194
Keywords Microalgae · Immobilization · Cyanobacteria · Biofilms ·
Bioremediation · Biodestruction · Bioremoval · Heavy metals · Alginate
7.1 Introduction
Photosynthetic organisms including cyanobacteria and eukaryotes (commonly
referred to below as microalgae) exist in their natural habitats as biofilms incorporating the cells of heterotrophic microorganisms and other microalgae embedded in
a matrix of the extracellular biopolymers. The cells in the biofilms form granules,
clusters, flakes, and other aggregates attached to the substrate or suspended in the
aqueous media. Therefore, the immobilized state is widespread, if not ubiquitous,
form of microalgae existence in nature (Coserton et al. 1995).
Currently, algal cells attached to assorted carriers are mostly used for production of biomass
and value-added metabolites, obtaining biohydrogen, and bioremoval of mineral nutrients,
metals, or dangerous low-molecular pollutants from wastewater streams. The immobilized
microalgae can also be incorporated into biosensors for the assessment of water pollution
degree (Mallick 2002; Eroglu et al. 2015). A topical issue of mass cultivation of microalgae
is harvesting of the biomass. Currently employed approaches like filtration, centrifugation,
and flocculation are energy- and/or time-consuming. Immobilization of the cells streamlines considerably harvesting of the biomass.
The main strengths of immobilized cells as compared with free (suspended) cell are
the improved substrate utilization, increased volumetric productivity, and enhanced
resistance to unfavorable factors, e.g., extreme pH, temperatures, and toxic compounds. The major disadvantage of immobilization, compared with cultivation of
suspended microalgae, is a higher cost. It should be emphasized that in real conditions, the successful application of immobilized MA is defined by optimal carries
and immobilization technique (Tables 7.1 and 7.2).
In this review, we summarize the evidence on immobilization of microalgae on
diverse carriers with a focus on immobilization effects on the cell metabolism and
viability and advantages and shortcomings of the immobilized microalgae cell
application in photobiotechnology.
7.2 Natural Biofilm as the Prototype of Artificially
Immobilized Microalgae
In nature, algae-bacteria associations are stabilized mainly by microalgae controlling their formation and productivity (O’Toole et al. 2000). The microalgae play
central role since they possess certain cell surface structures (mucous capsules or
colonial mucus) and produce exometabolites (Zvyagintsev et al. 1993; Branda et al.
2005; O’Toole et al. 2000). The latter promote growth and viability of other
S. Vasilieva et al.
Keywords Microalgae · Immobilization · Cyanobacteria · Biofilms ·
Bioremediation · Biodestruction · Bioremoval · Heavy metals · Alginate
7.1 Introduction
Photosynthetic organisms including cyanobacteria and eukaryotes (commonly
referred to below as microalgae) exist in their natural habitats as biofilms incorporating the cells of heterotrophic microorganisms and other microalgae embedded in
a matrix of the extracellular biopolymers. The cells in the biofilms form granules,
clusters, flakes, and other aggregates attached to the substrate or suspended in the
aqueous media. Therefore, the immobilized state is widespread, if not ubiquitous,
form of microalgae existence in nature (Coserton et al. 1995).
Currently, algal cells attached to assorted carriers are mostly used for production of biomass
and value-added metabolites, obtaining biohydrogen, and bioremoval of mineral nutrients,
metals, or dangerous low-molecular pollutants from wastewater streams. The immobilized
microalgae can also be incorporated into biosensors for the assessment of water pollution
degree (Mallick 2002; Eroglu et al. 2015). A topical issue of mass cultivation of microalgae
is harvesting of the biomass. Currently employed approaches like filtration, centrifugation,
and flocculation are energy- and/or time-consuming. Immobilization of the cells streamlines considerably harvesting of the biomass.
The main strengths of immobilized cells as compared with free (suspended) cell are
the improved substrate utilization, increased volumetric productivity, and enhanced
resistance to unfavorable factors, e.g., extreme pH, temperatures, and toxic compounds. The major disadvantage of immobilization, compared with cultivation of
suspended microalgae, is a higher cost. It should be emphasized that in real conditions, the successful application of immobilized MA is defined by optimal carries
and immobilization technique (Tables 7.1 and 7.2).
In this review, we summarize the evidence on immobilization of microalgae on
diverse carriers with a focus on immobilization effects on the cell metabolism and
viability and advantages and shortcomings of the immobilized microalgae cell
application in photobiotechnology.
7.2 Natural Biofilm as the Prototype of Artificially
Immobilized Microalgae
In nature, algae-bacteria associations are stabilized mainly by microalgae controlling their formation and productivity (O’Toole et al. 2000). The microalgae play
central role since they possess certain cell surface structures (mucous capsules or
colonial mucus) and produce exometabolites (Zvyagintsev et al. 1993; Branda et al.
2005; O’Toole et al. 2000). The latter promote growth and viability of other
S. Vasilieva et al.