74 Marine Macro- and Microalgae: An Overview
point for biofuels research, they lack one very important thing that eukaryotic microalgae can possess in
abundance-neutral lipids, which are rich in triacylglycerols (TAGs).
Greenhouse gas reductions and global warming
The combustion of fossil fuel generates carbon dioxide, a major greenhouse gas that is considered
as a huge threat because of its potential to cause severe global warming. Microalgae are particularly
considered for bio-fixation because of their ability to grow fast and fix greater amounts of carbon dioxide.
The bio-mitigation of carbon dioxide and other flue gases by microalgae have significantly gained interest
in reducing the emissions from coal-fired power plants. The algae biomass thus produced by capturing
carbon can be used in generating valuable products such as fuel, animal feed and fertilizer. Power plants
are the major sources of CO 2 and release 5.7 giga tones of carbon dioxide per year (Kadam 2001). CO 2 is
produced by both stationary and mobile sources. Microalgae offer a natural way to recycle carbon dioxide
from the flue gas and thus help in reducing the effects of global warming and climate change.
Microalgal biomass is composed of 45 to 50% carbon based on dry weight measurements
(Schlesinger 1991). The high carbon content of microalgae makes it suitable for storing carbon. CO 2
present is flue gas can significantly raise the growth rates of microalgae. Microalgae can be engineered in
open ponds or photobioreactors to maximize CO 2 conversion to biomass thereby sequestering carbon and
also producing a biofuel. The selection of microalgae is the most important factor in the bio-mitigation
of carbon dioxide from flue gases generated by power plants. The algae should have high growth and
CO 2 utilization rates. The other suitable characteristics for carbon dioxide bio-fixation are their ability
to tolerate SOx and NOx, and thrive in mass cultures without contamination. Lastly, the algae should
be chosen also considering the harvesting process. Algae with autoflocculation characteristics simplify
the harvesting step and minimize the energy and cost in the downstream processing of algae production
(Brennan and Owende 2010).
Algae (Chlorella vulgaris and Scenedesmus obliquus) are isolated from the water bodies near to the
power plants so that they are already adapted to the flue gases generated and environmental conditions
of that area were ideal for biofixation (De Morais and Costa 2007). They were able to grow in culture
media with 18% (v/v) CO 2 . Biological carbon sequestration using microalgae offers several advantages
over geological and ocean sequestration systems. Algae can sequester carbon dioxide directly and the
costs of separation of CO 2 gas are avoided. Microalgae production systems can be located near the power
plant: this does not require huge costs on transportation of CO 2 . The advantages of using microalgae
biofixation processes are: their ability to grow on flue gas, higher carbon fixation rates than other plants
and their potential to grow in wastewaters thereby minimizing the fresh water needs (Schenk et al. 2008).
The Solvay process can be modified to convert CO 2 from fossil fuel power plants to bicarbonates. The
carbon dioxide gas is passed through brine solution with ammonia as a catalyst under alkaline conditions
to produce sodium bicarbonate according to this chemical reaction (Huang et al. 2001).
CO 2 + NaCl + NH 3 + H 2 O → NaHCO 3 ↓ + NH 4 Cl (Gouveia and Oliveira 2008)
Sodium bicarbonate was a better carbon source for Scenedesmus than sodium carbonate. Carbon
dioxide can be utilized in the form of carbonate salts using Solvay process. These salts can be used as a
carbon source for algae growth when the power plant is not located near the algae pond. Algae can thus
be used for bio-fixation of CO 2 in industrial flue gases.
Conclusion
As far as the algal biomass production has concerned, currently there are lot of projects started in many
countries more particularly in India, China, United States, etc., and they are using the harvested biomass
for biofuel production because it might contain heavy metals and unwanted chemicals available since the
microalgae grown in municipal seawage or from effluent. This is best biological method recommended
by naturalists and scientists to protect environment clean. In this way, not only the waste water has treated
simultaneously the algae capturing atmospheric CO 2 thus it subsequently helps to reduce global warming.
point for biofuels research, they lack one very important thing that eukaryotic microalgae can possess in
abundance-neutral lipids, which are rich in triacylglycerols (TAGs).
Greenhouse gas reductions and global warming
The combustion of fossil fuel generates carbon dioxide, a major greenhouse gas that is considered
as a huge threat because of its potential to cause severe global warming. Microalgae are particularly
considered for bio-fixation because of their ability to grow fast and fix greater amounts of carbon dioxide.
The bio-mitigation of carbon dioxide and other flue gases by microalgae have significantly gained interest
in reducing the emissions from coal-fired power plants. The algae biomass thus produced by capturing
carbon can be used in generating valuable products such as fuel, animal feed and fertilizer. Power plants
are the major sources of CO 2 and release 5.7 giga tones of carbon dioxide per year (Kadam 2001). CO 2 is
produced by both stationary and mobile sources. Microalgae offer a natural way to recycle carbon dioxide
from the flue gas and thus help in reducing the effects of global warming and climate change.
Microalgal biomass is composed of 45 to 50% carbon based on dry weight measurements
(Schlesinger 1991). The high carbon content of microalgae makes it suitable for storing carbon. CO 2
present is flue gas can significantly raise the growth rates of microalgae. Microalgae can be engineered in
open ponds or photobioreactors to maximize CO 2 conversion to biomass thereby sequestering carbon and
also producing a biofuel. The selection of microalgae is the most important factor in the bio-mitigation
of carbon dioxide from flue gases generated by power plants. The algae should have high growth and
CO 2 utilization rates. The other suitable characteristics for carbon dioxide bio-fixation are their ability
to tolerate SOx and NOx, and thrive in mass cultures without contamination. Lastly, the algae should
be chosen also considering the harvesting process. Algae with autoflocculation characteristics simplify
the harvesting step and minimize the energy and cost in the downstream processing of algae production
(Brennan and Owende 2010).
Algae (Chlorella vulgaris and Scenedesmus obliquus) are isolated from the water bodies near to the
power plants so that they are already adapted to the flue gases generated and environmental conditions
of that area were ideal for biofixation (De Morais and Costa 2007). They were able to grow in culture
media with 18% (v/v) CO 2 . Biological carbon sequestration using microalgae offers several advantages
over geological and ocean sequestration systems. Algae can sequester carbon dioxide directly and the
costs of separation of CO 2 gas are avoided. Microalgae production systems can be located near the power
plant: this does not require huge costs on transportation of CO 2 . The advantages of using microalgae
biofixation processes are: their ability to grow on flue gas, higher carbon fixation rates than other plants
and their potential to grow in wastewaters thereby minimizing the fresh water needs (Schenk et al. 2008).
The Solvay process can be modified to convert CO 2 from fossil fuel power plants to bicarbonates. The
carbon dioxide gas is passed through brine solution with ammonia as a catalyst under alkaline conditions
to produce sodium bicarbonate according to this chemical reaction (Huang et al. 2001).
CO 2 + NaCl + NH 3 + H 2 O → NaHCO 3 ↓ + NH 4 Cl (Gouveia and Oliveira 2008)
Sodium bicarbonate was a better carbon source for Scenedesmus than sodium carbonate. Carbon
dioxide can be utilized in the form of carbonate salts using Solvay process. These salts can be used as a
carbon source for algae growth when the power plant is not located near the algae pond. Algae can thus
be used for bio-fixation of CO 2 in industrial flue gases.
Conclusion
As far as the algal biomass production has concerned, currently there are lot of projects started in many
countries more particularly in India, China, United States, etc., and they are using the harvested biomass
for biofuel production because it might contain heavy metals and unwanted chemicals available since the
microalgae grown in municipal seawage or from effluent. This is best biological method recommended
by naturalists and scientists to protect environment clean. In this way, not only the waste water has treated
simultaneously the algae capturing atmospheric CO 2 thus it subsequently helps to reduce global warming.