Biofuels from Biomass - Novel Combustion Concepts for Sustainable Energy Development - page 25

recalcitrance of LC biomass and expose the cellulosic material to cellulase. Though
globally huge efforts have been made to develop the pretreatment methods
(physical, chemical, and biochemical) and tremendous successes have also been
achieved, none of them have proved to be ef

cient and cost-effective, which could
be considered as an ideal method. Moreover, each of them differs in their degree of
ef ciency with the type of biomass. Combinations of pretreatment methods have

been also used for effective exposure of cellulosic material so as to be accessible to
enzyme. The next step, the hydrolysis of biomass into sugars, employing cellulase
is still a bottleneck in biochemical platform as major portion of the cost of this
process is consumed by this step due to high cost of enzyme. Cellulases currently
available commercially usually have a technical weakness its beta glucosidase has

weak tolerance for glucose, which interferes with the hydrolysis process.
Researchers have applied recombinant DNA technology for developing microbial
strains to produce cellulases with improved productivities and desirable properties,
whose substrate speci

—

city is yet another technical issue to be resolved for their

ef cient utilization. Designer cellulase could be a good possibility in the near future.

For economic sustainability, it would be necessary to utilize the C-6 and C-5
hydrolysates ef

ciently, including production of value-added products. An example
is the production if amino acids using C-5 hydrolysate by genetically modi ed

Corneybacterium sp. Depending upon the pretreatment method used, there could be
inhibitory chemicals such as furfural and acetic acid in the hydrolysate which
interfere with the yeast fermentation. Thus, either these should be removed from the
hydrolysate (additional process step causing cost increase) in such a way that sugars
too are not removed, or yeast strains should be developed having tolerance to such
chemicals, which requires biotechnological intervention. Two other approaches in
this regard are simultaneous sacchari

cation and fermentation and co-fermentation
(C-6 and C-5 sugars) using genetically modi ed microbes. On larger perspectives,

issues on land and water usage, carbon footprint, risks on venture capital for large-
scale plants, etc., need to be considered together for LC bioalcohol program. LC
bioethanol will be discussed in detail further in this chapter.

2.2 Biodiesel

Biodiesel is an alternative fuel similar to conventional or fossil diesel. It offers several
environmental bene ts compared to fossil diesel, the most important among which is,

that it can be described as carbon neutral. That means the fuel produces no net carbon
output in form of carbon dioxide. It is because the amount of CO 2 produced during its
combustion is equal to the amount of CO 2 absorbed or utilized from the environment
to be produced. It is safe, biodegradable and produces less air pollutant than petro-
leum-based diesel. It could be produced from vegetable oil, animal oil/fat, and waste
cooking oil. These oils can be converted into biodiesel via transesteri cation. Oil

crops such as rapeseed, soybean, and palm represent the most suitable source of oil for
biodiesel. Though vegetable oil possesses the greatest potential for biodiesel