human utilization, and therefore it is removed as waste through slaughtering and
other processing steps (Salminen and Rintala 2002; Forgács et al. 2012).
As all these waste components are dissimilar, their biogas production capacity is
quite different. Biogas production mainly depends on biodegradability of waste and
structure. Theoretically, highest production of biogas could be obtained from lipid
(1.01 Nm
3 CH 4 /kg VS) followed by protein (0.50 Nm
3 CH 4 /kg VS), and carbohydrate (0.42 Nm
3 CH 4 /kg VS) (Møller et al. 2004). Conversely, biodegradability
describes how much of a particular material is truly used throughout the method.
Various compounds such as sugars get spoiled rapidly and totally, whereas some
other ingredients lead to corrosion.
4.4.3 Pretreatment for Enhanced Biogas Production
It is essential to identify novel substrates to be used for anaerobic digestion (AD) to
fulfill the ever-increasing needs for biogas production. Throughout the world, along
with the abundance and availability of lignocellulosic biomass, their high carbohydrate content makes these materials a valuable feedstock for biofuel production.
About 50% of the biomass in the world has been computed for lignocellulose, and
simultaneously production of lignocellulose can be up to 200 billion tons per year
(Claassen et al. 1999; Zhang 2008). Presently, the use of lignocelluloses as a
feedstock for methane production is not extensive due to its recalcitrant structure,
which is the main challenge (Lehtomäki 2006; Seppälä et al. 2007; Hendriks and
Zeeman 2009).
Hydrolytic bacteria change insoluble complex organic matter into monomers and
soluble oligomers into amino acids, sugars, and fatty acids during the first phase of
AD, i.e., in hydrolysis phase (Fig. 4.1). In this process, enzymes like lipase,
cellulase, protease, hemicellulase, and amylase are included (Taherzadeh and Karimi
2008). Consequently, almost all types of substrates may be hydrolyzed in biogas
processes. On the other hand, the hydrolysis step is very much reliant on the
characteristics of a given substrate. Hydrolysis could progress earlier if the essential
enzymes are produced by microorganisms and have suitable surface area for physical contact between substrates and enzymes (Taherzadeh and Karimi 2008). However, substrate with complex structure, like cellulose, requires long periods to be
degraded, and the degradation is generally not completed (Deublein and Steinhauser
2011). Therefore, while using these types of substrates, the hydrolysis step is often
considered a rate-limited step (Vavilin et al. 1996; Taherzadeh and Karimi 2008).
The pretreatment steps convert the recalcitrant raw material into forms which can
be easily degraded by enzymatic and microbial processes. With the disruption of the
secondary cell wall structure, lignocelluloses reduce its complexity and thus facilitate downstream procedures (Zhang 2008). Alternatively, a pretreatment should be
expensive, and the polysaccharide-rich substrate should be obtained with limited
amount of inhibitory products.
Several types of manifestation have been suggested to enhance biogas production
from lignocellulosic biomass, which may be classified as biological, chemical, and
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G. Monika et al.
other processing steps (Salminen and Rintala 2002; Forgács et al. 2012).
As all these waste components are dissimilar, their biogas production capacity is
quite different. Biogas production mainly depends on biodegradability of waste and
structure. Theoretically, highest production of biogas could be obtained from lipid
(1.01 Nm
3 CH 4 /kg VS) followed by protein (0.50 Nm
3 CH 4 /kg VS), and carbohydrate (0.42 Nm
3 CH 4 /kg VS) (Møller et al. 2004). Conversely, biodegradability
describes how much of a particular material is truly used throughout the method.
Various compounds such as sugars get spoiled rapidly and totally, whereas some
other ingredients lead to corrosion.
4.4.3 Pretreatment for Enhanced Biogas Production
It is essential to identify novel substrates to be used for anaerobic digestion (AD) to
fulfill the ever-increasing needs for biogas production. Throughout the world, along
with the abundance and availability of lignocellulosic biomass, their high carbohydrate content makes these materials a valuable feedstock for biofuel production.
About 50% of the biomass in the world has been computed for lignocellulose, and
simultaneously production of lignocellulose can be up to 200 billion tons per year
(Claassen et al. 1999; Zhang 2008). Presently, the use of lignocelluloses as a
feedstock for methane production is not extensive due to its recalcitrant structure,
which is the main challenge (Lehtomäki 2006; Seppälä et al. 2007; Hendriks and
Zeeman 2009).
Hydrolytic bacteria change insoluble complex organic matter into monomers and
soluble oligomers into amino acids, sugars, and fatty acids during the first phase of
AD, i.e., in hydrolysis phase (Fig. 4.1). In this process, enzymes like lipase,
cellulase, protease, hemicellulase, and amylase are included (Taherzadeh and Karimi
2008). Consequently, almost all types of substrates may be hydrolyzed in biogas
processes. On the other hand, the hydrolysis step is very much reliant on the
characteristics of a given substrate. Hydrolysis could progress earlier if the essential
enzymes are produced by microorganisms and have suitable surface area for physical contact between substrates and enzymes (Taherzadeh and Karimi 2008). However, substrate with complex structure, like cellulose, requires long periods to be
degraded, and the degradation is generally not completed (Deublein and Steinhauser
2011). Therefore, while using these types of substrates, the hydrolysis step is often
considered a rate-limited step (Vavilin et al. 1996; Taherzadeh and Karimi 2008).
The pretreatment steps convert the recalcitrant raw material into forms which can
be easily degraded by enzymatic and microbial processes. With the disruption of the
secondary cell wall structure, lignocelluloses reduce its complexity and thus facilitate downstream procedures (Zhang 2008). Alternatively, a pretreatment should be
expensive, and the polysaccharide-rich substrate should be obtained with limited
amount of inhibitory products.
Several types of manifestation have been suggested to enhance biogas production
from lignocellulosic biomass, which may be classified as biological, chemical, and
112
G. Monika et al.