203
agarose, agaropectin, cellulose, carrageenans or alginates, polygalacturonic acid)
are suitable for this purpose (Moreno-Garrido 2008). Substrates and products can
diffuse in and out of the gel beads, while cells are retained inside the beads.
Nevertheless, the mass transfer kinetics is reduced in most entrapment systems
(Aksu et al. 2002) as compared to that in suspended cells. It should be noted that
natural polymers have higher nutrient/product diffusion rates as compared to the
synthetic polymers (Leenen et al. 1996).
Agar is one of the most widespread materials for polymeric bead formation
(Burdin and Bird 1994; Moreno-Garrido et al. 2005). Beads from calcium alginate
also found extensive use for microalgae immobilization (Eroglu et al. 2015). These
beads do not reduce growth of the entrapped microalgae by limiting the light propagation, and they are not toxic to microalgal cells (Leenen et al. 1996). Despite these
advantages, alginate beads do not uphold their polymeric structure in the wastewaters with high nutrient content and the presence of K
+
or Mg
2+
(Mallick 2006).
It was revealed that the mechanical resistance of natural polymers can be
strengthened after mixing them with chitosan (Zheng et al. 2005), Japanese konjac
flour (Kaya and Picard 1996), polyacrylamide (Kuu and Polack 1983), polyethyleneimine, glutaraldehyde, silica, genipin, and polyvinyl alcohol (Willaert 2017)
resulting in a more mechanically stable materials for microorganism entrapment.
Apart from mass transfer limitations, the negative effect of microalgae immobilization in polymeric beads includes the decreasing of the volume-to-surface ratios
and light supply to entrapped cells. To overcome these problems, the microalgae
entrapment in thin polymeric films is recently proposed to provide sufficient light
and nutrients to phototrophic microorganisms for increasing light-to-product conversion efficiency. Kosourov and Seibert (2009) immobilized C. reinhardtii inside
alginate films for the photoproduction of hydrogen; a few species of cyanobacteria
were entrapped in the hydrated latex coatings (Bernal et al. 2014). Chlorella sp.
entrapped in calcium alginate sheets was used to remove inorganic nutrient compounds from domestic wastewater.
Various nanofabrication processes have been applied for creation of new carriers
on the basis of electrospun nanofibers (Eroglu et al. 2015), laminar nanomaterials
such as graphene, and graphene oxide nanosheets (Wahid et al. 2013) for the thinlayer immobilization of microalgal cells. The new nanofiber materials possess high
level of porosity and surface-to-volume ratio, and their synthesis techniques allow
to create polymers of different shapes, from fibers to flat thin membranes
(Crandall 1996).
Reportedly, gels and films from cellulose nanofibrils which are renewable, biocompatible, and biodegradable material offered a range of advantages for the microalgae immobilization (Klemm et al. 2011). Recently, TEMPO-oxidized cellulose
nanofibrils cross-linked with Ca
2+
or polyvinyl alcohol were applied for
Chlamydomonas reinhardtii and Anabaena sp. entrapment in polymeric sheets
(Jämsä et al. 2018).
7 Biotechnological Applications of Immobilized Microalgae
agarose, agaropectin, cellulose, carrageenans or alginates, polygalacturonic acid)
are suitable for this purpose (Moreno-Garrido 2008). Substrates and products can
diffuse in and out of the gel beads, while cells are retained inside the beads.
Nevertheless, the mass transfer kinetics is reduced in most entrapment systems
(Aksu et al. 2002) as compared to that in suspended cells. It should be noted that
natural polymers have higher nutrient/product diffusion rates as compared to the
synthetic polymers (Leenen et al. 1996).
Agar is one of the most widespread materials for polymeric bead formation
(Burdin and Bird 1994; Moreno-Garrido et al. 2005). Beads from calcium alginate
also found extensive use for microalgae immobilization (Eroglu et al. 2015). These
beads do not reduce growth of the entrapped microalgae by limiting the light propagation, and they are not toxic to microalgal cells (Leenen et al. 1996). Despite these
advantages, alginate beads do not uphold their polymeric structure in the wastewaters with high nutrient content and the presence of K
+
or Mg
2+
(Mallick 2006).
It was revealed that the mechanical resistance of natural polymers can be
strengthened after mixing them with chitosan (Zheng et al. 2005), Japanese konjac
flour (Kaya and Picard 1996), polyacrylamide (Kuu and Polack 1983), polyethyleneimine, glutaraldehyde, silica, genipin, and polyvinyl alcohol (Willaert 2017)
resulting in a more mechanically stable materials for microorganism entrapment.
Apart from mass transfer limitations, the negative effect of microalgae immobilization in polymeric beads includes the decreasing of the volume-to-surface ratios
and light supply to entrapped cells. To overcome these problems, the microalgae
entrapment in thin polymeric films is recently proposed to provide sufficient light
and nutrients to phototrophic microorganisms for increasing light-to-product conversion efficiency. Kosourov and Seibert (2009) immobilized C. reinhardtii inside
alginate films for the photoproduction of hydrogen; a few species of cyanobacteria
were entrapped in the hydrated latex coatings (Bernal et al. 2014). Chlorella sp.
entrapped in calcium alginate sheets was used to remove inorganic nutrient compounds from domestic wastewater.
Various nanofabrication processes have been applied for creation of new carriers
on the basis of electrospun nanofibers (Eroglu et al. 2015), laminar nanomaterials
such as graphene, and graphene oxide nanosheets (Wahid et al. 2013) for the thinlayer immobilization of microalgal cells. The new nanofiber materials possess high
level of porosity and surface-to-volume ratio, and their synthesis techniques allow
to create polymers of different shapes, from fibers to flat thin membranes
(Crandall 1996).
Reportedly, gels and films from cellulose nanofibrils which are renewable, biocompatible, and biodegradable material offered a range of advantages for the microalgae immobilization (Klemm et al. 2011). Recently, TEMPO-oxidized cellulose
nanofibrils cross-linked with Ca
2+
or polyvinyl alcohol were applied for
Chlamydomonas reinhardtii and Anabaena sp. entrapment in polymeric sheets
(Jämsä et al. 2018).
7 Biotechnological Applications of Immobilized Microalgae