**2.1. Biomass and biodegradable waste**

Biomass is defined in twofold [12]. One is "*the total quantity or weight in a given area or volume*", which emphasizes its essential attribute as organic degradable substances. This definition is on a biological ecological basis. Another is "*organic matter used as a fuel, especially in a power station for the generation of electricity*", and this definition focuses the use of biomass for energy production. Similarly, Cambridge dictionary [13] defines biomass from both biological and engineering perspectives. From biological perspective, the biomass is defined as "*The total mass of living things in a particular area*". Herein, the inherent property of biomass as "living things" is focused. From engineering perspective, the biomass is defined as "*dead plant and animal materials suitable for using as a fuel*", and the property of biomass as a type of fuel is emphasized.

but also the ones obtained intentionally for bioenergy production is included (e.g. energy crops). However, those two terms can sometimes be interchangeable when the feedstock of bioenergy production mainly refers to the organic substances that have lost their usefulness value to the consumers, and this applies to the case study presented latter in this chapter.

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Based on processing technologies, the treatment of biomass and biodegradable waste can be categorized into four types: direct combustion, thermochemical conversion, biochemical conversion and non-value-added treatment. The first three types are waste-to-energy (WTE) processes aiming to exploit the remaining value of biomass and biodegradable waste, and the last one usually refers to landfill at which the remaining value is eventually lost. Landfill is usually the least expensive but a non-sustainable way for biodegradable waste treatment [17], and the portion of biodegradable waste landfilled has continuously decreasing in Europe due to the rigorous and comprehensive legislations. WTE is the transformation of biomass and biodegradable waste into energy, and it initially specifies the production of power and heat through the combustion of biomass and biodegradable waste [18]. Nevertheless, its meaning has broadened to include other means of bioenergy recovery with the rapid technological development. Bioenergy has been extensively used in different industries, i.e. transport sector, power generation, heating, agriculture and chemistry industry [19]. **Table 1** illustrates the alternative means for bioenergy production and non-value-added treatment of biomass and

Direct combustion has been widely used for over three decades in generating electricity and heat from biomass [20]. The principle is to utilize the heat generated by combustion of biomass for cooking, industrial process, direct home heating [21] or driving the steam power cycle for

Gasification WTE Syngas Chemistry,

Anaerobic digestion WTE Biogas, fertilizer Transport,

MBT WTE Biogas, fertilizer Transport,

transport

agriculture

agriculture

**Technology Method WTE/disposal Product Market** Thermochemical conversion Pyrolysis WTE Bio-oil Transport

Non-value-added treatment Landfill Disposal N/A N/A

Direct combustion Incineration WTE Electricity, heat Power, heating Biochemical conversion Composting WTE Fertilizer Agriculture

**Table 1.**Alternative technologies for bioenergy production and non-value-added treatment of biomass and biodegradable

**2.2. Treatment of biomass and biodegradable waste**

biodegradable waste.

*2.2.1. Direct combustion*

waste.

Biodegradable waste is another commonly used term to describe the feedstock of bioenergy production. Biodegradability is referred as the ability to decay naturally and non-harmfully [14]. According to Basel Convention [15], wastes are defined as "*substances or objects, which are disposed of or are intended to be disposed of or are required to be disposed of by provisions of national law*". Viewing from consumers' perspective, EU Directive 2008/98/EC [16] defines waste as "*an object the holder discards, intends to discard or is required to discard*". Based on the definition above, biodegradable waste is the portion of waste that can be decayed by nature.Biomass and biodegradable waste are the most important sources for bioenergy production, which mainly come from five sectors: forestry and timber, agriculture, fishery, waste management and wastewater treatment (**Figure 3**). It is noteworthy that the portion of biomass and biodegradable waste contributed by different sectors may vary dramatically from country to country, and the generation is significantly influenced by seasonality. Therefore, it is necessary to take into account of those variations and uncertainties in forecasting the amount of the feedstock for bioenergy production.

The difference between the two concepts is, compared with biodegradable waste, biomass that specifies a broader domain in which not only organic matters discarded by consumers

**Figure 3.** Sources of biomass and biodegradable waste.

but also the ones obtained intentionally for bioenergy production is included (e.g. energy crops). However, those two terms can sometimes be interchangeable when the feedstock of bioenergy production mainly refers to the organic substances that have lost their usefulness value to the consumers, and this applies to the case study presented latter in this chapter.

#### **2.2. Treatment of biomass and biodegradable waste**

Based on processing technologies, the treatment of biomass and biodegradable waste can be categorized into four types: direct combustion, thermochemical conversion, biochemical conversion and non-value-added treatment. The first three types are waste-to-energy (WTE) processes aiming to exploit the remaining value of biomass and biodegradable waste, and the last one usually refers to landfill at which the remaining value is eventually lost. Landfill is usually the least expensive but a non-sustainable way for biodegradable waste treatment [17], and the portion of biodegradable waste landfilled has continuously decreasing in Europe due to the rigorous and comprehensive legislations. WTE is the transformation of biomass and biodegradable waste into energy, and it initially specifies the production of power and heat through the combustion of biomass and biodegradable waste [18]. Nevertheless, its meaning has broadened to include other means of bioenergy recovery with the rapid technological development. Bioenergy has been extensively used in different industries, i.e. transport sector, power generation, heating, agriculture and chemistry industry [19]. **Table 1** illustrates the alternative means for bioenergy production and non-value-added treatment of biomass and biodegradable waste.

#### *2.2.1. Direct combustion*

**2. Bioenergy production from biomass and biodegradable waste**

Biomass is defined in twofold [12]. One is "*the total quantity or weight in a given area or volume*", which emphasizes its essential attribute as organic degradable substances. This definition is on a biological ecological basis. Another is "*organic matter used as a fuel, especially in a power station for the generation of electricity*", and this definition focuses the use of biomass for energy production. Similarly, Cambridge dictionary [13] defines biomass from both biological and engineering perspectives. From biological perspective, the biomass is defined as "*The total mass of living things in a particular area*". Herein, the inherent property of biomass as "living things" is focused. From engineering perspective, the biomass is defined as "*dead plant and animal materials suitable for using as a fuel*", and the property of biomass as a type of fuel is emphasized.

Biodegradable waste is another commonly used term to describe the feedstock of bioenergy production. Biodegradability is referred as the ability to decay naturally and non-harmfully [14]. According to Basel Convention [15], wastes are defined as "*substances or objects, which are disposed of or are intended to be disposed of or are required to be disposed of by provisions of national law*". Viewing from consumers' perspective, EU Directive 2008/98/EC [16] defines waste as "*an object the holder discards, intends to discard or is required to discard*". Based on the definition above, biodegradable waste is the portion of waste that can be decayed by nature.Biomass and biodegradable waste are the most important sources for bioenergy production, which mainly come from five sectors: forestry and timber, agriculture, fishery, waste management and wastewater treatment (**Figure 3**). It is noteworthy that the portion of biomass and biodegradable waste contributed by different sectors may vary dramatically from country to country, and the generation is significantly influenced by seasonality. Therefore, it is necessary to take into account of those variations and

uncertainties in forecasting the amount of the feedstock for bioenergy production.

The difference between the two concepts is, compared with biodegradable waste, biomass that specifies a broader domain in which not only organic matters discarded by consumers

**2.1. Biomass and biodegradable waste**

186 Energy Systems and Environment

**Figure 3.** Sources of biomass and biodegradable waste.

Direct combustion has been widely used for over three decades in generating electricity and heat from biomass [20]. The principle is to utilize the heat generated by combustion of biomass for cooking, industrial process, direct home heating [21] or driving the steam power cycle for


**Table 1.**Alternative technologies for bioenergy production and non-value-added treatment of biomass and biodegradable waste.

electricity generation [22]. Due to the high level of moisture content, combustion promoters are usually used in order to improve the conversion efficiency. Coal is the most frequently used promoter, and co-combustion of biomass/biodegradable waste with coal has dominated the bioenergy production market in some countries, i.e. Sweden, Japan, etc. However, environmental challenges, i.e. emission of CO<sup>2</sup> , SOx and NOx , from the co-combustion process are the major bottleneck for this method for bioenergy recovery [23]. Furthermore, as the common challenge of incineration plant, the flying ash is another pollutant that needs lots of efforts and costs to deal with so that the environmental influence is minimized.

some cases, aerobic digestion and anaerobic digestion are combined for the treatment of biodegradable waste, e.g. wastewater sludge [35]. MBT combines mechanical pre-treatment and anaerobic digestion. The pre-treatment of biomass through different physical and mechanical processes breaks the physical structure and improves the quality of the input organic substances for anaerobic digestion [36], and the efficiency of bioenergy production is improved as well. Comparing with aerobic composting, both anaerobic digestion and MBT processes have

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much higher requirement for creating thermostatic and anaerobic environment.

**biodegradable waste**

**3.1. A value chain model for bioenergy production**

value creation and appreciation through the whole network.

**3. Value chain analysis of bioenergy production from biomass and** 

The concept of value chain was originally proposed by Porter from financial perspective to account the sequential value creation and appreciation through the whole network comprised by different companies and enterprises [37]. This concept is usually accompanied with another word with similar meaning: supply chain (i.e. in [38, 39]). The difference between those two concepts is sometimes negligible especially when the value creation and appreciation process over the material flow are predominately accounted. However, a recent study by Holweg and Helo [40] has explicitly distinguished the two concepts from the perspective of their focuses. Supply chain management focuses on the links and interactions among different companies from the operational level considering strategies, methodologies, design, planning and operation of an efficient and effective multi-stakeholder inner- and/or inter-company network. However, value chain mainly concerns the value-added activities from one company to another within the network and the opportunities and challenges for maximizing the overall

The value chain of bioenergy production from biomass and biodegradable waste has been extensively modelled in the literature. Balaman and Selim [41] proposed a biomass-to-energy value chain model and a decision support tool for maximizing the overall profit generated through bioenergy production. A simplified value chain model is developed by Parker et al. [42], and the primary target of the model is to improve the economic value of biofuel production from biomass. An et al. [43] formulated a computational model to optimize the overall profit of a lignocellulosic biofuel value-added chain. Kim et al. [44] developed a four-echelon value chain framework for biofuel production through fast pyrolysis conversion. The maximization of the overall value creation from bioenergy production is focused by Kim et al. [45] and Dal Mas et al. [46]. The maximization of the value creation is sometimes formulated in an opposite way that minimizes the system cost. Chen and Fan [47] formulated a bioethanol production value chain model that applies mixed integer programming for minimizing the overall system cost. Aksoy et al. [48] developed an optimization model for minimizing the transportation cost of bioenergy production from woody biomass and mill waste. The environmental benefits of bioenergy production have been increasingly focused in recent years. A value-added chain of bioenergy production from biomass is modelled by Lam et al. [49],

which focuses on the mitigation of carbon footprint of bioenergy production.

#### *2.2.2. Thermochemical conversion*

Thermochemical conversion utilizes constant and high temperature combined with catalysts to convert biomass inside the boiler to biofuel and bioenergy through changing their physical properties and chemical structure [24]. The main technologies of thermochemical conversion of biomass and biodegradable waste include pyrolysis, gasification, liquefaction and torrefaction [25], among which pyrolysis and gasification are considered the most promising ones [26]. Pyrolysis is a fundamental method to transform biomass into crude-like liquid bio-oil [27], and after the chemical decomposition, the liquid bio-oil can be converted to the combustion fuels mainly used for transport and chemical industry [28]. The principle of pyrolysis process is the combination of thermal and chemical decomposition with the help of catalysts at relatively lower temperature (450–600° C) and longer vapor residence time in absence of oxygen for converting the organic substances to liquid bio-oil with charcoal and gases as the by-products [24, 29]. Gasification is another important thermochemical technology that converts different kinds of biomass into syngas. The main composition of syngas is methane, hydrogen, carbon dioxide and carbon monoxide, which are extensively applied in space heating, power generation, transport and chemical industry [30]. Different from pyrolysis, gasification process requires relatively higher temperature (700–1300°C) with the absence or limited oxygen environment in order to optimize the production of syngas [23, 26]. Recently, with the technological development, the probability of biomass and biodegradable waste gasification at lower temperature has also been discussed (e.g. [31]).

#### *2.2.3. Biochemical conversion*

Biochemical conversion utilizes biological and chemical processes with the help of aerobic or anaerobic microorganism to transform biomass into biogas and bio-rest, and the main biochemical technologies are composting, anaerobic digestion and mechanical biological treatment (MBT). Composting is an aerobic digestion process and a popular method for the treatment of biomass and biodegradable waste (e.g. Finland). The basic principle is to use biochemical process with the help of aerobic microorganism under open air environment for converting biomass into environmentally friendly bio-rest, which can be used as fertilizer. Anaerobic digestion is the most popular biochemical technology for bioenergy production, and thousands of anaerobic digestion bioenergy production plants have been established all over the world [32]. Through the biochemical decomposition process with the help of anaerobic bacteria at constant temperature in the absence of oxygen, the biomass can be transformed into not only bio-rest but also energy-rich biogas [33]. Biogas is mainly comprised by methane (60%) and carbon dioxide (40%), and it is mainly used as vehicle fuels after cleaned and upgraded [34]. In some cases, aerobic digestion and anaerobic digestion are combined for the treatment of biodegradable waste, e.g. wastewater sludge [35]. MBT combines mechanical pre-treatment and anaerobic digestion. The pre-treatment of biomass through different physical and mechanical processes breaks the physical structure and improves the quality of the input organic substances for anaerobic digestion [36], and the efficiency of bioenergy production is improved as well. Comparing with aerobic composting, both anaerobic digestion and MBT processes have much higher requirement for creating thermostatic and anaerobic environment.
