Environmental Engineering Reference
In-Depth Information
Figure 8. Fragment of lignin structure.
The third component of lignocellulosic feedstock is lignin, made of phenolic polymers
(see Figure 8). Even if lignin cannot be hydrolyzed to sugars and then fermented, it is useful
for other purposes. For instance, it can be used in its polymeric forms as adhesives for wood
materials, cement additive and so on, or can be fractionated into low molecular mass
compounds (e.g. phenols), completely degraded to gas or liquid bio-oil through gasification
or pyrolysis, or burnt as a solid fuel to generate heat and electricity.
Table 1 reports the composition of some lignocellulosic biomass which can constitute the
raw materials for biorefinery systems. The abundance of the three main components can vary
significantly among the feedstocks. For instance, lignin ranges from 17% in wheat straw up to
28% in softwood.
3.1.6. Organic residues and others
This group refers to the other biomass raw material sources that do not fall into the other
categories, i.e. the organic fraction of Municipal Solid Waste (MSW), manure, wild fruits and
crops and residues from the food production chain (such as fresh fruit and vegetable). The
physical and chemical characteristics of this wide spectrum of biomass resources vary largely.
Certain streams such as sewage sludge, manure from dairy and swine farms and residues from
food processing are very wet, with moisture contents over 70%. Therefore, these feedstocks
are more suited for an anaerobic digestion process to generate biogas, rather than other
biofuels or chemicals (Berglund and Börjesson, 2006). Other streams, such as organic MSW,
may be more or less contaminated with heavy metals or other elements (Faaij et al., 1997).
Clearly, the different properties and characteristic of the biomass wastes require the
application of different conversion technologies.
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