201
(1972) observed different adhesion rates of Chlorella cells during different growth
stages and found that the cells in logarithmic (exponential) phase attached more
vigorously. The cells of Anabaena doliolum exerted the maximal capability of
immobilization at the exponential phase of the culture growth; this capability
declined or was retained at the stationary phase (Mallick and Rai 1994). By contrast, the efficiency of C. vulgaris cell immobilization on polyethylenimine-based
materials was higher in stationary-phase cultures; in the exponentially growing cultures, the attachment efficiency was 23–27% lower (Vasilieva et al. 2018). It is
likely that the increased polysaccharide layer that C. vulgaris cells develop at the
stationary phase facilitates electrostatic interaction between the cells and the polycationic sorbents. Interestingly, live cells attached the carriers more effectively
when compared to heat-killed cells, showing the implementation of active mechanisms in the process of algae immobilization (Sekar et al. 2004).
A major problem common to immobilization of viable cells is their leakage from
the surface of the immobilization matrixes. For irreversible steady attachment of
microalgal cells to carrier surface, the latter can be pretreated. The use of carriers
impregnated with ligands containing amine groups for immobilization of microorganisms on glass surface (Tsygankov et al. 1994) results in 800 times increase in the
number of attached cells as compared to untreated glass.
Polymers based on cross-linked polyethylenimine were applied for C. vulgaris
cell immobilization. A considerable rise of the immobilization efficiency was documented via electrostatic interaction of the negatively charged microalgae surface
and positively charged amino groups of sorbents (Vasilieva et al. 2018). Natural
materials such as chitin or chitosan are also widely used for steady binding of
microalgae cells. It was also revealed that the effectiveness of microalgae and polycationic polymer interaction depends on pH and ionic strength of the surrounding
media (Codd 1987).
The covalent binding with toxic reagents (dialdehydes, diisocyanates) is more
suitable for immobilization of dead microalgae cells (Moreno-Garrido 2008) as the
strong chemical interaction damages the cell surface and reduces viability of cells.
As compared to nonporous materials, porous carriers are also more preferable
for adsorptive immobilization as they have an open network of cavities through
which nutrient medium may pass (Willaert 2017). The porous materials can be
developed from fiberglass mats, cotton fiber, polyester fibers, and reticulate polyurethane foam. Among all, polyurethane foam has advantages as a matrix such as
being highly porous and nontoxic to the microalgae cells. Immobilization of C. vulgaris cells was achieved by their migration into polyurethane foam blocks (Travieso
et al. 1996). Loofa biomass is a commonly used natural material (Akhtar et al. 2004)
consisting of a fibrous network with a high degree of porosity. It possesses a high
specific surface area and mechanical strength combined with biodegradability, nontoxicity, and low cost.
When microalgal cells grow attached to porous materials, they still can be confined inside the large pores. In this case, the system with immobilized microalgae
can be compared to gel entrapment of microalgae which is the widespread immobilization technique (Willaert 2017).
7 Biotechnological Applications of Immobilized Microalgae
(1972) observed different adhesion rates of Chlorella cells during different growth
stages and found that the cells in logarithmic (exponential) phase attached more
vigorously. The cells of Anabaena doliolum exerted the maximal capability of
immobilization at the exponential phase of the culture growth; this capability
declined or was retained at the stationary phase (Mallick and Rai 1994). By contrast, the efficiency of C. vulgaris cell immobilization on polyethylenimine-based
materials was higher in stationary-phase cultures; in the exponentially growing cultures, the attachment efficiency was 23–27% lower (Vasilieva et al. 2018). It is
likely that the increased polysaccharide layer that C. vulgaris cells develop at the
stationary phase facilitates electrostatic interaction between the cells and the polycationic sorbents. Interestingly, live cells attached the carriers more effectively
when compared to heat-killed cells, showing the implementation of active mechanisms in the process of algae immobilization (Sekar et al. 2004).
A major problem common to immobilization of viable cells is their leakage from
the surface of the immobilization matrixes. For irreversible steady attachment of
microalgal cells to carrier surface, the latter can be pretreated. The use of carriers
impregnated with ligands containing amine groups for immobilization of microorganisms on glass surface (Tsygankov et al. 1994) results in 800 times increase in the
number of attached cells as compared to untreated glass.
Polymers based on cross-linked polyethylenimine were applied for C. vulgaris
cell immobilization. A considerable rise of the immobilization efficiency was documented via electrostatic interaction of the negatively charged microalgae surface
and positively charged amino groups of sorbents (Vasilieva et al. 2018). Natural
materials such as chitin or chitosan are also widely used for steady binding of
microalgae cells. It was also revealed that the effectiveness of microalgae and polycationic polymer interaction depends on pH and ionic strength of the surrounding
media (Codd 1987).
The covalent binding with toxic reagents (dialdehydes, diisocyanates) is more
suitable for immobilization of dead microalgae cells (Moreno-Garrido 2008) as the
strong chemical interaction damages the cell surface and reduces viability of cells.
As compared to nonporous materials, porous carriers are also more preferable
for adsorptive immobilization as they have an open network of cavities through
which nutrient medium may pass (Willaert 2017). The porous materials can be
developed from fiberglass mats, cotton fiber, polyester fibers, and reticulate polyurethane foam. Among all, polyurethane foam has advantages as a matrix such as
being highly porous and nontoxic to the microalgae cells. Immobilization of C. vulgaris cells was achieved by their migration into polyurethane foam blocks (Travieso
et al. 1996). Loofa biomass is a commonly used natural material (Akhtar et al. 2004)
consisting of a fibrous network with a high degree of porosity. It possesses a high
specific surface area and mechanical strength combined with biodegradability, nontoxicity, and low cost.
When microalgal cells grow attached to porous materials, they still can be confined inside the large pores. In this case, the system with immobilized microalgae
can be compared to gel entrapment of microalgae which is the widespread immobilization technique (Willaert 2017).
7 Biotechnological Applications of Immobilized Microalgae