Alternative Green Biofuel from Microalgae: A Promising Renewable Resource 249
consequent increasing price of oil (Yanan et al. 2010) has motivated researchers to find alternate sources
of energy from renewable feedstocks (Jasvinder and Gu 2010). Therefore, biofuels from renewable
feedstocks can thus be an alternative to reduce our dependency on fossil fuel and help safeguard the
environment and economic sustainability (Mussgnug et al. 2010). For example, energy produced from
combustible renewables and waste biomass has the highest potential than that of other renewable sources,
and accounted for 10.0% of the total primary energy supply, compared to hydro energy (2.2%) and
other energy sources including geothermal, solar, wind, and heat (0.7%) (IEA 2010). Hence, renewable
combustible energy sources such as liquid biofuels will likely play a crucial role as an alternative to
fossil fuels in the near future, contributing to the effort of diversifying global energy sources rather than
electricity or hydrogen (Zhao 2017). In this regard, it is crucial to explore renewable and cost-effective
sources of energy in the near future. Phototrophic biomass is one of the main renewable energy resources
available. In contrast to other renewables, biomass represents the only source of liquid, solid, and gaseous
fuels that can be treated in a number of different ways to provide such biofuels. Biofuels are also a
suitable option due to their biodegradability, renewability, and the ability of producing exhaust gases
of acceptable quality (Bhatti et al. 2008). Most transportation (bio) fuels are liquids, as vehicles usually
require high energy densities fuels (Demirbas 2008) that are easy to transport and handle.
Environmental advantages of biofuels
Biodiesel properties
Biofuels such as biodiesel, bioethanol, biomethane, and biohydrogen, but also propanol and butanol,
among others are being obtained from renewable resources like sugar cane, corn, vegetable oils,
lignocellulosic waste, and microalgal biomass. Biodiesel is typically defined as a mixture of fatty acid
alkyl esters. “Bio” stands for being produced from a biological source in contrast to the traditional
petroleum-based diesel fuel. “Diesel” refers to liquid fuel having a cetane number suitable for ignition
and its use in diesel engines. Technically, biodiesel must follow international specifications for its use in
diesel engines as diesel fuel. Biodiesel refers to the pure fuel designated as B100 before blending with
diesel fuel. Biodiesel blends are represented as “BXX” in which “XX” represents the percentage of
biodiesel contained in the blend. For example, B20 is 20% biodiesel and 80% petroleum diesel (Knothe
et al. 1996).
In view of environmental considerations, biodiesel is referred to as ‘carbon neutral’ because all
the carbon dioxide (CO 2 ) released during consumption has been sequestered from the atmosphere for
the growth of terrestrial plants, microalgae, and others (Barnwal and Sharma 2005). Biodiesel forms
thus a closed carbon cycle, as CO 2 released in the atmosphere upon biodiesel combustion is recycled by
growing photosynthetic organisms, which are later processed into biofuel (Kumar et al. 2010).
The main advantage of biodiesel is that it is a renewable, non-toxic, and biodegradable liquid biofuel
(Gerpen 2005). This biofuel also combusts in a clean way, possessing a heating value of 39–41 MJ/Kg,
which is comparable with that of petrodiesel (43 MJ/Kg). Other parameters like the cetane number, flash
point, and kinematic viscosity are mostly similar to those of petrodiesel (Knothe and Steidley 2005;
Demirbas 2009) and appear to reduce emissions of air pollutants and carcinogens (Shakeel et al. 2009).
One of the most important advantage of biodiesel compared to many other alternative transportation
fuels is that it can be used in existing diesel engines with little or no modification (Lam and Lee 2012).
Using biodiesel instead of petrodiesel will significantly reduce acid rain formation and will most probably
mitigate global warming, by lowering net carbon monoxide, sulphur (SOx) and nitrogen (NOx) oxides,
and hydrocarbon emissions, displaying also a very low risk of explosion from vapours (Antolin et al. 2002;
Abreu et al. 2005; Barnwal and Sharma 2005). The lack of toxic and carcinogenic aromatic compounds
in biodiesel can also lead to a reduced impact on human health and the environment by the resulting
combustion gases. When the fuel is switched from low-sulphur petroleum diesel to biodiesel, there is
a drastic drop in the carbon monoxide emissions as most organic compounds are converted into carbon
dioxide instead. Biodiesel virtually eliminates the notorious black soot emissions associated with diesel
engines and the total particulate matter emissions are also significantly lower. Usage of biodiesel needs,
consequent increasing price of oil (Yanan et al. 2010) has motivated researchers to find alternate sources
of energy from renewable feedstocks (Jasvinder and Gu 2010). Therefore, biofuels from renewable
feedstocks can thus be an alternative to reduce our dependency on fossil fuel and help safeguard the
environment and economic sustainability (Mussgnug et al. 2010). For example, energy produced from
combustible renewables and waste biomass has the highest potential than that of other renewable sources,
and accounted for 10.0% of the total primary energy supply, compared to hydro energy (2.2%) and
other energy sources including geothermal, solar, wind, and heat (0.7%) (IEA 2010). Hence, renewable
combustible energy sources such as liquid biofuels will likely play a crucial role as an alternative to
fossil fuels in the near future, contributing to the effort of diversifying global energy sources rather than
electricity or hydrogen (Zhao 2017). In this regard, it is crucial to explore renewable and cost-effective
sources of energy in the near future. Phototrophic biomass is one of the main renewable energy resources
available. In contrast to other renewables, biomass represents the only source of liquid, solid, and gaseous
fuels that can be treated in a number of different ways to provide such biofuels. Biofuels are also a
suitable option due to their biodegradability, renewability, and the ability of producing exhaust gases
of acceptable quality (Bhatti et al. 2008). Most transportation (bio) fuels are liquids, as vehicles usually
require high energy densities fuels (Demirbas 2008) that are easy to transport and handle.
Environmental advantages of biofuels
Biodiesel properties
Biofuels such as biodiesel, bioethanol, biomethane, and biohydrogen, but also propanol and butanol,
among others are being obtained from renewable resources like sugar cane, corn, vegetable oils,
lignocellulosic waste, and microalgal biomass. Biodiesel is typically defined as a mixture of fatty acid
alkyl esters. “Bio” stands for being produced from a biological source in contrast to the traditional
petroleum-based diesel fuel. “Diesel” refers to liquid fuel having a cetane number suitable for ignition
and its use in diesel engines. Technically, biodiesel must follow international specifications for its use in
diesel engines as diesel fuel. Biodiesel refers to the pure fuel designated as B100 before blending with
diesel fuel. Biodiesel blends are represented as “BXX” in which “XX” represents the percentage of
biodiesel contained in the blend. For example, B20 is 20% biodiesel and 80% petroleum diesel (Knothe
et al. 1996).
In view of environmental considerations, biodiesel is referred to as ‘carbon neutral’ because all
the carbon dioxide (CO 2 ) released during consumption has been sequestered from the atmosphere for
the growth of terrestrial plants, microalgae, and others (Barnwal and Sharma 2005). Biodiesel forms
thus a closed carbon cycle, as CO 2 released in the atmosphere upon biodiesel combustion is recycled by
growing photosynthetic organisms, which are later processed into biofuel (Kumar et al. 2010).
The main advantage of biodiesel is that it is a renewable, non-toxic, and biodegradable liquid biofuel
(Gerpen 2005). This biofuel also combusts in a clean way, possessing a heating value of 39–41 MJ/Kg,
which is comparable with that of petrodiesel (43 MJ/Kg). Other parameters like the cetane number, flash
point, and kinematic viscosity are mostly similar to those of petrodiesel (Knothe and Steidley 2005;
Demirbas 2009) and appear to reduce emissions of air pollutants and carcinogens (Shakeel et al. 2009).
One of the most important advantage of biodiesel compared to many other alternative transportation
fuels is that it can be used in existing diesel engines with little or no modification (Lam and Lee 2012).
Using biodiesel instead of petrodiesel will significantly reduce acid rain formation and will most probably
mitigate global warming, by lowering net carbon monoxide, sulphur (SOx) and nitrogen (NOx) oxides,
and hydrocarbon emissions, displaying also a very low risk of explosion from vapours (Antolin et al. 2002;
Abreu et al. 2005; Barnwal and Sharma 2005). The lack of toxic and carcinogenic aromatic compounds
in biodiesel can also lead to a reduced impact on human health and the environment by the resulting
combustion gases. When the fuel is switched from low-sulphur petroleum diesel to biodiesel, there is
a drastic drop in the carbon monoxide emissions as most organic compounds are converted into carbon
dioxide instead. Biodiesel virtually eliminates the notorious black soot emissions associated with diesel
engines and the total particulate matter emissions are also significantly lower. Usage of biodiesel needs,