduction of the benefit in this scenario. It can therefore be concluded that the introduction of composting alone cannot improve the environmental impact of solid waste management in Macau. 3.1.5. Scenario 4dsource separation and incineration The goal of Scenario 4 was to investigate the potential to improve the current MSW management system through further enhancing the source separation process. It can be seen from Table 7 that when the recycling proportion of source separation was increased to 30%, the environmental benefits were significantly increased, and source separation became the most important
Table 9 Main contributors to environmental impacts for Scenario 1 (Pt). Category Resources Emissions to air Emissions to water
Others Total
Oil, crude, in ground Nitrogen oxides Methane, biogenic Arsenic, ion Cadmium, ion Copper, ion Nickel, ion Zinc, ion
Transportation
Landfill
Total
442.97 168.3456 0.0005 3.29 1.29 0.11 0.35 0.13 251.98 868.46
264.20 15.77 650.60 338.87 6984.45 4413.70 380.68 437.06 521.89 14007.23
707.17 184.1156 650.6005 342.16 6985.74 4413.81 381.03 437.19 773.87 14875.69
contributor to the benefits. It can be concluded that the improvement of source separation will be beneficial to the management of MSW in Macau. The distribution of contributions to the environmental impacts or benefits in the scenario 4 was similar to those some of the other scenarios. The environmental benefits for Scenario 4 as a whole were 9020.83 Eco-indicator ’99 points, caused by avoiding both the oil and natural gas consumption, and the SO2 and PM2.5 emissions to air, together accounting for 52.69% of the environmental benefits. Compared to Scenario 0, Scenario 4 shows the highest potential (117.55%) for increasing the benefits. The major environmental improvement was realized from source separation. 3.1.6. Scenario 5dintegrated waste management (source separation, composting, and incineration) In order to test a combination of options in an integrated MSW management system, life cycle assessment was performed for Scenario 5. As shown in Table 7, the source separation and incineration processes contributed the most environmental benefits of the integrated management system, and the main impacts were from the transportation process. Composting and landfill contributed very little to either the impacts or benefits. For the four processes, their contributions to the environmental impacts or benefits were similar to that of some of the other scenarios. The environmental benefits of Scenario 5 as a whole were 7710.96 Eco-indicator ’99 points, mainly caused by avoiding both the oil and natural gas consumption, together accounting for 35.75% of the environmental benefits. Compared to Scenario 0, Scenario 5 is also a good option, with higher benefits (85.96%). 3.1.7. Comparison of scenarios For the Eco-indicator ’99 method, it can be seen that among the 6 scenarios, only Scenario 1 generated more environmental impacts, while all the other 5 scenarios can bring environmental benefits. Of the five scenarios, Scenario 4 was of most importance, accounting for about 30.41% of all the benefits, followed by Scenario 5 (26.00%), Scenario 2 (18.22%), Scenario 0 (13.98%), and Scenario 3 (11.39%). As discussed above, source separation and incineration could generate larger influences on the environmental impacts or benefits than other treatment processes, and are the more important recycling technologies. For the current management system of MSW in Macau, in order to achieve more environmental benefits in the future, improvement of the source separation process will be the most important (as in Scenario 4, for example). Although it was expected that Scenario 5 (integrated management system) would be the best MSW management system (Zhao et al., 2009), actually Scenario 4 performed better than Scenario 5
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Table 10 Main contributors to environmental impacts for Scenario 2 (Pt). Category Resources
Emissions to air
Emissions to water
Gas, natural, in ground Oil, crude, in ground Occupation, forest, intensive Carbon dioxide Nickel Sulfur dioxide Nitrogen oxides Particulates, <2.5 um Benzopyrene Arsenic, ion Cadmium, ion
Others Total
Source separation
Transportation
Compost
Landfill
Total
1360.00 1540.00 314.00 243.00 58.90 208.00 77.40 97.20 596.00 220.00 94.30 903.4 5710.00
9.71 147.00 0.0024 17.80 0.24 5.06 3.99 1.93 0.00 1.09 0.43 100.99 288.00
84.70 31.00 0.01 18.20 1.83 47.20 2.96 8.31 0.00 7.79 7.24 18.12 60.30
2.22 29.60 0.00014 0.82 0.06 1.36 0.78 0.61 0.00 0.55 0.13 40.90 77.10
1432.77 1394.4 314.01 206.18 60.43 154.38 75.59 102.97 596.00 226.15 100.98 743.39 5405.20
in our study. This result could be attributed mainly to two aspects: 1) the assumption, in our study, that the electricity avoided was from mainland China (the coal thermal power plant); 2) the high heat and treatment efficiency of the incineration plant in Macau.
4. Conclusions
3.2. Sensitivity analysis to recycling rates This section discusses the results of a sensitivity analysis based on different recycling rates in the source separation process, ranging from 10% to 90%, on the basis of Scenario 5. That analysis indicates that as the recycling proportions of paper, metals and plastics range from 10% to 90%, the solid waste for the incineration plant will vary from 44% to 24% of all the MSW, while the solid waste proportion of the compost will stay the same (45.65% of all the MSW). It is appropriate to test the influence of the recycling rate within these ranges, because the recycling potential of paper, metals and plastics in Macau’s MSW cannot be exactly assessed, due to the fluctuating compositions of MSW. Fig. 3 illustrates the sensitivity of the environmental impacts to the recycling rate in Scenario 5. It is obvious that total environmental benefits from Scenario 5 will increase as the recycling rate increases. There is an approximately linear relation of inverse proportion between the recycling rate and environmental benefit, with a coefficient of determination R2 ¼ 0.9999. This linear relation allows the conclusion that, when implementing the integrated MSW management strategy, a 20% change in the overall recycling rates would induce about the same change (3349 Pt) in total environmental benefits in the opposite direction. Resource recycling in the source separation process makes a considerable contribution to environmental benefits, proving that source
0 10% Recycling
30% Recycling
50% Recycling
70% Recycling
90% Recycling
Eco-indicator'99 points (Pt)
-2000 -4000 -6000 -8000 -10000 -12000 -14000 -16000
separation will be more and more important to improving the environmental benefits of the MSW management system in the future.
Resources Ecosystem Quality Human Health
-18000 Fig. 3. Sensitivity analysis of Scenario 5 to recycling rate.
With the recent rapid economic development in Macau, along with population growth, increased prosperity and tourism in recent years, the amount of waste generated in Macau has also been increasing, exerting great pressure on waste management in Macau’s limited land area. In this study, from a life-cycle perspective, the current Macau MSW management system and five other potential scenarios were evaluated to explore the potential for reducing the environmental impacts of different MSW management strategies in Macau. The results for Scenario 0 show that the current management system of MSW in Macau can treat and dispose of the MSW well and at the same time can generate large environmental benefits by recycling the valuable recovered resources (paper, plastics, and metals) and generating electricity. In Scenario 1, the environmental impacts would become more serious; hence it is not appropriate to apply this scenario in the future. Compared with Scenario 0, a 30.35% environmental benefits increase can be achieved by enhancing the source separation process and adding composting (Scenario 2). In Scenario 3, there would be an 18.51% environmental benefit reduction, compared to Scenario 0. Scenario 4 showed the highest potential (117.55%) for increasing the environmental benefits. Scenario 5 is also a good option, with higher benefits (85.96%) than Scenario 0. The analysis shows that, in each scenario (expect Scenario 1), the waste treatment processes, including source separation and incineration, dominate the environmental impacts; while processes such as collection and transportation, composting, and landfill, have a relatively small influence. The sensitivity analysis for the recycling rate reveals an approximately linear relation of inverse proportion between the recycling rate and the environmental impacts from the waste management system. Recycling of valuable resources makes a significant contribution to environmental impact reduction, compared to the other treatment processes. Based on our findings, the preferable MSW management systems are Scenarios 4 and 5. However, given the limited financial support and current waste management practices, the first priority for achieving environmental impacts mitigation would be Scenario 4, because this scenario is basically an enhancement of the current MSW management systemdimprovements in the source separation process. The present analysis focuses only on environmental impacts, which is only one environmental consideration related to waste
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management. In order to build a more complete picture of MSW management, further research should include analysis of the economic performance of the system. Since there are at present no research studies focusing on life cycle assessment of MSW in Macau, the LCA research on MSW in our study can provide some useful data on the environmental impacts of MSW, thereby helping governors and managers better understand the environmental pollution situation and put forward the appropriate management policies to deal with the serious MSW issues in Macau. Acknowledgment This study was funded by the National High Technology Research and Development Program of China (863 program, 2009AA06Z304), and the University of Macau. References Bjorklund, A.E., Finnveden, G., 2007. Life cycle assessment of a national policy proposaldthe case of a Swedish waste incineration tax. Waste Manage. 27, 1046e1058. Bovea, M.D., Powell, J.C., 2006. Alternative scenarios to meet the demands of sustainable waste management. J. Environ. Manage. 79, 115e132. Bovea, M.D., Ibáñez-Forés, V., Gallardo, A., Colomer-Mendoza, F.J., 2010. Environmental assessment of alternative municipal solid waste management strategies. A Spanish case study. Waste Manage. 30, 2383e2395. Brambilla Pisoni, E., Raccanelli, R., Dotelli, G., Botta, D., Melià, P., 2009. Accounting for transportation impacts in the environmental assessment of waste management plans. Int. J. Life Cycle Assess. 14, 248e256. Buttol, P., Masoni, P., Bonoli, A., Goldoni, S., Belladonna, V., Cavazzuti, C., 2007. LCA of integrated MSW management systems: case study of the Bologna District. Waste Manage. 27, 1059e1070. Carlsson Reich, M., 2005. Economic assessment of municipal waste management systemsdcase studies using a combination of life cycle assessment (LCA) and life cycle costing (LCC). J. Clean Prod. 13, 253e263. Chen, T., Lin, C., 2010. CO2 emission from municipal solid waste incinerator: IPCC formula estimation and flue gas measurement. J. Environ. Eng. Manage. 20 (1), 9e17. Chen, W.J., Nie, Z.R., Wang, Z.H., 2006. Life cycle inventory and characterization of flat glass in China. China Building Mater. Sci. Technol. 3, 54e58 (in Chinese). Cherubini, F., Bargigli, S., Ulgiati, S., 2009. Life cycle assessment (LCA) of waste management strategies: landfilling, sorting plant and incineration. Energy 34 (12), 2116e2123. Cleary, J., 2009. Life cycle assessments of municipal solid waste management systems: a comparative analysis of selected peer-reviewed literature. Environ. Int. 35, 1256e1266. Contreras, F., Hanaki, K., Aramaki, T., Connors, S., 2008. Application of analytical hierarchy process to analyze stakeholders preferences for municipal solid waste management plans, Boston, USA. Resour. Conserv Recycl. 52, 979e991. De Feo, G., Malvano, C., 2009. The use of LCA in selecting the best MSW management system. Waste Manage. 29, 1901e1915.
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