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metabolites, as the cell growth in polymeric gels is often limited. Self-immobilization
of cells is widely used for low-cost products, such as biofuels. It should be noted
that most widely used methods intended for heterotrophic microorganisms are
applicable to microalgae immobilization as well if they will not restrict the light
propagation in the cultivation systems.
Immobilization serves to maintain a high proportion of metabolically active cells
and hence to increase the efficiency of the biotechnological processes. In many
cases, immobilization of whole cells can improve conditions for cell differentiation
and cell communication and also provide a favorable microenvironment, nutrient
concentration gradient, so that the metabolic activities of microalgae cells can be
increased. The main advantages of microalgae cell immobilization over the free cell
systems are the following (Willaert 2017; Moreno-Garrido 2008; De-Bashan and
Bashan 2010):
• Higher cell densities
• Easier biomass harvesting from cultural media
• Repeated or continuous use
• No mixing requirements
• Cell growing at higher dilution rates
• Higher resistance to toxic compounds
• Enhanced resistance to shear stress
• Shortening of the culture growth lag
• Improved substrate utilization
• Increased productivity per unit of the reactor volume
• Reduced risk of contamination
• Better tolerance to the inhibition by end products
• Improved genetic stability
• Improved conditions for cell differentiation and cell-to-cell communication
7.3.1 Immobilization Techniques with a Carrier
Current immobilization techniques with support materials or carriers are classified
into two key types—passive and active immobilization. The passive immobilization
is the process of cell attachment to a carrier that harnesses the natural ability of
microorganisms to adhere to the solid surfaces (Moreno-Garrido 2008). This is the
most simple and least mildly stressful method of microorganism immobilization
mimicking the cell attachment in nature.
In opposition, the methods of active immobilization are the process of compulsory confinement of cells within the bulk of the carrier (López et al. 1997) and carried out mainly via entrapment of microalgae in different gels. The incorporation of
microalgae in beads or sheets made of polymers can provide the increase of cell
density and offer additional protection from contamination by external microorganisms and unfavorable environment (Sinitsin et al. 1994). Unicellular and small colonial algal forms are more appropriate for the active entrapment, while the adsorptive
S. Vasilieva et al.
metabolites, as the cell growth in polymeric gels is often limited. Self-immobilization
of cells is widely used for low-cost products, such as biofuels. It should be noted
that most widely used methods intended for heterotrophic microorganisms are
applicable to microalgae immobilization as well if they will not restrict the light
propagation in the cultivation systems.
Immobilization serves to maintain a high proportion of metabolically active cells
and hence to increase the efficiency of the biotechnological processes. In many
cases, immobilization of whole cells can improve conditions for cell differentiation
and cell communication and also provide a favorable microenvironment, nutrient
concentration gradient, so that the metabolic activities of microalgae cells can be
increased. The main advantages of microalgae cell immobilization over the free cell
systems are the following (Willaert 2017; Moreno-Garrido 2008; De-Bashan and
Bashan 2010):
• Higher cell densities
• Easier biomass harvesting from cultural media
• Repeated or continuous use
• No mixing requirements
• Cell growing at higher dilution rates
• Higher resistance to toxic compounds
• Enhanced resistance to shear stress
• Shortening of the culture growth lag
• Improved substrate utilization
• Increased productivity per unit of the reactor volume
• Reduced risk of contamination
• Better tolerance to the inhibition by end products
• Improved genetic stability
• Improved conditions for cell differentiation and cell-to-cell communication
7.3.1 Immobilization Techniques with a Carrier
Current immobilization techniques with support materials or carriers are classified
into two key types—passive and active immobilization. The passive immobilization
is the process of cell attachment to a carrier that harnesses the natural ability of
microorganisms to adhere to the solid surfaces (Moreno-Garrido 2008). This is the
most simple and least mildly stressful method of microorganism immobilization
mimicking the cell attachment in nature.
In opposition, the methods of active immobilization are the process of compulsory confinement of cells within the bulk of the carrier (López et al. 1997) and carried out mainly via entrapment of microalgae in different gels. The incorporation of
microalgae in beads or sheets made of polymers can provide the increase of cell
density and offer additional protection from contamination by external microorganisms and unfavorable environment (Sinitsin et al. 1994). Unicellular and small colonial algal forms are more appropriate for the active entrapment, while the adsorptive
S. Vasilieva et al.