Philip ManninoTingyu WenKaixuan Xu

Atmospheric CO2 Capture and Biofuel Production of Microalgae

Purpose, Identity of Microalgae

The increasing amount of carbon dioxide produced from burning fossil fuels has

led to a climate change that could have serious and catastrophic consequences.

Therefore, any method that can capture the carbon dioxide from flue gas and prevent

it from entering the atmosphere is of the utmost importance. Microalgae can be used

to not only capture CO2 from flue gas, but the captured CO2 can be utilized as

biofuels.1 Because of their ability to fix CO2 as either dissolved CO2 or CO2 salts such

as Na2CO3, NaHCO3, or H2CO3, microalgae have higher photosynthetic efficiency

than terrestrial plants.2 This fact leads many researchers to believe that microalgae are

the best candidates for carbon capture. Like all plants, microalgae get their energy

from a process known as the Calvin Cycle (scheme 1). Three molecules of Ribulose

1,3 bisphosphate react with three molecules of CO2 catalyzed by the enzyme rubisco

to generate six molecules of 3-phosphoglycerate (the carbons that come from carbon

dioxide are in red). These six molecules are reduced using six molecules of ATP and

six molecules of NADPH (the ATP and NADPH are generated during the light

dependent stage of photosynthesis) to produce six molecules of glyceraldehyde 3-

phosphate. Five of these molecules are used to regenerate the three molecules of

ribulose 1,3 bisphosphate and one is used to make half of glucose (2 cycles are

necessary to produce one full glucose molecule). Under certain conditions, the

glucose is broken down and stored as triglycerides (TGs).

A few groups have proposed that these TGs, which are carbon dense, would be

1

Philip ManninoTingyu WenKaixuan Xubest stored underground so as to lower the atmospheric CO2 concentration.3 Many

other groups, however, have proposed utilizing these TGs as biofuels. The most

widely accepted method for converting these TGs into biofuel is through a process

known as transesterification1 (scheme 2). In this process, the TGs are reacted with

three equivalents of an alcohol, typically methanol, producing three long chain esters

and glycerol. The three long chain esters would then be isolated and used as biofuels.

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Philip ManninoTingyu WenKaixuan Xu

O

O-23OP

OH

OH

OPO3

-2

Ribulose 1,3-bisphosphate

3 + CO

O

3rubisco

Carbon Fixation OH

OPO3

-26

3-Phosphoglycerate

Reduction

OHC

HO

OPO3

-2

Glyceraldehyde 3-Phosphate

1 Glyceraldehyde 3-Phosphate

1/2 Glucose

Triglycerides

CH

O

OHHO

HO

6

6 ATP

6 NADPH3 ATP

Scheme 1: The Calvin Cycle

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Philip ManninoTingyu WenKaixuan Xu

H2C

HC

H2C

O

O

OO

R

O

RO

R

Triglyceride

+ 3 CH3OH

H2C

HC

H2C

OH

OH

OH

O

RO+

Alcohol Glycerol

3

Esters

Scheme 2: Transesterification

4

Philip ManninoTingyu WenKaixuan XuMicroalgae lipid through transesterification reaction with microwave

irradiation:

The suitability of Nannochloropsis sp. Lipid was determined by Fourier Transform

Infra-Red Spectrometry (FT-IR). In the FT-IR spectra, every peak is assigned to a

functional group. There are two shape peaks at 2839 and 2949 cm-1, showing the

vibration of C-H bond on carbohydrates and lipid. The peak at 1012 cm -1 indicates C-

O-C bond of polysaccharides. The bending of methyl lipids was shown at 1450 cm -1.

A broad peak at 3251 cm-1 shows the O-H stretching from water and N-H stretching

from proteins of Nannochloropsis sp. Another functional group from the proteins is at

1643 cm-1, indicating amide 1 (C=O) stretching. These results show the presence of

methyl and methylene groups, indicating the methyl ester formation. FT-IR spectra

also shows that the most suitable time for microwave treatment for biodiesel

production is 30 min. (Figure 1) 1

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Philip ManninoTingyu WenKaixuan Xu

Figure 1: FT-IR spectra at three different duration of microwave treatment

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Philip ManninoTingyu WenKaixuan XuGrowth and Lipid Productivity of Nannochloropsis sp. With different

concentrations of CO2 in Gaseous and Solution Form:

Microalgae grow at higher CO2 concentration (1–10%) present higher biomass

productivity compared to those grow at atmospheric CO2 concentration. Table 1

summarizes the experiments done on microalgae for atmospheric CO2 capture. CO2

removal rates and biomass productivity when growing autotrophically were recorded.

A pre-processing of gaseous stream may be performed to concentrate CO2 to increase

the efficiency of CO2 capture by microalgae. Besides the CO2 concentration,

temperature and light intensity can also affect microalgae growth and, consequently,

the CO2 fixation rates and biomass productivity. The photosynthetic efficiency of

microalgae and CO2 solubility drop at high temperatures. Intense light penetrates

better into high-density cultures.2

Nannochloropsis sp. strain was cultivated within five different concentrations of

CO2 (1, 10, 15, 20, and 25%) (v/v). According to figure 2, CO2 concentration at 15%

gave the most rapid growth of Nannochloropsis sp., producing the highest dry

biomass weight of 0.441 g/L at day 8. The second highest dry weight is 0.392 g/L on

day 8 at 10% of CO2 concentration. Throughout the cultivation period, the

Nannochloropsis sp. strain indicated an increasing trend at the first 8 days at 10%,

15%, and 20% concentrations of CO2. At 1% CO2 as a control group, the strain grew

much slower than other concentrations. The concentration of CO2 in the atmosphere is

about 0.0387% (v/v)4, which is not as high as the best growth condition for

microalgae. However, from combustion processes, wastes gases contains more than

7

Philip ManninoTingyu WenKaixuan Xu15% CO2, showing a possibility as a source for industrial microalgae production.

From other researchers’ study, there is a specific growth rate of Nannochloropsis sp.,

increasing from 0.33-0.52/day cultivated with atmosphere air with 15% CO2.5 All the

results show that high concentration of CO2 boosts photosynthetic efficiency. Thus,

microalgae can produce a higher quantity of biomass within a shorter time. On the

other hand, the Nannochloropsis sp. strain produced maximum amount of lipid with

15% CO2 showing in Figure 3. The total lipid productivity was determined after eight

days of cultivation under five different CO2 gas concentrations. The highest yield of

lipid productivity is 18.93mg/L per day with 15% CO2.

Solute carbonates or dissolved CO2 can be absorbed directly by microalgae. In this

study, the ability of microalgae growth with carbonate salts from fuel gases was

measured by a series solutions containing HCO3- and CO32- in five concentrations

(2,5,10,15,20% (v/v)). The results show an increasing rate on the dry biomass weight

as the carbonate concentration increased. (Figure 4) The highest dry biomass of 0.55g

was found at the 20% carbonate on day 10, corresponding to the highest dry biomass

of 0.44g at the 15% CO2 gas on day 8. These observations indicate that growth rate of

microalgae in solute carbonate condition is better and faster than in CO2 gas

conditions. Figure 5 shows the effect of series fuel gas solution on lipid productivity.

Nannochloropsis sp. produce more in a more concentrated fuel gas condition. The

maximum yield of lipid productivity was found at 20% carbonate solution with 23

mg/L per day. It was also 27% higher than that produced by the 2% carbonate

solution.

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Philip ManninoTingyu WenKaixuan Xu

Table 1: Atmosphere carbon capture by microalgae.

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Philip ManninoTingyu WenKaixuan Xu

Figure 2: Comparison of dry biomass vs times of Nannochloropsis sp. strain cultivated in five different flasks with CO2 concentrations of 1, 10, 15, 20 and 25% (v/v).

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Philip ManninoTingyu WenKaixuan Xu

Figure 3: Comparison of lipid productivity vs CO2 level of Nannochloropsis sp. strain cultivated in five different flasks with CO2 concentrations of 1, 10, 15, 20 and 25% (v/v).

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Philip ManninoTingyu WenKaixuan Xu

Figure 4: Comparison of dry biomass vs times of Nannochloropsis sp. strain cultivated in sodium bicarbonate/sodium carbonate series solutions with concentration of 2, 5, 10, 15, 20% (v/v).

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Philip ManninoTingyu WenKaixuan Xu

Figure 5: Comparison of lipid productivity vs flue gas solution (%) of Nannochloropsis sp. strain cultivated in sodium bicarbonate/sodium carbonate series solutions with concentration of 2, 5, 10, 15, 20% (v/v).

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Philip ManninoTingyu WenKaixuan XuMerits and Deficiencies

Compared to terrestrial plants, microalgae have higher efficiency in converting

solar energy into biomass (ten times higher than terrestrial plants). These

microorganisms present high growth rate with some species double their cell count in

few hours. High growth rate ensures high CO2 fixation rate. 1.83 kg of CO2 can be

fixed via cultivating one kilogram of microalgae. Species such as Anabaena sp. and

Chlorella vulgaris presents high CO2 fixation rates at 1.45 g L-1 d-1 and 6.24 g L-1 d-1,

respectively.6 Compared to other plants, arable land not required with microalgae

production. They are also easier to grow. Even lower grade water (wastewater) could

be used as culture medium. Anaerobic digestion of microalgae, which includes

processes such as: hydrolysis, acidogenesis, acetogenesis and methanogenesis,

converts organic biomass into volatile fatty acids and methane under little or without

oxygen conditions.7 In addition to converting lipid to ester as biofuel (mentioned in

the beginning), some species are able to produce a considerable amount of methane.

Saccharina latissima and Ulva lactuca can produce 68.2 and 95.6 ml of methane per

gram of algae, in 36 and 42 days respectively.8 If the purity of recovered methane is

higher than 95%, the gaseous mixture can be shipped as compressed natural gas.9

Anaerobic digestion also converts the biomass into plant nutrients that can be recycled

to sustain the microalgae growth and to provide even greater yields. The production of

biofuel by microalgae is essentially a carbon neutral process with zero emission of

CO2, because the CO2 generated from biomass combustion can be reused for

microalgae growth. In addition, when compared with biofuels produced from other

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Philip ManninoTingyu WenKaixuan Xuraw materials, microalgal biofuels present high productivity and high grade oil

production (petroleum fuel substitutes). Microalgae farm has many other merits: (i)

they help protect the biodiversity of the oceans by providing shelters and serving as

feeding/ nursery grounds for many organisms8; (ii) it can be incorporated in

aquaculture systems as the oxygen produced by microalgae improves the respiration

of cultivated animals; (iii) some microalgae, like seaweed, are excellent food sources

due to its high protein and fiber content as well as low total lipid; (iv) microalgae can

synthesize a number of molecules with biological activities, such as phenolic

compounds, carotenoids, alkaloids and polysaccharides that can be used in

pharmaceutical and cosmetic industries.10

Currently, the main challenges to biofuel production by microalgae are related

to the viability of large-scale commercialization of microalgae, because it still

requires large investment and high energy consumption associated to the production

and downstream processes of biomass. Additionally, the low atmospheric CO2

concentration limits microalgae growth. Integration of a physicochemical process to

concentrate CO2 in feeding gaseous stream to microalgal cultures will enhance

microalgal productivities and CO2 capture efficiencies. Furthermore, future studies on

light distribution and nutrients are needed to enhance microalgae growth condition

and optimize productivity.11 Nevertheless, it is believed that a sustainable microalgal

biofuel production can be possible in 10 years and microalgae-based biofuels are a

promising solution for global climate change.

Large point sources, being the primary source of CO2 emission, have gained

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Philip ManninoTingyu WenKaixuan Xumuch attention over the years as an experimental field for CO2 capture methods.

However, even if CO2 emissions from large point sources were immediately reduced

to zero, climate change would still continue due to the existing greenhouse gas present

in the atmosphere. Diffuse sources constitute half of CO2 emissions. Despite being

more expensive and less efficient than CO2 capture from point sources, CO2 capture

from atmosphere is still an important complement. Microalgae play an important role

in stabilizing atmospheric CO2 concentration by capturing this pollutant directly from

air. It has the following advantages compared to other point-source carbon capture

methods: (i) it captures CO2 from any part of the economy emitted at different

location and time; (ii) an algae farm can be located anywhere; (iii) CO2 transport

infrastructure is not required; (iv)microalgae are very eco-friendly, due to the absence

of toxicity and biodegradability.12 Maity et al. (2014)13 reported a possible reduction

of half CO2 emissions with the using of microalgae based biofuel instead of

petroleum-based transportation fuels. It is expected that the operation of large-scale,

commercial biomass energy systems under stringent climate policies can help reduce

the atmospheric CO2 concentration to between 400 and 450 ppm at the end of the

century.14

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1 Saifuddin, N.; Aisswarya, K.; Juan, Y. P; Priatharsini, P. Sequestration of High Carbon Dioxide

Concentration for Induction of Lipids in Microalgae for Biodiesel Production. Journal of Applied

Sciences 2015. 15(8), 1045-1058.

2 Moreira, D.; Pires, J.C.M. Atmospheric CO2 capture by algae: Negative carbon dioxide emission

path. Bioresource Technology 2016. 215, 371-379.

3 R. Sayre. Microalgae: The Potential for Carbon Capture. BioScience 2010, 60, 722-726.

4 Kumar, A.; S. Ergas, X.; Yuan, A.; Sahu; Zhang, Q. et al., Enhanced CO2 fixation and biofuel

production via microalgae: Recent developments and future directions. Trends Biotechnical. 2010,

28, 371-380.

5 Jiang, L.; Luo, S.; Fan, X.; Yang, Z.; Guo, R. Biomass and lipid production of marine microalgae

using municipal wastewater and high concentration of CO2. Applied Energy 2011, 88, 3336-3341.

6 Ghorbani, A.; Rahimpour, H.R.; Ghasemi, Y.; Zoughi, S.; Rahimpour, M.R. A review of carbon

capture and sequestration in Iran: microalgal biofixation potential in Iran. Renew. Sustain. Energy

2014, 35, 73–100.

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Eng. 2015, 32 (4), 567–575.

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10 Tabarsa, M.; Rezaei, M.; Ramezanpour, Z.; Waaland, J.R. Chemical compositions of the marine

algae Gracilaria salicornia (Rhodophyta) and Ulva lactuca (Chlorophyta) as a potential food source.

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Emission Path. Bioresource Technology 2016, 215, 371–379.

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gases using microalgae: engineering aspects and biorefinery concept. Renew. Sustain. Energy Rev.

2012, 16 (5), 3043–3053.

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production, mitigation of greenhouse gas emissions and wastewater treatment: present and future

perspectives – a mini review. Energy 2014, 78, 104–113.

14 Luckow, P.; Wise, M.A.; Dooley, J.J.; Kim, S.H.; Large-scale utilization of biomass energy and

carbon dioxide capture and storage in the transport and electricity sectors under stringent CO2

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