**2.1 Incineration/combustion**

Combustion is the most common waste energy recovery technology used in the production of heat, steam, and electricity. Historically, this technology is considered one of the most "dirty" and polluting processes in waste management and disposal; however, advances in the treatment of emissions in the late 1980s and early 1990s, along with the development of command and control technologies and the pretreatment of waste, have led to combustion once again attracting the attention of researchers and investors around the world. In general, a modern incineration facility consists of pretreatment and/or sorting line from where the wastes are continuously and uniformly fed to a furnace (**Figure 1**). The furnace operates at very high temperatures to ensure complete combustion. The combustion parameters are continuously controlled, and emissions are treated in a set of filters to ensure the removal of the toxic pollutants. As a WtE technology, combustion is very mature with the most recent studies focused on the recovery of energy and ashes resulting from the co-combustion or co-incineration of different wastes in nonspecialized equipment [4]. In fact, this process is widely used for thermal energy recovery of waste forms with good calorific value [5]. In 2016, for example, 28% of municipal solid waste (MSW) generated in the EU-28 was incinerated [6]. Furthermore, about 13.1% of hazardous waste was incinerated with and without energy recovery [7].

**33**

**Technology** Combustion/

incineration

Reduction of mass (70%) and volume (80%), fast and simple process, energy recovery

High capital cost, public opinion objection, toxic slag production, air pollution (dioxins)

Wide range of applications and feedstocks, high conversion efficiency

High capital cost, high sensibility processes, low flexibility, risk of mechanical failure, tars production

Production of toxic compounds, partial

Transformation of

lignite, solubilization of

degradation

hemicellulose

High yield, reduced syngas

High capital, maintenance and

Bio-oils, biochar,

syngas

operation costs, high bio-oil viscosity

treatment, reduction of waste

volume (90%)

Hydrothermal

Higher LHV bio-oil and low

Low conversion efficiency (20–60%),

Heavy oil, intermediate

Additives, high-value

TRL7/CRI1

Steeper Energy, Denmark; PNNL,

chemicals, transportation,

heating, and electricity

USA;

Genifuel, USA;

PilotABP, Spain; TERAX, New

Zealand

TRL7/CRI1

Torplant, Switzerland;

ECN, Netherlands;

Norris Thermal Technologies,

Vega Biofuels, USA

value chemicals

higher pressure equipment and higher

capital cost

moisture content

liquefaction

Torrefaction

Homogeneous and stable

Low-energy density, high ash quantity

Torrefied biomass

Heating, electricity

products, easy pelletizing,

high LHV, hydrophobic

*TRL, technological readiness level; CRI, commercial readiness index.*

**Table 1.**

*Comparative summary of different thermochemical conversion technologies [8–10].*

Explosive

decompression

Pyrolysis

Gasification

**Benefits**

**Limitations**

**Products and by-products** Heat for boilers and furnaces. Potential metal recovery from slag

Heating, electricity

TRL9/CRI4

H2, CO-rich syngas

Heating, electricity,

TRL9/CRI3

Energos, Norway;

Vaskiluodon Voima, Finland

TRL9/CRI2

transportation, fuels and

high-value chemicals

Heating, electricity,

transportation, fuels, and

high-value chemicals

Additives, high-value

TRL8/CRI2

ABRITech, Canada;

Ensyn Several, Canada;

Metso, Finland; Rise, Sweden

chemicals, transportation,

heating, and electricity

Biochar for soil

remediation

Sugars, digestible

products

**Applications**

**TRL/CRI/demonstration projects**

*Review of Biofuel Technologies in WtL and WtE DOI: http://dx.doi.org/10.5772/intechopen.84833*


*Review of Biofuel Technologies in WtL and WtE DOI: http://dx.doi.org/10.5772/intechopen.84833*

*Elements of Bioeconomy*

potentially reducing environmental pollution.

**2.1 Incineration/combustion**

The future adoption of the concept of circular economy is, therefore, a necessary change of paradigm, in contrast to the current linear model. This new concept is increasingly viewed as a source of innovation in products, processes, and business models, opening excellent opportunities that should be seen by companies and organizations as competitive advantages in a dynamic and global market [3]. Specifically, with a circular flux in the consumption of resources, every waste generated is a potential raw material for another process, introducing novel ways of valorization and development of second and third generation products. The benefits are clear as few wastes would be generated and disposed of without treatment,

Updated knowledge of current technologies is a crucial factor in determining the most suitable processes to valorize different types of wastes in future biorefineries. These waste biorefineries are facilities that integrate the necessary technologies in order to convert biomass feedstocks and other wastes into usable products, ensuring that circular economy transitions from theory to the real world. The available waste streams can either be transformed by technologies producing biofuels (waste-to-liquids, WtL) or energy (waste-to-energy, WtE) with both categories expected to be a key element in future waste management. Based on this, in this chapter, we briefly review the current state of main WtL and WtE technologies within a perspective of their use as tools for managing post-process residues and by-products. The review ends with a brief discus-

sion on future developments regarding mentioned technological options.

**2. WtL and WtE technologies: historical and technological overview**

Biorefineries are a way to achieve sustainable waste management with many environmental and economic benefits. However, waste streams are often very selective in terms of the technological option most suitable for their valorization. As such, a complete understanding of each technology is a fundamental resource to determine if the different wastes available can be viewed as a raw material for valuable products. **Tables 1–3** summarize the different thermochemical, biological, and chemical processes discussed. A brief description of each technology follows.

Combustion is the most common waste energy recovery technology used in the production of heat, steam, and electricity. Historically, this technology is considered one of the most "dirty" and polluting processes in waste management and disposal; however, advances in the treatment of emissions in the late 1980s and early 1990s, along with the development of command and control technologies and the pretreatment of waste, have led to combustion once again attracting the attention of researchers and investors around the world. In general, a modern incineration facility consists of pretreatment and/or sorting line from where the wastes are continuously and uniformly fed to a furnace (**Figure 1**). The furnace operates at very high temperatures to ensure complete combustion. The combustion parameters are continuously controlled, and emissions are treated in a set of filters to ensure the removal of the toxic pollutants. As a WtE technology, combustion is very mature with the most recent studies focused on the recovery of energy and ashes resulting from the co-combustion or co-incineration of different wastes in nonspecialized equipment [4]. In fact, this process is widely used for thermal energy recovery of waste forms with good calorific value [5]. In 2016, for example, 28% of municipal solid waste (MSW) generated in the EU-28 was incinerated [6]. Furthermore, about 13.1% of hazardous waste was incinerated with and without energy recovery [7].

**32**

**Table 1.**

*Comparative summary of different thermochemical conversion technologies [8–10].*

