212
The algae-algae immobilization is also promising. Thus, monocultures of
Rhodobacter sphaeroides or Chlorella sorokiniana are unable to simultaneously
remove acetate, propionate, ammonia, nitrate, and phosphate, while the mixed culture is capable of this (Ogbonna et al. 2000). It should be noted that interactions
among organisms in mixed-culture photobiofilms also are not well understood
(Kesaano and Sims 2014).
7.5.3 Removal of Heavy Metals
Heavy metal pollution is an increasingly important problem nowadays. Cells of
microalgae can accumulate diverse elements including heavy metals in high concentrations, so they are widely used for their removal from wastewater (Nascimento
and Xing 2006; Saeed and Iqbal 2006).
Adsorption of metal ions on the surface of microalgal cells proceeds via binding
to cell wall and/or cytoplasmic membrane and surface structures. Efficiency of
heavy metal removal depends on the microalgal cell total surface area. Accordingly,
increasing the cell density by immobilization results in a significant increase of
heavy metal adsorption from wastewater (Malik 2004). For removing of heavy metals, microalgae are frequently attached to the surface of various natural (alginates,
chitosan, carrageenan) and synthetic (polypropylene, polysulfone, polyacrylamide)
carriers. The seaweeds Sargassum sp. and Ulva sp. were also used for immobilization of the microalgae Tetraselmis chuii and the cyanobacterium Spirulina maxima
(Da Costa and De França 1996).
The biomass of dead microalgae cells is also be very efficient in accumulation of
heavy metals: cyanobacterium P. laminosum biomass immobilized in beads of polysulfone and epoxy resin was successfully used for Cu(II), Fe(II), Ni(II), and Zn(II)
(Blanco et al. 1999). It was detected that the amount of biosorbed metal increased
with biomass content and can be retained for several cycles of biosorption followed
by acid desorption. The cells of Ascophyllum nodosum immobilized in hydrophilic
polyurethane foam effectively adsorbed copper from the aqueous media (Alhakawati
and Banks 2004). The using of Microcystis sp. cells for copper removal from the
media gave better result than chemical adsorption with sodium polystyrene sulfonate (NaPSS) (Jang et al. 1999).
Chlorella sorokiniana immobilized on loofa sponges (Akhtar et al. 2008) was
used for bioremoval of nickel, cadmium, chromium, and lead from industrial wastewater: the maximum adsorption capacity for Cd and Ni was ca. 192 mg g
−1
and
71 mg g
−1
of the immobilized biomass, respectively. The adsorption efficiency was
always higher for immobilized microalgae than that estimated for suspended cells.
Notably, loofa sponge itself without immobilized cells adsorbed only a small
amount of this metal. The maximum amount of lead was absorbed in 5 min at pH 5,
and adsorption efficiency was 96%.
Alginate-immobilized cells of Chlamydomonas reinhardtii were successfully
exploited for mercury, cadmium, and lead removal from wastewater (Bayramoğlu
S. Vasilieva et al.
The algae-algae immobilization is also promising. Thus, monocultures of
Rhodobacter sphaeroides or Chlorella sorokiniana are unable to simultaneously
remove acetate, propionate, ammonia, nitrate, and phosphate, while the mixed culture is capable of this (Ogbonna et al. 2000). It should be noted that interactions
among organisms in mixed-culture photobiofilms also are not well understood
(Kesaano and Sims 2014).
7.5.3 Removal of Heavy Metals
Heavy metal pollution is an increasingly important problem nowadays. Cells of
microalgae can accumulate diverse elements including heavy metals in high concentrations, so they are widely used for their removal from wastewater (Nascimento
and Xing 2006; Saeed and Iqbal 2006).
Adsorption of metal ions on the surface of microalgal cells proceeds via binding
to cell wall and/or cytoplasmic membrane and surface structures. Efficiency of
heavy metal removal depends on the microalgal cell total surface area. Accordingly,
increasing the cell density by immobilization results in a significant increase of
heavy metal adsorption from wastewater (Malik 2004). For removing of heavy metals, microalgae are frequently attached to the surface of various natural (alginates,
chitosan, carrageenan) and synthetic (polypropylene, polysulfone, polyacrylamide)
carriers. The seaweeds Sargassum sp. and Ulva sp. were also used for immobilization of the microalgae Tetraselmis chuii and the cyanobacterium Spirulina maxima
(Da Costa and De França 1996).
The biomass of dead microalgae cells is also be very efficient in accumulation of
heavy metals: cyanobacterium P. laminosum biomass immobilized in beads of polysulfone and epoxy resin was successfully used for Cu(II), Fe(II), Ni(II), and Zn(II)
(Blanco et al. 1999). It was detected that the amount of biosorbed metal increased
with biomass content and can be retained for several cycles of biosorption followed
by acid desorption. The cells of Ascophyllum nodosum immobilized in hydrophilic
polyurethane foam effectively adsorbed copper from the aqueous media (Alhakawati
and Banks 2004). The using of Microcystis sp. cells for copper removal from the
media gave better result than chemical adsorption with sodium polystyrene sulfonate (NaPSS) (Jang et al. 1999).
Chlorella sorokiniana immobilized on loofa sponges (Akhtar et al. 2008) was
used for bioremoval of nickel, cadmium, chromium, and lead from industrial wastewater: the maximum adsorption capacity for Cd and Ni was ca. 192 mg g
−1
and
71 mg g
−1
of the immobilized biomass, respectively. The adsorption efficiency was
always higher for immobilized microalgae than that estimated for suspended cells.
Notably, loofa sponge itself without immobilized cells adsorbed only a small
amount of this metal. The maximum amount of lead was absorbed in 5 min at pH 5,
and adsorption efficiency was 96%.
Alginate-immobilized cells of Chlamydomonas reinhardtii were successfully
exploited for mercury, cadmium, and lead removal from wastewater (Bayramoğlu
S. Vasilieva et al.