53
agricultural waste, forestry residuals and energy crops, have a lower biodegradability compared to other sorts of biomass, explained by the high content of recalcitrant
biopolymer structures in their composition. Progress is being made to enhance biodegradability of cellulose, hemicellulose and lignin structures in lingo-cellulosic
biomass, but some efforts should still be done for their efficient conversion to fuel
gas [25]. For instance, after crop harvesting, large quantities of residuals that are not
adequate for animal feed can be biochemically converted to produce secondgeneration liquid biofuels, biomethane and biohydrogen, thus significantly contributing to social and environmental sustainability [22]. At present, about 5% of
residues coming from the main agricultural crops are used for biogas production,
but this share is assumed to increase to 25% by 2030 and to 50% by 2050 [26]. The
range of suitable substrates for biogas production expands continuously as additional materials are tested for their biochemical methane potential and substrate
pretreatment strategies are being developed. For example, Córdoba et al. fermented
spent sawdust from mushroom cultivation and obtained a biogas potential of about
200 mL/gVS biogas, at a rough biomethane concentration of 70%, showing that
although the value is not high compared to other feedstock materials, Gymnopilus
pampeanus has the ability to improve the biodegradation of sawdust [27].
Huge quantities of residual biomass are also generated by the livestock industry.
Studies have shown that the manure of about 25 billion animal units from farming
worldwide, mainly referring to those from piggeries, dairy farms and poultry farms,
could be collected and used to obtain substantial quantities of biomethane in anaerobic digestion processes. This could be translated by up to 370 billion m
3
fuel gas
or 3800 TWh energy produced globally [26].
Food waste is another potential substrate for fuel gas production. It is permanently generated in the domestic and industrial sectors, being commonly unavoidable, responsible for financial loss and requiring immediate disposal. The World
Biogas Association estimates that one-third of the food quantity being produced
annually becomes unsuitable for human consumption or for animal feeding and it is
directly dumped to landfill [28]. Due to its high humidity (70–90%) and the wide
organic fraction content, food waste is considered a suitable substrate for biomethane or biohydrogen production in fermentation processes which successfully serve
for energy and nutrient recovery. Thereby, one tonne of wet food waste used as
substrate in anaerobic digestion could generate 150–180 m
3
biogas, while the total
amount of residuals coming from the food industry would provide up to 100 billion m
3
pure biomethane or 1100 TWh energy in the form of heat and electricity
[26]. Moreover, several strategies for increasing biomethane production from biodegradable municipal wastes have been developed in numerous experimental studies,
either by optimization of process factors or by using additives, such as Fe 3 O 4
nanoparticles or urea-capped Fe 3 O 4 nanoparticles [29, 30]. Research results are
encouraging since optimal fermentation conditions could provide efficient bioconversion of waste, meaning that higher biomethane production, better nutrient recovery and shorter fermentation durations would be obtained.
Moreover, the annual volume of sewage sludge is expected to increase in line
with the demographic growth and level of urbanization [31]. A proper stabilization
Biochemical Conversion of Residual Biomass: An Approach to Fuel Gas and Green…
agricultural waste, forestry residuals and energy crops, have a lower biodegradability compared to other sorts of biomass, explained by the high content of recalcitrant
biopolymer structures in their composition. Progress is being made to enhance biodegradability of cellulose, hemicellulose and lignin structures in lingo-cellulosic
biomass, but some efforts should still be done for their efficient conversion to fuel
gas [25]. For instance, after crop harvesting, large quantities of residuals that are not
adequate for animal feed can be biochemically converted to produce secondgeneration liquid biofuels, biomethane and biohydrogen, thus significantly contributing to social and environmental sustainability [22]. At present, about 5% of
residues coming from the main agricultural crops are used for biogas production,
but this share is assumed to increase to 25% by 2030 and to 50% by 2050 [26]. The
range of suitable substrates for biogas production expands continuously as additional materials are tested for their biochemical methane potential and substrate
pretreatment strategies are being developed. For example, Córdoba et al. fermented
spent sawdust from mushroom cultivation and obtained a biogas potential of about
200 mL/gVS biogas, at a rough biomethane concentration of 70%, showing that
although the value is not high compared to other feedstock materials, Gymnopilus
pampeanus has the ability to improve the biodegradation of sawdust [27].
Huge quantities of residual biomass are also generated by the livestock industry.
Studies have shown that the manure of about 25 billion animal units from farming
worldwide, mainly referring to those from piggeries, dairy farms and poultry farms,
could be collected and used to obtain substantial quantities of biomethane in anaerobic digestion processes. This could be translated by up to 370 billion m
3
fuel gas
or 3800 TWh energy produced globally [26].
Food waste is another potential substrate for fuel gas production. It is permanently generated in the domestic and industrial sectors, being commonly unavoidable, responsible for financial loss and requiring immediate disposal. The World
Biogas Association estimates that one-third of the food quantity being produced
annually becomes unsuitable for human consumption or for animal feeding and it is
directly dumped to landfill [28]. Due to its high humidity (70–90%) and the wide
organic fraction content, food waste is considered a suitable substrate for biomethane or biohydrogen production in fermentation processes which successfully serve
for energy and nutrient recovery. Thereby, one tonne of wet food waste used as
substrate in anaerobic digestion could generate 150–180 m
3
biogas, while the total
amount of residuals coming from the food industry would provide up to 100 billion m
3
pure biomethane or 1100 TWh energy in the form of heat and electricity
[26]. Moreover, several strategies for increasing biomethane production from biodegradable municipal wastes have been developed in numerous experimental studies,
either by optimization of process factors or by using additives, such as Fe 3 O 4
nanoparticles or urea-capped Fe 3 O 4 nanoparticles [29, 30]. Research results are
encouraging since optimal fermentation conditions could provide efficient bioconversion of waste, meaning that higher biomethane production, better nutrient recovery and shorter fermentation durations would be obtained.
Moreover, the annual volume of sewage sludge is expected to increase in line
with the demographic growth and level of urbanization [31]. A proper stabilization
Biochemical Conversion of Residual Biomass: An Approach to Fuel Gas and Green…