211
immobilizing matrix. It was found (Garbayo et al. 2000) that C. reinhardtii immobilized in Ca alginate did not consume nitrate at a concentration below 0.14 mM,
but freely suspended cells consumed it nearly completely.
Despite the limited division rate of microalgal cells in beads, the immobilization
can enhance the metabolic activity of cells providing higher rate and efficiency of
wastewater treatment as compared to suspended cells. Within 3 days, immobilized
C. vulgaris cells consumed more than 95% of ammonium and 99% of phosphate,
while the removal efficiency of free cells was two times lower (Hameed and Ebrahim
2007). Zhang et al. (2008) established that the cell density of immobilized microalgae was the key factor that determined the efficiency of nutrient removal. Higher
rates of nutrient removal can be achieved through higher cell density in alginate gels
when thickness of polymeric sheets was 2–3 mm.
Thermophile strains are particularly suitable for nutrient bioremoval at high temperatures (> 30 °С). Thermophilic cyanobacterium Phormidium laminosum, immobilized on hollow cellulose fibers, was applied for nutrient removal in a tubular
photobioreactor at 43 °C (Sawayama et al. 1998).
The rate of nutrient uptake is enhanced if the carrier used for microalgae immobilization also binds the nutrients. For example, carrageenan adsorbs ammonium
cations, while chitosan has high affinity to anions (phosphate, nitrate, and nitrite)
(Mallick and Rai 1994).
Reportedly, MA can accumulate P in excess of growth requirements which is
known as luxury uptake (Solovchenko et al. 2016). Luxury P uptake probably
developed as an adaptive mechanism of microalgae in response to unstable P availability (Watanabe et al. 1988). The immobilization of green microalgae Scenedesmus
sp. and Chlorella sp. capable of luxury P uptake (Azad and Borchardt 1970) resulted
in high levels (up to 90%) of P removal from wastewater (Shi et al. 2007; Wei
et al. 2008).
The nutrient removal efficiency could be significantly increased by preliminary
cultivation of microalgae in nutrient-depleted media (Solovchenko et al. 2016;
Urrutia et al. 1995). The study (Zhang et al. 2007) demonstrated that immobilization of Chlorella sp. entrapped in alginate screens for starvation-wastewater treatment process would be a prospective method for the wastewater treatment. During
four cycles of starvation treatment, the nutrient removal efficiency was up to 100%
because of high cell growth, but after the fifth cycle, the N and P removal efficiency
decreased because of light shading and longtime starvation of microalgae.
Apart from single-species microalgae immobilization, the idea of more than one
microorganism attachment on the support materials can contribute to the higher
effectiveness of bioremediation process. As discussed above, algal-bacterial consortia can benefit from co-immobilization in different carriers (De-Bashan et al. 2004),
as photosynthesis of the entrapped microalgae cells can be limited due to decreasing
of CO 2 supply. In many cases, wastewater contains organic P species which are
scarcely uptook by microalgae. At the same time, bacteria often possess enzymes to
mineralize the organic P compounds and provide the higher bioavailability of P in
wastewater (Lim et al. 2007).
7 Biotechnological Applications of Immobilized Microalgae
immobilizing matrix. It was found (Garbayo et al. 2000) that C. reinhardtii immobilized in Ca alginate did not consume nitrate at a concentration below 0.14 mM,
but freely suspended cells consumed it nearly completely.
Despite the limited division rate of microalgal cells in beads, the immobilization
can enhance the metabolic activity of cells providing higher rate and efficiency of
wastewater treatment as compared to suspended cells. Within 3 days, immobilized
C. vulgaris cells consumed more than 95% of ammonium and 99% of phosphate,
while the removal efficiency of free cells was two times lower (Hameed and Ebrahim
2007). Zhang et al. (2008) established that the cell density of immobilized microalgae was the key factor that determined the efficiency of nutrient removal. Higher
rates of nutrient removal can be achieved through higher cell density in alginate gels
when thickness of polymeric sheets was 2–3 mm.
Thermophile strains are particularly suitable for nutrient bioremoval at high temperatures (> 30 °С). Thermophilic cyanobacterium Phormidium laminosum, immobilized on hollow cellulose fibers, was applied for nutrient removal in a tubular
photobioreactor at 43 °C (Sawayama et al. 1998).
The rate of nutrient uptake is enhanced if the carrier used for microalgae immobilization also binds the nutrients. For example, carrageenan adsorbs ammonium
cations, while chitosan has high affinity to anions (phosphate, nitrate, and nitrite)
(Mallick and Rai 1994).
Reportedly, MA can accumulate P in excess of growth requirements which is
known as luxury uptake (Solovchenko et al. 2016). Luxury P uptake probably
developed as an adaptive mechanism of microalgae in response to unstable P availability (Watanabe et al. 1988). The immobilization of green microalgae Scenedesmus
sp. and Chlorella sp. capable of luxury P uptake (Azad and Borchardt 1970) resulted
in high levels (up to 90%) of P removal from wastewater (Shi et al. 2007; Wei
et al. 2008).
The nutrient removal efficiency could be significantly increased by preliminary
cultivation of microalgae in nutrient-depleted media (Solovchenko et al. 2016;
Urrutia et al. 1995). The study (Zhang et al. 2007) demonstrated that immobilization of Chlorella sp. entrapped in alginate screens for starvation-wastewater treatment process would be a prospective method for the wastewater treatment. During
four cycles of starvation treatment, the nutrient removal efficiency was up to 100%
because of high cell growth, but after the fifth cycle, the N and P removal efficiency
decreased because of light shading and longtime starvation of microalgae.
Apart from single-species microalgae immobilization, the idea of more than one
microorganism attachment on the support materials can contribute to the higher
effectiveness of bioremediation process. As discussed above, algal-bacterial consortia can benefit from co-immobilization in different carriers (De-Bashan et al. 2004),
as photosynthesis of the entrapped microalgae cells can be limited due to decreasing
of CO 2 supply. In many cases, wastewater contains organic P species which are
scarcely uptook by microalgae. At the same time, bacteria often possess enzymes to
mineralize the organic P compounds and provide the higher bioavailability of P in
wastewater (Lim et al. 2007).
7 Biotechnological Applications of Immobilized Microalgae