Introduction - Biotechnological Applications of Microalgae - page 3

population increase) (Guillard and Sieracki, 2005). Microalgal enumeration methods
are described in detail in Chapter 4 of this volume.
The important factors affecting microalgal growth are light intensity, tempera-
ture, nutrients, CO 2 availability, pH, and salinity (Bhola et al., 2011; Rosenberg et al.,
2011). Other factors such as conductivity, oxidation/reduction potential (ORP), total
dissolved solids (TDS), and biological factors such as protozoa are also important.
These factors must be closely monitored to prevent failure of the cultivation system,
especially when growing microalgae on a large commercial scale.
There are essentially two commonly used methods for microalgal cultivation,
namely open raceway ponds and photobioreactors. The design, and the pros and cons,
of these cultivation systems are discussed in detail in Chapter 5. The open raceway
system is amenable to large-scale microalgal cultivation because it is simple and cost
effective to operate. Despite these attractive features, microalgal biomass harvesting
still remains a huge challenge. Harvesting microalgal biomass is technically difficult
because the biomass exists as a dilute aqueous suspension. Furthermore, microalgal
cells are very difficult to remove due to their miniscule size (<20 µm), similar in
density to water (Lavoie and De la Noue, 1986), and strong negative surface charge,
particularly during exponential growth (Moraine et al., 1979; Park et al., 2011). It is a
relatively daunting task to surmount these drawbacks.
Several methods are available for dewatering and recovering microalgal biomass,
such as centrifugation, flocculation, gravity settling, microfiltration, and dissolved
air floatation (DAF) inter alia (Lavoie and de la Noue, 1986; Molina Grima et al.,
2003) . The technology for microalgal biomass harvesting is still in its infancy, and
trials on suitable combinations of these methods are currently underway (Williams
and Laurens, 2010). The use of the centrifugation technique on a large scale is not
cost effective due the colossal amounts of power consumption (Mutanda et al., 2011).
The techniques available for microalgal harvesting and dewatering are discussed at
length in Chapter 6.
There are several techniques that are used for extracting lipids from microal-
gal biomass (Lewis et al., 2000). Most of these methods are destructive; however,
it is desirable to develop nondestructive methods for continuous extraction of
lipids from live microalgal cells. The solvent extraction system using a mixture
of solvents such as hexane and methanol are commonly used. Other methods are
sonication and microwave-assisted extraction. The Bligh and Dyer method (1959)
has been commonly used in many applications, whereby lipids are extracted from
biological material using a combination of chloroform and methanol (Lewis et al.,
2000). Extracting lipids from microalgal biomass is a real challenge because it is
intracellular and therefore requires a cell disruption step. Currently, research is
ongoing to develop cost-effective and efficient lipid extraction strategies (Molina-
Grima et al., 2003; Williams and Laurens, 2010). Subsequent to lipid extraction, it
is desirable to accurately identify the lipid and characterize the lipids using highly
analytical techniques. This is done to establish whether the lipids extracted are suit-
able for application to biodiesel production. Techniques that are widely used for
the analysis of lipids are gas chromatography with mass spectrometry (GC-MS),
liquid chromatography (LC), matrix-assisted laser desorption/ionization-time