approaches. The harvesting approach must be performed with at most care that it
should not damage (e.g., due to shear forces) or contaminate (e.g., due to application
of chemical flocculent) the biomass. The acceptable level of contamination depends
on the final use of the biomass, and therefore the selection of method of harvesting
may depend on the application of biomass. As microalgae cells (5–20 μm) are small
in size, the application of both filtration and gravity-based methods are tricky, and
the other key limitation is high harvesting cost of microalgae biomass [21, 46, 49,
54].
The efficiency of extraction and harvesting methods is based on physical characteristics of the microalgae strain (e.g., cell wall property and cell size) and the end
product’s application.
By properly designing the dewatering or harvesting method and via recycling of
nutrients and water, the processing costs can be reduced. The algal biomass
harvesting can be made easy by selective cultivation of colonial species [55]. The
water requirement can be decreased to a greatest extent (up to 90%) by proper
recycling of water after the harvest of biomass or use of sea or wastewater. The
choice of harvesting method varies from species to species, and also it is based on the
cost criteria of energy extraction process.
8 Post-Harvest Processing: Conversion of Microalgal
Biomass to Biofuels and Bioproducts
Once harvest is complete, the algal biomass obtained should be dried for further
processing and manufacture of bioproducts and biofuels. This can be done by
performing different techniques of drying such as sun drying, freeze drying, lyophilization, heat-/oven-based drying, and spray drying. Each approach however has its
own advantages and disadvantages. For instance, heat or oven drying consumes
more energy, whereas sun and drum drying are not effective and economical as
quoted by [56]. Other procedures, such as freezing and lyophilization, are seen as
efficient but expensive methods. The drying techniques are based on a number of
factors like species type, time, maintenance of culture, reuse of media, and suitability
for industrial scale [51, 57]. The present techniques used for drying and harvesting
are not efficient, and more innovations are the need of the hour.
After drying, cell disruption of microalgae to release cellular components and oil
bodies can be performed by various methods, which include ultrasonic-assisted
extraction, high press machine, chemical method, supercritical fluid extraction,
enzymatic method, microwave, autoclaving, bead beating, osmotic pressure method,
Soxhlet method, and homogenizer. Sometimes the extraction of lipids could not be
effective due to poor cell disruption and improper lipid extraction process. This can
be overcome by careful cell disruption selection and lipid extraction techniques.
Sometimes renowned lipid extraction techniques such as Folch et al. [58] and Bligh
and Dyer [59] using solvents such as chloroform, hexane, and dichloromethane
Algal Biomass for Biofuels and Bioproducts
151
should not damage (e.g., due to shear forces) or contaminate (e.g., due to application
of chemical flocculent) the biomass. The acceptable level of contamination depends
on the final use of the biomass, and therefore the selection of method of harvesting
may depend on the application of biomass. As microalgae cells (5–20 μm) are small
in size, the application of both filtration and gravity-based methods are tricky, and
the other key limitation is high harvesting cost of microalgae biomass [21, 46, 49,
54].
The efficiency of extraction and harvesting methods is based on physical characteristics of the microalgae strain (e.g., cell wall property and cell size) and the end
product’s application.
By properly designing the dewatering or harvesting method and via recycling of
nutrients and water, the processing costs can be reduced. The algal biomass
harvesting can be made easy by selective cultivation of colonial species [55]. The
water requirement can be decreased to a greatest extent (up to 90%) by proper
recycling of water after the harvest of biomass or use of sea or wastewater. The
choice of harvesting method varies from species to species, and also it is based on the
cost criteria of energy extraction process.
8 Post-Harvest Processing: Conversion of Microalgal
Biomass to Biofuels and Bioproducts
Once harvest is complete, the algal biomass obtained should be dried for further
processing and manufacture of bioproducts and biofuels. This can be done by
performing different techniques of drying such as sun drying, freeze drying, lyophilization, heat-/oven-based drying, and spray drying. Each approach however has its
own advantages and disadvantages. For instance, heat or oven drying consumes
more energy, whereas sun and drum drying are not effective and economical as
quoted by [56]. Other procedures, such as freezing and lyophilization, are seen as
efficient but expensive methods. The drying techniques are based on a number of
factors like species type, time, maintenance of culture, reuse of media, and suitability
for industrial scale [51, 57]. The present techniques used for drying and harvesting
are not efficient, and more innovations are the need of the hour.
After drying, cell disruption of microalgae to release cellular components and oil
bodies can be performed by various methods, which include ultrasonic-assisted
extraction, high press machine, chemical method, supercritical fluid extraction,
enzymatic method, microwave, autoclaving, bead beating, osmotic pressure method,
Soxhlet method, and homogenizer. Sometimes the extraction of lipids could not be
effective due to poor cell disruption and improper lipid extraction process. This can
be overcome by careful cell disruption selection and lipid extraction techniques.
Sometimes renowned lipid extraction techniques such as Folch et al. [58] and Bligh
and Dyer [59] using solvents such as chloroform, hexane, and dichloromethane
Algal Biomass for Biofuels and Bioproducts
151