colloidal dispersion. It is a mixture of oil with an ester, alcohol (butanol, hexanol,
and octanol), water, and surfactant. Some problems such as incomplete combustion,
nozzle failure, and carbon deposition have arisen with the use of micro-emulsified
biodiesel (Koh and Ghazi 2011).
1.4.5 Biochemical Fermentation/Anaerobic Digestion
Anaerobic digestion (AD) is the conversion of algal biomass into a biogas. Biomass
consists of methane (CH 4 ) and CO 2 , with traces of hydrogen sulfide (EU 1999). It
involves the breakdown of organic matter to produce a gas with an energy content of
about 20–40% of the lower heating value of the feedstock. This process is applicable
for wet algal biomass with high moisture content (80–90% moisture). It is not a
popular pathway for algal residue conversion. Microalgae with high proportion of
proteins (i.e., low C/N ratio) can affect the performance of the anaerobic digester and
also result in increased ammonium production. Co-digestion with a high C/N ratio
product (e.g., waste paper) can resolve this problem. High sodium ions can also
trigger toxic nature to some anaerobic microorganisms, and only feasible for saltadapted microorganisms to perform anaerobic digestion of marine algae (Brennan
and Owende 2010). Some macroalgae (Ulva lactuca, Gracilaria vermiculophylla,
Saccharina latissima) have been anaerobically digested to produce methane in a
range of 0.1–0.3 LCH4/g volatile solids (VS). It has reported that microalgae
(codigested with other feedstocks) such as Spirulina platensis, Scenedesmus sp.,
and Chlorella sp. yield methane in range of 0.2–0.3 L CH 4 /g VS, whereas other
microalgae like Tetraselmis sp., Chlorella vulgaris, Scenedesmus obliquus, and
Phaeodactylum tricornutum produced methane from 0.17 to 0.28 L CH 4 /g VS
when digested as sole feedstock (Marzano et al. 1982; Zamalloa et al. 2012).
Pretreatments (thermal, chemical, thermochemical, and biological) of algal biomass
have been also studied to improve biogas production (Table 1.2).
1.4.6 Thermochemical Conversion
Thermochemical conversion covers the consumption of energy to convert organic
components in biomass (a fuel source) to yield different chemical state (oil and
residue). The thermochemical conversion processes involve heating of biomass at
high temperatures. There are some basic approaches: such as direct combustion,
gasification, thermochemical liquefaction, and pyrolysis.
1.4.6.1 Combustion
Combustion is the burning of biomass in air. It converts the chemical energy stored
in the biomass into heat, mechanical power, or electricity using different process
equipment. Combustion produces hot gases at temperatures around 800–1000
C.
This is an older method of utilizing biomass for obtaining energy (Goyal et al. 2008;
Ryan 2009a, b).
1 Algal Biofuel: A Sustainable Approach for Fuel of Future Generation
13
and octanol), water, and surfactant. Some problems such as incomplete combustion,
nozzle failure, and carbon deposition have arisen with the use of micro-emulsified
biodiesel (Koh and Ghazi 2011).
1.4.5 Biochemical Fermentation/Anaerobic Digestion
Anaerobic digestion (AD) is the conversion of algal biomass into a biogas. Biomass
consists of methane (CH 4 ) and CO 2 , with traces of hydrogen sulfide (EU 1999). It
involves the breakdown of organic matter to produce a gas with an energy content of
about 20–40% of the lower heating value of the feedstock. This process is applicable
for wet algal biomass with high moisture content (80–90% moisture). It is not a
popular pathway for algal residue conversion. Microalgae with high proportion of
proteins (i.e., low C/N ratio) can affect the performance of the anaerobic digester and
also result in increased ammonium production. Co-digestion with a high C/N ratio
product (e.g., waste paper) can resolve this problem. High sodium ions can also
trigger toxic nature to some anaerobic microorganisms, and only feasible for saltadapted microorganisms to perform anaerobic digestion of marine algae (Brennan
and Owende 2010). Some macroalgae (Ulva lactuca, Gracilaria vermiculophylla,
Saccharina latissima) have been anaerobically digested to produce methane in a
range of 0.1–0.3 LCH4/g volatile solids (VS). It has reported that microalgae
(codigested with other feedstocks) such as Spirulina platensis, Scenedesmus sp.,
and Chlorella sp. yield methane in range of 0.2–0.3 L CH 4 /g VS, whereas other
microalgae like Tetraselmis sp., Chlorella vulgaris, Scenedesmus obliquus, and
Phaeodactylum tricornutum produced methane from 0.17 to 0.28 L CH 4 /g VS
when digested as sole feedstock (Marzano et al. 1982; Zamalloa et al. 2012).
Pretreatments (thermal, chemical, thermochemical, and biological) of algal biomass
have been also studied to improve biogas production (Table 1.2).
1.4.6 Thermochemical Conversion
Thermochemical conversion covers the consumption of energy to convert organic
components in biomass (a fuel source) to yield different chemical state (oil and
residue). The thermochemical conversion processes involve heating of biomass at
high temperatures. There are some basic approaches: such as direct combustion,
gasification, thermochemical liquefaction, and pyrolysis.
1.4.6.1 Combustion
Combustion is the burning of biomass in air. It converts the chemical energy stored
in the biomass into heat, mechanical power, or electricity using different process
equipment. Combustion produces hot gases at temperatures around 800–1000
C.
This is an older method of utilizing biomass for obtaining energy (Goyal et al. 2008;
Ryan 2009a, b).
1 Algal Biofuel: A Sustainable Approach for Fuel of Future Generation
13