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7 Benefits of CO[sub(2)] Sequestration by Mineral Carbonation
CARBON CAPTURE AND STORAGE
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Algae-based Carbon Capture and Sequestrations
Xiaolei Zhang, Song Yan, R. D. Tyagi, Rao Y. Surampalli and
Tian C. Zhang
Increasing emission of greenhouse gases caused by the growing need in the
amount of fossil fuel has received a considerably attention because of the predicted
relationship with global warming (Surampalli et al. 2013). Carbon capture and
sequestration (CCS), mainly refers to carbon dioxide capture and sequestration, is an
efficient technology for mitigating climate change (Zhang and Surampalli 2013).
Various sequestration methods such as ocean sequestration, soil sequestration, terrestrial
and marine vegetation sequestration, and geologic formation sequestration, have been
reported (Pan et al. 2003; Adhikari et al. 2009; Nicot et al. 2009; Strand and Benford
2009; Zhang and Surampalli 2013). Ocean carbon sequestration and geologic carbon
sequestration are considered to be the most acceptable carbon sequestration methods in
comparison with other methods because of the abundantly available sources (oceans and
underground geologic formations). However, the possibility of the carbon leakage in
ocean and/or geologic carbon sequestration has inhibited their applications. On the other
hand, vegetation carbon sequestration, also called carbon dioxide biofixation, is
receiving a great deal of interest. Vegetation carbon sequestration is a process in which
vegetation (e.g., trees, crops, grasses, and algae) uses carbon dioxide as a carbon source
to form energy-rich organic compounds (for growth) through photosynthesis (Eq. 12.1).
It is a method that simultaneously decreases the amount of carbon dioxide in the
atmosphere and creates value-added products for human beings.
6CO2 + 12 H 2O ⎯⎯⎯⎯
→ C6 H12O6 + 6O6
Among all the vegetation, algae are superior to others in carbon sequestration due
to its fast growth rate (10 to 50 times faster than other plants such as trees and crops) and
the possibility of using them for producing green energy such as biodiesel, protein, etc.
(Usui and Ikenouchi 1997; Borowitzka 1999; Bush and Hall 2006; Chisti 2007; Li et al.
CARBON CAPTURE AND STORAGE
2008; Meng et al. 2009). In addition, most of algae grow in the aqua environment, which
leads the algae-based carbon sequestration more favorable than other vegetation carbon
sequestration because of the land saving. Moreover, it is reported that algae could also
absorb the gases such as SOX and NOX, which are the major cause of acid rain (Rushing
2008). Various macro- and micro-algae, such as Chlorella sorokiniana, Chlorella
vulgaris, Chlorella pyrenoidosa, Chaetomorpha linum, Haematococcus Pluvialis,
Pterocladiella capillacea, Scenedesmus obliquus, Spirulina platensis, cultivated in either
open ponds or closed photoreactors, have been reported in carbon sequestration (Jeong
et al. 2003; Aresta et al. 2005; Moheimani 2005; Huntley and Redalje 2007; de Morais
and Costa 2007; Liebert 2008; Oilgae 2011). Although these algae are mainly applied
for environmental control such as the purification of flue gases (Douskova et al. 2009;
Suryata et al. 2010) and wastewater treatment (Benemann 2002; Wang et al. 2010),
some algae (e.g., Chlamydomonas reinhardtti) have hundreds of genes that are uniquely
associated with carbon dioxide capture and generation of biomass as indicated by studies
on genes in the algal genomes (Oilgae 2011).
Recently, considerable studies have concluded that algae, the third generation
feedstock researched for bio-energy production, is the best agent for the biologically
capturing carbon dioxide from large-scale emitters such as power plants and industries
(e.g., Oilgae 2011; PPCCS 2013). Algae are also a sensible choice with regard to their
fast proliferation rates, extensive tolerance to wild, extreme environments, and their
potential for comprehensive cultures (Oilgae 2011). In this chapter, the principle and
carbon cycle of algae-based carbon dioxide sequestration are described first, and then
influence factors are considered, followed by the applications of algae-based carbon
sequestration and cost estimation. The chapter ends with some discussions about future
perspective and conclusions.
12.2 Principle and Carbon Cycle
As any other terrestrial plant-based carbon sequestration, algae accomplish
carbon dioxide fixation through photosynthesis. As shown in Eq. 12.2, algae can convert
carbon dioxide to biomass and oxygen under sufficient supply of nutrients, photons, and
water through photosynthesis. Some studies used CH1.8N0.17O0.56 to represent the
composition of typical algae (Bayless et al. 2003, 2009); thereby, according to Eq. 12.2,
every 44 g of carbon dioxide can produce 25 g of algae biomass through algae
photosynthesis, which is a rather efficient way to fix carbon dioxide.
CO2 + H2O + Nutrients + Photons → Algae biomass + O2
As shown in Eq. 12.2, water, nutrients, and light also take significant parts in the
process. Algae grow in high moisture conditions (usually in aqua conditions), and
CARBON CAPTURE AND STORAGE
therefore, water is considered to be always sufficient during the process. Nutrients
(nitrogen and phosphorus) can be added by adding chemicals or wastewater which
contains abundant nutrients (Benemann 2002). Photons are from the sun or illumination
should a cultivation reactor be used (Hon-nami and Kunito 1998; Aresta et al. 2005).
Photons (Sun or
Algae (moisture condition)
Figure 12.1. Carbon dioixde fixation by algae and possible usage of algae. CO2 is first
‘eaten’ by algae for biomass growth, which will be collected/used to produce valuable
substances. After the algal substances being consumed, sequestered CO2 will finally be
released to the atmosphere as CO2, and thereafter, be captured by algae as food again
The products of Eq. 12.2 are algae biomass and oxygen. The increased biomass
can be used for human food supplements, animal feed, or raw materials for making
ethanol, methane, and biodiesel according to the algae properties, and finally will be
CARBON CAPTURE AND STORAGE
converted to carbon dioxide again through combustion (biofuels) or biodegradation
(food supplements and animal feed) (Becker 2004). Oxygen will go back to the
atmosphere and be used for respiration of living beings. The whole process of algae
carbon sequestration is simply exhibited in Figure 12.1. As shown in Figure 12.1, the
carbon cycle in algae-based carbon sequestration is an endless chain of carbon dioxide
fixation and release without net carbon dioxide impact.
12.3 Effects of Major Factors
The efficiency of algae-based carbon sequestration is affected by many factors
such as algae species, cultivation condition, carbon dioxide concentration, and other
components of the feeding gas. In this section, the effect of some major factors on algaebased carbon dioxide sequestration is discussed.
12.3.1 Algae Strains Effect
Algae are known as a rich source of protein (50–60% dry weight), lipid (2%–50%
dry weight), and vitamins. Various algae, including high vitamin content algae, high
CO2 tolerance algae, high lipid content algae, etc., have been reported to be capable of
fixing carbon dioxide (Hanagata et al. 1992; Becker 1994; Graham and Wilcox 2000;
Pedroni et al. 2004; Aresta et al. 2005; Rengel 2008). Usually, algae selection is based
on the project purpose. For example, when algae are prepared for vitamin supplement,
algae with high productivity of target vitamins will be used in carbon dioxide
sequestration. In addition, algae growth rate is significantly important in determining the
use of algae for carbon dioxide sequestration as well. Algae with high growth rates also
refer to having high carbon dioxide sequestration rate as well as high production rate on
protein, lipid, or vitamins. Additionally, it is also considered to be beneficial in saving
the cultivation area. Stromgren (1984) observed that, among three algae, Pelvetia
fastigiata, Pterocladia capillacea and Z. farlowii, Pterocladia capillacea had a greater
growth rate than the other two algae under the similar cultivation condition. The report
suggests that algae selection be necessary in order to achieve high growth rate for carbon
In the early 1930s, researchers have observed that algae (Chlorococcurn sp.)
were capable of producing vitamins (Gunderson and Skinner 1934). Berg-Nilsen (2006)
pointed out that Spirulina and Chlorella had high value in protein production.
Chlamydomonas reinhardtii was reported being a good source of therapeutic proteins
(protein content > 50%) (Rasala et al. 2010). Oleaginous algae have been extensively
studied for biodiesel production. Several algae species such as Botryococcus sp.,
Chlorella sp., Oedogonium sp., and Spirogyra sp. show great potential in biodiesel
production (Banerjee et al. 2002; Hossain and Salleh 2008; Francisco et al. 2010). Velea
CARBON CAPTURE AND STORAGE
et al. (2009) investigated 35 strains of microalgae to sequester carbon dioxide and to
produce oil for biodiesel production, and they found that the lipid content of some
microalgae such as Chlorobotrys species was up to 70% dry weight and the protein
content was around 40–43 %. The studies reveal that selection of algae in carbon dioxide
sequestration should comply with the expecting utilization of algae biomass.
12.3.2 Reactor Effect
Bioreactors used for algae carbon dioxide cultivation include lakes, raceway
ponds, oceans, plate photobioreactor, carboy photobioreactor, and tubular
photobioreactor (Jeong et al. 2003; Ono and Cuello 2004; Moheimani 2005). Compared
to open algae cultivation systems (lakes, raceway ponds, oceans), closed
photobioreactors provide higher algae productivities and better control on the cultivation
condition such as temperature, medium pH, salinity, light intensity, and concentrations
of nutrients (Jeong et al. 2003). However, in photobioreactors artificial light is usually
used, which increases the cost of carbon sequestration, while open algae cultivation
systems mostly rely on natural light (sunlight), which can avoid the addition of the
energy that is usually needed in closed photobioreactors (Douskova et al. 2009).
Because the cultivation condition has a significant impact on the composition and
productivity of algae (Dauta et al. 1990; Suryata et al. 2010), photobioreactors are
preferred. In order to reduce the cost of algae-based carbon dioxide sequestration using
closed photobioreactors, researchers employed solar electrical energy generation
systems to convert sunlight into electricity, which then was used to supply light for the
photobioreactors. To some extend the algae cultivation cost could be reduced through
the application of solar electrical energy generation. Additionally, a natural light and
artificial light combination system is also an efficient method for reducing the
cultivation cost. For instance, the greenhouse photobioreactor system placed in a
greenhouse can take the advantage of the sunlight in day and generate artificial light at
night. Therefore, compared to the cultivation system which depends on either net
sunlight (which works only in day) or net artificial light (which consumes a large
amount of energy), the greenhouse photobioreactor system prolongs the cultivation time
from around 12 hours (for the outdoor system) to 24 hours and save some extra energy
12.3.3 Effects of Cultivation Conditions
Algae cultivation conditions, such as pH, salinity, nutrient concentrations of the
medium, temperature and light intensity of the cultivation system, are essential factors in
algae-based carbon sequestration because they determine the algae productivity and the
process efficiency. Furthermore, they also affect the accumulation of protein, vitamins,
and lipid, which are associated with algae-based carbon sequestration cost when the final
use of the algae is considered as a part of the cost of algae cultivation. Table 12.1 shows
CARBON CAPTURE AND STORAGE
some major growth parameters for algae. For flue-gas CO2 capture, the species that
survive best in acidic conditions and high temperature are more desirable.
Table 12.1. Major growth parameters for algae (Oilgae 2011)
High CO2 fixation rate, densely culturable
High growth ability, high temperature tolerance
High amino acid content; good digestibility
(effective fodder); grow well under acidic
conditions; not easily contaminated
High CO2 tolerance, like acidic cultures
Accumulates lipid granules inside the cell; high
temperature and CO2 tolerance; like acidic cultures
High pH tolerance
DT = doubling time.
pH. Studies reported that pH requirement varied according to the algae species
(Chen and Durbin 1994; Yang and Gao 2003). Chen and Durbin (1994) studied the pH
effect on the growth of marine algae, Thalassiosira pseudonana, and observed that the
algae grew best at pH of 8.8 to 9.4, which was due to the pH effect on algae metabolism
(EPOCA 2009). In algae-based carbon dioxide sequestration, the pH of the algae
cultivation system becomes very important as it also affects the solubility and
availability of carbon dioxide in the system besides the effect on algae metabolism
(Moheimani 2005). The form of carbon dioxide in aqua solution could be free carbon
dioxide, bicarbonate, and carbonate, depending on the pH. Most of the researchers
agreed that free carbon dioxide was the major available carbon source in algae
photosynthesis, which was predicted that only free carbon dioxide could bind with
enzyme ribulose bisphosphate carboxylase to accomplish the photosynthesis process
(Blackman and Smith 1911; Rabinowitch 1945; Cooper et al. 1969; Riebesell et al.
1993). Moreover, some studies reported that bicarbonate also impacted the
photosynthesis of algae and predicted that certain algae were capable of dehydrating
bicarbonate into carbon dioxide in cells (Badger et al. 1980, Kaplan et al. 1980, Beardall
and Raven 1981; Falkowski, 1991). However, it is still debatable that bicarbonate is one
form of the substrates in the algae photosynthesis process because the studies on
bicarbonate limitation in algae cultivation displayed that photosynthesis was not limited
by bicarbonate limitation (Riebesell et al. 1993; Chen and Durbin 1994). Therefore, as
the pH of the algae cultivation system increases, free carbon dioxide concentration will
be decreased, and thus, the photosynthesis process will be inhibited due to the carbon
source (carbon dioxide) limitation. Low pH also could inhibit algae growth due to the
enhanced toxicity to the algae from heavy metals, which usually exists in the cultivation
system (Luderitz and Nicklisch 1989) and the decrease in photosynthetic activity of
algae (Baker et al. 1983).
CARBON CAPTURE AND STORAGE
In short, pH effect on algae carbon dioxide sequestration is mainly due to the
effect of pH on algae metabolism, the type of carbon species in the cultivation systems,
and algae photosynthetic activity. The optimal pH of the cultivation system should be
determined before cultivation according to the algae species and the supplied carbon
Temperature. As any living beings, algae have a range of suitable growth
temperature. Usually, algae could functionalize normally between 10 ºC and 30 ºC, and
the growth rate of algae increases as temperature increases within this temperature range
(Laws et al. 1988; Suryata et al. 2010). Temperature effect on the activity of
photosynthesis enzymes of algae is the main reason of temperature effect on algae
growth because low or high temperature could inactive enzyme activities (Daniel et al.,
2008). However, studies revealed that some algae can tolerate low temperature (< 10 ºC)
or high temperature (> 30 ºC). Hence, the algae which can bear high temperature such as
Cyanidium caldarium and Synechococcus elongatus could be used for sequestering the
flue-gas CO2 which are usually with high temperatures (around 120 ºC); the algae which
can bear low temperature could be used for sequestering carbon dioxide in cold regions
(Seckbach et al. 1971; Miyairi 1995). Temperature is controllable in indoor cultivation
systems while the temperature varies in the day and year in outdoor algae carbon dioxide
sequestration systems. This is one of the reasons that closed photobioreactor has a higher
carbon dioxide sequestration efficiency than outdoor open ponds.
Salinity. Salinity effect on algae growth is mainly due to the effect of osmotic
stress and ion stress on algae cell growth. Generally, salinity should be controlled
according to the algae species. Suryata et al. (2010) reported that the optimal salinity for
blue-green microalgae was around 1.5%. Up to date, salinity effect on algae carbon
sequestration has not been paid sufficient attention. However, it has been stimulated
recently to study the salinity effect on algae-based carbon sequestration because it has
been accepted by the public that using algae growing in oceans could be the most
profitable and practical way to sequester carbon dioxide due to the large available ocean
Light. Light is one of the key factors in algae carbon sequestration as it is the
base of energy conversion (luminous energy to chemical energy) (Bouterfas et al. 2002,
2006). Light intensity is usually used to evaluate light effect on algae-based carbon
dioxide sequestration because it, to some extent, determines the penetration and
distribution of light (Meseck et al. 2005). Bouterfas et al. (2002) reported that the
appropriate light intensity for algae growth was around 400 μmol photons/(m2·s). For
the cultivation system with a light source from artificial light, the light effect can be
avoided by light adjustment and reactor design. However, for the cultivation system with
the light source from natural light (the Sun), the light effect is significant in algae-based
carbon dioxide sequestration. Generally, the appropriate reactor design can improve the
CARBON CAPTURE AND STORAGE
light penetration and distribution, and hence decrease the light impact on algae
cultivation (Bayless et al.2003). Furthermore, stirring is also a method to improve the
light penetration and distribution to the algae cultivation system with the light source
from natural light since the stirring would offer an equal light exposure opportunity to
the algae in deep position of the reactor (pond or lake). However, the stirring strategy is
with the risk of reduce the productivity of algae when the shear stress is higher than
algae tolerance (Ogbonna and Tanaka 1997; Stepan et al. 2002). Some studies employed
lenses, glass or plastic cones, optical fibers, and quartz or acrylic rods to enhance light
receive of algae (Tredici and Zittelli 1998).
Apart from light intensity, light/dark cycle, also called photoperiod, is another
essential element in algae growth (Bouterfas et al. 2006). The optimal light/dark cycle
for algae growth varies according to the algae species (Brand and Guillard 1981).
Bouterfas et al. (2002) reported that Selenastrum minutum, Coelastrum micropurum f.
astroidea, and Cosmarium subprotumidum showed the best growth under the light/dark
cycle of 15h/9h.
Nutrients. The basic nutrients in algae growth are nitrogen and phosphorus. For
large scale cultivation systems, it is not practical to add nutrients in the system due to the
cost consideration. Therefore, large scale algae-based carbon dioxide sequestration can
cooperate with treatment of wastewater which is rich in nitrogen and phosphorus (Lau et
al. 1996). For small scale cultivation systems, compared to cooperating with wastewater
treatment, the addition of nutrients into the reactor is a more efficient way to supply
nutrients to algae (Stepan et al. 2002). In fact, the nutrient source and addition amount
should be determined according to the reality. For instance, in carbon dioxide
sequestration from flue gases of power plants, some of the nutrients, mainly referring to
nitrogen, are available in the flue gases, and thus, nutrient addition should be adjusted
according to the composition of the flue gases (Brown 1996; Matsumoto et al. 1997).
12.3.4 Mixing Effect
Mixing is significantly important for open pond algae cultivation systems
because the algae in deep location may not be able to obtain enough photons to complete
the photosynthesis without mixing due to the shade from the top layer algae in the pond.
In addition, mixing also influences the transfer of substances, including carbon dioxide,
nitrogen, phosphate, and minerals. However, an appropriate mixing intensity is required
because too much mixing intensity could harm algae, while too less mixing intensity
could not reach the demand to assist substance transfer (Ogbonna and Tanaka 1997;
Jungo et al. 2001; Stepan et al. 2002). In addition, mixing could influence pH stability of
the cultivation system (Persoone et al. 1980). Usually, direct injection of carbon dioxide
into the algae cultivation system is the most common way for carbon dioxide addition.
However, the addition of a large amount of carbon dioxide into the cultivation system
CARBON CAPTURE AND STORAGE
would cause a decrease in local pH. Therefore, appropriate mixing is required in algaebased carbon dioxide sequestration. Moreover, mixing would also enhance oxygen
diffusion into the atmosphere and thus promote the photosynthesis process (Eq. 12.2).
Drapcho and Brune (2000) observed that the carbon fixation rate increased 50% when a
proper mixing was performed. Moheimani (2005) reported that the growth rate and
productivity of algae, Pleurochrysis carterae, showed an increasing trend when the
mixing speed was increased from 0 to 200 rpm, while when the mixing speed was
beyond 200 rpm, the growth rate and productivity of algae started to decrease. It was
also observed that algae started dying when the mixing speed was up to 600 rpm.
Marshall and Huang (2010) used a numerical model to stimulate the mixing effect on
algae productivity and reported that a proper mixing would significantly enhance the
algae production rate. Moreover, mixing would also improve the transfer rate of carbon
dioxide to liquid because turbulence can decrease the thickness of the liquid boundary
layer (Yang and Cussler 1986).
12.3.5 Carbon Dioxide Concentration and Transportation Effect
As discussed in Section 12.3.3, free carbon dioxide is the major substrate in an
algae photosynthesis process. Researchers reported that carbon dioxide concentration
had a great impact on carbon metabolism and photochemical properties of algae cells
(Badger et al. 1980; Kaplan et al. 1980; Spalding et al. 1984). Hence, carbon dioxide
concentration would significantly impact algae productivity. Low carbon dioxide
concentration will inhibit algae productivity due to the limited supply of the substrate
(carbon dioxide). For instance, using algae to fix carbon dioxide in the air would not be
effective because the concentration of carbon dioxide in the air is only around 0.03‒
0.06%. It was also reported that high carbon concentration would inhibit algae growth
because of the possibility of pH decrease when a high concentration of free carbon
dioxide presents in the cultivation system.
Although CO2 concentrations vary, depending on the flue gas source, 15–20%
(v/v) is a typically-assumed amount of concentration (PPCCS 2013). Kumar et al. (2010)
used algae, Spirulina platensis, to fix carbon dioxide from gas mixtures with carbon
dioxide contents of 15%, 30%, and 100% (v/v), respectively, and observed that algae
productivity was reduced, and even the death of algae occurred during the long term
cultivation with these high carbon dioxide concentrations. On the contrary, some studies
reported that some algae such as Chlorella vulgaris, Chlorococcum littorale, and
Scenedesmus sp., could tolerance to high carbon dioxide concentration (13%, 60%, and
80% (v/v)) (Hanagata et al. 1992; Kodama et al. 1993; Douskova et al. 2009). These
studies suggest that the capability for algae to tolerance to high carbon dioxide
concentration varies with the algae species. Therefore, in algae carbon dioxide
sequestration, algae can be selected according to the carbon dioxide concentration in the
target gases. For instance, the algae with best productivity under carbon dioxide