Tải bản đầy đủ - 0 (trang)
7 Benefits of CO[sub(2)] Sequestration by Mineral Carbonation

7 Benefits of CO[sub(2)] Sequestration by Mineral Carbonation

Tải bản đầy đủ - 0trang

CARBON CAPTURE AND STORAGE



337



Six, J., Conant, R.T., Paul, E.A., and Paustian, K. (2002). “Stabilization mechanisms of

soil organic matter: Implications for C-saturation of soils.” Plant and Soil,

241(2), 155‒176.

Smith, P., Powlson, D., Glendining, M., and Smith, J.O. (1997). “Potential for carbon

sequestration in European soils: preliminary estimates for five scenarios using

results from long-term experiments.” Global Change Biology, 3(1), 67‒79.

Solomon, S., Qin, D., Manning, M., Chen, Z., Marquis, M., Averyt, K., Tignor, M., and

Miller, H. (2007). The Physical Science Basis. Contribution of Working Group I

to The Fourth Assessment Report of The Intergovernmental Panel on Climate

Change, Climate Change 2007: The Physical Science Basis, New York, USA.

Studdert, G.A., and Echeverria, H.E. (2000). “Crop rotations and nitrogen fertilization to

manage soil organic carbon dynamics.” Soil Science Society of America Journal,

64(4), 1496‒1503.

Sundquist, E.T., Burruss, R., Faulkner, S., Gleason, R., Harden, J., Kharaka, Y., Tieszen,

L., and Waldrop, M. (2008). “Carbon sequestration to mitigate climate change.”

US Department of the Interior, US Geological Survey. Retrieved from:

http://pubs.usgs.gov/fs/2008/3097/pdf/CarbonFS.pdf.

Tanthachoon, N., Chiemchaisri, C., and Chiemchaisri, W. (2007). “Utilisation of

municipal solid waste compost as landfill cover soil for reducing greenhouse gas

emission.” International Journal of Environmental Technology and

Management, 7(3), 286‒297.

Tsang, C.F., Benson, S., Kobelski, B., and Smith, R. (2002). “Scientific considerations

related to regulation development for CO2 sequestration in brine formations.”

Environmental Geology, 42(2‒3), 275‒281.

Turhollow A.F., and R.D. Perlack. (1991). “Emissions of CO2 from energy crop

production.” Biomass and Bioenergy, 1(3), 129‒135.

Uhlen, G. (1991). “Long-term effects of fertilizers, manure, straw and crop rotation on

total-N and total-C in soil.” Acta Agriculturae Scandinavica, 41(2), 119‒127.

Uhlen, G., and Tveitnes, S. (1995). “Effects of long-term crop rotation, fertilizers, farm

manure and straw on soil productivity.” Norwegian Journal of Agricultural

Sciences, 9, 143‒161.

UNIDO (2010). Global Technology Roadmap for CCS in Industry. Policy Workshop,

http://www.unido.org/fileadmin/user_media/Services/Energy_and_Climate_Cha

nge/Energy_Efficiency/CCS/annexes.II.pdf (Jan19, 2014).

VanDevender, K., and Pennington, J.A. (2004). “Organic burial composting of cattle

mortality.” FSA1044, Cooperative Extension Service, University of Arkansas

Division of Agriculture, US Department of Agriculture.

Wanichpongpan, W., Gheewala, S.H., and Towpraynoon, S. (2004). “Environmental

evaluation of energy production from landfill gas in a life cycle perspective. A

case study Nakhon Ratcharima.” The Joint International Conference on

Sustainable Energy and Environment (SSE), Hua Hin, Thialand, 595‒599.



338



CARBON CAPTURE AND STORAGE



West, T.O., and Post, W.M. (2002). “Soil organic carbon sequestration rates by tillage

and crop rotation: A global data analysis.” Soil Science Society of America

Journal, 66(6), 1930‒1946.

Witter, E., Mårtensson, A.M., and Garcia, F.V. (1993). “Size of the soil microbial

biomass in a long-term field experiment as affected by different n-fertilizers and

organic manures.” Soil Biology and Biochemistry, 25(6), 659‒669.

Witzke, P., Banse, M., Gömann, H., Heckelei, T., Breuer, T., Mann, S., Kempen, M.,

Adenäuer, M., and Zintl, A. (2008). “Modelling of energy-crops in agricultural

sector models‒a review of existing methodologies.” JRC42597, European

Commission, Joint Research Centre (JRC), Institute for Prospective

Technological Studies (IPTS), Spain.

Woodall, C.W., Heath, L.S., and Smith, J.E. (2008). “National inventories of down and

dead w oody material forest carbon stocks in the United States: Challenges and

opportunities.” Forest Ecology and Management, 256(3), 221‒228.

Woodall, C.W. (2010). “Carbon flux of down woody materials in forests of the North

Central United States.” International Journal of Forestry Research, 2010, 1‒10.

Zhang, T.C., and Surampalli, R.Y. (2013). “Carbon capture and storage for mitigating

climate changes.” Chapter 20 in Climate Change Modeling, Mitigation and

Adaptation, Surampalli, R., Zhang, T.C., Ojha, C.S.P., Gurjar, B.R., Tyagi, R.D.,

and Kao, C.M. (eds.), ASCE, Reston, Virginia, February 2013, 538‒569.



CHAPTER 12



Algae-based Carbon Capture and Sequestrations

Xiaolei Zhang, Song Yan, R. D. Tyagi, Rao Y. Surampalli and

Tian C. Zhang



12.1 Introduction

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.



Light

6CO2 + 12 H 2O ⎯⎯⎯⎯

→ C6 H12O6 + 6O6



(12.1)



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.



339



340



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



(12.2)



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



341



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

illumination)



Nutrients

(wastewater or

addition)



Carbon dioxide

(atmosphere or

flue gases)



Algae (moisture condition)



Oxygen



Biofuel

(biodiesel,

methane,

ethanol.

Hydrogen,

etc.)



Food

supplement



Biomass



Animal

feed



Water



Fertilizers



Others



Biodegradation

Combustion



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



342



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

dioxide sequestration.

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



343



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

(Berg-Nilsen 2006).



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



344



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)



a



Species

Chlorococcum sp.



Temp (oC)

15–27



pH

4–9



CO2%

≤ 70



DT (h)a

8



Features

High CO2 fixation rate, densely culturable



Chlorella sp.



15–45



3–7



≤ 60



2.5–8



High growth ability, high temperature tolerance



Euglena gracilis



23–27



3.5



≤ 100



24



High amino acid content; good digestibility

(effective fodder); grow well under acidic

conditions; not easily contaminated



Galdieria sp.



≤ 50



1–4



≤ 100



13



High CO2 tolerance, like acidic cultures



Viridiella sp.



15–42



2–6



≤5



2.9



Accumulates lipid granules inside the cell; high

temperature and CO2 tolerance; like acidic cultures



Synechococcus lividus



44–55



≤ 8.2



≤ 70



8



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



345



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

dioxide concentration.

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

area.

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



345



346



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



347



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



Tài liệu bạn tìm kiếm đã sẵn sàng tải về

7 Benefits of CO[sub(2)] Sequestration by Mineral Carbonation

Tải bản đầy đủ ngay(0 tr)

×