Microalgal Biomass Production 69
(Powell et al. 2008). The phosphorus consumption rate in algae depends on phosphorus concentration in
both the environment and the cells, and on pH, temperature (Sancho et al. 1997).
Algae offer a great potential for performing wastewater treatment using algae. After primary and
secondary treatment is fed to a race track reactor. Algae and bacteria are cultured in these reactors. Algae
are continuously mixed to keep the cells in suspension and expose them periodically to light. Algae
provide the dissolved oxygen required for bacterial decomposition of organic matter and bacteria provide
carbon, nitrogen, and phosphorus essential for algal growth by degrading wastewater components
(Garcia et al. 2000). Algae remove the nutrients directly through uptake and harvesting of the biomass.
Nitrogen and phosphorus are removed indirectly by ammonia-nitrogen volatilization and orthophosphate
precipitation, respectively. Directly and indirectly, the growth rate of algae controls the efficiency of
nitrogen and phosphorus removal. The efficiency of nutrient removal is determined by cellular retention
time, solar radiation, and temperature (Garcia et al. 2000).
Munoz and Guieysse (2006) described microalgae enhance the removal of nutrients, organic
contaminants, heavy metals, and even pathogens from domestic wastewater and furnish an interesting
raw material for the production of high-value chemicals or biogas. The use of algae in wastewater
treatment is being well established with treatment plants in operation in California (Oswald 1988). The
improvement in the quality of wastewater and the fermentation of the resulting biomass to methane were
implemented (Pulz and Scheibenbogen 1998). The cultivation of algae as a source of animal feed in that
respect, animal wastes represent a good source of substrates for the culture of Spirulina. By employing an
integrated approach one can easily conceive the treatment of wastes with concomitant production of algal
biomass for animal feeds. Spirulina deals with the recycling of animal wastes and most often with pig
wastes, because intensive pig production is causing very serious problems of water pollution worldwide.
Accumulation of heavy metals especially Cd by Scenedesmus bijugus (Playfair) V. may show
saturation in 2 h. In a similar study with Cd and Pb, S. bijugus could accumulate 80% of the heavy metals
within the first 12 h. Mallick and Rai (1994) explained the algae-based systems for the removal of toxic
minerals such as Pb, Cd, Hg, Se, Sn, Ni, As, and Br also showed great promise. The hydrocarbon rich
microalga, Botroyococcus braunii consumed nitrate and phosphate in secondary treated water. Removals
of toxic metals like As, Cr, Cd, and inorganic compounds have also reported (Sawayama et al. 1995).
The use of Dunaliella salina as a potential test organism for the simple determination of changes in the
chlorophyll content under standard conditions can be recognized as qualitative and quantitative measures
of toxic residues (Yarden et al. 1993). Dunaliella species have also shown to be exceptionally tolerant of
heavy metals such as Cu, Pb, and chlorinated hydrocarbons. Dunaliella tertiolecta Butcher can tolerate
Cu concentration near saturation level for seawater (approx. 0.6 ug Cu mL
–1
) (Visviki and Rachlin 1991).
The effective concentration of the toxic chemicals like copper and cadmium was reduced by the marine
alga, D. minuta Lerche, in both acute and chronic exposures. The incredible ability of the halophilic alga,
D. salina in the treatment of salt refinery effluent was studied. Their appearance, odor, TDS, turbidity, pH,
hardness, BOD, and COD concentrations of anions and cations were reduced considerably. A significant
percentage of heavy metals Ba (56.5%), Al (46%), Ag (32.4), and Sr (4.8%) were also removed (PeralesVela et al. 2006; Raja et al. 2008).
Biomass harvest
Biomass harvesting is a kind of technique and it accounts 15–20% of the production costs. The very
small size of algae and their low concentration in the culture medium makes the cell recovery, harder one.
The harvesting cannot be done by a single process because of the several species of algae with varying
characteristics like shape, size and motility that influence to a big extent for their settling. Centrifugation
is one of the most commonly used techniques to harvest microalgae in a lab scale as well in R&D
laboratories. Algae are commonly used as a feed for aquaculture and they harvested by centrifuging to
produce concentrates with longer shelf-life. Filter presses are used to recover fairly large microalgae
like Spirulina sp. but are not suitable for smaller microalgae like Scenedesmus, Dunaliella, and
Chlorella. The major costs involved in centrifugation are depreciation and maintenance of equipment
(> 20000 L) (Richmond 2004). Using centrifuge in algal industries to harvest biomass is not a recommended
(Powell et al. 2008). The phosphorus consumption rate in algae depends on phosphorus concentration in
both the environment and the cells, and on pH, temperature (Sancho et al. 1997).
Algae offer a great potential for performing wastewater treatment using algae. After primary and
secondary treatment is fed to a race track reactor. Algae and bacteria are cultured in these reactors. Algae
are continuously mixed to keep the cells in suspension and expose them periodically to light. Algae
provide the dissolved oxygen required for bacterial decomposition of organic matter and bacteria provide
carbon, nitrogen, and phosphorus essential for algal growth by degrading wastewater components
(Garcia et al. 2000). Algae remove the nutrients directly through uptake and harvesting of the biomass.
Nitrogen and phosphorus are removed indirectly by ammonia-nitrogen volatilization and orthophosphate
precipitation, respectively. Directly and indirectly, the growth rate of algae controls the efficiency of
nitrogen and phosphorus removal. The efficiency of nutrient removal is determined by cellular retention
time, solar radiation, and temperature (Garcia et al. 2000).
Munoz and Guieysse (2006) described microalgae enhance the removal of nutrients, organic
contaminants, heavy metals, and even pathogens from domestic wastewater and furnish an interesting
raw material for the production of high-value chemicals or biogas. The use of algae in wastewater
treatment is being well established with treatment plants in operation in California (Oswald 1988). The
improvement in the quality of wastewater and the fermentation of the resulting biomass to methane were
implemented (Pulz and Scheibenbogen 1998). The cultivation of algae as a source of animal feed in that
respect, animal wastes represent a good source of substrates for the culture of Spirulina. By employing an
integrated approach one can easily conceive the treatment of wastes with concomitant production of algal
biomass for animal feeds. Spirulina deals with the recycling of animal wastes and most often with pig
wastes, because intensive pig production is causing very serious problems of water pollution worldwide.
Accumulation of heavy metals especially Cd by Scenedesmus bijugus (Playfair) V. may show
saturation in 2 h. In a similar study with Cd and Pb, S. bijugus could accumulate 80% of the heavy metals
within the first 12 h. Mallick and Rai (1994) explained the algae-based systems for the removal of toxic
minerals such as Pb, Cd, Hg, Se, Sn, Ni, As, and Br also showed great promise. The hydrocarbon rich
microalga, Botroyococcus braunii consumed nitrate and phosphate in secondary treated water. Removals
of toxic metals like As, Cr, Cd, and inorganic compounds have also reported (Sawayama et al. 1995).
The use of Dunaliella salina as a potential test organism for the simple determination of changes in the
chlorophyll content under standard conditions can be recognized as qualitative and quantitative measures
of toxic residues (Yarden et al. 1993). Dunaliella species have also shown to be exceptionally tolerant of
heavy metals such as Cu, Pb, and chlorinated hydrocarbons. Dunaliella tertiolecta Butcher can tolerate
Cu concentration near saturation level for seawater (approx. 0.6 ug Cu mL
–1
) (Visviki and Rachlin 1991).
The effective concentration of the toxic chemicals like copper and cadmium was reduced by the marine
alga, D. minuta Lerche, in both acute and chronic exposures. The incredible ability of the halophilic alga,
D. salina in the treatment of salt refinery effluent was studied. Their appearance, odor, TDS, turbidity, pH,
hardness, BOD, and COD concentrations of anions and cations were reduced considerably. A significant
percentage of heavy metals Ba (56.5%), Al (46%), Ag (32.4), and Sr (4.8%) were also removed (PeralesVela et al. 2006; Raja et al. 2008).
Biomass harvest
Biomass harvesting is a kind of technique and it accounts 15–20% of the production costs. The very
small size of algae and their low concentration in the culture medium makes the cell recovery, harder one.
The harvesting cannot be done by a single process because of the several species of algae with varying
characteristics like shape, size and motility that influence to a big extent for their settling. Centrifugation
is one of the most commonly used techniques to harvest microalgae in a lab scale as well in R&D
laboratories. Algae are commonly used as a feed for aquaculture and they harvested by centrifuging to
produce concentrates with longer shelf-life. Filter presses are used to recover fairly large microalgae
like Spirulina sp. but are not suitable for smaller microalgae like Scenedesmus, Dunaliella, and
Chlorella. The major costs involved in centrifugation are depreciation and maintenance of equipment
(> 20000 L) (Richmond 2004). Using centrifuge in algal industries to harvest biomass is not a recommended