## 1 Introduction
### Waste to Energy in Asia  
Due to the potential depletion of fossil fuel and climate change, Southeast Asian countries have looked to renewable and alternative energies to reduce greenhouse gas emissions and other environmental impacts from the energy sector [9]. On the other hand, the growing urban population will accelerate the amount of annual waste generation (approximately 97 million tons per year in  
Figure 3: Actual and projected bioenergy demand in non-OECD Asia, 1990–2035 [11]. Figure 2: Access to electricity (2015 and 2020), electricity consumption per capita (2014), and CO\({}_{2}\) emission per capita (2014) in Southeast Asian countries [9]. 2015 to 165 million tons per year by 2025) in these countries [1; 12], requiring significant investment in waste management to cope with the increase in waste [5]. The rapid urban population growth that has boosted waste generation and electricity demand has led to a possible alternative solution in Southeast Asia. Waste-to-energy--a catch-all for different technologies that allows countries to get rid of waste and generate electricity at the same time--is one obvious and quick solution to these two needs [5]. Therefore, the technologies constitute a meeting point for the waste management and energy sectors to work together and benefit from each other in the most efficient manner [2]. Actually, waste-to-energy is also a kind of biomass energy, offering benefits not only to minimize the waste crisis but also to meet the actual fossil-free high demand [2] and to reduce the greenhouse gas emissions and climate change impacts [13]. Nowadays, it has become a type of renewable energy utilization that can provide environmental and economic benefits in the world [13]. Currently, there are more than 2200 thermal waste treatment plants all over the world with a total capacity of 300 million tons per year, and it has been estimated that more than 600 new waste-to-energy facilities will be built with a capacity of 170 million tons per year by 2025 [2; 14]. China had 7.3 gigawatts of energy production across 339 power plants in 2017, and they are expecting to grow to 10 gigawatts and 600 plants by 2020 [5]. The selection of the most suitable technology is based on social, economic, and technical factors, as well as environmental strategies to ensure the best outcomes [2]. In Europe, the most widespread options for upgrading waste treatment are the incineration of grey waste and anaerobic digestion (AD), often combined with the composting of the separated fraction of organic waste [3]. When it comes to waste-to-energy plants, there are regional preferences--gasification is in favor in South Asia, while grate incineration is generally used in Europe [3]. As described in Figure 4, the most common waste-to-energy technologies in the developing world include [2; 15; 16; 17];  
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2. Thermal conversion (incineration, pyrolysis, gasification, and plasma gasification). 3. Biochemical conversion (fermentation, anaerobic digestion, landfills with gas capture, and microbial fuel cell). 4. Chemical conversion (esterification). Figure 4: Most common waste-to-energy technologies [15; 16]. Note: CHP is Combined Heat and Power. The future trends in the area are in the direction of biological hydrogen production (photo-biological process and dark fermentation), bio-electrochemical processes (microbial fuel cells (MFCs), microbial electrolysis cells (MECs), and hydrothermal carbonization [2]. Technologies such as the incineration process have been advantageous, not only for reductions in the mass and volumes of initial waste but also for energy recovery and the reduction of land use for landfills [18]. When incinerated, waste can be reduced to 80-85% by weight and 95-96% by volume [19]. Additionally, incineration can be considered as a net greenhouse gas (GHG) reducer if GHG reductions, achieved by accounting for waste-to-energy, exceed GHG emissions [20]. Nowadays, waste-to-energy plants are most often tailor made, depending on very specific local requirements.