Electricity generation and GHG emission reduction potentials through different municipal solid waste management technologies: A comparative review

Renewable and Sustainable Energy Reviews 79 (2017) 414–439

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Electricity generation and GHG emission reduction potentials through different municipal solid waste management technologies: A comparative review ⁎

MARK

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Mohammad Ali Rajaeifara,b, , Hossein Ghanavatib,c, , Behrouz B. Dashtid, Reinout Heijungse, ⁎ Mortaza Aghbashlof,⁎⁎, Meisam Tabatabaeib,c, a

Department of Biosystems Engineering, Faculty of Agriculture, University of Tabriz, Tabriz, Iran Biofuel Research Team (BRTeam), Karaj, Iran Microbial Biotechnology Department, Agricultural Biotechnology Research Institute of Iran (ABRII), Agricultural Research, Education and Extension Organization (AREEO), Karaj, Iran d Iran Renewable Energy Organization (SUNA), 1468611387, Tehran, Iran e Centre of Environmental Science, Leiden University, P.O. Box 9518, 2300 RA, Leiden, The Netherlands f Department of Mechanical Engineering of Agricultural Machinery, Faculty of Agricultural Engineering and Technology, College of Agriculture and Natural Resources, University of Tehran, Karaj, Iran b c

A R T I C L E I N F O

A BS T RAC T

Keywords: Electricity production Global warming contribution Life cycle assessment Municipal solid wastes Waste treatment technologies

The increasing trend in the consumption of various materials has also led to a huge increase in the final waste streams especially in the form of municipal solid waste (MSW) and the consequent environmental pollutions in particular greenhouse gas (GHG) emissions. These have made MSW management a significant environmental issue for governments and policy-makers. To address these challenges, developed countries have implemented sustainable material management (SMM) strategies which have been comprehensively reviewed herein. Moreover, waste generation statistics reported for most of the developed and developing countries as well as the existing gaps in MSW management among these countries have been fully discussed. The present paper was also aimed at comprehensively assessing electricity generation potentials from MSW using an integrated solid waste management system (including three different technologies of anaerobic digestion (AD), incineration, and pyrolysis-gasification) while the consequent GHG emission reduction potentials as a result of their implementation were also explored. To facilitate the understanding of the potential impacts of these treatment strategies, Iran's data were used as a case study. More specifically, the theoretical and technical potentials of electricity generation were calculated and the GHG emission reduction potentials were estimated using a life cycle assessment (LCA) approach. Overall, it was found that 5005.4–5545.8 GW h of electricity could be generated

Abbreviations: GHG, Greenhouse gas; MSW, Municipal solid wastes; SMM, Sustainable materials management; AD, Anaerobic digestion; LFG, Landfill gas; WTE, Waste to energy; ISWM, Integrated solid waste management; USA, United States of America; EPA, Environmental Protection Agency; MW, Megawatts; RCRA, Resource conservation and recovery act; C & D, Construction and demolition; EU, European Union; GGAS, Greenhouse gas abatement scheme; ACCU, Australian carbon credit units; LAC, Latin America & the Caribbean; GDP, Gross domestic product; LP, Linear Programming; UK, United Kingdom; LCA, Lifecycle assessment; USD, United States dollar; PAHs, Polycyclic aromatic hydrocarbons; PE, Polyethylene; PS, Polystyrene; PVC, Polyvinyl chloride; PET, Polyethylene terephthalate; G-PI, Gasification with Plasma gas cleaning; FP-C, Fast pyrolysis and combustion; G-SC, Gasification with syngas combustion; MW h/day, Megawatt hour per day; GIS, Geographic information system; Ptheoritical, Theoretical potential; Pdegradable, Potential of the degradable fraction; Pdry, Potential of the fraction with high heating value; HHV, high heating value; Pdry-inc, Potential of the dry fraction with high heating value for incineration; Pdry-pg, Potential of the dry fraction with high heating value for pyrolysis–gasification; Pthechnical, Technical potential; CHP, Combined heat and power; Ptechnical-AD, Technical potential of AD technology; GGAS, Greenhouse gas abatement scheme; Ptechnical-pg, Technical potential of pyrolysis–gasification technology; Sc, Scenario; FU, Functional unit; LCI, Life cycle inventory; LCIA, Life cycle impact assessment; Pdry-inc, Global warming potential ⁎ Corresponding authors at: Biofuel Research Team (BRTeam), Karaj, Iran. ⁎⁎ Corresponding author. E-mail addresses: [email protected] (M.A. Rajaeifar), [email protected], [email protected] (H. Ghanavati), [email protected] (M. Aghbashlo), [email protected], [email protected] (M. Tabatabaei). http://dx.doi.org/10.1016/j.rser.2017.04.109 Received 26 September 2016; Received in revised form 7 January 2017; Accepted 28 April 2017 Available online 23 May 2017 1364-0321/ © 2017 Elsevier Ltd. All rights reserved.

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from MSW in Iran annually which could lead to approximately 3561–4844 thousand tons of avoided CO2eq. Such GHG reductions would be translated into approximately 0.5% of Iran's annual GHG emissions and would be considered a promising achievement given Iran's international GHGs reduction commitment, i.e., 4% reduction of anthropogenic GHGs emissions by 2030 below the business as usual scenario. Such findings could also be modeled for the other developing countries around the world where efficient MSW management is yet to be implemented.

economy, from extraction or harvesting of materials (e.g., mining, forestry, and agriculture), to production and transport of goods, and finally to the use and reuse of materials, and, if necessary, disposal. In line with that, waste management through sustainable management strategies such as source reduction and reuse, recycling, and energy recovery could play an important role in the SMM. ‘‘Source reduction and reuse’’ aims at achieving waste minimization and thus, reducing the amount of waste entering the waste stream [7]. This option is an essential prerequisite for any waste management strategies as well. ‘‘Source reduction and reuse’’ also includes preventing/enforcing acts to ensure optimized utilization of energy and resources throughout the upstream activities of materials production. An example for this option is the “lightweighting” of beverage cans which could result in less aluminum usage while maintaining the same function; or reusing half-printed papers in printing which could ultimately cause additional carbon sequestration in the forests through reduced tree harvesting [3,8]. Overall, “source reduction and reuse” could offer several advantages such as saving natural resources, conserving energy, reducing pollution of upstream activities, reducing the toxicity of waste, and finally saving both consumers and producers their hard-earned dollars [8]. Through ‘‘recycling’’ of a specific amount of a given material, environmental emissions associated with its re-fabrication from virgin inputs could be avoided. However, there is a necessity to use efficient recycling systems in order to maximize the environmental and economic benefits of recycling [8]. By considering this, recycling could offer numerous advantages including preventing the emission of a great deal of GHGs and water pollutants, energy savings, further develop-

1. Introduction Growing global population, rapidly-increasing urbanization, as well as vast industrial and economic developments have collectively led to increased consumption of various commodities such as food, minerals, metals, plastics, wood products, etc. This increasing trend in consumption is believed to continue to accelerate, while simultaneously shifting away from renewable resources like agricultural and forestry products toward non-renewable resources such as fossil fuel-derived and metal products [1]. Moreover, various practices involved in the supply chain of these materials, i.e., extraction, harvesting, processing, transportation, and waste disposal have resulted in a variety of environmental pollutions especially greenhouse gas (GHG) emissions [2,3]. This is in fact ascribed to the energy and/or resources required during various life cycle stages of these commodities. Overall, this increasing trend in consumption of materials has led to a huge increase in final waste streams especially in form of municipal solid waste (MSW) and hence, MSW management is considered a significant environmental issue for governments and policy-makers [4]. For instance, in the year 2012, approximately 1.3 billion metric tons of MSW were generated globally, and this amount is expected to rise to approximately 2.2 billion tons by the year 2025 [5]. It should be noted that at the first glance, waste management might seem a bit irrelevant to materials consumption, however, formerly called MSW management reports and strategies are now emerging as sustainable materials management (SMM) reports and strategies which also includes consumption features [6]. More specifically, SMM refers to how material resources should be managed as they flow through the

Fig. 1. a) Population (in million), total MSWs generation (in million tons) and MSWs generation per capita (kg person−1 day−1) in the USA (1960–2013). b) Changes in the contribution of different MSWs treatment options in the USA (1960–2013).

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different processes should be considered to effectively deal with these materials at a given condition. In this point of view, there are no overall ‘best’ or ‘worst’ waste management options/strategy and different options could be potentially appropriate for different waste fractions [9]. Such a vision has led to the integrated solid waste management (ISWM) concept which is capable of delivering both environmental and economic sustainability. The present review was aimed at comprehensively reviewing and discussing MSW generation throughout the world as well as major different waste treatment options available for electricity generation from MSW. Moreover, electricity generation potentials from MSW using an ISWM system (including three different technologies, i.e., AD, incineration, and, pyrolysis–gasification) as well as the consequent GHG emissions reduction potentials of these treatment options were thoroughly discussed. To facilitate the understanding of the potential impacts of these treatment strategies, Iran's data were used as a case study. More specifically, the theoretical and technical potentials of electricity generation were calculated and GHG emission reduction potentials were estimated using an LCA approach.

ment of greener technologies, supply of valuable raw materials to industry, job creation, resources conservation for future generations, and elevation of the need for new landfills and incinerators [3,8]. Through a variety of processes including landfill gas (LFG) recovery, anaerobic digestion (AD), incineration, gasification, and pyrolysis, ‘‘energy recovery’’ could help with the conversion of energy from nonrecyclable waste materials into useable electricity, heat, or fuel [8,9]. Energy recovery; often called waste to energy (WTE), could bring about some beneficial features such as establishing renewable energy resources, reducing carbon emissions originated from fossil-oriented energy production, reducing methane emissions from landfills, and reducing the volume of wastes introduced to landfills (except for LFG recovery) [4,10,11]. Beside the above-mentioned strategies, ‘‘waste disposal’’ is also an option which is generally considered as the least environmentallypreferred option especially when implemented in the majority of developing countries. This is ascribed to the fact that waste disposal in these countries are often characterized by inadequate collection services, little or no leachate/landfill gas treatment, and uncontrolled dumping [9]. On the contrary, in the developed countries, landfills are well-engineered to collect leachate, to ensure the maximum capture of methane gas (a byproduct of waste decomposition), and to utilize the generated methane as energy carrier in order to reduce the environmental burden of landfilling. Moreover, landfills in these countries are well operated in compliance with the environmental regulations on wastes [8,12]. The options reviewed above were also considered as the backbone of the waste management hierarchy which categorizes waste management options from most environmentally-preferred to least environmentally-preferred ones [8]. However, it should be highlighted that categorizing the options as the most environmentally-preferred to least environmentally-preferred (as implemented by the waste management hierarchy) does not necessarily help with determining the option of the lowest environmental burdens and the highest economical-sustainability under different circumstances. In better words, since there is a variety of different materials flowing through the waste stream,

2. MSW generation: a global overview 2.1. United States of America (USA) The United States of America (USA) with a population of 316.5 million in 2013 generated over 254.1 million tons of MSW in the same year which was more than twice as the value generated in the year 1960 (Fig. 1a) [6,13]. However, the MSW generation per capita (kg person−1 day−1) increased by two-third during the same period. In fact, the generation, recycling, composting, and disposal of MSW in the USA have changed substantially over the last few decades (Fig. 1b) [3]. More specifically, disposal of generated waste in landfills decreased from 93% (of the total MSW generated) in 1960 to less than 53% in 2013. Meanwhile, the recycling rate of MSW changed from 5.6 million tons in 1960 (less than 10% of the generated MSW) to 87.6 million tons (more than 34% of the generated MSW) in 2013, out of which 64.7 million

Fig. 2. a) Population (in million), total MSWs generation (in million tons) and MSWs generation per capita (kg person−1 day−1) in the European Union (EU)-27 (1995–2013). b) Changes in the contribution of different MSWs treatment options in the European Union (EU)-27 (1995–2013).

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generation varied considerably in the EU, ranging from 747 kg per capita in Denmark to 272 kg per capita in Romania [18]. It is worth quoting that although these variations depend on how wastes are collected and managed, they reflect differences in consumption patterns, living standards, urbanization, and economic wealth among the studied countries [16]. The overall trends of MSW treatment during the period of 1995– 2013 depicts that the EU members moved toward a sustainable management of MSW over the last few years (Fig. 2b) [16–18]. Although the MSW generation has increased in 2013 compared with the year 1995, disposal of the generated wastes in landfills decreased from 63.8% (of the total MSW generated) in 1995 to less than 31% in 2013. This reduction in MSW landfilling is attributed to the implementation of the European legislations on wastes such as Directive 94/ 62/EC and Directive 1999/31/EC. Directive 94/62/EC refers to packaging and packaging wastes by which all the member states were required to recover a minimum of 50% of all packaging put on the market [19]. While Directive 1999/31/EC refers to landfill stipulation by which all the member states were obliged to reduce the amount of biodegradable municipal wastes ending in landfills to 75% by 16 July 2006, to 50% by 16 July 2009, and to 35% by 16 July 2016 [20]. It is worth mentioning that Directive 62/1994 also required the member countries to implement alternative scenarios to avoid landfilling the organic fraction of MSW by using composting (including fermentation), incineration, and pre-treatment (such as mechanical-biological treatment; including physical stabilization) approaches. Moreover, the recycling rate of MSW has changed from 25 million tons (11.1% of the generated MSW) in 1995 to 66 million tons (27.3% of the generated MSW) in 2013 showing the highest increase rate among the various treatment methods used in the EU. Meanwhile, composting process increased from 14 million tons (6.2% of the generated MSW) in 1995 to 36 million tons (14.9% of the generated MSW) in 2013. Incineration, however, had the lowest increase rate among the treatment approaches from 32 million tons in 1995 to 62

tons were recovered through recycling while over 22 million tons were recovered through composting. In better words in the year 2013, 0.5 kg of the waste produced by each person per day in the USA (out of the total value of 2 kg person−1 day−1 in 2013) was subjected to recycling, 0.26 kg was sent to combustion facilities, and only 0.17 kg was used for composting. Hence, 134.3 million tons of the MSW generated in 2013 (i.e., 52.8% of the total value) was still discarded in landfills (1.05 kg person−1 day−1) [6]. It should be noted that based on the estimations put forth by the Environmental Protection Agency (EPA), approximately 560 landfills with LFG energy recovery were operational in the USA in July 2011. These projects generated approximately 1730 MW (MW) of electricity per year and delivered 310 million cubic feet day−1 of LFG to direct-use applications while an additional 510 landfills were identified as attractive opportunities for future project development [14]. All these statistics and projects show that the US has achieved a remarkable progress in waste monitoring and management by pursuing the sustainable material management goals for reducing the environmental burdens caused by MSW. More specifically, the implementation of environmental laws and regulations in the USA, such as resource conservation and recovery act (RCRA), the federal landfill regulations, the federal regulations for composting, the federal regulations for construction and demolition debris (C & D), etc. played a significant role in the achievements made. 2.2. European Union (EU) Fig. 2a illustrates the population (in million), total MSW generation (in million tons) and MSW generation per capita (kg person−1 day−1) in the European Union (EU)-27 over time. In 2013, the EU-27 members with a population of 502.16 million generated more than 241 million tons of MSW which was 7.1% more than what generated in 1995 [15– 17]. Meanwhile, the MSW generation per capita had a very slight increase (from 1.3 to 1.32 kg person−1 day−1). However, the total MSW

Fig. 3. a) Population (in million), total MSWs generation (in million tons) and MSWs generation per capita (kg person−1 day−1) in Australia (1980–2013). b) Changes in the contribution of different MSWs treatment options in Australia (1980–2013).

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target legislation, have led to an impressive progress in resource recovery over the past decade. Notably, among the approximately 458 operational landfills in Australia, 65 landfills with LFG energy recovery (ranging in size from 400 kW to 13 MW) and 250 landfills with gas capture and flaring are operational [28]. Therefore, the LFG energy recovery is a promising energy resource for a vast proportion of landfill operators, creating a financial liability by preventing penalties to be imposed on future emissions while it also offers potentials to realize revenue through Australian carbon credit units (ACCU) for legacy waste abatement.

million tons in 2013. It is also worth quoting that due to technical problems in collecting data by the EU, the incineration data do not segregate incineration with and without energy recovery [16]. 2.3. Australia Fig. 3a presents the population (in million), total MSW generation (in million tons), and MSW generation per capita (kg person−1 day−1) in Australia over time (when data was available) [21–24]. As shown, Australians generated around15 million tons of MSW in the year 2013 with a population of 23.1 million, which was higher by 45.3% compared with the MSW generated in 1980. However, the MSW generation per capita (kg person−1 day−1) decreased by 7.6% during the same period. Nevertheless, 1.77 kg MSW person−1 day−1 is still considered high marking Australia as one of the main MSW per capita producers in the world. The progresses achieved in MSW treatment during the years 1980– 2013 have caused Australians to move towards a sustainable MSW management over the last few years albeit at a slower pace in comparison with the USA and the EU (Fig. 3b) [23,25–27]. More specifically, the disposal of the generated MSW in the Australian landfills decreased from 88% (out of the total MSW generated) in 1980 to 48.1% in 2013. Meanwhile, the recycling/composting rate of MSW also changed from 1.2 million tons in 1980 (12% of the generated MSW) to 6.54 million tons (more than 43% of the generated MSW) in 2013. However, it should be mentioned that there is no data available on the exact portions of MSW recycled and/or composted. Moreover, energy recovery has shown the lowest level of increase in the reference period by only 8.2%. Overall, the achievements made in the implementation of environmental laws and regulations in Australia such as, national waste policy, ACT No Waste Strategy, the NSW greenhouse gas abatement scheme (GGAS), the national greenhouse and energy reporting system (Act 2007), and federal mandatory renewable energy

2.4. Asia, Africa, Latin America and the Caribbean (LAC) Asia with 48 countries and more than 4.2 billion inhabitants (2012) is the Earth's largest (30% of Earth's land area) and most populous continent [29]. Following Asia, Africa including 54 countries and 1.07 billion inhabitants is the second largest (20.4% of Earth's land area) and the second-most-populous continent in the world [29]. The vastness and large number of countries in these continents along with the lack of a unit system for collecting waste generation and management data have caused difficulties in assessing the waste management trends over time. Based on the latest report published by World Bank (2012), the annual waste generation in East Asia and the Pacific Region was approximately 270 million tons per year with an average per capita of 0.95 kg person−1 day−1 [5,30]. Almost 70% of the waste generation in this region was contributed by China. Countries in South Asia produced approximately 70 million tons of MSW per year, with an average per capita of 0.45 kg person−1 day−1 [5]. The annual waste generated in Eastern Europe and Central Asia has been estimated at least 93 million tons with an average per capita of 1.1 kg person−1 day−1. In the Middle East and North Africa, the MSW generated per year is 63 million tons with an average per capita of 1.1 kg person−1 day−1 [5]. Fig. 4 shows

Fig. 4. MSWs generation per capita in different regions in Asia.

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Korea [34]. Koreans produced 17.88 million tons of MSW in 2010 which was less by 41.7% compared with the huge amount of MSW generated in 1990 (Fig. 6a) [32,35]. Meanwhile, MSW generation per capita decreased from 1.96 kg person−1 day−1 in 1990 to 0.98 kg person−1 day−1 in 2010. MSW management and recycling programs in South Korea encouraged the reusing of wastes as an energy resource. Over the past years, targeted policies have significantly increased the recycling rate while creating thousands of jobs in an endeavor to build a resource recirculation society. For instance, the recycling rate of MSW significantly increased between the years 1990 and 2010 (from 4.7% to 58.4% of the total MSW generated, respectively) while the amount of landfill was impressively decreased in the reference period (from 93.6% of the total MSW generated in 1990 to 15.9% in 2010) (Fig. 6b) [32].

the MSW generation per capita in different regions in Asia [5]. In continuation, waste generation and its management in some of the either most-developed or most-populated countries/regions in Asia are reviewed more comprehensively as follows: 2.4.1. Japan Japan is one the most developed and industrialized countries in the Asian region, paying a specific attention to its environmental quality especially in terms of waste management. Although Japan has a solid system for waste management and recycling at the moment, it also experienced problems similar to those faced by today's developing countries [31]. Developments in different waste treatment technologies alongside improvements in different waste management laws and regulations have made Japan as one of the leading countries in waste management. In 2010, Japanese (with a population of around 128.1 millions) produced 45.4 million tons of MSW which showed a decreasing trend of 9.8% compared with that of 1990 (Fig. 5a) [31– 33]. In the meantime, MSW generation per capita also decreased from 1.11 kg person−1 day−1 to 0.97 kg person−1 day−1. Waste management approach in Japan is dominated by incineration treatment where 76.72% of the wastes were incinerated in 2010 implying an increasing value of 4.7% compared with the year 1990 (Fig. 5b) [32]. It is worth quoting that the incineration without energy recovery has decreased from 7.2% in 1990 to 6.2% in 2010. Increasing the recycling rates of MSW alongside decreasing landfilling of MSW reveals that Japan is moving toward a more sustainable MSW management approach.

2.4.3. China China as the most populated country in the world while owing the second largest economy is a developing country in East Asia. In 2009, 1.3 billion Chinese produced 157.3 million tons of MSW which was 132.5% higher compared with that of 1990 (Fig. 7a) [32]. The MSW per capita also increased from 0.16 kg person−1 day−1 in 1990 to 0.32 kg person−1 day−1 in 2009. The most important problem associated with MSW management in China is the widespread landfilling which is the least preferred method to dispose of the waste but is still popular in China. More specifically, in 2009, 56.6% of the generated MSW were subjected to landfilling which showed an increasing trend compared with 1990 (Fig. 7b) [32]. Moreover, most of the landfills are now under the pressure of being rapidly filled up and there are lots of landfills which do not fulfill the environmental standards of landfills for gas recovery [36]. Zhang et al. [37] discussed the challenges faced in MSW management in China and offered a number of solutions for improving the waste management situation in China, such as 1) proper organization and management of MSW by local governments to avoid out-of-the-system waste collection, 2) systematic waste separation

2.4.2. South Korea South Korea is one of the emerging developed countries in the East Asia with a developed market and a high-income economy. The South Korean government has implemented a sustainable waste management strategy since the1990s focusing on demand-side management for reducing waste generation at the source. This was a turning point which made possible further improvements in MSW management in

Fig. 5. a) Population (in million), total MSWs generation (in million tons) and MSWs generation per capita (kg person−1 day−1) in Japan (1990–2010). b) Changes in the contribution of different MSWs treatment options in Japan (1990–2010).

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Fig. 6. a) Population (in million), total MSWs generation (in million tons) and MSWs generation per capita (kg person−1 day−1) in South Korea (1990–2012). b) Changes in the contribution of different MSWs treatment options in South Korea (1990–2012).

Fig. 7. a) Population (in million), total MSWs generation (in million tons) and MSWs generation per capita (kg person−1 day−1) in China (1990–2009). b) Changes in the contribution of different MSWs treatment options in China (2001–2009).

mechanisms (e.g., foreign investment and international services) for improving MSW management, and 6) improving the waste fee levying system, and raising waste collection disposal fees [37].

especially for organic wastes, 3) improving the recycling industry's performance through increasing professionalization, market development, and clearer operating standards, 4) improving the criteria for liners and leachate collection systems, 5) using various financial 420

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Fig. 8. MSWs generation per capita in the Sub-Saharan Africa.

consider the need for the business sector to adequately treat the waste it generates [38]. Based on the report published by Tello Espinoza et al. [38], MSW treatment activities prior to disposal, i.e., recycling, composting, thermal treatment, as well as the other techniques to generate energy from waste are still incipient in the LAC region, while such methods are

2.4.4. Sub-Saharan Africa In the Sub-Saharan Africa, approximately 62 million tons of waste is produced annually (in 2012) with an average waste generation per capita of 0.65 kg person−1 day−1 which is the second lowest value (after South Asia) recorded in the world [5]. However, there is a lack of data on waste management trends over time for this region. Fig. 8 shows the MSW generation per capita in the Sub-Saharan Africa [5].

2.4.5. LAC region Latin America and the Caribbean (LAC) region with a population of 468.8 million produced 160 million tons of MSW in 2010 [5,38]. While experiencing an increasing trend in MSW generation in the region during the last decade, LAC countries also made their best efforts to deal with such huge deals of urban solid wastes through increasing the coverage rate of MSW management by street sweeping, collection, and final disposal. For instance, while the urban population in LAC increased by 63 million during the 2002–2010, over 111 million additional urban population received collection services. During 2002–2010, the total street sweeping coverage increased from 72% to 82.3% (covering extra 93 million residents) and collection service coverage increased from 81% to 93.4% (covering extra 111 million residents). More impressively, between the years 2002 and 2010, the final disposal coverage through sanitary landfills had the highest growth among the other treatments from 22.5% to 54.4%. This means that the final disposal system could cope with the waste generated by 225 million individuals, nearly 164 million more individuals compared with the year 2002 [38–40]. Fig. 9 shows the MSW generation per capita in LAC region [38]. On the other hand and in spite of these major positive developments in MSW management occurred during 2002–2010 in this region, more improvement are still required in some areas, i.e., 1) proper disposal of 50% of MSW which is still not managed properly; 2) improving the financial ability of municipalities to establish financially self-sustaining services in order to make further developments in the waste management sector; 3) improving the MSW collection in some marginal districts of urban areas; 4) increasing the MSW's recycling rate which is currently low in the region and is being carried out by the informal sector; 5) enhancing the quality of landfills in some countries (in the region) where the control standards necessary to qualify them as sanitary landfills are not met; 6) increasing energy saving from recycling; 7) closing the unsymmetrical information gap between municipal authorities and the general public on one hand as well as between municipal authorities and private workers (through establishing regulations in both economic and technical aspects in the waste management sector), and 8) increasing the political and legal will to

Fig. 9. MSWs generation per capita in LAC region.

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Renewable Energy Organization (SUNA), the average per capita generation of MSW in Iran was 0.751 kg person−1 day−1. On the other hand, although MSW generation per capita in Iran was lower than global average, there was a large gap between the MSW treatment activities in Iran, i.e., recycling, LFG recovery, and thermal treatments and the world's quality standards, caused serious shortcoming in managing the waste generated. For instance, unlike what seen in the developed countries, landfilling was the major waste treatment strategy throughout the country and increased from 8.5 million tons in 2002 (82.3% of the total generated MSW) to 11.1 million tons (71% of the total generated MSW) in 2014 (Fig. 10b). More specifically, the amount of MSW landfilled in 2007 was still too high implying the failure of waste management diversification policies and acts in Iran. Moreover, no landfills in Iran (except those located in Mashhad and Shiraz metropolitans) fulfilled the environmental standards required for LFG and leachate recovery, caused adverse environmental burdens in these cities. Following landfilling, composting was ranked second among MSW treatment options and was increased from 1.6 million tons in 2002 (15.7% of the total generated MSW) to 3.8 million tons in 2014 (24.3% of the total generated MSW) (Fig. 10b). In case of recycling, in spite of the fact that its implementation in Iran dates back several years ago, this treatment option showed a disappointing increase from 2% of the total generated waste in 2002 to only 3.5% in 2014 (Fig. 10b). This could be ascribed to the facts that MSW in cities are mainly subjected to a separation process by the informal sector before collection by municipalities and also the recycling systems in most cities takes place at a low capacity and by using out-of-date facilities. In the case of waste-to-energy treatments, the utilization of AD approach was increased from 0% of the total generated MSW in 2002 to 0.7% in 2014 (Fig. 10b). In fact, this treatment option was recently introduced to the Iranian waste management system and was implemented by only one of the 22 regions of Tehran province. In this point of view, this technique is anticipated to be further implemented by the

widely used in developed countries. More specifically, there is a great lack of formal recycling of MSW in sorting plants as most of recycling is performed by the informal sector. It should be noted that composting has been shown as a promising potential in the carbon market of the LAC region and has been implemented many times by the member countries. Moreover, although the incineration approach has not been used much in the LAC, there is a great potential to use efficient thermal treatment technologies such as incineration in large cities located in the LAC region [38]. 2.5. Iran Iran is the second largest economy in the Middle East region after Saudi Arabia, and is one of the developing countries facing many environmental problems caused by industrialization and urbanization. One of the most critical problems challenging the Iranian authorities in the current decade is the adverse environmental consequences of traditional waste management scenarios in Iran. In 2014, 55.5 million Iranian living in country's urban areas produced more than 15.6 million tons of MSW which was by 50.9% higher compared with the year 2002 (Fig. 10a). However, it should be mentioned that there was a peak in MSW generation in 2007 when 16 million tons of wastes was generated which was higher than that of 2002 and 2014 by 54% and 2.3%, respectively. Such fluctuation in MSW generation could imply that generation, recycling, composting, and disposal of MSW in Iran has not been completely influenced by waste management policies and acts over the last decade due their inefficiency and weak implementation and that they have been mainly impacted by other factors such as inflation rate. Table 1 shows the latest data available on urban population, MSW generation (tons day−1), MSW generation per capita (kg person−1 day−1), and the portion of urban population and MSW generation for each province in Iran. Based on the records provided by Iran's

Fig. 10. a) Population (in million), total MSWs generation (in million tons) and MSWs generation per capita (kg person−1 day−1) in Iran (2002–2014). b) Changes in the contribution of different MSWs treatment options in Iran (2002–2014).

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Table 1 The latest data available on urban population, MSW generation (tons day−1), MSW generation per capita (kg person−1 day−1), and the portion of urban population and MSW generation for each province in Iran. Province

Urban population (Thousands people)

MSW generation (tons day−1)

MSW generation per capita (kg person−1 day−1)

Urban population (%)

MSW generation (%)

Ardabil Alborz Bushehr Chaharmahal and bakhtiari East Azerbaijan Esfahan Fars Golestan Guilan Hamadan Hormozgan Ilam Kohgiluyeh and BoyerAhmad Kerman Kermanshah Khuzestan Kurdistan Lorestan Markazi Mazandaran North Khorasan Qazvin Qom Razavi Khorasan Semnan Sistan and Baluchestan South Khorasan Tehran West Azerbaijan Yazd Zanjan Iran (Urban population)

834 2269 742 542 2639 4262 3288 952 1543 1056 830 369 367

695 1747 676 424 2066 3674 2473 661 1247 967 661 276 186

0.833 0.770 0.911 0.783 0.783 0.862 0.752 0.694 0.808 0.916 0.796 0.748 0.507

1.49 4.07 1.31 0.97 4.81 7.77 5.79 1.69 2.79 1.94 1.47 0.67 0.65

1.62 4.07 1.58 0.99 4.82 8.57 5.77 1.54 2.91 2.25 1.54 0.64 0.43

1767 1382 3349 1019 1099 1087 1722 463 915 1137 4494 505 1333 434 11,563 1999 887 662 55,510

1263 998 2411 819 679 798 1429 344 705 691 3344 376 749 309 9713 1565 444 493 42,883

0.715 0.722 0.720 0.804 0.618 0.734 0.830 0.742 0.770 0.608 0.744 0.745 0.562 0.711 0.840 0.783 0.501 0.745 0.751

3.15 2.53 6.00 1.84 2.01 1.95 3.14 0.83 1.64 2.04 8.04 0.91 2.32 0.69 21.07 3.60 1.66 1.18 100.00

2.95 2.33 5.62 1.91 1.58 1.86 3.33 0.80 1.64 1.61 7.80 0.88 1.75 0.72 22.65 3.65 1.04 1.15 100.00

also examined the electricity production potential from AD and incineration, as well as pyrolysis–gasification technique and their respective consequential GHG emissions reductions in Iran.

other municipalities in the near future. Likewise, incineration technology which was recently implemented by Tehran municipality increased from 0% of the total generated MSW in 2002 to 0.5% in 2014 showing a great necessity for its further implementation in the near future. It should also be mentioned that there is currently no pyrolysis–gasification facilities operated by the municipalities in Iran, however, these techniques have been introduced recently by the Iranian government as potential technologies for waste treatment. Hence, the present study

3. Gross domestic product and MSW generation: emerging decoupling policies Since economic growth is generally the key driving force behind the

Fig. 11. MSWs generation per capita and GDP with examples from countries of low, medium, and high incomes.

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used. In this point of view, the policies laid forth for decoupling economic growth and the associated environmental harms are attracting more attentions. However, the questions still remains about which economic and environmental policies could have more decoupling impacts [6,41]. Based on the literature, MSW generation per capita is proportional to the GDP per capita [38,42,43]. Fig. 11 shows the MSW generation per capita and GDP with examples from countries of low, medium, and high incomes. As the GDP increases toward high income countries, the MSW generation per capita increases as well. On the contrary, it should be noted that Japan showed a disproportional relationship between

increasing volumes of waste generation, the trends related to MSW generation and its per capita value are mainly compared alongside the gross domestic product (GDP) trends. In other words, the world trends show that the growth rate in materials consumption and consequently MSW generation is coupled with economic growth but still owing a lower growth pace compared with that of the world economy [5,6]. This is due to the fact that the consumption pattern has changed toward ‘eco-efficiency’ during the last decades, i.e., less material-intensive products and services are offered. Moreover, the efficiency of materials consumption has increased by improving energy efficiency, technological advancements, and by recycling vaster variety of the raw materials

Table 2 MSW composition in Iran and the other countries around the world. Province

Organic

Plastic

PET

Glass

Textiles

Ferrous metals*

Non-Ferrous metals

Paper/ Cardboard

Hazardous

Wood

Leather

C&D

Other

Ardabil Alborz Bushehr Chaharmahal and bakhtiari East Azerbaijan Esfahan Fars Golestan Guilan Hamadan Hormozgan Ilam Kohgiluyeh and BoyerAhmad Kerman Kermanshah Khuzestan Kurdistan Lorestan Markazi Mazandaran North Khorasan Qazvin Qom Razavi Khorasan Semnan Sistan and Baluchestan South Khorasan Tehran West Azerbaijan Yazd Zanjan Iran's average USA EU-27 Australia Japan South Korea Chinai Chinaj Sub-Saharan Africa LAC World (2009) Low-Income Lower Middle Income Upper Middle Income High Income

60.1 73.4 78.8 69.3 71.9 69.4 61.1 63 62.8 78.6 75.8 69 72.6

10 4.8 4 3.5 5.9 9.4 9.8 7.25 14.6 5.1 6.08 6.05 4

1.1 1.2 0.4 1.4 0.6 1.1 1.4 1.9 1.3 0.9 0.76 2.1 1.9

1.3 1.4 1.4 3.2 1.2 2.4 1 2 0.9 2 2.4 2.24 1.9

4.8 3.9 1.2 1.9 4.4 4.8 2.6 5.5 1.5 2 0.9 3.96 2.1

2 1.9 1.9 4.9 0.6 1.4 2.3 1.1 0.1 1.3 2.37 0.69 1.6

0.1 0.4 0.3 0.3 0.2 0.1 1 0.05 0.01 0.1 0.13 0.03 0.6

13.8 4.9 7.4 9 4.8 6.6 15.1 15.1 15.1 4.1 6.5 8.23 6.9

0.4 0.3 0.3 0.2 0.3 0.5 0.6 0 0 0 0.3 0.4

1.3 1.8 1.1 2.3 3.9 1.7 1.9 1.9 1.4 0.8 1.5 1.5 2

1.4 1.6 0.3 0.3 1.8 1.1 1.5 1.2 1.3 0.8 0.76 1.1 1.8

1.7 1.6 0.4 3.5 2.1 0.7 0.9 0.1 0.6 1.8 0.1 2.1 1.9

2.0 2.8 2.5 0.2 2.3 0.8 0.8 0.9 0.39 2.5 2.7 2.7 2.3

75.3 74.1 64.9 66.1 77.7 78.5 79.17 71.7 68 59.6 73.1 73.28 52.2 71.4 71.2 77.07 70.4 68.4 70.26 28.1a 31a 47.46a 26 28 65 41 57 54 46 64 59 54 28

4.5 3.8 5.3 5.9 7 5.1 6.5 5.6 6.8 9.7 5.3 4.8 4.9 6.7 5.9 6.6 6.2 5 6.33 12.8 12 5.22h 9 8 13 4 13 12 10 8 12 11 11

1.2 1 1 1.6 0.8 0.9 0.3 0.4 0.7 3 0.4 0.9 1.2 0.8 1.3 0.8 0.8 0.4 1.08 b b b b b b b b b b b b b b

2.3 2 3.6 2.1 0.9 0.9 1 2.3 1.3 1.3 1.2 1.1 2.8 1.9 1.6 1.2 3.2 2 1.81 4.5 5 4.71 7 5 2 2 4 4 5 3 3 5 7

3 3.2 3.4 3.4 2 2.1 1.4 5.1 2.8 5.4 5.7 6.1 8.5 6.1 3.6 1.7 3.4 3.5 3.55 9c 4 2.36c b b b b b b b b b b b

0.3 0.1 4.1 1.1 0.7 1 1.1 1.1 3.5 1.5 1.5 0.9 1.1 1.6 2.1 0.8 1.1 2.6 1.56 9.1d 2f 3.53d 8d 7d 1d 1d 4d 2d 4d 3d 2d 3d 6d

0.03 0.02 0.2 0.03 0.1 0.1 0.03 0.03 0.1 0.1 0.2 0.02 0.2 0.1 0.4 0.03 0.1 0.1 0.17 b 1 b b b b b b b b b b b b

6.7 8.8 8.2 8.8 8.1 8.4 6.9 7.9 9.7 14 8.6 10.2 18.7 7.2 9.6 3.8 6.8 13.1 9.13 27e 18 23.08e 46e 24e 9e 5e 9e 16e 17e 5e 9e 14e 31e

0.9 0.68 0.4 0.5 0 0 0 0.5 0.5 1.0 0.5 0.3 0.5 0.4 0.3 0.5 0 0.3 0.35 0 b 2.24 b b b b b b b b b b b

1.1 2 3.6 2 0.4 0.2 1.1 0.3 3.4 1.3 0.6 0.2 3 0.5 1.8 1 0.3 1.4 1.53 6.2 b 1.53 b b b b b b b b b b b

0.5 1 0.6 1.6 0.6 0.8 0.4 0.9 0.4 1.8 1.4 1 1.3 1.1 0.6 3 0.8 0.9 1.09 b b b b b b b b b b b b b b

1.6 1.2 3.4 4.37 1.3 0.2 0.3 2.07 1.9 1.1 0.9 0.2 3.6 2 0.6 1.1 4.8 1.3 1.59 0 5 4.48 b b b b b b b b b b b

2.57 2.1 1.3 2.5 0.4 1.8 1.8 2.1 0.9 0.2 0.6 1 2 0.2 1 2.4 2.1 1 1.58 3.3 22g 5.39 12 28 10 47 13 12 18 17 15 13 17

b. Not mentioned. * Including Iron alloys. a Including Food waste and Yard trimmings. c Rubber, leather & textiles. d All types of metal. e Only paper waste was reported. f Only Steel. g Including 10% other combustible, 3% nappies and other sanitary, 1% white goods and 8% other (not-specified). h Plastic and PET. i Population Using Gas. j Population Using Coal.

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5. Comparison of the world data on MSW generation and management

these factors. More specifically, Japan is classified as a high income country while its MSW generation per capita is in the range of middleincome countries. The success of the decoupling policies implemented by Japan could be the main reason behind such enhancement.

The overall comparison of the world data on MSW generation and management shows that the volume of MSW generated is strongly proportional with the population and GDP growth. Based on the World bank report (2012), the fastest growth in MSW generation rate belonged to China, followed by some parts of East Asia, Eastern Europe, and the Middle East [5]. On the other hand, it should be highlighted that the methane emission originated from MSW disposal is the main factor behind the strong correlation between MSW generation rate and its global warming contribution. Thus, governments and policy makers in these parts of the world should choose a more holistic approach in order to manage the MSW. The projections show that MSW generation is expected to increase by about 0.9 billion tons during 2012–2025, rising from 1.3 billion tons to 2.2 billion tons in the mentioned period [5]. This growth would be more severe in lower-income and developing countries where a large portion of their municipal budget are assigned to the MSW management [5]. A more in-depth comparison of the data presented in the study (Figs. 1–10) shows that waste management options in the developed countries have changed towards more efficient waste management scenarios during recent decades, i.e., exploiting more energy and materials from waste stream while introducing less pollution into the environment. For example, landfilling of MSW in the USA reduced by 40% between 1960 and 2013, while recycling, composting, and energy recovery treatments experienced a significant growth during the same period. The progress observed in MSW management is somehow the same in many other developed countries in the EU, as well as Australia, Japan and South Korea. However, moving towards a specific option for waste management highly depends on the established and dominant technologies available in a country, e.g., waste incineration in Japan. On the contrary, waste management options and the entire waste management system (including wastes reduction and their collection) in the lower-income, middle-income, and most of the developing countries are still far from ideal. This is attributed to; 1) less technological development achieved in these countries, 2) lack of appropriate practices and legislations for waste management and waste reduction in the industry, 3) lack of integrated waste picking systems, 3) lack of integrated waste management scenarios, 4) lack of investment in the waste management industry by the private sector. On the other hand, it should be noted that since a poor management of MSW leads to higher down-stream costs associated with the environmental and human health concerns [5], developing countries, lower and middle income countries are strongly encouraged to invest more in order to establish the most appropriate waste management strategies while also considering their financial and technological constraints. Besides, a systematic approach using a careful monitoring from MSW collection to final treatment is needed in these countries in order to effectively deal with the critical issues faced in MSW management, such as unauthorized dumping, irregular waste delivery time by citizens, waste transportation issues, and finding the best treatment based on financial and technical limitations.

4. MSW composition Although the main ingredients of MSW are to some extent identical throughout the world, the total waste generated as well as the density and the proportion of the constituents vary widely among countries [42]. There are many factors influencing the proportion of MSW` composition such as level of economic development, geographic location and climate, cultural and traditional norms, and energy sources used [5,44]. Country income level is commonly considered as a good index for determining the level of economic development which could in turn influence the proportion of waste constituents. The level of organic fraction ending up in MSW is generally higher in low-income countries compared with the countries of higher income level. More specifically, as level of economic wealth and urbanization increases, disposal of inorganic materials increases, while that of the organic fraction decreases [5]. However, lifestyle may overshadow income level in altering the proportion of waste constituents. For instance, based on the data released by the World Bank in 2012, Iran was categorized as a lower-middle-income country and the organic fraction of MSW was reportedly at 59%. In 2014, however, Iran was classified as an uppermiddle-income economy and it was expected that the organic fraction of MSW would decrease. On the contrary and based on the data presented in Table 2, an average organic fraction of 69% in the same year, i.e., 2014 was recorded. In general, as countries develop and become more urbanized, the waste composition changes in favors of less home-cooking, mainly relying on ready-made foodstuff leading to an increased consumption of packaging materials, i.e., paper packaging, plastics, multi material packing items. As a matter of fact, the traditional lifestyle and eating habits in Iran have been maintained to a large extent over the course of time, i.e., more home-cooking and less fast foods usage, which in turn resulted in an increase in organic fraction of MSW stream opposing the anticipations. Table 2 also compares the MSW composition in Iran with the other countries around the world. The MSW composition based on income level was also included in the table. Geographic location could also influence the proportion of waste constituents through changes in the pattern of building materials used (e.g., wood vs. steel), ash content (commonly from household heating), amount of street sweepings (e.g., can be as much as 10% of a city's waste stream in dry locations), and horticultural wastes. Moreover, factors related to the climate such as season change, precipitation, and humidity could influence the MSW composition. More specifically, in some parts of the world where heat generation is generally accomplished by using biomass or coal, the contribution of ash in the final waste stream in the winter is significantly higher than in summer. Precipitation and humidity could also change the moisture content of the waste especially where the collection systems use un-containerized vehicles [5]. The source of energy used in a country could also significantly influence the MSW composition especially in low-income countries or regions where energy for heating, cooking, and lighting might not come from district heating systems or the electricity grid [5]. For instance, the two different MSW compositions in China (Table 2) show how the type of energy source could influence the proportion of waste constituents. More specifically, when coal was used for home application purposes (heating-cooking), the contribution of the ‘other’ materials from total waste stream was significantly higher than when only natural gas was used (47% vs. 10%) due to the high ash content ending up in the final waste stream [5].

6. Electricity generation from MSW using different waste treatments: a literature review Among different MSW treatment options available, WTE technologies could offer both advantages of efficient managing of wastes as well as providing electricity in an environmentally-friendly and economically-viable manner [45]. Nevertheless, WTE technologies should be implemented as a part of an ISWM system in order to achieve a thorough reuse of the materials and energy contained in waste streams in a sustainable way. In such context, LFG recovery, AD, incineration, gasification, and pyrolysis have attracted a great deal of attention. 425

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sibility studies [70–74,76,89–91]. In a comprehensive study, Mao et al. [62] reviewed the recent achievements in biogas production using the AD process [62]. They concluded that since the biogas production technology is well-established, further studies should be more focused on optimization strategies such as the factors affecting the efficiency of the AD process and accelerants [62]. The potential of producing biogas and electricity from residual biomass (including MSW) in Jordan was reviewed and assessed by Al-Hamamre et al. [92]. Their outcomes revealed that the 387,000 t MSW year−1 produced annually in the country could offer the highest biogas production potential with a share of 35.18% compared with the other biomass feedstock studied i.e., agricultural residues and animal manure. Moreover, the share of MSW in electricity production (by direct combustion of the produced biogas) was estimated at about 40% [92]. However, they did not look into the environmental or economic benefits of using these feedstocks as a source of energy production which is an essential pre-requisite of establishing renewable energy scenarios, In a review article, Edwards et al. [78] comparatively discussed the effects of governmental policies in promoting AD use and development in five developed countries with the highest number of AD plants, i.e., Australia, Denmark, Germany, the United Kingdom (UK), and USA [78]. Their study identified climate change, energy security, regional development, waste management and recovery policies as the key drivers for AD use and development [78].

6.1. Electricity generation using LFG recovery Since electricity generation using LFG recovery is a well-established technology and is widely used in the world, recent studies are mostly focused on optimization of electricity generation, assessing potential of employing LFG recovery in current landfills as well as evaluating the economic and environmental aspects of this technique in different waste management systems [46–57]. In a very recent study conducted by Yechiel and Shevah [58], the economic benefits of converting LFG to electricity were demonstrated using a Linear Programming (LP) Model [58]. Their results indicated that the implementation of an intermittent power generation regime (in which LFG electricity was generated and supplied at peak load hours) could offer significantly higher economic returns compared with a continuous power generation. Moreover, they also argued that the net benefits of electricity generation using LFG recovery could be further improved through optimization approaches such as LP [58]. Their study would have been more conclusive if they had employed multi objective optimization models for WTE optimization in order to simultaneously consider both economic and environmental problems. Moreover, in-depth comparison of environmental impacts between electricity generation using LFG and methane recovery routes (for heating, hydrogen or methanol production purposes) could have also improved the reliability of the results presented by Yechiel and Shevah [58]. Fazeli et al. [59] reviewed the current status of waste management in Malaysia and analyzed the sustainability of promising WTE technologies [59]. They highlighted that although the Malaysian government has been attempting to upgrade the existing landfills, further attempts should be made in order to implement LFG recovery. This seems like an advisable strategy for the other developing countries whose governments are also striving to improve landfills standards. They also argued that electricity generation using LFG would be of great interest in Malaysia due to lower time and investment credits required while incineration, gasification, and pyrolysis technologies were also found as promising options for Malaysia from the sustainability point of view [59]. One major drawback of this review study was the lack of a sustainability assessment (environmental/economic/social assessment) and a thorough comparison among the proposed future technologies in Malaysia. Moreover, their conclusions would have been of more interest if they had elaborated on the electricity generation potentials using all the proposed technologies. Tozlu et al. [60] reviewed the recently-implemented WTE technologies in Gaziantep metropolitan city (Turkey) and presented some concluding remarks and recommendations for further development of the MSW management in the city. Among these guidelines retrofitting of the old facilities as well as constructing new plants for waste management using LFG recovery or new technologies (such as incineration) were highlighted [60]. However, the suggestions made were not built upon a sustainability basis, e.g., proposing incineration without any further clarification on the pre-combustion processes needed considering the regional situation and MSW composition seems impractical. Moreover, they failed to perform any environmental assessments in order to prove the privilege of the proposed scenarios.

6.3. Electricity generation using incineration As one of the most effective approaches for simultaneous reduction of the volume of waste (especially bulky ones) and energy recovery, waste incineration could also help with the reduction of GHG emissions [93]. These main advantages of waste incineration has led to widespread implementation of this technique around the world while its different aspects, e.g., technological developments [94–98], assessing the potential of electricity generation using incineration [45,47,99,100], economic and techno-economic analyses [49,53,101], and environmental impact assessment [49,102–105] have been extensively investigated. In a comprehensive study, Ouda et al. [100] reviewed the global status of WTE technologies with an emphasis on Saudi Arabia as a case study and examined the waste management opportunities in the country using two scenarios, i.e., 1) incineration and 2) refuse derived fuel (RDF) along with bio-methanation from 2012 to 2035 [100]. They claimed that incineration technology could offer more renewable electricity with a relatively higher efficiency and lower operational cost in Saudi Arabia. However, there are limitations on employing this technology in Saudi Arabia, e.g., the need for treatment of air-borne and water-borne pollutants as well as the necessity of ash treatment [100]. Their findings would have been more conclusive if they had employed more comprehensive analyses in order to select the best scenario, i.e., LCA, economic and techno economic investigations. In a very recent study, Tsai [93] investigated the efficiency of power generation in Taiwanese incineration power plants [93]. The results obtained highlighted that despite the revenue of USD 154 million brought by electricity generation in the incineration plants, the energy efficiency in the plants were relatively low due to heat discharge to the air (i.e., lack of efficient heat recovery). Accordingly, there is a necessity to exploit the heat energy produced from MSW in the incineration plants by means of improving the boilers’ heat exchange efficiency, adopting district heating and cooling systems, as well as competitive pricing for the steam/heat purchased from MSW incineration plants [93]. A much more systematic study would also consider the economic and techno-economic aspects of heating and cooling systems. Although the number of research studies on WTE incineration has increased steadily since 2009 [106], developing countries have less contribution to these studies due to the lack of/less availability of

6.2. Electricity generation using AD Organic fraction makes up a great portion of MSW and can be converted into value-added products (i.e., compost or biogas) through aerobic or anaerobic biodegradation processes. Biogas could offer more advantages as it contains 50–70% methane as a source of renewable energy especially for electricity generation [61]. Numerous research studies have been conducted on different aspects of electricity generation through AD, e.g., process efficiency and optimization [62–69], assessing the potential of electricity generation using AD [70–75], policy assessments [76–81], economic and techno-economic analyses [61,76,82,83], environmental impact assessment [2,84–88], and fea426

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to the inconstancy of MSW's composition as well as their variations in size and moisture content which could adversely affect these processes since pyrolysis and gasification require very careful feedstock preparation [109]. Moreover, the efficiency of the current gasifiers as well as gas cleaning systems (tar separation) needs to be improved for commercial purposes [113].

incineration establishments in these countries. In fact, the application of WTE incineration technologies in these countries is generally faced with many challenges, e.g., technological and economical limitations, the necessity of further emission treatments (e.g., air emissions, ash, etc.), existing low-cost waste treatment options, lack of long-term policies and real futuristic visions. Therefore, much effort is still required in order to boost international collaborations in WTE incineration, e.g., technology transfer while it is also essential to deviate policy making process in these countries from short-term to long-term orientation.

7. Electricity generation and GHG emission reduction potentials from MSW in Iran 7.1. Efficient waste management systems

6.4. Electricity generation using pyrolysis and gasification There are two fundamental criteria for any efficient waste management system, i.e., the capability to reduce the amount of waste produced, and to effectively manage the waste generated [9]. Reducing the amount of produced waste or so-called ‘less waste’ includes a variety of social and industrial attempts in order to prevent waste generation. This is in fact implemented by seeking the best ways to produce more goods and services using less resources (including energy) while also releasing less pollutions and wastes. In the view of the first criterion, there are two major deficiencies in the existing regulations and implementation procedures concerning wastes in Iran. The first is attributed to the industrial sector which is not generally operated in compliance with Iran's 2004 Waste Management Act. It should be highlighted that the recent increases in the cost of primary energy carriers has to some extent forced the industry towards more careful utilization of materials and energy resources to produce goods more efficiently; i.e., less waste generation [126]. Nevertheless, there is still a long ways to go before ‘waste prevention’ in this section could be achieved. The second deficiency is attributed to the society, an important factor in materializing an efficient waste management system. In most courtiers around the world, residents are charged a flat rate (constant based) for household waste collection, however in some countries, e.g., USA and Germany, waste collection charges are dependent on the volume or in some cases the mass of waste generated (scale based). Iran follows the first scheme but the rate imposed is considerably low at around USD 1 per month for all municipal services including waste collection. This is a major barrier for improving the efficiency of municipal solid waste management systems in Iran. This is ascribed to the fact that scale-based taxation on waste generation could lead to the generation of less household wastes, and also prevention of unauthorized dumping or other illegal alternative disposal routes [9]. As mentioned earlier, the second fundamental criterion concerns the implementation of an effective system for waste management. As discussed already, established waste management options in Iran include:1) landfilling without leachate treatment and LFG recovery (being conducted in most provinces, 2) landfilling with LFG recovery but without leachate treatment (in Shiraz and Mashhad cities), 3) composting the organic fraction of MSW (in 15 out of the 31 provinces), and 4) energy recovery through AD and incineration (only in Tehran province). It should be noted that currently many of the existing landfills in the country are approaching their maximum capacity. On the other hand, the growing urbanization and the consequent environmental challenges originated from the huge amounts of waste generated have made the current situation more severe. These have caused the Iranian government to further target ISWM systems such as combinations of AD, incineration, and pyrolysis–gasification techniques. In line with these developments, this section of the present study is aimed at reviewing and assessing electricity generation potential from MSW using ISWM systems including three different technologies (i.e., AD, incineration, and, pyrolysis–gasification) as well as the consequent GHG emission reductions which could be achieved through the implementation of these treatment options in Iran. For this purpose, the theoretical and technical potentials of electricity generation were

In addition to the incineration technology, pyrolysis and gasification are also the other main available thermochemical conversion processes which could be combined with the other treatments, e.g., melting, plasma, distillation, etc. [107–109]. Although these technologies are well established in the petrochemical and power industries as well as for fuel production such as coke and town gas for many years, the number of large scale MSW gasification or pyrolysis plants is very limited. Therefore, research efforts are still on-going to further adopt these technologies with MSW at commercial scale. These studies are focused on the main aspects of pyrolysis and gasification, e.g., technological developments [110–116], assessing the potential of electricity generation using these processes [48,117,118], economic and techno-economic assessments [108,119], and LCA [120–125]. In a review study, Asadullah [113] comprehensively discussed the logistics and technological challenges faced by commercial gasification power plants from feedstock collection to electricity generation [113]. The conclusions drawn marked the gasification of feedstocks and gas cleaning stages as the most challenging parts in typical commercial gasification processes. In line with that, the author concluded that further development of updraft or downdraft gasifiers as well as physical and catalytic tar separation methods for commercial purposes are the key factors in order to improve the efficiency of using feedstocks [113]. In an innovative and practical study, Zhou et al. [116] investigated the polycyclic aromatic hydrocarbons (PAHs) formation though the pyrolysis of nine different MSW fractions, i.e., xylan, cellulose, lignin, pectin, starch, polyethylene (PE), polystyrene (PS), polyvinyl chloride (PVC), and polyethylene terephthalate (PET) [116]. The findings of the study showed that among the investigated fractions, pyrolysis of PS led to the highest level of PAHs, followed by PVC, PET and lignin [116]. Also, the amount of PAHs released by plastic wastes stood higher than that of waste biomass [116]. The amount and mechanism of PAH release through the pyrolysis of different fractions of MSW as well as the amount of the produced gas and solid resides could be instrumental in selecting suitable feedstock for the pyrolysis processes. Evangelisti et al. [122] compared the environmental impacts of three dual-stage advanced WTE technologies with those of conventional MSW treatments, i.e. 1) landfilling with LFG recovery and 2) incineration, both with electricity generation. The three advanced MSW treatments were 1) gasification with plasma gas cleaning (G-Pl), 2) fast pyrolysis and combustion (FP-C), and 3) gasification with syngas combustion (G-SC) [122]. They concluded that in addition to the electrical efficiency of a power plant, the differences in the nature of the treatment involved (i.e., thermochemical vs. biological) as well as the more waste processing performed in the dual-stage technologies (metal recovery in G-Pl vs. incineration) affected the environmental burdens of the compared scenarios. Overall, G-Pl was selected as the best scenario and was proposed to be used as a benchmark for developing high efficiency WTE technologies in the future [122]. Although pyrolysis and gasification seems appealing in the view of efficiency and environmental emissions, large scale MSW plants characterized by high gasification efficiency and high energy recovery are yet to be established around the world [108,110]. This is in fact due 427

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where Pdegradable is the potential of degradable fraction of MSW (MW), Rbio represents degradable waste production rate (ton/d), 150 is the constant rate of biogas production (m3/ton), 0.6 (or 60%) is the average concentration of methane in produced biogas, 38,000 is the high heating value (HHV) of methane (kJ/m3) and 1.157×10−8 is the constant factor of the equation. The potential of the fraction with high heating value for incineration was calculated using the following equation:

calculated and the consequent GHG emission reductions were estimated using a life cycle assessment approach. Finally, theoretical and technical potential for each province (in MW h/day) were collected using a spatial approach at national scale to provide an overview of the provinces with considerable electricity generation/GHG emission reduction potentials from their MSW. The spatial approach was implemented based on a geographic information system (GIS) using national level maps and were presented at province level.

Pdry−inc (MW) = RHHV × CV × 1.157 × 10−5 7.2. Theoretical potential (Ptheoritical) of electricity generation from MSW in Iran

where Pdry-inc is the potential of the dry fraction with high heating value for incineration (MW), RHHV stands for waste production rate of the fraction with high heating value (ton/d), CV is the calorific value of MSW (kJ/kg), and 1.157×10−5 is the constant factor of the equation. The potential of the dry fraction with high heating value for pyrolysis–gasification was calculated using the following equation:

Theoretical potential is the maximum electricity generation capability of a dedicated waste treatment technology using various types of wastes. The method used herein for the calculation of Ptheoritical of electricity generation from MSW considered the obtainable energy from organic and combustible fractions of mixed MSW while excluded the non-combustible fraction (which is generally subjected to recycling or landfilling). Fig. 12 shows the process used for estimating the maximum potential energy generated in the form of Ptheoritical. Accordingly, the whole fraction of metal and glass are excluded from incineration or pyrolysis–gasification as they have negative effect on these processes. Afterwards, the recyclable part of metal and glass are separated at the recycling stage and the non-recyclable parts are subjected to landfill. Moreover, a recyclable part of plastic, PET, paper, and cardboard are separated at the recycling stage and the other (nonrecyclable) parts of these wastes are subjected to incineration or pyrolysis–gasification. It is also worth mentioning that since exploiting energy in the form of heat is highly dependent on the local and spatial characteristics, therefore, only electricity production potential was considered in the calculations [75,127]. The Ptheoritical of electricity production from MSW includes two main parts as showed in Eq. (1): 1) the potential of the degradable fraction (Pdegradable) and 2) the potential of the fraction with high heating value (Pdry) i.e., dry fraction excluding iron and glass. Accordingly, among the three introduced options (i.e., AD, incineration, and pyrolysis–gasification), either the combination of AD and incineration or the combination of AD and pyrolysis–gasification could be implemented.

Ptheoretical = Pdegradable + Pdry

Pdry−pg (MW) = RHHV × CV × 1.51 × 10−5

(4)

where Pdry-pg is the potential of the dry fraction with high heating value for pyrolysis–gasification (MW), RHHV denotes waste production rate of the dry fraction with high heating value (ton/d), CV is the calorific value of MSW (kJ/kg), and 1. 1.51×10−5 is the constant factor of the equation. The Ptheoritical indicates the amount of energy available when the best available technology is used. However, this potential does not represent the real amount of energy production from MSW since the efficiency of the energy production systems used are not considered in the calculations. 7.3. Technical potential (Pthechnical) Technical potential is the real capability of electricity production using a dedicated waste treatment technology while considering technical and structural constraints, i.e., substrate availability, production rate, and the efficiency of energy production systems used. Similar to Ptheoritical, the technical potential (Pthechnical) of electricity production from MSW includes two main parts: 1) the potential of the degradable fraction and 2) the potential of the dry fraction with high heating value (excluding iron and glass). The difference between Ptheoritical and Pthechnical is due to the fact that when calculating the Pthechnical, the energy efficiency of the production systems was also considered. Moreover, including a separation and recycling process for input materials (MSW) before they are subjected to a waste treatment approach could potentially make some other differences between these indices. The three mentioned treatment options and their respective

(1)

The potential of degradable fraction (or Ptheoritical of AD) was calculated in compliance with the following equation:

Pdegradable (MW) = Rbio × 150 × 0.6 × 38000 × 1.157 × 10−8

(3)

(2)

Fig. 12. The process used for estimating the maximum potential energy generated in the form of Ptheoritical.

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the incineration process can be used to generate electricity, provide district heating, or supply steam for industrial customers. Based on an intended application, the equipment used in an incineration plant may fall into four main categories, i.e., pretreatment facility, combustion system, energy recovery system, and flue gas cleaning system. The most important issues when using incineration technology are 1) using a material separation process to remove hazardous, bulky or recyclable materials before combustion, 2) using an efficient flue-gas cleaning system, 3) keeping the average annual lower calorific value to at least 7 MJ/kg (and this must never fall below 6 MJ/kg in any seasons), and 4) preparing a controlled landfill for residue disposal [137]. Waste incineration could offer strong benefits for the treatment of certain types of wastes, e.g., volume reduction, detoxification, environmental impact mitigation, regulatory compliance, energy recovery, stabilization in landfills, and sanitation (removal of pathogenic organisms) [138]. On the contrary, the high investment and operation costs, operating problems (variability in wastes composition), requirement for trained work force, potential secondary environmental impacts (due to using inefficient flue gas cleaning systems, inappropriate system designs, or inefficient combustion systems), and technical risks (associated with the risk that a new incinerator may not work as envisioned or in extreme cases may not function at all) are all the potential disadvantages of incineration. Nevertheless, incineration technology has persisted as an important concept in waste management and incineration systems are being developed widely to meet the needs and standards of municipalities, commercial and industrial firms, and institutions [138]. When assessing the electricity generation potential of incineration technology, only the fraction of MSW with a high heating value should be considered. The Ptheoritical of electricity generation using incineration technology was calculated based on Eq. (3). However, as mentioned earlier, Ptheoritical does not reflex the real amount of energy production from MSW. In this point of view, Ptechnical of incineration could be a true indicative of the electricity production potential and could be calculated using the following equation:

Table 3 Requirements to remove gaseous components for biogas utilization options [130]. Application

H 2S

CO2 removal

H2O removal

Gas heater (boiler) Kitchen stove Stationary engine (CHP) Vehicle fuel Natural gas grid

< 1000 ppm Yes < 500 ppm Yes Yes

no no no yes yes

no no moisture removal yes yes

methodological approach in calculating Pthechnical of electricity production are outlined below. 7.3.1. AD As a simple definition, anaerobic digestion (AD) is a process in which organic materials are subjected to a microbial decomposition in an oxygen-free environment. This process leads to two important products, i.e., biogas (principally comprising of CH4 and CO2) and semi-solid residues also known as digestate. The produced biogas could be combusted to generate energy in combined heat and power (CHP) engines, internal combustion engines, boilers, kitchen stoves, or could be introduced to the natural gas grid [128–130]. However, biogas needs to be purified before final consumption by means of removing CO2, as well as sulfane (H2S), water, and the other impurities. The removal of the impurities is performed based on an intended use, i.e., there is no need to remove all impurities for all applications (Table 3). Accordingly, biogas treatment may consists of dewatering, removal of H2S, removal of oxygen and nitrogen, removal of siloxanes, removal of ammonia, removal of particulates, and removal of CO2 (for upgrading to biomethane). Biogas upgrading technologies (also known as biomethane purification technologies) could be used to increase the CH4 concentration in the biogas and to meet specific natural gas standards [131]. There are several industrial methods used for upgrading biogas which are based on the following main unit operations: (1) absorption (physical – purisol, selexol, rectisol, water scrubbing; chemical – MEA, DEA, MDEA solvents), (2) adsorption (pressure swing adsorption, thermal swing adsorption), (3) permeation (high pressure and low pressure membranes), (4) and cryogenic approach [131–134]. The digestate exiting the AD process could be used as a fertilizer for agricultural/ horticultural purposes. However, it needs further treatment (normally through composting) in order to be prepared for such applications [135]. The Ptheoretical of electricity generation using AD technology was previously calculated based on Eq. (2). However, the Ptheoretical does not reflex the real amount of energy production from MSW since the efficiency of the energy production systems used are not considered in the calculations. Ptechnical capable of showing the real amount of electricity production through AD could be calculated using the following equation:

Ptechnical−AD (MW) = Rbio × 150 × 0.6 × 38000 × 1.157×10−8 × 0.35

Ptechnical−inc (MW) = RHHV × CV × 1.157 × 10−5 × 0.2

(6)

where Ptechnical-inc is the Ptechnical of incineration technology (using dry materials excluding iron and glass)(MW), RHHV represents waste production rate for the dry fraction with high heating value (ton/d), CV is the calorific value of MSW (kJ/kg), 1.157×10−5 is the constant factor of the equation and 0.2 shows the typical efficiency of incinerators. 7.3.3. Pyrolysis–gasification Pyrolysis is a thermochemical decomposition of organic materials into a medium calorific gas, liquid, and a char fraction in the absence of oxygen, through the combination of thermo cracking and condensation reactions [110,135]. In another word, pyrolysis is an irreversible reaction which involves indirect heating of carbon-rich materials at elevated temperatures in the absence of oxygen and under pressure. There is a wide range of feedstock which are suitable for a pyrolysis facility including mixed organic wastes, sewage sludge, agricultural wastes, paper, cloth, and plastics [110,139,140]. Pyrolysis leads to three major products, i.e., gas stream (uncondensed gases from pyrolysis) containing H2, CH4, CO, CO2, C2H6, and C2H4; tar/oil (condensed gases from pyrolysis) including methane, acetone, acetic acid; and char-pure carbon, with other inert materials and heavy metals [135]. Based on the type of pyrolysis employed and the reaction parameters, the relative proportions of these products could be changed. More specifically, there are three main types of pyrolysis treating feedstock in different ways leading to different portion of products, i.e., slow pyrolysis or carbonization, conventional pyrolysis, and fast/flash pyrolysis (further divided into vacuum and fluidized bed types) [135].

(5)

where Ptechnical-AD is the Ptechnical of AD technology (MW), Rbio represents degradable waste production rate (ton/d), 150 is the constant rate of biogas production (m3/ton), 0.6 (or 60%) is the average concentration of methane in the produced biogas, 38,000 is the high heating value (HHV) of methane (kJ/m3), 1.157×10−8 is the constant factor of the equation and 0.35 is the typical efficiency of CHP engines. 7.3.2. Incineration Waste incineration is the controlled process of burning combustible wastes to produce gases and residues containing little or no combustible materials [136]. This process converts the wastes into ash, flue gas, and heat or steam. In some cases, the heat or steam generated by 429

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7.4. Estimation of GHG emission reduction potentials by life cycle assessment (LCA) approach

On the other hand, gasification is the process of heating carbonaceous wastes in an atmosphere with slightly reduced oxygen concentration [107]. This process converts solid wastes into fuel or syngas through gas forming reactions and is widely used for energy conversion from coal, MSW, and biomass [135,141–143]. The first step of a gasification process involves heating and drying of the carbonaceous materials. Depending on the type of gasification process, pyrolysis also takes place (devolatilization step), converting the dried feedstock into gas vaporized liquids, and a solid char residue. The devolatilization step normally takes place in a controlled, low air environment in a primary chamber (at around 450 °C). The final step of gasification takes place in a secondary chamber at between 700 and 1000 °C (depending on gasification reactor type). The resulting products consist of a variety of gases, i.e., hydrogen, carbon monoxide, carbon dioxide, water, and methane (and much smaller concentrations of larger hydrocarbon molecules, such as ethene and ethane) [135]. The gasification technologies have been introduced as an attractive alternative to incineration for energy and resource recovery [110]. In a two-stage pyrolysis–gasification system, untreated raw MSW are subjected to a pyrolysis reaction at around 1200 °C. In At this stage, an exothermic reaction takes place and the product gas is generated during the gasification stage. During the process, heavy metals such as mercury and zinc are volatized at 800 °C. Fine dust removal is the last stage which happens is accomplished by passing the product gas through a series of scrubbers. It should be noted that any remaining waste materials are turned into inert residues. There are commercial plants using a two-stage pyrolysis–gasification system across Europe and Japan [144]. In order to calculate the Ptechnical of pyrolysis–gasification, only the fraction of MSW with a high heating value should be considered. The Ptheoritical of electricity generation using pyrolysis–gasification technology was calculated based on Eq. (4). However, based on the previous justification, the Ptheoritical does not show the real amount of energy production from MSW. Therefore, the Ptechnical of pyrolysis–gasification was used for estimating the true electricity generation potential:

Ptechnical−pg (MW) = RHHV × CV × 1.51 × 10−5 × 0.2

In order to evaluate the GHG emission reductions by using MSW as a source of electricity production (instead of fossil fuels), a life cycle assessment (LCA) was carried out. By definition, LCA is ‘the compilation and evaluation of the inputs, outputs, and potential environmental impacts of a product system throughout its life cycle’ [145,146]. LCA could provide a holistic environmental assessment that can help decision makers evaluate the environmental impacts of different scenarios pertaining the production of a specific product, delivering a specific service, and/or a management system [145,147,148]. LCA has been frequently used to evaluate and compare the environmental aspects of MSW management scenarios as well [2,86,149–152]. Based on ISO14040 series, every LCA study should consist of the following steps: 1) goal and scope definition; 2) inventory analysis; 3) impact assessment and 4) interpretation (of the results) [146]. 7.4.1. Goal and scope definition, life cycle inventory and life cycle impact assessment The goal of the present LCA study was evaluating the GHG emission reduction potentials by using MSW as a source of electricity production through the application of three different technologies, i.e., AD, incineration, and, pyrolysis–gasification. Moreover, the amount of the electricity generated through these waste treatments were assumed to avoid fossil-oriented electricity considering the local electricity grid mix of each province. Fig. 13 presents the scope and system boundaries of the present study. Accordingly, two different scenarios were investigated and compared in this study, i.e., scenario 1 (Sc–1): electricity production from the combination of AD and incineration technologies, and scenario 2 (Sc–2): electricity production from the combination of AD and pyrolysis–gasification technologies. It is also worth quoting that waste recycling and the consequent avoided products were included in the scenarios (Fig. 13). Moreover, the capital goods (buildings and machineries) used in MSW treatment facilities, electric power plants, as well as the transportation of fossil fuels to these plants were excluded from the scope of the study. In addition, collection and transportation of MSW were not included either. As a calculation tool, SimaPro software version 8.1 was used to perform the LCA study along with its associated database (professional). In order to find the environmental burden associated with the transport, materials and energy employed in the study, the Ecoinvent database v3.0 (2014) was used. Functional unit (FU) is an important aspect of the scope definition. More specifically, FU expresses the function of the products offering a way to equalize differences in performance [153]. Based on the

(7)

where Ptechnical-pg is the Ptechnical of pyrolysis–gasification technology (using dry materials excluding iron and glass)(MW), RHHV denotes waste production rate for the fraction with high heating value (ton/d), CV is the calorific value of MSW (kJ/kg), 1.157×10−5 is the constant factor of the equation, and 0.2 shows the typical efficiency of pyrolysis– gasification plants.

Fig. 13. Scope and system boundaries of the present LCA study.

430

431

Including technical consumptions at the plants.

0.0 5.15E+08 0.0 0.0 5.30E+08 4.30E+09 0.0 0.0 3.98E+08 1.28E+08 6.23E+08 0.0 0.0 0.0 1.30E+08 2.38E+09 0.0 0.0 1.84E+09 6.13E+08 0.0 3.74E+08 0.0 5.75E+08 0.0 0.0 0.0 5.12E+08 0.0 0.0 0.0

Ardabil Alborz Bushehr Chaharmahal and bakhtiari East Azerbaijan Esfahan Fars Golestan Guilan Hamadan Hormozgan Ilam Kohgiluyeh and Boyer-Ahmad Kerman Kermanshah Khuzestan Kurdistan Lorestan Markazi Mazandaran North Khorasan Qazvin Qom Razavi Khorasan Semnan Sistan and Baluchestan South Khorasan Tehran West Azerbaijan Yazd Zanjan

a

Natural gas (m )

3

Province

Steam turbine

0.0 6.21E+06 0.0 0.0 7.63E+05 1.88E+07 0.0 0.0 7.51E+07 0.0 1.00E+06 0.0 0.0 0.0 0.0 4.75E+05 0.0 0.0 8.15E+05 0.0 0.0 8.10E+05 0.0 1.34E+06 0.0 1.40E+05 0.0 5.92E+05 0.0 0.0 0.0

Diesel (l) 0.0 4.86E+08 0.0 0.0 1.69E+09 1.76E+07 0.0 0.0 0.0 5.07E+08 1.28E+09 0.0 0.0 1.07E+08 7.80E+08 1.07E+09 0.0 0.0 5.84E+07 1.81E+09 0.0 1.26E+09 0.0 8.13E+08 0.0 3.96E+08 0.0 0.0 0.0 0.0 0.0

Fuel oil (l) 6.09E+08 9.37E+08 2.53E+09 8.52E+05 8.42E+07 1.80E+09 4.45E+09 7.80E+08 2.28E+09 4.58E+06 1.95E+09 3.53E+06 0.0 2.00E+09 6.85E+08 1.84E+09 1.01E+09 6.13E+07 0.0 6.63E+08 9.41E+08 8.71E+08 9.74E+08 2.79E+09 7.77E+08 6.55E+07 7.38E+08 4.84E+09 1.28E+09 1.68E+09 6.14E+08

Natural gas (m )

3

2.15E+08 2.27E+08 3.92E+08 0.0 1.50E+06 5.04E+08 8.30E+08 1.37E+08 4.58E+08 0.0 1.39E+08 0.0 0.0 4.98E+08 1.70E+08 4.80E+08 1.73E+08 7.06E+05 0.0 4.06E+06 1.01E+08 3.67E+08 1.34E+08 3.65E+08 8.51E+07 1.21E+09 1.01E+08 1.18E+09 3.92E+08 4.58E+08 1.11E+08

Diesel (l)

Gas turbine or combined cycle

4.31E+05 0.0 6.03E+06 0.0 0.0 0.0 2.14E+06 0.0 0.0 0.0 1.59E+06 0.0 0.0 8.70E+04 0.0 0.0 1.70E+06 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 1.18E+07 5.20E+05 0.0 0.0 0.0 0.0

Diesel (l)

Diesel Generator

Table 4 Electricity generation and GHG emissions per MW h in Iranian power plants for each province and for different types of power plants.

2.45E+06 8.66E+06 8.85E+06 3.41E+03 8.73E+06 2.32E+07 2.01E+07 2.72E+06 1.30E+07 2.52E+06 1.35E+07 1.24E+04 0.0 1.10E+07 6.38E+06 2.09E+07 5.46E+06 1.32E+05 7.25E+06 1.24E+07 3.24E+06 1.20E+07 4.78E+06 1.68E+07 2.77E+06 4.78E+06 2.60E+06 2.45E+07 5.75E+06 8.88E+06 2.28E+06

MW h

Total gross productiona

662.7 533.9 615.1 435.3 698.1 540.4 492.4 630.1 469.4 685.8 640.3 497.1 0.0 463.6 652.1 575.5 403.7 823.8 496.5 615.0 587.8 568.8 428.2 549.7 568.3 934.5 596.8 509.3 566.5 464.7 594.9

CO2 (kg)

5.2 3.1 5.0 3.7 3.8 1.6 4.0 5.1 3.3 3.8 4.1 4.3 0.0 3.7 4.3 2.7 3.3 7.0 0.2 3.6 4.9 3.6 3.5 3.7 4.7 6.0 4.9 3.8 4.5 3.7 4.8

SO2 (kg)

Emissions Per MW h

2.6 1.5 2.2 1.3 1.4 1.5 1.7 2.2 1.6 1.4 1.6 1.5 0.0 1.6 1.7 1.6 1.4 2.4 1.2 1.3 1.9 1.5 1.4 1.6 1.9 4.4 2.0 1.8 2.1 1.7 2.1

NOx (kg)

0.3 0.3 0.4 0.3 0.2 0.4 0.3 0.4 0.3 0.2 0.3 0.4 0.0 0.3 0.2 0.3 0.3 0.6 0.3 0.2 0.4 0.2 0.3 0.3 0.4 0.1 0.4 0.3 0.3 0.3 0.4

CO (kg)

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the production of avoided products through recycling were adopted from the Ecoinvent v3.0 database. Moreover, the background data sets for the electricity generation in power plants for each province in Iran were adopted from the detailed statistics of electricity generation provided by the Iran Ministry of Energy on 2014 [155] (see Section 8 for detailed data, Table 4). The foreground data set for this assessment including the waste generation rate, waste composition, and consequent electricity generation due to different waste management technologies were gathered and calculated through the course of the present study (Tables 1, 2 and 5). More specifically, the foreground data were collected within a oneyear period (2014) for each province in order to validate the data quality and reducing the uncertainty of the data. The emission factors for calculating GHG emissions from electricity generation in Iranian power plants were adopted from Mazandarani et al. [156]. Moreover, the emission factors used for the calculation of GHG emissions released by the different MSW management technologies were adopted from the literature, i.e., AD process from Rajaeifar et al. [2], incineration from EPA [3], and pyrolysis–gasification from [157–160]. It should be mentioned that net emissions of each waste management scenario were calculated by subtracting the (1) emissions of non-biogenic CO2 and the other GHGs arising from the process itself (i.e., AD, incineration or pyrolysis–gasification) and (2) GHG emissions due to material consumptions at a facility from (3) the avoided GHG emissions from the electric utility sector and (4) the avoided GHG emissions due to the recovery and recycling of materials (i.e., plastic, PET, glass, ferrous metals, non-Ferrous metals, paper, and cardboard). In the view of life cycle impact assessment (LCIA), many comprehensive and frequently used models are available. However, as the present study was only focused on a single issue, i.e., global warming potential (GWP), therefore, IPCC 2007 GWP 100a (a time horizon of 100 years) was chosen as the LCIA method [161].

literature, there are four major classes of FU used in waste management studies, i.e., 1) unitary FU (e.g., management of 1 ton of waste), 2) generation-based FU (i.e., based on waste generation in a delimited region for a specified period of time), 3) input-based FU (i.e., based on the amount of wastes entering a given facility) and 4) output-based FU (i.e., based on the waste by-products) [154]. Laurent et al. [154] reported that most of the LCA studies employed a unitary FU based on the management of 1 ton of waste. However, when selecting this type of FU, the waste composition needs to be clarified so that the results could be compared. This study employed two different FUs for comparing the scenarios, one based on waste management outlook and the other FU was based on energy recovery. More specifically, in the view of managing the municipal wastes, ‘1 ton of waste managed’ was selected as the FU and the waste composition were specified for each province. This approach could help find the amount of GHG emissions/reductions through the treatment of each ton of waste in each province. While energy recovery was employed as the baseline for FU in order to compare the GHG emissions results. In fact, the second functional unit was chosen as ‘1 MW h of electricity produced’ for all the different scenarios studied. Therefore, the scenarios 1 and 2 were compared based on the treatment of 1 ton of waste managed and subsequently they were compared with each other again based on 1 MWh of electricity generation. Electricity generation in both scenarios were assumed to avoid fossil-oriented electricity generation, considering the local electricity grid mix of each province. As the second phase in an LCA study, life cycle inventory (LCI) analysis includes all recognized inputs/outputs to or from the system boundary [145]. In fact, this phase of LCA studies involves collection of the data which are necessary to reach the goals of the intended LCA study [146]. The background data sets for crude oil extraction, natural gas extraction, production of diesel, natural gas, and fuel oil as well as

Table 5 Ptheoritical and Ptechnical of electricity generation from MSW (based on the total MSW generated each day). Pthechnical

Ptheoritical Province

Pdegradable (MW)

Pdry-inc (MW)

Pdry-pg (MW)

AD (MW)

Incineration (MW)

pyrolysis–gasification (MW)

Ardabil Alborz Bushehr Chaharmahal and bakhtiari East Azerbaijan Esfahan Fars Golestan Guilan Hamadan Hormozgan Ilam Kohgiluyeh and Boyer-Ahmad Kerman Kermanshah Khuzestan Kurdistan Lorestan Markazi Mazandaran North Khorasan Qazvin Qom Razavi Khorasan Semnan Sistan and Baluchestan South Khorasan Tehran West Azerbaijan Yazd Zanjan

15.8 48.9 20.0 11.2 57.5 98.7 56.5 15.7 30.1 29.7 18.8 7.3 5.1 36.0 28.7 59.5 20.7 20.4 23.8 43.7 9.4 18.2 15.7 92.8 10.5 14.4 7.5 267.6 46.2 12.4 12.8

44.9 70.5 20.8 14.1 94.9 191.9 151.9 39.7 90.6 32.5 25.0 13.7 7.3 46.5 39.7 103.8 40.2 26.2 29.0 52.7 14.1 32.4 46.8 134.3 16.0 47.6 11.7 435.8 62.8 18.4 21.4

58.6 92.1 27.2 18.4 123.8 250.4 198.2 51.8 118.2 42.5 32.6 17.9 9.5 60.7 51.9 135.5 52.4 34.2 37.8 68.8 18.4 42.3 61.1 175.3 20.9 62.2 15.2 568.7 82.0 24.0 27.9

5.5 17.1 7.0 3.9 20.1 34.5 19.8 5.5 10.5 10.4 6.6 2.6 1.8 12.6 10.0 20.8 7.3 7.2 8.3 15.3 3.3 6.4 5.5 32.5 3.7 5.1 2.6 93.7 16.2 4.4 4.5

4.9 8.9 2.5 1.5 12.4 20.0 15.5 4.4 8.1 3.7 2.8 1.5 0.9 5.4 5.0 12.5 4.7 2.5 3.1 5.6 1.7 3.6 4.7 16.3 1.9 6.3 1.3 47.9 7.3 2.0 2.5

6.4 11.6 3.2 2.0 16.2 26.1 20.2 5.8 10.6 4.8 3.6 2.0 1.1 7.1 6.5 16.3 6.1 3.3 4.1 7.3 2.2 4.8 6.1 21.2 2.5 8.2 1.7 62.5 9.5 2.7 3.3

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in the calculation of Pthechnical. While an efficient recycling system could reduce the Ptechnical to a certain extent, its higher efficiency would ultimately lead to lower environmental burdens especially GHG emissions associated with the re-fabrication of raw materials for industry. Therefore, an efficient recycling system is an inseparable part of a successful ISWM. Based on the results obtained herein (Table 5), Tehran province had the highest Ptheoritical (i.e., the sum of Pdegradable and Pdry) of electricity generation with values of 703.3 MW and 836.3 MW, for the scenario 1 (AD and incineration) and 2 (AD and pyrolysis–gasification), respectively. Following Tehran province, five provinces, i.e., Esfahan, Razavi Khorasan, Fars, Khuzestan, and East Azerbaijan possessed the highest Ptheoritical, respectively. It is also worth highlighting that these provinces including Tehran province are the most populated cities in Iran facing many environmental challenges today especially managing a huge amount of wastes generated on a daily basis as well as the huge amount of GHG emissions released. As mentioned earlier, the Ptheoritical indicates the amount of energy available when the best available technology is used. However, this potential does not reflex the real amount of energy production from MSW. The results of the present survey on Ptechnical demonstrated that Tehran province also had the highest Ptechnical of electricity generation form MSW with values of 141.6 MW and 156.2 MW for the scenario 1 and 2, respectively. Exactly similar to Ptheoritical, five provinces of Esfahan, Razavi Khorasan, Fars, Khuzestan, and East Azerbaijan had the highest Ptheoritical, respectively. This potential could be very promising for the six mentioned metropolitan areas of Iran especially in addressing the growing environmental crises faced such as their huge amount of GHG emissions. Therefore, establishing an ISWM system encompassing either of the examined scenarios is highly recommended for these provinces. In order to establish such systems, three prerequisites are needed, i.e., encouraging the private sector to invest in the waste industry, finding best locations to establish waste management sites, and increasing the efficiency of the existing recycling systems or establishing new sites. Figs. 14 and 15 illustrate the Ptheoritical and Ptechnical (in MWh/day) for the scenarios 1 and 2. As the spatial disaggregation maps show, Tehran province had the highest Ptheoritical with electricity generation values of 15417.2 and 18331.7 MW h day−1 for scenarios 1 and 2, respectively. Likewise, this province had the highest Ptechnical with electricity generation values of 3103 and 3423.4 MW h day−1 for scenarios 1 and 2, respectively. In fact, the huge amount of daily waste generation in this province (i.e., 9713 ton day−1) could potentially lead to a promising opportunity for electricity production and reducing the environmental pollutions

8. Electricity production from fossil resources in Iran: current status Electricity generation in Iran is mainly dominated by fossil fuel resources in power plants. Based on the 2014 Iran Ministry of Energy report, at least 93.2% of the electricity production in Iran is fossil-fuel oriented with natural gas contributing 71.8% of this figure followed by fuel oil (15.6%), and diesel (12.6%) [155]. Table 4 tabulates electricity generation in Iranian power plants for each province and for different types of power plants. Moreover, GHG emissions per MWh of electricity generation were calculated and included in the table. Based on the data presented in Table 4, Tehran (the capital of Iran and the most populous province) had the highest electricity generation with more than 24 million MW h per year. However, Sistan and Balochestan province, with a lower annual electricity generation rate, had the highest GHG emissions per MW h of electricity generation. This could be ascribed to the differences in the types of power plants and different types of fuel used in the power plants located in these provinces. More specifically, the combustion of a certain amount of a given fuel in a steam turbine power plant does not necessarily emit the same amount of GHG emissions compared with when it is combusted in a combined cycle or diesel generator power plant. It is also worth mentioning that among the 31 provinces, Kohgiluyeh and BoyerAhmad province supplies all its electricity from the hydropower resources which are considered renewable and hence, the GHG emissions of electricity generation per MWh for this province were calculated as zero. 9. Electricity generation potential from MSW in Iran 9.1. Results and future prospects The calculation methods for the Ptheoritical and Ptechnical of electricity generation from MSW were introduced earlier in the Sections 7.2 and 7.3 and the results are tabulated in Table 5. As could be clearly comprehended from the data presented in Table 5, Ptechnical is much lower than the Ptheoritical due to the facts that when calculating the Ptechnical, the energy efficiency of the production systems was also considered. Moreover, in reality, the input materials are generally subjected to a separation and recycling process and then the rest is subjected to different treatments leading to a lower electricity generation potential. In better words, only the input materials which are not separated and/or recycled (and are going to be subjected to the incineration or pyrolysis–gasification processes) would be considered

Fig. 14. Spatial disaggregation maps of the Ptheoritical (in MW h/day) for the scenarios 1 and 2.

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Fig. 15. Spatial disaggregation maps of the Ptechnical (in MW h/day) for the scenarios 1 and 2.

to the results obtained, the GHG emission reduction potentials through implementation of the Sc–2 was found much higher than that of the Sc–1. This is mainly ascribed to the existing differences in treatment principles of the two technologies. More specifically, incineration process is done under an uncontrolled airflow resulting in a higher CO2, NOx and SOx emission to the atmosphere, whereas pyrolysis–

associated with fossil-based electricity generation and current conventional waste management treatments. More specifically, by the implementation of the proposed scenarios in form of an ISWM system, Tehran could get rid of this huge amount of wastes which has already caused lots of environmental and spatial problems for this province. The situation is the same for the above-mentioned five provinces (Esfahan, Razavi Khorasan, Fars, Khuzestan and, East Azerbaijan) as well. Based on the generated maps, these provinces also had considerably high Ptheoritical and Ptechnical (in MW h/day) which could be also promising. It is worth highlighting that according to the Ptechnical (in MW h/ day) results obtained herein, the electricity generation from MSW could substitute 4.6–5.1% of fossil electricity generation in Tehran, around 2% in Esfahan, around 2.5% in Razavi Khorasan, around 1.5% Fars, around 1.4% in Khuzestan, and around 3.3% in East Azerbaijan provinces. The most promising substitution rate among the studied provinces belonged to Lorestan province in which 58–63% of the fossiloriented electricity could be avoided by waste-to-electricity scenarios. More interestingly, some provinces including Kohgiluyeh and BoyerAhmad, Chaharmahal and bakhtiari, and Ilam which could export their MSW-oriented electricity since the Ptechnical in these provinces exceeds the total gross electricity generation from fossil resources. For the whole country, MSW-oriented electricity could supply 5005.4– 5545.8 GW h per year (Ptechnical of Sc-1 and Sc-2, respectively) which could substitute approximately 2–2.2% of fossil-oriented electricity in Iran. Although numerically low but at national scale any rates of fossil fuel substitution with renewable energy carriers would lead to huge impacts over the course of time. Moreover, managing wastes by employing the mentioned scenarios could bring about other important environmental and social benefits as well, i.e., avoiding emissions due to uncontrolled landfilling, avoiding emissions originated from raw material production, creating job opportunities, and solving the problems associated with land scarcity for wastes disposal.

Table 6 GHG emission reduction potentials (kg CO2eq) of different scenarios based on 1 ton of waste managed as FU.

9.2. GHG emission reduction potentials (LCA results and interpretation) In line with the goal of the present LCA study, Table 6 shows the results of GHG emissions reduction potential of different scenarios based on 1 ton of waste managed. Considering this FU (i.e., 1 ton of waste managed) two scenarios, i.e., Sc–1 (AD and incineration) and Sc–2 (AD and pyrolysis–gasification) were compared herein. According 434

Province

AD and incineration (Sc–1)

AD and pyrolysis– gasification (Sc–2)

Ardabil Alborz Bushehr Chaharmahal and bakhtiari East Azerbaijan Esfahan Fars Golestan Guilan Hamadan Hormozgan Ilam Kohgiluyeh and BoyerAhmad Kerman Kermanshah Khuzestan Kurdistan Lorestan Markazi Mazandaran North Khorasan Qazvin Qom Razavi Khorasan Semnan Sistan and Baluchestan South Khorasan Tehran West Azerbaijan Yazd Zanjan

−290.6 −206.6 −256.6 −217.7

−414.7 −288.9 −295.0 −251.9

−236.6 −205.3 −344.1 −288.7 −309.8 −250.3 −273.5 −212.7 −84.1

−330.5 −331.7 −427.2 −395.3 −416.7 −315.9 −325.9 −302.8 −122.6

−173.1 −240.6 −228.5 −175.8 −329.5 −209.9 −239.7 −176.6 −238.1 −249.3 −173.7 −180.5 −337.8 −184.4 −238.6 −221.0 −164.9 −236.5

−240.3 −299.6 −297.9 −250.6 −402.6 −266.8 −300.3 −279.7 −308.3 −373.0 −276.2 −285.4 −464.1 −307.8 −316.4 −287.9 −250.6 −299.4

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potentials (Fig. 16) show that by implementing the scenario 1 at least 17 provinces would be classified to have moderate to high potential for global warming reduction. The situation is far better when implementing the scenario 2 as 21 provinces were classified to have moderate to high potential for global warming reduction. Comparing the theoretical and technical potential maps with the maps presented for the GHG emission reduction potentials showed that the provinces with the highest theoretical or technical potential for electricity production from MSW did not necessarily have the highest GHG emission reduction potentials. The main reason behind this result is in fact the difference in the composition of waste collected and recycled in each province and the regime of fossil electricity generation in the power plants. The results of the overall assessment show that 5005.4– 5545.8 GW h of electricity per year could be generated from MSW in Iran. It is estimated that by implementing the studied scenarios, approximately 3561–4844 thousand tons of CO2eq could be avoided. These reductions could bring about 2–2.2% GHG reductions in the electricity generation sector which could be promising for the current Iranian situation. Based on the latest data available, Iran's GHG emissions stand at 698.38 Mton CO2eq [166] and according to the above-mentioned reduction potentials by exploiting energy from MSW, Iran could avoid approximately 0.5% of its GHG emissions. This would be considered a promising achievement given Iran's international GHGs reduction commitment, i.e., 4% reduction of anthropogenic GHGs emissions by 2030 below the business as usual scenario [167]. Such findings could also be modeled for other developing countries around the world where efficient MSW management is yet to be implemented. It should also be taken into account that the GHG emission reduction potentials (Fig. 16) could yield important economic benefits

gasification process is done under a controlled volume of air, and thus, the mentioned emissions are significantly lower. The results are also consistent with those of Zaman [162], Arafat and Jijakli [163], Arena [107], Chen and Yin [110], Zaman [164] and Khoshnevisan et al. [165]. The other factor making Sc-2 better than Sc-1 in terms of GHG emission reduction potentials is the higher electricity generation rate by Sc-2 (see Table 5). More specifically, the higher electricity generation could prevent a higher amount of fossil-oriented electricity and consequently avoid more GHG emissions to the atmosphere. The results also revealed that Fars province would have the highest GHG emissions reduction potential (344.1 kg CO2eq per ton of waste) if Sc-1 was implemented (Table 6). Following this province, Sistan and Baluchestan, Lorestan, and Guilan provinces had the highest GHG emission reduction potentials, respectively. When comparing the global warming contributions based on the Sc-2, Sistan and Baluchestan province had the highest GHG emission reduction potential (464.1 kg CO2eq per ton of waste). Following this province, Fars, Guilan, and Ardabil provinces had the highest GHG emission reduction potentials (based on this scenario), respectively. The existing differences in the composition of wastes collected and recycled in each province as well as different regime of electricity generation in the fossil power plants are the main reasons behind the differences in the GHG emission reduction potentials among provinces. Overall, 1 ton of waste managed in Iranian provinces could reduce the GHG emissions by (Min.) 84.1 to (Max.) 344.1 kg CO2eq ton−1 if the scenario 1 would be implemented and by (Min.) 122.6 to (Max.) 464.1 kg CO2eq ton−1 if the scenario 2 would be implemented. Table 7 illustrates the results concerning the GHG emission reduction potentials based on 1 MW h of electricity produced through the mentioned scenarios. As discussed earlier, it is obvious that Sc-2 could have a higher potential in reducing the global warming contribution. Based on the results obtained, among different provinces, Fars province had the highest potential in reducing the global warming effects by implementing the Sc-1, followed by Lorestan, Sistan and Balochestan, and Guilan provinces, respectively. If the Sc-2 were implemented, Lorestan province would have the highest potential in reducing the global warming effects followed by Fars, Sistan and Balochestan, and Guilan provinces, respectively. In both scenarios, the differences in GHG reduction potentials among the provinces were caused by the differences in the composition of wastes collected and recycled in each province as well as different regimes of electricity generation in the fossil power plants which could be avoided by the waste-oriented electricity generation. The overall assessment showed that 1 MW h electricity production from fossil power plants releases an average amount of 658.1 kg CO2eq to the environment. However, producing 1 MW h of electricity from MSW through the combination of AD and incineration technologies (Sc–1) or using the combination of AD and pyrolysis–gasification technologies (Sc–2) could reduce the average amount of GHG emissions to the environment by 700.4 and 854.7 kg CO2eq, respectively. Interpretation of the results revealed that when implementing both scenarios (Sc–1 and Sc–2), the avoided emissions due to recycling process had a significant impact on the final global warming contribution rather than avoided fossil-oriented electricity (i.e., electricity from MSW which avoids the production of fossil-oriented electricity). This fact simply shows the significant effect of an efficient recycling system on the overall net emissions and on reducing the overall global warming contribution. Nevertheless, without considering the avoided emissions of recycling, the avoided emissions of electricity generation were solely higher than all the emissions produced through both MSW management scenarios (Sc–1 and Sc–2). The situation was opposite for Kohgiluyeh and Boyer-Ahmad province in which all the electricity produced was originated from renewable resources. For this province, establishing an effective waste recycling system is a necessity in order to have an efficient waste management system. The spatial disaggregation maps of the GHG emission reduction

Table 7 GHG emission reduction potentials (kg CO2eq) based on 1 MW h of electricity produced (as FU) trough different scenarios.

435

Province

AD and incineration (Sc-1)

AD and pyrolysis– gasification (Sc-2)

Ardabil Alborz Bushehr Chaharmahal and bakhtiari East Azerbaijan Esfahan Fars Golestan Guilan Hamadan Hormozgan Ilam Kohgiluyeh and BoyerAhmad Kerman Kermanshah Khuzestan Kurdistan Lorestan Markazi Mazandaran North Khorasan Qazvin Qom Razavi Khorasan Semnan Sistan and Baluchestan South Khorasan Tehran West Azerbaijan Yazd Zanjan

−846.3 −610.5 −793.1 −743.8

−1056.3 −773.0 −844.8 −792.7

−669.6 −616.9 −1040.2 −836.6 −917.7 −775.7 −838.7 −632.4 −256.5

−837.8 −896.4 −1139.0 −1008.4 −1089.5 −906.7 −917.1 −807.4 −340.0

−528.8 −715.2 −725.6 −531.5 −1036.6 −640.2 −731.0 −534.0 −733.8 −744.8 −521.7 −533.8 −952.7 −568.7 −730.1 −651.8 −526.0 −727.2

−672.2 −808.7 −848.9 −676.4 −1174.3 −751.3 −846.7 −765.8 −855.4 −977.4 −752.9 −764.3 −1119.9 −861.8 −877.7 −775.7 −728.7 −829.3

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Fig. 16. Spatial disaggregation maps of the GHG emission reduction potentials for the scenarios 1 and 2.

other developing countries around the world where efficient MSW management is yet to be implemented.

as well since the damages avoided could also be rewarded economically. Such benefits are generally awarded in recognition of the reduced risk to human health and welfare achieved by lowering the GHG emissions as well as global warming and climate change risks [168,169].

Acknowledgments The authors would like to thank Biofuel Research Team (BRTeam), Agricultural Biotechnology Research Institute of Iran (ABRII), Iran Renewable Energy Organization (SUNA), University of Tehran, and Iranian Biofuel Society (IBS) for supporting this study.

10. Conclusions and future outlook The increasing trend in the consumption of various commodities, as well as various practices involved in the supply chain of these materials have resulted in a variety of environmental pollutions especially GHG emissions. This increasing trend in consumption of materials has also led to a huge increase in final waste streams especially in form of MSW which has made MSW management a significant environmental issue for governments and policy-makers. In this point of view, developed countries have implemented SMM strategies comprehensively reviewed herein. Moreover, waste generation statistics were reported for most of the lower-income, middle-income, and developing countries/regions and the existing gaps in MSW management level among these countries were fully discussed. The present paper was also aimed at comprehensively reviewing and assessing electricity generation potentials from MSW using an integrated solid waste management system (including three different technologies of AD, incineration and, pyrolysis-gasification) while the consequent GHG emission reduction potentials as a result of their implementation were also discussed. To facilitate the understanding of the potential impacts of these treatment strategies, Iran's data were used as a case study. More specifically, the theoretical and technical potentials of electricity generation were calculated and GHG emission reduction potentials were estimated using an LCA approach. Accordingly, it was revealed that due to the fact that at least 93.2% of the electricity production in Iran is fossil-fuel oriented, the electricity generation from MSW could be a promising approach especially in reducing the global warming contribution of fossil–oriented electricity generation. Overall, it was found that 5005.4–5545.8 GWh of electricity per year could be generated from MSW in Iran which could lead to approximately 3561–4844 thousand tons of avoided CO2eq. Such GHG reductions would be translated into approximately 0.5% of Iran's annual GHG emissions and would be considered a promising achievement given Iran's international GHGs reduction commitment, i.e., 4% reduction of anthropogenic GHGs emissions by 2030 below the business as usual scenario. Such findings could also be modeled for the

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