52
Some of the conventional substrates for energy production, particularly energy
crops, have been the subject of controversies like the ‘food-versus-fuel debate’,
discussing about the pressure that fuel crops pose on agricultural land use, which
may have caused increased prices on edibles, feed and fibres [14]. Consequently, in
2018, the EU Parliament stepped in to settle the conflict by releasing a new directive
which promoted the use of renewable sources for energy production. By different
provisions, this directive reinforced the sustainability criteria of bioenergy which
includes the indirect land use change caused by biofuel production from agricultural
crops [15]. Research in this field is meant to develop technologies that provide the
best opportunities for answering strategic requirements at local, regional and global
levels, focusing on waste recovery strategies.
Moreover, according to a report released by the World Bank in 2018, the annual
production of residues is assumed to rise by 70%, reaching 3.40 billion tonnes in
2050 [16], which is mainly influenced by expected rapid population growth around
the world, from 7.7 billion at the end of 2019 to over 9.1 billion in 2050 [17, 18]. In
other words, world population growth causes higher demand for edibles and other
basic commodities, which will lead in turn to the amplification of agro-industrial
activities [19] and to an alarming increase in the volume of agricultural residues and
food industry waste and wastewaters. On the other side, the amount of municipal
waste is expected to go up with increasing population density. Broadly speaking, the
share of organic residuals in the amount of municipal waste is about 64%, but this
could withstand important differences at regional level, depending on several features, such as geographical position and climate, standard of living, education, and
local waste management policies [16]. Waste must be therefore managed in a sustainable way, with priority on recycling and advanced processing to obtain reusable
products, as provided within a circular economy [20].
Waste biomass or organic residuals could be used as valuable renewable raw
materials in the manufacturing of several products (biofuels, polymers and chemicals, building products, resins, enzymes, etc.). Unfortunately, only a low volume of
organic waste is currently directed to become a feedstock in electricity generation
processes or towards obtaining value-added products [19, 21], although conventional technologies have greatly improved and novel processes have also been
developed [22]. Anaerobic digestion (AD) is one of the most promising waste management technologies, as it can provide both garbage sanitation and energy generation in the form of biogas. At present, biogas production units bring high economic
benefits at industrial scale [23], promoting pollution reduction and local development. Not yet established extensively, dark fermentation (DF) is another waste-toenergy emerging process, used for biohydrogen production from substrates such as
crop and farm residuals, industrial organic waste and wastewaters, sewage sludge,
etc. [24].
Crop residues, which are primarily lignocellulosic materials, are among the most
widespread biomass wastes. This type of vegetal waste is considered as plentiful,
easily available resource, and many research activities have been directed towards
increasing the possible use of lignocellulosic biomass in biomethane and biohydrogen production. Despite its abundance, lignocellulosic biomass, including some
C. Mateescu and A.-D. Dima
Some of the conventional substrates for energy production, particularly energy
crops, have been the subject of controversies like the ‘food-versus-fuel debate’,
discussing about the pressure that fuel crops pose on agricultural land use, which
may have caused increased prices on edibles, feed and fibres [14]. Consequently, in
2018, the EU Parliament stepped in to settle the conflict by releasing a new directive
which promoted the use of renewable sources for energy production. By different
provisions, this directive reinforced the sustainability criteria of bioenergy which
includes the indirect land use change caused by biofuel production from agricultural
crops [15]. Research in this field is meant to develop technologies that provide the
best opportunities for answering strategic requirements at local, regional and global
levels, focusing on waste recovery strategies.
Moreover, according to a report released by the World Bank in 2018, the annual
production of residues is assumed to rise by 70%, reaching 3.40 billion tonnes in
2050 [16], which is mainly influenced by expected rapid population growth around
the world, from 7.7 billion at the end of 2019 to over 9.1 billion in 2050 [17, 18]. In
other words, world population growth causes higher demand for edibles and other
basic commodities, which will lead in turn to the amplification of agro-industrial
activities [19] and to an alarming increase in the volume of agricultural residues and
food industry waste and wastewaters. On the other side, the amount of municipal
waste is expected to go up with increasing population density. Broadly speaking, the
share of organic residuals in the amount of municipal waste is about 64%, but this
could withstand important differences at regional level, depending on several features, such as geographical position and climate, standard of living, education, and
local waste management policies [16]. Waste must be therefore managed in a sustainable way, with priority on recycling and advanced processing to obtain reusable
products, as provided within a circular economy [20].
Waste biomass or organic residuals could be used as valuable renewable raw
materials in the manufacturing of several products (biofuels, polymers and chemicals, building products, resins, enzymes, etc.). Unfortunately, only a low volume of
organic waste is currently directed to become a feedstock in electricity generation
processes or towards obtaining value-added products [19, 21], although conventional technologies have greatly improved and novel processes have also been
developed [22]. Anaerobic digestion (AD) is one of the most promising waste management technologies, as it can provide both garbage sanitation and energy generation in the form of biogas. At present, biogas production units bring high economic
benefits at industrial scale [23], promoting pollution reduction and local development. Not yet established extensively, dark fermentation (DF) is another waste-toenergy emerging process, used for biohydrogen production from substrates such as
crop and farm residuals, industrial organic waste and wastewaters, sewage sludge,
etc. [24].
Crop residues, which are primarily lignocellulosic materials, are among the most
widespread biomass wastes. This type of vegetal waste is considered as plentiful,
easily available resource, and many research activities have been directed towards
increasing the possible use of lignocellulosic biomass in biomethane and biohydrogen production. Despite its abundance, lignocellulosic biomass, including some
C. Mateescu and A.-D. Dima