quality of the lipid is, the more competitive the final product will be. Therefore,
optimization of the steps involved is critical and has been the focus of many patent
applications.
3.3.1 Harvesting and Dewatering of Microalgae Cells
The harvesting process involves two sets of operations, i.e., bulk harvesting and
concentrating the resultant slurry (Brennan and Owende 2010). Recently published
patents such as US6000551 and US7022509B2 are focused on a promising and
sustainable way as bulk harvesting alternative, i.e., gas flotation or adsorptive
bubble separation process. This method not only removes the need for flocculants
application, but it is also capable of lysing algal cells concurrent to gathering. In
addition, inventors have also developed a number of hydrophobic chemical treatments for harvesting algal cells from broth. More specifically, by adding a
hydrophobic liquid/flocculent with lower salinity, the microalgae suspension forms
a top phase comprising the hydrophobic liquid and at least a portion of the
microalgal cells and a bottom phase comprising the aqueous solution (see the
patents US20110165662A1 and US4958460A).
Based on the microalgae size or density, several methods for dewatering
of concentrated algal suspension are available. Conventional processes like filtration, gravity, mesh lining centrifugal sedimentation, chemical coagulation and
flocculation, use of adsorbents, magnetic separators as well as ultrasonic aggregation have been explained in the patents US4554390A, US20090317886A1,
US20090134091A1, US8399239B2, US8399239B2, US8772004B2, and
EP2747890A1.
3.3.2 Lipid Extraction
Once an algal biomass is dewatered and dried, only then high-value products could
be extracted. Various methods for algal lipid extraction have been developed
among which oil press machine, organic solvent extraction, supercritical fluid,
subcritical water, and electrochemical extraction methods have seen significant
technological advances over the course of recent years. In general, to achieve a
desired extraction productivity, some important consideration should be taken, e.g.,
optimization of pretreatment steps, type and amounts of selected solvents, etc.,
which have been the aim of several patent applications (see patents
US20150252285A1, US20120083617, US20120238732A1, and US20140243540).
It should be noted that the fuel properties of biodiesel are significantly influenced by
the extraction method used.
Overall, extracting algal oil from the microalgae cells could be achieved through
biological or non-biological cell wall rupturing methods. More specifically, the lysis
can be performed with vapor (see the patent US2009081742A1), solvents (such as
methylene chloride as elaborated upon in the patent US4554390A), mechanical
14 Recent Patents on Biofuels from Microalgae
303
optimization of the steps involved is critical and has been the focus of many patent
applications.
3.3.1 Harvesting and Dewatering of Microalgae Cells
The harvesting process involves two sets of operations, i.e., bulk harvesting and
concentrating the resultant slurry (Brennan and Owende 2010). Recently published
patents such as US6000551 and US7022509B2 are focused on a promising and
sustainable way as bulk harvesting alternative, i.e., gas flotation or adsorptive
bubble separation process. This method not only removes the need for flocculants
application, but it is also capable of lysing algal cells concurrent to gathering. In
addition, inventors have also developed a number of hydrophobic chemical treatments for harvesting algal cells from broth. More specifically, by adding a
hydrophobic liquid/flocculent with lower salinity, the microalgae suspension forms
a top phase comprising the hydrophobic liquid and at least a portion of the
microalgal cells and a bottom phase comprising the aqueous solution (see the
patents US20110165662A1 and US4958460A).
Based on the microalgae size or density, several methods for dewatering
of concentrated algal suspension are available. Conventional processes like filtration, gravity, mesh lining centrifugal sedimentation, chemical coagulation and
flocculation, use of adsorbents, magnetic separators as well as ultrasonic aggregation have been explained in the patents US4554390A, US20090317886A1,
US20090134091A1, US8399239B2, US8399239B2, US8772004B2, and
EP2747890A1.
3.3.2 Lipid Extraction
Once an algal biomass is dewatered and dried, only then high-value products could
be extracted. Various methods for algal lipid extraction have been developed
among which oil press machine, organic solvent extraction, supercritical fluid,
subcritical water, and electrochemical extraction methods have seen significant
technological advances over the course of recent years. In general, to achieve a
desired extraction productivity, some important consideration should be taken, e.g.,
optimization of pretreatment steps, type and amounts of selected solvents, etc.,
which have been the aim of several patent applications (see patents
US20150252285A1, US20120083617, US20120238732A1, and US20140243540).
It should be noted that the fuel properties of biodiesel are significantly influenced by
the extraction method used.
Overall, extracting algal oil from the microalgae cells could be achieved through
biological or non-biological cell wall rupturing methods. More specifically, the lysis
can be performed with vapor (see the patent US2009081742A1), solvents (such as
methylene chloride as elaborated upon in the patent US4554390A), mechanical
14 Recent Patents on Biofuels from Microalgae
303