84
3 Advanced Technologies (Biological and Thermochemical) …
Austria, Spain, Italy, Switzerland, the Netherlands and the UK in order to meet
the requirements of the 1999 European Union Landfill Directive [92, 93]. Approximately, 180 MBT plants were constructed in Europe to divert biodegradable waste
from landfills between 1990 and 2010 [94]. By 2005, 80 plants with capacities ranging
from 20,000 to 480,000 t/y and a compulsive capacity of 8,500,000 t/y have been
constructed [92]. The most common treatments used in these plants are mechanical treatment coupled with aerobic composting. This is by far, the most proven and
economical technology, which is suitable for source-separated biodegradable wastes
as well as unsegregated MSW. The next common treatments are mechanical treatments coupled with anaerobic digestion, followed by a limited number of treatments
coupling aerobic drying with mechanical separation [92].
3.2.3 Fermentation
Fermentation is a process in which the waste cellulosic or organic material of biomass
is converted into liquid ethanol using various yeasts and microorganisms. In this
process, the organic materials are first converted into sugars through hydrolysis and
then the sugars are fermented to produce dilute ethanol, which is then further distilled
to produce a biofuel grade ethanol [95]. Bioethanol is a liquid fuel with a high
octane number and is mostly blended with gasoline as transportation fuels, or for
the synthesis of Ethyl Tertiary Butyl Ether (ETBE) as an octane increaser [96]. The
problems of using bioethanol in transportation fuels are its corrosive effect on fuel
injector and electric fuel pump due to the hygroscopic nature of bioethanol, engine
start-up problem in cold weather conditions due to its relatively higher flashpoint,
and the tribological effect on lubricant properties that affect the engine performance
[96].
Sugar- and starch-containing feedstock such as wheat, sugarcane or corn have
been the main sources for the production of bioethanol. However, they are predominantly used for food and using them for biofuel production is criticized due to the
food versus fuel dilemma [97]. Generally, biofuels can be categorized into first-,
second- and third-generation based on the type of feedstock used. First-generation
biofuels are produced from food sources such as corn, wheat, sugarcane and starch.
There are many environmental and food concerns on the use of first-generation
biofuels, because they affect the food supply and security and land-use change as
a result of the large conversion of agricultural crops to biofuels. Second-generation
biofuels are produced from non-food biomass such as lignocellulosic materials from
the forest and agriculture residues and industrial organic wastes such as straw, grass,
woods, sawdust and others. Third-generation biofuels are produced mainly from
microalgae as the feedstock [98].
Since the production of first-generation bioethanol is non-sustainable and uneconomical, at present most focus is on second- and third-generation bioethanol production. However, the lignocellulosic or microalgal biomass needs pre-treatments to
remove lignin, breakdown the carbohydrates and convert them into simple sugars or
3 Advanced Technologies (Biological and Thermochemical) …
Austria, Spain, Italy, Switzerland, the Netherlands and the UK in order to meet
the requirements of the 1999 European Union Landfill Directive [92, 93]. Approximately, 180 MBT plants were constructed in Europe to divert biodegradable waste
from landfills between 1990 and 2010 [94]. By 2005, 80 plants with capacities ranging
from 20,000 to 480,000 t/y and a compulsive capacity of 8,500,000 t/y have been
constructed [92]. The most common treatments used in these plants are mechanical treatment coupled with aerobic composting. This is by far, the most proven and
economical technology, which is suitable for source-separated biodegradable wastes
as well as unsegregated MSW. The next common treatments are mechanical treatments coupled with anaerobic digestion, followed by a limited number of treatments
coupling aerobic drying with mechanical separation [92].
3.2.3 Fermentation
Fermentation is a process in which the waste cellulosic or organic material of biomass
is converted into liquid ethanol using various yeasts and microorganisms. In this
process, the organic materials are first converted into sugars through hydrolysis and
then the sugars are fermented to produce dilute ethanol, which is then further distilled
to produce a biofuel grade ethanol [95]. Bioethanol is a liquid fuel with a high
octane number and is mostly blended with gasoline as transportation fuels, or for
the synthesis of Ethyl Tertiary Butyl Ether (ETBE) as an octane increaser [96]. The
problems of using bioethanol in transportation fuels are its corrosive effect on fuel
injector and electric fuel pump due to the hygroscopic nature of bioethanol, engine
start-up problem in cold weather conditions due to its relatively higher flashpoint,
and the tribological effect on lubricant properties that affect the engine performance
[96].
Sugar- and starch-containing feedstock such as wheat, sugarcane or corn have
been the main sources for the production of bioethanol. However, they are predominantly used for food and using them for biofuel production is criticized due to the
food versus fuel dilemma [97]. Generally, biofuels can be categorized into first-,
second- and third-generation based on the type of feedstock used. First-generation
biofuels are produced from food sources such as corn, wheat, sugarcane and starch.
There are many environmental and food concerns on the use of first-generation
biofuels, because they affect the food supply and security and land-use change as
a result of the large conversion of agricultural crops to biofuels. Second-generation
biofuels are produced from non-food biomass such as lignocellulosic materials from
the forest and agriculture residues and industrial organic wastes such as straw, grass,
woods, sawdust and others. Third-generation biofuels are produced mainly from
microalgae as the feedstock [98].
Since the production of first-generation bioethanol is non-sustainable and uneconomical, at present most focus is on second- and third-generation bioethanol production. However, the lignocellulosic or microalgal biomass needs pre-treatments to
remove lignin, breakdown the carbohydrates and convert them into simple sugars or