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This paper assesses the global and sectoral implications of the growing demand for bio-based inputs for energy and fuel production. This paper also pinpoints the importance of relative prices between bio-based and fossil inputs in the petroleum and electricity sector and current advances in the production of biofuel. First generation biofuels continue to be substantially subsidized, and this has contributed to the increasing use of such fuel. This report reviews the current status of second and third generation biofuels. Second generation biofuels are made from cellulose, which is in more abundant supply than the first generation biofuel feedstock. Whereas third generation biofuels have become an innovative alternative that offers a wide variety of exceptional benefits. Nowadays the production of biodiesel from microalgae is an option that has attracted strong interest of the scientific community and should be evaluated to determine the technical, technological, economic and environmental sustainability of the process. Industrial biotechnology with its competitive, clean and clever use of bio-based technologies can play a key role in making biofuels more sustainable.
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Sciknow Publications Ltd. RSE 2014, 1(2):29-34
Open Journal of Renewable and Sustainable Energy DOI: 10.12966/rse.09.03.2014
©Attribution 3.0 Unported (CC BY 3.0)
Advances and Biotechnological Applications in Biofuel Production:
A Review
Tenzin Tseten and Thirupathihalli Pandurangappa Krishna Murthy*
Department of Biotechnology, Sapthagiri College of Engineering, Bangalore-560057, India
*Corresponding author (email: )
Abstract - This paper assesses the global and sectoral implications of the growing demand for bio-based inputs for energy and
fuel production. This paper also pinpoints the importance of relative prices between bio-based and fossil inputs in the petroleum
and electricity sector and current advances in the production of biofuel. First generation biofuels continue to be substantially
subsidized, and this has contributed to the increasing use of such fuel. This report reviews the current status of second and third
generation biofuels. Second generation biofuels are made from cellulose, which is in more abundant supply than the first
generation biofuel feedstock. Whereas third generation biofuels have become an innovative alternative that offers a wide variety
of exceptional benefits. Nowadays the production of biodiesel from microalgae is an option that has attracted strong interest of
the scientific community and should be evaluated to determine the technical, technological, economic and environmental
sustainability of the process. Industrial biotechnology with its competitive, clean and clever use of bio -based technologies can
play a key role in making biofuels more sustainable.
Keywords - Biofuel, Fossil Fuels, Biomass Feedstock, Cellulose, Microalgae
1. Introduction
Each and every solution is crucial to shift towards future with
a sustainable energy resources and healthy goods production.
Hence the energy source has to be more efficient and
processes for the production of sustainable energy resource
have to be improved with complete new technologies.
Biotechnological applications with its clean and chicanery use
of bio-based technologies can play a vital role in making
biofuels more sustainable [1]. Fossil fuels are hydrocarbons,
primarily coal, fuel oil or natural gas, formed from the
remains of dead plants and animals. Fossil fuels because of its
high heating potential, availability and ignition properties and
it has been used as a source for transportation and other
energy purposes [2]. Due to speedy fossil fuel depletion, the
global warming, rising future energy requirement and demand,
and climatic changes because of emission of the fossil fuel,
we are forced to search for alternative source of energy.
Among various alternative sources available today, biofuel is
the one of the best alternative source of energy for
diminishing dependency on fossil fuel by replacing it fully or
partially [3]. Through sustainable biofuel production and
continuous speedy improvements in both bio feedstock and
processes for biofuel production, it is possible to reduce the
dependency on non- renewable fossil fuels and to provide
national energy security [4]. Biofuel is any solid, liquid or
gaseous fuels derived from organic biomass which is any
living matter such as field crops, wood products, water plants,
and municipal solid waste that is converted into energy [5]. As
an alternative for fossil fuel in the transportation part, biofuel
can become critical for solving environmental troubles
because of these reasons: it minimizes greenhouse gases
(GHG) emission, and does not need much engine
modifications, it also improves national security and provides
employment and finally supports rural development [2]. To
move successfully towards biofuel future, the use of modern
biotechnology is extremely important and the cost of
conversion from bio feedstock into biofuel has already been
reduced using modern biotechnology [4, 6].
2. History
Ever since human discovered fire, charcoal, woodchips and
cattle dung have been used as a source of energy and still
today people used these solid fuels for heating and cooking in
many parts of the world. In mid 1700s and early 1800s, Oil
extracted from whale was broadly used for lighting purposes
[7]. From more than a century, biofuel has been around us
Rudolph Diesel in late 19th century used peanut oil to generate
power and he is the one who started using vegetable oil for the
production of energy source. Diesel also developed first
working engine that runs on peanut oil at the World’s
Exhibition in Paris in 1900 [8, 9]. Henry Ford was also an
initial proponent of biofuel and he developed the Model T car
in 1903 which was totally designed to use hemp derived
30 Open Journal of Renewable and Sustainable Energy (2014) 29-34
biofuel as fuel [10].
Fig. 1. Evolution of world biofuel production in million tons [11]
Because of the features such as productivity, obtain ability,
low greenhouse gas content, biodegradability and
renewability makes biofuel more advantageous over other
non-renewable fossil fuel and production of these sustainable
biofuel is rapidly increasing all over the world every year [8].
As long as fossil oil prices remained close to US $20 per
barrel (bbl), biofuel production stagnated around 10 Mtoe.
When fossil oil prices started to soar as from 2000, biofuel
production followed the same pattern. It is however
noteworthy that the 2009 decline in fossil oil prices had no
effect on the upward trend of biofuel production (Figure 1)
[11]. In 2007, around 90% of global biofuel production was
from US, Brazil and Europe [12].
Fig. 2. World biofuel production in 2007 [12]
3. Advancement in Biofuel Production
3.1. Primary biofuel
Fuelwood such as woodchips, pellets, animal waste and crop
residues have been used in an unprocessed form by man
primarily for cooking and heating purposes ever since human
discovered fire [5]. Fuelwoods, generally unprocessed
biomass of wood are commonly used for producing fire
specially for cooking and the most common form of fuelwood
is charcoal that mainly comprises of carbon and produces
more heat and energy [13]. Because of an ever-expanding
world population, requiring more food, more resources, more
production and more infrastructures, there was huge increase
in the growth of oil demand from 1996 to 2012 as shown in
Figure. 3.
Fig. 3. World oil demand.
(Source available:
3.2. First generation biofuel
Ethanol is the one of the most renowned first generation
biofuel which is prepared from sugar cane or sugar beets or
maize by fermentation process. Different alcohol can be made
by using different fermentation organism such as butanol.
Overall production of bioethanol in 2006 was about 51 billion
litres with Brazil and the United States both of which
contributes around 18 billion litres, or 35 per cent of the total.
China and India contributed 11 per cent to global ethanol
production in 2006. Figure 4 clearly shows increased in world
bioethanol production from about 9 Mtoe (in 1990) to 40
Mtoe (in 2009). There is also steady increase in the world
share for the production of various biofuel as shown in Figure
Fig. 4. World ethanol and biodiesel production, 1975-2010.
(Source available:
Open Journal of Renewable and Sustainable Energy (2014) 29-34 31
Fig. 5. Shares of world production of cereals, vegetable oils
and sugar plant used for biofuel production.(Source available:
The major reasons behind the rapid increase in the
production of 1st generation biofuel in OECD countries are
national energy security, support rural development and
agricultural industries and reduction of GHG emissions.
Though first generation biofuel shows net benefit in terms of
above reasons, it also have few disadvantages which includes
higher production cost, competing with food crops causing
increase in food price, causing water scarcity in some region
and limited reduction in GHG emission [14]. Bioalcohol and
other first generation biofuels are generally made from
biofeedstock which can also be used for the production for
human food [15]. Fast increase in demand for and production
of biofuels, mainly bioethanol from maize and sugarcane, has
had several effects on grain supply-and-demand systems
because of which the price of rice and wheat and other crops
have increased (Figure. 6).
Fig. 6. Simulated Real Grain Prices, 2000-2007 (US$/metric ton)
Note: Grain price is the production-weighted average of rice, wheat, maize,
and other coarse grains. (Source: IFPRI IMPACT).
In near future, utilization of first generation biofuel is
expected to cause many challenges due to which
biotechnologists are forced to look for alternative or
advancement in biofuel and hence with the help of advance
biotechnology, second generation biofuel came into existence
[16]. Bioethanol, biodiesel, biogas, syngas and solid biofuel
are the examples of first generation biofuel.
3.3. Second generation biofuel
World production of second generation biofuel has been
increased rapidly in last few years because of its additional
sustainable features over first generation biofuel which is
primarily made from food crops but commercially these
biofuels are not yet produced. According to a survey
conducted by IEA, speedy increase in second generation
biofuel demand has been noticed for stabilizing concentration
of CO2 in the atmosphere at 450 parts per million(ppm) [17].
Second generation biofuels are generally produced from
lignocellulosic biofeedstocks which seems to have more
potential to reduce GHG emissions and supply for these
feedstocks are more compared to first generation biofuel [15].
Lignocellulosic biofeedstock enables the use of non-food
crops and less expensive biomass which completely replaces
the direct use of food crops for biofuel production which has a
strong adverse effect on agriculture worldwide [18].
Second-generation biofuels can be further classified in terms
of the process used to convert the biomass to fuel:
biochemical or thermochemical.
3.3.1. Second-generation biochemical biofuel
Second-generation biochemically-produced alcohol fuels are
often referred to as “cellulosic ethanol” and “cellulosic
biobutanol”. Figure. 7 shows the basic steps for producing
bioethanol which includes pre-treatment, saccharification,
fermentation, and distillation. Pretreatment is designed to help
separate cellulose, hemicellulose and lignin so that the
complex carbohydrate molecules constituting the cellulose
and hemicellulose can be broken down by enzyme-catalyzed
hydrolysis (water addition) into their constituent simple
sugars[19].The sugar molecules are easily fermented to
ethanol using well-known micro-organisms, and some
micro-organisms for fermentation to butanol are also known.
3.3.2. Second-generation thermochemical biofuels.
In this method, conversion of biomass into biofuel involves
high temperature and pressure than biochemical process.
Conversion of biomass begins with gasification or pyrolysis
where the biomass is heated at high temperature converting
biomass into a mixture of gases followed by the removal of
impurities such as carbon dioxide which are present in the gas
mixture. Carbon monoxide (CO), hydrogen(H2) and small
quantity of methane(CH4) are major constituents of clean gas
commonly known as syngas after the removal of CO2. With
the help of catalyst, the CO and H2 reacts with each other to
give liquid biofuel as shown below in Figure 8 [1].
32 Open Journal of Renewable and Sustainable Energy (2014) 29-34
Fig. 7. Simplified depiction of process steps for production of
second generation fuel ethanol [1]
Fig. 8. Simplified depiction of process steps for
thermochemical biofuels production [1].
3.4. Third generation biofuels
In response to the problems of second generation biofuel, new
approach came up with the solution of utilizing algae biomass
with the help of microbial enzymes to achieve better quality
and more efficient sustainable biofuel [20].The elevated cost
of oil, the trend to continue growing or to remain at soaring
levels and the exhaustion of reserves has affected global
energy security. The third-generation biofuels are emerging as
a promising alternative to using microalgae biomass avoid
making use of raw materials that come from food sources [21].
Different bioconversion processes such as biochemical,
thermochemical, chemical and direct combustion can be used
to obtain various types of biofuel as shown in Figure 9. The
demand for liquid fuels in transport is increasing at an
alarming rate. Currently, fatty acid methyl esters (FAME) are
considered to be used as liquid biofuels for diesel engines.
They are typically prepared from vegetable oils or animal fats.
Since these materials are mainly meant for consumption,
other renewable sources of natural triacylglycerols (TAG) are
sought. One of the most prominent alternatives is microalgae
[22]. Most of the microalgae species are photoautotrophic,
that is, they convert solar energy into chemical forms through
photosynthesis. Their photosynthetic mechanism is
comparable to land based plants, but due to a simple cellular
structure, and their underwater habitat, where they have
efficient access to water, CO2 and other nutrients, they are
generally more efficient in converting solar energy into
biomass [23]. Microalgae have a very good prospective as
biodiesel precursors since many of them are very rich in oils,
at times with oil contents over 80% of their dry weight, even
though all species are not suitable as biodiesel production oils
[24]. There are many advantages of using microalgae as a
source of biofuel production. They can double their biomass
in less than 24 hours. Additionally they can be grown in
wastewater, or any non-potable water. The synthesis of
microalgae biodiesel could be integrated with the CO2
removal from power generation facilities for waste water
treatment from which microalgae would remove NH4
+, NO3
and PO4
3-[25]. However, there are certain limitations in using
microalgae for synthesis of biofuel. Microalgae
biomass-based biofuel have several problems which include
the optimization of high density and large surface units of
production. The location of the microalgae production unit
may also pose a difficulty [26].
Fig. 9. Conversion process for biofuel production from algal
biomass [5]
Another alternative which can be considered as third
generation biofuel is cellulose biomass. Discarded cellulosic
biomass obtained from forestry, agriculture, and municipal
sources are prospective raw materials for the synthesis of
biofuel. An efficient way of producing it is consolidated
bioprocessing (CBP).In this technique, cellulose production,
substrate hydrolysis, and fermentation are accomplished in a
single process step by microorganisms that express
cellulolytic (and hemicellulolytic) enzymes [27]. Apart from
microalgae, there are few other sources to produce biofuel
from oily biomass. Multiple prokaryotes and eukaryotes can
accumulate high amounts of lipids. But, as is the case with
microalgae, not all species are suitable for biodiesel
production due to the differences in the kind of storage lipids.
Thus, as stated by [28] many prokaryotes produce polymeric
compounds such as poly (3-hydroxybutyrate) (PHB) or other
Open Journal of Renewable and Sustainable Energy (2014) 29-34 33
polyhydroxyalkanoates (PHAs), whereas only a few genera
show accumulation of certain triacylglycerols (TAGs) and
wax esters (WEs) in the form of intracellular lipid bodies.
Conversely, storage TAGs are frequently found in eukaryotes,
while PHAs are absent, and WE accumulation has only been
reported in jojoba. All these lipids are carbon and energy
storage compounds that guarantee the metabolism for
viability during starvation stage. Analogous to the formation
of PHAs, TAGs and WE, synthesis is promoted by cellular
stress and during imbalanced growth; for instance, by
nitrogen insufficiency along with the abundance of a carbon
source [29].
4. Application of Biotechnology in
Biofuel Production
Biotechnology uses eye-catching way of producing biofuel
which increases the yield without much increase in the energy
needed for production. In the past few decades, significant
improvement has been made with the help of molecular
biology so as to improve the microbial activity and enzymes
[30]. The use of Genetically Modified Organisms (GMOs) is
found to be most efficient and quick method to improve
biofuel conversion, particularly in case of lignocellulosic
biomass [31]. With the help of biotechnology, structure of cell
wall and composition of lignocellulosic in plant cell can be
modified to enhance ethanol yield per acre [32].
Biotechnology can influence yield density by varying plant
physiology, their architecture, along with their photosynthetic
efficiency and it has also shown its ability to lessen agronomic
inputs for instance herbicide and pesticides. Advancement is
rapidly being made on characters which enable crops to take
up and consume nutrients more resourcefully, thus equipping
them to be grown with less amount of fertilizer. Producing
biomass crops on supposed “marginal” acres, such as land
that is highly dry, or with deprived soil characteristics, can
raise the scale of biofuel production without any influence on
food production acres. Biotechnology is focusing on the
development of drought, cold, salt and heat plants as well as
plants that can survive on a wide range of soil conditions. For
a biomass feedstock plant, a higher level of cellulose and
hemi-cellulose content would give better fermentation yield
and hence gallons of ethanol per ton of biomass. This results
in added net energy per acre and more revenue. Research has
already been carried out successfully for the cloning of genes
that code for cellulases and polygalacturonase enzymes to
develop low-cost effective biorefinery strategy to achieve
maximum biomass conversion and improved gas
chromatography-mass spectrophotometry method that has
been developed by researchers at TAMUK in understanding
the catalytic action of the expressed enzymes in the
bioconversion process [33]. Difficulties faced by the biofuel
manufacturers in processes such as microbial digestion and
fermentation can effectively reduce by enhanced
biotechnological processes [6].
5. Conclusions
According to Current state-of-the-art knowledge, Green
House Gas can be abridged within the next 30-40 years and
the demand for low carbon dioxide emission fuel in all forms
of automobile is enormous. Because of fast growing price of
crude oil with several adverse effects on environment, the
demand for the biofuel production has increased. Liquid
biofuel such as bioethanol, biodiesel and gaseous biofuel such
as biomethane, biohydrogen have developed as an effective
alternative to the fossil fuel resource. To reduce the
dependency on fossil fuel, biofuel was found to be most
efficient alternative among various existing source of energy.
Biofuel can replace the effective use of fossil fuel which is
known reason for the greenhouse effect. Researches have
shown that first generation biofuel that is crop biofuel has a
durable influence on agriculture world-wide. Second
generation biofuels are generally made from non-crop
biomass by two different fundamental approaches
(biochemical and thermochemical second generation biofuel).
Cellulose because of its easy availability, price and ability to
be proficiently degraded by cellulolytic bacteria, it has
become an eye-catching biofeedstock for the production of
second generation biofuel. A wide range of agricultural and
industrial residues, from lignocellulosic forestry and domestic
waste can be used as precursors of biofuels with the help of
microbial enzymes. Biofuels production plant design,
heterogeneous catalysts and enzyme immobilization
techniques, protein engineering of lipases, alcohol
dehydrogenases or hydrolases to increase their activity and
reusability, genetic engineering of microbes to facilitate both
the pretreatment of precursors, and the synthesis and
purification of the biofuels. Biotechnology plays a crucial role
in biofuel production. It helps in decreasing agronomic inputs,
in optimizing process characteristics and in engineering the
plants to produce high yield and hence high energy. With
progresses in the field of biotechnology, improvements in
synthesis of biofuels can be expected.
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Global environmental protection is of immediate concern that can only be achieved by avoiding the use of fossil fuels and tailpipe emissions. In addition, investment on waste disposal is not economical; however, recycling of the same waste for renewable energy production is favorable in the economic and social development of the society in an eco-friendly manner. Utilization of biodegradable wastes, such as agricultural and forestry residues, and non-edible plant matter for value-added bioproducts is a promising, inexpensive, and abundant clean substitute of fossil fuels. There has been extensive research on the conversion of lignocellulosic materials to biofuels over the past few decades. The recalcitrance of lignin in crop residues, however, impedes polysaccharide accessibility and its transformation into commercially significant choice of value-added products. Traditional physiochemical and thermal methods are hampered by high-cost processing steps in pretreatment and saccharification, and also require additional maintenance and care due to the generation of eco-unfriendly compounds. Recent advances in novel consolidated bioprocessing through mixed consortium are promising choices to reduce both the number of operational steps and the production of inhibitors with higher conversion efficiency. Although biofilm-based technologies have been successfully applied for wastewater and solid waste treatment, their potential application in biofuel production has been unexplored. The present review focuses on the state-of-the-art development of biofuel production by mixed consortium and also recent strategies to improve biofuel yield including the metabolic pathway construction.
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0Lignocellulosic biomass has potential for bioethanol, a renewable fuel. A limitation is that bioconversion of the complex lignocellulosic material to simple sugars and then to bioethanol is a challenging process. Recent work has focused on the genetic engineering of a biocatalyst that may play a critical role in biofuel production. Escherichia coli have been considered a convenient host for biocatalysts in biofuel production for its fermentation of glucose into a wide range of short-chain alcohols and production of highly deoxygenated hydrocarbon. The bacterium Pectobacterium carotovorum subsp. carotovorum (P. carotovorum) is notorious for its maceration of the plant cell wall causing soft rot. The ability to destroy plants is due to the expression and secretion of a wide range of hydrolytic enzymes that include cellulases and polygalacturonases. P. carotovorum ATCC™ no. 15359 was used as a source of DNA for the amplification of celB, celC and peh. These genes encode 2 cellulases and a polygalacturonase, respectively. Primers were designed based on published gene sequences and used to amplify the open reading frames from the genomic DNA of P. carotovorum. The individual PCR products were cloned into the pTAC-MAT-2 expression vector and transformed into Escherichia coli. The deduced amino acid sequences of the cloned genes have been analyzed for their catalytically active domains. Estimation of the molecular weights of the expressed proteins was performed using SDS-PAGE analysis and celB, celC and peh products were approximately 29.5 kDa, 40 kDa 41.5 kDa, respectively. Qualitative determination of the cellulase and polygalacturonase activities of the cloned genes was carried out using agar diffusion assays.
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As a promising alternative energy source, biofuel imparts a remarkable role for the sustainability and security in energy sector. Strategies, including policy recommendations have been set to put forward the development and implementation of biofuel by different countries. Recent exploitation of Asian biofuels policy is one step towards destination. These types of activity behind the biofuels would be the catalyst for the productiveness of policy set by individual territory like Malaysia, Thailand, Vietnam, etc. This is the high time to standardize, policy recommendation and implementation of biofuels taking into consideration on the feedstock, geographical location, and availability. Pertinent comparison with well-established ASTM and European standards are highly recommended. Sector wise (viz. transportation, industrial) bio fuel policy is now crucial as well. Factors, which would be taking into account, prior to recommend a policy includes feed-stocks available, biofuel infrastructure of the country, compatibility with present automotive materials and performance and emission behaviour. This study sought to explore the investigation of several policies with regards to biofuel and advocates some key factors which could be helpful for diminution of biofuels inferiorities.
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Depletion of petroleum derived fuel and environmental concern has promoted to look over the biofuel as an alternative fuel sources. But a complete substitution of petroleum derived fuels by biofuel is impossible from the production capacity and engine compatibility point of view. Yet, marginal replacement of diesel by biofuel can prolong the depletion of petroleum resources and abate the radical climate change caused by automotive pollutants. Energy security and climate change are the two major driving forces for worldwide biofuel development which also have the potential to stimulate the agro-industry. Nonetheless, there are other problems associated with biofuel usage such as automotive engine compatibility in long term operation and also food security issues that stem from biofuel production from food-grade oil-seeds. Moreover, severe corrosion, carbon deposition and wearing of engine parts of the fuel supply system components are also caused by biodiesel. Discussing all this advantages and disadvantages of biodiesel, it is comprehended that, a dedicated biodiesel engine is the ultimate solution for commercializing biodiesel. Brazil successfully boosted their bioethanol marketing by introducing flexible-fuel vehicles (FFV), which have a dedicated engine for both ethanol and gasoline. A similar approach can bring a breakthrough in biofuel commercialization and production. So dedicated biofuel engine is a challenge for mass commercialization and utilization of biofuel. In this lecture worldwide biofuel scenario is assessed by biofuel policies and standards. Different biofuel processing techniques are also summarized. Some guidelines on dedicated biofuel engine are prescribed. Minor modifications on the engine may not cost much; but continuous research and development is still needed.
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Biofuel production from renewable sources is widely considered to be one of the most sustainable alternatives to petroleum sourced fuels and a viable means for environmental and economic sustainability. Microalgae are currently being promoted as an ideal third generation biofuel feedstock because of their rapid growth rate, CO 2 fixation ability and high production capacity of lipids; they also do not compete with food or feed crops, and can be produced on non-arable land. Microalgae have broad bioenergy potential as they can be used to produce liquid transportation and heating fuels, such as biodiesel and bioethanol. In this review we present an overview about microalgae use for biodiesel and bioethanol production, including their cultivation, harvesting, and processing. The most used microalgal species for these purposes as well as the main microalgal cultivation systems (photobioreactors and open ponds) will also be discussed.
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This report reviews the current status of second generation biofuels. First generation biofuels continue to be substantially subsidized, and this has contributed to the increasing use of such fuel. However, recent studies claim that the future of biofuels lies in second generation biofuels, in particular biochemical ethanol made from cellulose. Thus, in this report we ask the following three questions: How far is second generation biofuels from being a competitive GHG abatement technology? Is it likely that first generation biofuels will bridge the development of second generation biofuels? Should trade policy be used to protect domestic infant second generation biofuels industry from import of low cost first generation biofuels from developing countries? Summary Current state-of-the-art knowledge concludes that green house gas (GHG) emissions must be controlled and reduced within the next 30-40 years. The transport sector contributes almost a fifth of the current global emissions, and its share is likely to increase in the future. Hence, there is a huge demand for low emission solutions for all modes of transport.
The chemical structures of the primary cell walls of the grasses and their progenitors differ from those of all other flowering plant species. They vary in the complex glycans that interlace and cross-link the cellulose microfibrils to form a strong framework, in the nature of the gel matrix surrounding this framework, and in the types of aromatic substances and structural proteins that covalently cross-link the primary and secondary walls and lock cells into shape. This review focuses on the chemistry of the unique polysaccharides, aromatic substances, and proteins of the grasses and how these structural elements are synthesized and assembled into dynamic and functional cell walls. Despite wide differences in wall composition, the developmental physiology of grasses is similar to that of all flowering plants. Grass cells respond similarly to environmental cues and growth regulators, exhibit the same alterations in physical properties of the wall to allow cell growth, and possess similar patterns of wall biogenesis during the development of specific cell and tissue types. Possible unifying mechanisms of growth are suggested to explain how grasses perform the same wall functions as other plants but with different constituents and architecture.
This article calls for engaging the public and private sectors of developing and industrialized coun-tries in a global clean cooking fuel initiative (GCCFI) to bring about a worldwide shift to clean fluid fuels for cooking and heating in 10-15 years' time --with an emphasis on providing clean fuel to the poorest households. This initiative is crucial to implementation of the Millennium De-velopment Goals and the Plan of Implementation of the World Summit on Sustainable Development. The article builds on (1) analyses in this special issue of Energy for Sustainable Development of challenges to sustainable development posed by use of solid fuels for cooking and water heating (and for space heating in temperate climates) and opportunities for addressing them by bringing about a shift to clean fluid fuels, and (2) an extensive and compelling literature on the problems posed by this reliance on solid fuels.
In the search for renewable energy, third generation biofuels have become an innovative alternative that offers a wide variety of exceptional benefits. A major advantage of third generation fuels is that the raw materials used as a source does not compete with food sources also have a high percentage of yields per unit area. Nowadays the production of biodiesel from microalgae is an option that has attracted strong interest of the scientific community and should be evaluated to determine the technical, technological, economic and environmental sustainability of the process. Exergy analysis is a useful tool for measure the quantity and quality of the energy sources and analyze the process sustainability previously mentioned, besides, exergy analysis has been widely used in the design, simulation and the global evaluation and improvement of the processes. The relationship between exergy, energy and environment can recognize that the exergy is closely related to sustainable development. This methodology requires analyzing material and energy flows of each stage of the production process. In this study exergy analysis was applied on two scenarios taking a production capacity of 100,000 t/y of biodiesel from microalgae biomass. Chlorella vulgaris (Chlorella sp) was used as reference algae. This algae has been widely studied and their characteristics are well known, also one of the algae that have a higher percentage of lipids. In this work a basic process for biodiesel production is showed, comprising the following steps: transesterification, separation and washing the biodiesel. Thermodynamic variables as entropy, enthalpy, Gibbs free energy were determined for all process steps and exergetic losses using the software ASPEN-PLUS ® . Finally the exergetic efficiency was calculated for the overall process. The results confirm the potential of third generation biofuels microalgae as an energy source.
Petroleum dependency is a challenge that can potentially be partly offset by agricultural production of biofuels, while decreasing net, non-renewable carbon dioxide output. Plants have not been domesticated for modern biofuel production, and the quickest, most efficient, and often, the only way to convert plants to biofuel feedstocks is biotechnologically. First generation biofuel feedstock sources: sugarcane and cereal grains to produce bioethanol and biobutanol and oilseeds to produce biodiesel compete directly with needs for world food security. The heavy use of oilseed rape releases quantities of methyl bromide to the atmosphere, which can be prevented by gene suppression. Second generation bioethanolic/biobutanolic biofuels will come from cultivated lignocellulosic crops or straw wastes. These presently require heat and acid to remove lignin, which could be partially replaced by transgenically reducing or modifying lignin content and upregulating cellulose biosynthesis. Non-precipitable silicon emissions from burning could be reduced by transgenically modulating silicon content. The shrubby Jatropha and castor beans should have highly toxic protein components transgenically removed from their meal, cancer potentiating diterpenes removed from the oils, and allergens from the pollen, before extensive cultivation. Algae and cyanobacteria for third generation biodiesel need transgenic manipulation to deal with “weeds”, light penetration, photoinhibition, carbon assimilation, etc. The possibilities of producing fourth generation biohydrogen and bioelectricity using photosynthetic mechanisms are being explored. There seem to be no health or environmental impact study requirements when the undomesticated biofuel crops are grown, yet there are illogically stringent requirements should they transgenically be rendered less toxic and more efficient as biofuel crops.
Bio-fuels are important because they replace petroleum fuels. A number of environmental and economic benefits are claimed for bio-fuels. Bio-ethanol is by far the most widely used bio-fuel for transportation worldwide. Production of bio-ethanol from biomass is one way to reduce both consumption of crude oil and environmental pollution. Using bio-ethanol blended gasoline fuel for automobiles can significantly reduce petroleum use and exhaust greenhouse gas emission. Bio-ethanol can be produced from different kinds of raw materials. These raw materials are classified into three categories of agricultural raw materials: simple sugars, starch and lignocellulose. Bio-ethanol from sugar cane, produced under the proper conditions, is essentially a clean fuel and has several clear advantages over petroleum-derived gasoline in reducing greenhouse gas emissions and improving air quality in metropolitan areas. Conversion technologies for producing bio-ethanol from cellulosic biomass resources such as forest materials, agricultural residues and urban wastes are under development and have not yet been demonstrated commercially.