210
able to produce hydrogen under stressful conditions, e.g., in the absence of sulfur in
the cultivating medium. Sulfur starvation blocks the synthesis of photosystem
II-specific proteins, inhibits photosynthesis, and eventually facilitates the hydrogen
production by phototrophic cells (Melis et al. 2000). Chlamydomonas reinhardtii
seems to be one of the most promising organisms for biohydrogen production on an
industrial scale (Kosourov and Seibert 2009; Laurinavichene et al. 2008).
Cyanobacterial strains capable of nitrogen fixing are promising for evolving H 2
as a by-product of their nitrogenase activity. Significantly, nitrogenase is protected
from the inhibitory effect of oxygen in heterocysts (Kosourov and Seibert 2009). It
was shown (Kayano et al. 1981) that the hydrogen productivity of cyanobacterium
Anabaena N-7363 immobilized in 2% carrageenan gel was 2.4 times higher in comparison with the suspended algal cells (up to 3.24 mmol per hour per 1 g dry gel).
Alginate bead entrapment of C. reinhardtii resulted in a better retention of
hydrogenase activity since the alginate layer delays oxygen penetration into microalgae cells. As a result, the cells entrapped in alginate produce more hydrogen as
compared to free cells (Kosourov and Seibert 2009). The rates of hydrogen production by C. reinhardtii cells immobilized on glass fibers and suspended cells were
similar, but the period of hydrogen evolution was longer for the attached cells
(Laurinavichene et al. 2008).
7.5.2 Bioremoval of Nutrients from Wastewater
Biotreatment with microalgal cultures is a promising biotechnological application
for remediation of wastewater (including agricultural wastewater) as compared to
currently used technologies (Solovchenko et al. 2013). Microalgae application for
treatment of nutrient-rich wastewater allows to remove nitrogen and phosphorus
and obtain biomass enriched with these nutrients (Mallick 2002). Fertilizer production is among the most promising methods of nutrient-enriched microalgal biomass
utilization. The promising approach is usage of algal turf scrubbers for farm wastewater treatment which support the load rate of 2700 kg of N and 400 kg of P per
1 ha per year, yielding 27,000 kg ha
−1
of dry microalgae biomass (Pizarro et al. 2006).
The approaches to nutrient capture by immobilized microalgal cells include (i)
their entrapment in natural polymer gels (de-Bashan et al. 2015) and (ii) passive
immobilization on the surface of biodegradable and nontoxic carriers (Abe et al.
2008). Chlorella vulgaris immobilized in alginate removed 80% of ammonium and
99% of phosphate from wastewater during 24 hours (Travieso et al. 1992). The cells
of Scenedesmus immobilized in alginate sheets also effectively removed nutrients
from tertiary wastewater (Zhang et al. 2008). The chitosan-immobilized cells of
Phormidium sp. remove up to 95% of nitrates and 87% of phosphate within 24 hours
(de la Noue and de Pauw 1988).
At low nutrient concentrations, their consumption by gel-entrapped microalgal
cells can be limited, possibly due to decreasing the nutrient diffusion through the
S. Vasilieva et al.
able to produce hydrogen under stressful conditions, e.g., in the absence of sulfur in
the cultivating medium. Sulfur starvation blocks the synthesis of photosystem
II-specific proteins, inhibits photosynthesis, and eventually facilitates the hydrogen
production by phototrophic cells (Melis et al. 2000). Chlamydomonas reinhardtii
seems to be one of the most promising organisms for biohydrogen production on an
industrial scale (Kosourov and Seibert 2009; Laurinavichene et al. 2008).
Cyanobacterial strains capable of nitrogen fixing are promising for evolving H 2
as a by-product of their nitrogenase activity. Significantly, nitrogenase is protected
from the inhibitory effect of oxygen in heterocysts (Kosourov and Seibert 2009). It
was shown (Kayano et al. 1981) that the hydrogen productivity of cyanobacterium
Anabaena N-7363 immobilized in 2% carrageenan gel was 2.4 times higher in comparison with the suspended algal cells (up to 3.24 mmol per hour per 1 g dry gel).
Alginate bead entrapment of C. reinhardtii resulted in a better retention of
hydrogenase activity since the alginate layer delays oxygen penetration into microalgae cells. As a result, the cells entrapped in alginate produce more hydrogen as
compared to free cells (Kosourov and Seibert 2009). The rates of hydrogen production by C. reinhardtii cells immobilized on glass fibers and suspended cells were
similar, but the period of hydrogen evolution was longer for the attached cells
(Laurinavichene et al. 2008).
7.5.2 Bioremoval of Nutrients from Wastewater
Biotreatment with microalgal cultures is a promising biotechnological application
for remediation of wastewater (including agricultural wastewater) as compared to
currently used technologies (Solovchenko et al. 2013). Microalgae application for
treatment of nutrient-rich wastewater allows to remove nitrogen and phosphorus
and obtain biomass enriched with these nutrients (Mallick 2002). Fertilizer production is among the most promising methods of nutrient-enriched microalgal biomass
utilization. The promising approach is usage of algal turf scrubbers for farm wastewater treatment which support the load rate of 2700 kg of N and 400 kg of P per
1 ha per year, yielding 27,000 kg ha
−1
of dry microalgae biomass (Pizarro et al. 2006).
The approaches to nutrient capture by immobilized microalgal cells include (i)
their entrapment in natural polymer gels (de-Bashan et al. 2015) and (ii) passive
immobilization on the surface of biodegradable and nontoxic carriers (Abe et al.
2008). Chlorella vulgaris immobilized in alginate removed 80% of ammonium and
99% of phosphate from wastewater during 24 hours (Travieso et al. 1992). The cells
of Scenedesmus immobilized in alginate sheets also effectively removed nutrients
from tertiary wastewater (Zhang et al. 2008). The chitosan-immobilized cells of
Phormidium sp. remove up to 95% of nitrates and 87% of phosphate within 24 hours
(de la Noue and de Pauw 1988).
At low nutrient concentrations, their consumption by gel-entrapped microalgal
cells can be limited, possibly due to decreasing the nutrient diffusion through the
S. Vasilieva et al.