Chapter 3
Advanced Technologies (Biological
and Thermochemical)
for Waste-to-Energy Conversion
Abstract This chapter reviews various technologies for waste to energy conversion. The advantages and disadvantages of each technology are discussed in this
chapter. The effectiveness of a specific waste-to-energy process is determined based
on the thermal potential of the waste, effectiveness of the system and the type of
produced energy. The two main technologies for energy recovery from waste materials are thermochemical and biological conversions. Thermochemical conversion is
defined as the decomposition of organic matters as a result of heating and/or oxidation of biomass and chemical reactions. It mainly includes combustion, gasification,
pyrolysis and hydrothermal liquefaction. Combustion or incineration is an old and
developed technology for the degradation of organics in the presence of oxygen. It
can be performed as co-firing of biomass with coal for higher conversion efficiency
and less fouling and corrosion problems compared to the combustion of biomass
feedstock. Pyrolysis, defined as the decomposition of biomass in the absence of
oxygen, produces syngas, liquid fuels and biochar. Hydrothermal liquefaction is
another thermochemical process for the conversion of biomass to liquid fuels in the
presence of water as the reaction medium. It involves a series of reactions, producing
bio-crude oil, water-soluble products, solid residue and non-condensable gases as the
main products. Another thermochemical process is gasification which involves the
conversion of biomass into gaseous products using a gasifying agent. On the other
hand, the biochemical conversion methods use microorganisms and enzymes in addition to heat and other chemicals to breakdown the biomass into gaseous or liquid
fuels. Examples of biochemical conversions include anaerobic digestion, mechanical biological treatment and fermentation. Anaerobic digestion is the breakdown
of biodegradable materials in the absence of oxygen. This process results in the
reduction of volatile solids and the production of biogas that can be used to produce
electricity and heat or cleaned and used as a natural gas substitute. Mechanical biological treatment is the integration of some of the waste management facilities such as
materials recovery facilities (MRFs), composting and anaerobic digestion plants to
recover recyclables and compost or digest the organic fraction of the waste through
biological treatment. Fermentation involves the conversion of organic materials into
bioethanol using various yeasts and microorganisms. Whereas, conversion of lignocellulosic biomass into ethanol is complex and expensive and there are still some
© Springer Nature Singapore Pte Ltd. 2021
L. Nazari et al., Advanced and Emerging Technologies for Resource Recovery
from Wastes, Green Chemistry and Sustainable Technology,
https://doi.org/10.1007/978-981-15-9267-6_3
55
Advanced Technologies (Biological
and Thermochemical)
for Waste-to-Energy Conversion
Abstract This chapter reviews various technologies for waste to energy conversion. The advantages and disadvantages of each technology are discussed in this
chapter. The effectiveness of a specific waste-to-energy process is determined based
on the thermal potential of the waste, effectiveness of the system and the type of
produced energy. The two main technologies for energy recovery from waste materials are thermochemical and biological conversions. Thermochemical conversion is
defined as the decomposition of organic matters as a result of heating and/or oxidation of biomass and chemical reactions. It mainly includes combustion, gasification,
pyrolysis and hydrothermal liquefaction. Combustion or incineration is an old and
developed technology for the degradation of organics in the presence of oxygen. It
can be performed as co-firing of biomass with coal for higher conversion efficiency
and less fouling and corrosion problems compared to the combustion of biomass
feedstock. Pyrolysis, defined as the decomposition of biomass in the absence of
oxygen, produces syngas, liquid fuels and biochar. Hydrothermal liquefaction is
another thermochemical process for the conversion of biomass to liquid fuels in the
presence of water as the reaction medium. It involves a series of reactions, producing
bio-crude oil, water-soluble products, solid residue and non-condensable gases as the
main products. Another thermochemical process is gasification which involves the
conversion of biomass into gaseous products using a gasifying agent. On the other
hand, the biochemical conversion methods use microorganisms and enzymes in addition to heat and other chemicals to breakdown the biomass into gaseous or liquid
fuels. Examples of biochemical conversions include anaerobic digestion, mechanical biological treatment and fermentation. Anaerobic digestion is the breakdown
of biodegradable materials in the absence of oxygen. This process results in the
reduction of volatile solids and the production of biogas that can be used to produce
electricity and heat or cleaned and used as a natural gas substitute. Mechanical biological treatment is the integration of some of the waste management facilities such as
materials recovery facilities (MRFs), composting and anaerobic digestion plants to
recover recyclables and compost or digest the organic fraction of the waste through
biological treatment. Fermentation involves the conversion of organic materials into
bioethanol using various yeasts and microorganisms. Whereas, conversion of lignocellulosic biomass into ethanol is complex and expensive and there are still some
© Springer Nature Singapore Pte Ltd. 2021
L. Nazari et al., Advanced and Emerging Technologies for Resource Recovery
from Wastes, Green Chemistry and Sustainable Technology,
https://doi.org/10.1007/978-981-15-9267-6_3
55