Environmental Engineering Reference
In-Depth Information
investigated [73, 74]. However, significant progress has been made within a rela-
tively short period; we may see some systems in commercial operation in the
near future [72].
For full commercialization, torrefaction reactors still require to be optimized to
economically meet end-user requirements and achieve market standardization of
the product [12, 44]. Certain characteristics need to be proven or scaled-up in
order to meet commercial expectations [3, 44, 75]. A major operation challenge is
achieving optimum torrefaction process control of the biomass feed, process tem-
perature and residence time to ensure optimal thermal efficiency and consistent
torrefied product [12, 51, 70, 76].
3.4
Biological Processing
3.4.1
Fermentation
Fermentation involves the use of microorganisms such as bacteria and fungi to
transform sugars into products. Bioconversion of biomass into products through
fermentation is a very flexible process which could lead to a wide range of prod-
ucts including biofuels, biochemicals, or biomaterials. Traditionally, sugar or
starch crops such as sugarcane and corn have been used for bioethanol production
[1]. More recently, agricultural by-products from cereals [77-80] or municipal
waste such as food waste [81-84] have been used as feedstock for bioconversion
to further lower the production cost.
An overview of bioconversion processes, from biomass through fermentation,
is summarized in Figure 3.14. Biomass is pretreated before undergoing the
fermentation step. For lignocellulosic biomass, the pretreatment step is aimed at
removing lignin and hemicellulose in order to increase the subsequent hydrolysis
step for glucose production, thereby increasing the product fermentation yield.
Chemical pretreatment methods such as acid/alkaline hydrolysis are commonly
used. Subsequently, the remaining cellulosic-rich biomass is digested by cellulase
in order to produce glucose. The hydrolysate formed is a nutrient-rich medium,
which serves as a generic feedstock in the subsequent microbial fermentation.
Chemicals
Fermentable
sugars
Fuels
Biomass
Pretreatment
Hydrolysis
Fermentation
Bio-polymers
Figure 3.14
Biomass conversion routes of bioproduct formation through fermentation.
