50
1 Introduction
Limited conventional fuel reserves, but also the increasing greenhouse gas emissions leading to extreme climatic phenomena, have urged the concerns of scientists
and energy project developers around the world in implementing solutions for transition from fossil-based resources to zero-carbon renewable fuels [1]. A report
released by the World Energy Council in 2019 stated that technological innovations,
climate change and more tense geopolitics have become fundamental drivers to
reshape the world of energy; thus, the use of sustainable bioenergy is expected to
increase by one-third in 2040 from today’s levels [2].
Worldwide, there is a steady increase in the interest of the public and private
environment in developing projects aimed at capitalizing residual biomass for the
production of green energy and value-added by-products [3]. Residual biomass,
also named ‘waste biomass’, is addressed to biomass that is not produced for its
direct use, for example, as energy source, but is a waste product generated in other
agricultural or technological processes. Residual biomass may include landscape
biomass (agricultural and forestry), animal manure, biodegradable fraction of
municipal waste [4] and algal biomass remaining after oil extraction [5–7].
Using waste biomass as raw material for new technological processes has become
a requirement much promoted by energy and environmental policies over the past
decade within the concept of circular bioeconomy, offering important advantages
for sustainability, such as no additional land required to produce biomass; waste
reduction for new production chains, thus contributing to a closed-loop resource
use; avoidance of GHG emissions from residual biomass if left to rot on the ground;
etc. [3, 4].
There are several approaches used for biomass conversion to produce bioenergy,
which may be classified into the following two major categories: thermochemical
conversion (combustion for heat or electricity, pyrolysis to bio-oil and charcoal,
catalytic liquefaction to marketable liquids and gasification to syngas) and biochemical conversion to produce biogas, biohydrogen, bioethanol and biodiesel [8,
9]. Regarding biochemical conversion, it includes three types of different processes,
which are anaerobic digestion, alcoholic fermentation and photobiological reactions, all of them involving microorganisms or enzymes to transform biopolymers
in gaseous or liquid biofuels [10]. Besides enzymes which are biological catalysts
aimed to lower the activation energy for biochemical reactions, some researches
have also proved that mineral catalysts such as zeolites added to the fermentation
mass in anaerobic digestion processes can facilitate microbial fermentation and
increase the biomass to biomethane conversion yields. More specifically, zeolites
can help the anaerobic digestion processes by adsorbing ammonia and other toxicants in the system, thus shortening the duration of the lag phase of microbial
growth and accelerating methane production [11, 12].
With attention focused exclusively on the biochemical conversion processes, this
chapter aims to examine and discuss currently applied technologies and recent
research trends for the residual biomass recovery to fuel gas (biomethane and
C. Mateescu and A.-D. Dima
1 Introduction
Limited conventional fuel reserves, but also the increasing greenhouse gas emissions leading to extreme climatic phenomena, have urged the concerns of scientists
and energy project developers around the world in implementing solutions for transition from fossil-based resources to zero-carbon renewable fuels [1]. A report
released by the World Energy Council in 2019 stated that technological innovations,
climate change and more tense geopolitics have become fundamental drivers to
reshape the world of energy; thus, the use of sustainable bioenergy is expected to
increase by one-third in 2040 from today’s levels [2].
Worldwide, there is a steady increase in the interest of the public and private
environment in developing projects aimed at capitalizing residual biomass for the
production of green energy and value-added by-products [3]. Residual biomass,
also named ‘waste biomass’, is addressed to biomass that is not produced for its
direct use, for example, as energy source, but is a waste product generated in other
agricultural or technological processes. Residual biomass may include landscape
biomass (agricultural and forestry), animal manure, biodegradable fraction of
municipal waste [4] and algal biomass remaining after oil extraction [5–7].
Using waste biomass as raw material for new technological processes has become
a requirement much promoted by energy and environmental policies over the past
decade within the concept of circular bioeconomy, offering important advantages
for sustainability, such as no additional land required to produce biomass; waste
reduction for new production chains, thus contributing to a closed-loop resource
use; avoidance of GHG emissions from residual biomass if left to rot on the ground;
etc. [3, 4].
There are several approaches used for biomass conversion to produce bioenergy,
which may be classified into the following two major categories: thermochemical
conversion (combustion for heat or electricity, pyrolysis to bio-oil and charcoal,
catalytic liquefaction to marketable liquids and gasification to syngas) and biochemical conversion to produce biogas, biohydrogen, bioethanol and biodiesel [8,
9]. Regarding biochemical conversion, it includes three types of different processes,
which are anaerobic digestion, alcoholic fermentation and photobiological reactions, all of them involving microorganisms or enzymes to transform biopolymers
in gaseous or liquid biofuels [10]. Besides enzymes which are biological catalysts
aimed to lower the activation energy for biochemical reactions, some researches
have also proved that mineral catalysts such as zeolites added to the fermentation
mass in anaerobic digestion processes can facilitate microbial fermentation and
increase the biomass to biomethane conversion yields. More specifically, zeolites
can help the anaerobic digestion processes by adsorbing ammonia and other toxicants in the system, thus shortening the duration of the lag phase of microbial
growth and accelerating methane production [11, 12].
With attention focused exclusively on the biochemical conversion processes, this
chapter aims to examine and discuss currently applied technologies and recent
research trends for the residual biomass recovery to fuel gas (biomethane and
C. Mateescu and A.-D. Dima