Abalist, R. O., & Youkparigha, F. O. (2026). Comparative Evaluation of Growth Dynamics, CO₂ Sequestration, and Bio-Oil Production in Three Microalgae Species under Controlled Conditions. International Journal of Research, 13(1), 332–341. https://doi.org/10.26643/ijr/2026/10
Richard Otayoor Abalist1
and Felix Okponanabo Youkparigha1
1Department of Biological
Sciences, Niger Delta University, Wilberforce Island, P.O Box 071, Bayelsa
State, Nigeria.
Corresponding
Author Email: richardotami3@gmail.com
Abstract
Microalgae
represent a promising biological platform for carbon capture and renewable fuel
production. This study compared the growth performance, CO₂ sequestration
efficiency, pigment accumulation, and lipid/bio-oil productivity of Chlorella
vulgaris, Nannochloropsis oculata, and Spirulina platensis
cultured under controlled conditions. Growth was monitored for 20 days, and
biomass increased significantly in all species, with C. vulgaris
exhibiting the highest final dry weight (2.90 g/L), followed by S. platensis
(2.72 g/L) and N. oculata (2.18 g/L). CO₂ removal was greatest in C.
vulgaris (64% at 10% CO₂), compared with Nannochloropsis (25%) and Spirulina
(22%). Chlorophyll a content peaked in C. vulgaris (18.4 µg/mL). Lipid
content was highest in Nannochloropsis (40.8%), although Chlorella
achieved competitive lipid yield due to higher biomass. FAME analysis revealed
dominance of desirable biodiesel fatty acids (C16:0, C18:1, C18:2). The
comparative analysis indicates that Chlorella vulgaris is best suited
for biomass-driven CO₂ sequestration applications, whereas Nannochloropsis
oculata is optimal for high-yield bio-oil production. Integrating high-biomass (Chlorella)
and high-lipid (Nannochloropsis) species may provide a synergistic
strategy for maximizing CO₂ fixation and biofuel output in commercial
microalgal systems. Future work should explore scale-up dynamics and
optimization of CO₂ delivery.
Keywords:
Microalgae; CO₂ sequestration; Bio-oil; Biodiesel; Chlorella vulgaris; Nannochloropsis oculata; Spirulina platensis;
Lipid productivity; FAME; Growth dynamics.
Introduction
Microalgae
have emerged as one of the most promising biological resources for sustainable
energy production and climate change mitigation due to their rapid growth
rates, high photosynthetic efficiency, and ability to accumulate substantial
biochemical compounds (Chisti, 2007; Draaisma et al., 2013). Unlike terrestrial
plants, microalgae do not require arable land and can thrive in controlled
environments, making them suitable for integration into closed-loop carbon
capture and renewable fuel systems. Their ability to use CO₂ as a primary
carbon source during photosynthesis positions them as natural bioreactors for
greenhouse gas reduction, which has attracted substantial research attention in
recent decades (Wang et al., 2008).
Among
the diverse microalgal species, Chlorella vulgaris, Nannochloropsis
oculata, and Spirulina platensis are widely studied due to their
adaptability to various environmental conditions and their desirable
biochemical profiles. Chlorella vulgaris is known for its fast growth,
high protein content, and excellent CO₂ fixation capacity, making it a model
organism in carbon sequestration research (Kumar et
al., 2010). Nannochloropsis oculata is notable for its ability to
accumulate large quantities of lipids, particularly polyunsaturated fatty
acids, which are essential for high-quality biodiesel production (Rodolfi et
al., 2009). Conversely, Spirulina platensis (a cyanobacterium) is
recognized for its rich pigment composition and nutritional value but typically
contains lower lipid levels compared with eukaryotic microalgae (Becker, 2013).
The
growing global demand for sustainable energy has further intensified interest
in microalgae-based biofuels. Microalgae can produce high-value fatty acids
such as palmitic (C16:0), oleic (C18:1), and linoleic acids (C18:2), which are
critical components of biodiesel that meet international fuel quality standards
(Hu et al., 2008). In addition, microalgal oils exhibit high conversion
efficiencies during transesterification, making them superior to many
conventional plant oils. Understanding species-specific differences in lipid
accumulation and fatty acid composition is therefore essential for optimizing
microalgal biofuel production systems.
Carbon
sequestration efficiency also varies greatly among microalgal species, and it
is influenced by factors such as CO₂ concentration, light intensity, nutrient
availability, and strain genetics. Studies have shown that elevated CO₂
conditions can significantly enhance growth and photosynthetic activity in many
microalgae by increasing carbon availability for metabolic processes (Sydney et
al., 2010). However, tolerance to high CO₂ varies among species, and
identifying strains that maintain optimal productivity under enriched CO₂ is
crucial for industrial-scale biofixation applications.
Pigment
synthesis, including chlorophyll a and b, is another critical physiological
parameter because it directly influences photosynthetic capacity and biomass
yield. Species with higher pigment concentrations typically demonstrate
stronger growth under controlled lighting, leading to improved carbon
assimilation and higher biomass productivity (Ritchie, 2006). Understanding
pigment dynamics among Chlorella, Nannochloropsis, and Spirulina
under controlled conditions provides insight into their photosynthetic
performance and suitability for large-scale cultivation.
Given
the growing need for integrated carbon capture and renewable bioenergy
solutions, a comparative assessment of these three widely utilized species Chlorella
vulgaris, Nannochloropsis oculata, and Spirulina platensis is
essential. This study evaluates their growth dynamics, CO₂ sequestration
capacity, pigment concentration, lipid yield, and bio-oil quality under
standardized laboratory conditions. Such comparative analyses provide useful
insights for selecting the most suitable species for carbon mitigation and
biofuel production, informing future applications in bioenergy, industrial CO₂
recycling, and sustainable biotechnological systems.
MATERIALS AND METHODS
3.1 Study Design
This
study investigated the potential of selected microalgae species for CO₂
sequestration and bio-oil production under controlled laboratory conditions. A
completely randomized design (CRD) was employed, with each treatment replicated
three times. Microalgae species evaluated included Chlorella vulgaris, Spirulina
platensis, and Nannochloropsis oculata. Each species was cultured in
separate photobioreactors and exposed to controlled CO₂ concentrations.
3.2
Microalgae Collection and Identification
Pure
strains of C. vulgaris, S. platensis, and N. oculata were
obtained from a standard algal culture bank. Identification was confirmed
through morphological examination using a compound microscope (×400) and
comparison with standard taxonomic keys.
3.3
Culture Media Preparation
BG-11
medium (for Chlorella and Nannochloropsis) and Zarrouk’s medium
(for Spirulina) were prepared according to standard protocols. Media
were autoclaved at 121 °C for 15 min and cooled before inoculation. pH was
adjusted to 7.2–7.5.
3.4
Photobioreactor Setup
Algae
were cultivated in 5-L glass photobioreactors equipped with: Aeration system
(0.5 vvm), Controlled CO₂ supply (0%, 5%, and 10% CO₂), Continuous light source
(3000–3500 lux) and Temperature control at 25 ± 2 °C. Biomass was harvested on
days 0, 5, 10, 15, and 20
3.5
Growth Measurements
Optical density (OD₆₈₀) was measured daily using a UV–Vis
spectrophotometer. Biomass dry weight (g/L) was determined by filtering 50 mL
of culture, drying at 105 °C for 24 h, and weighing to constant mass. Net Biomass Increase” is: Final – initial biomass (g/L),
3.6
CO₂ Sequestration Calculation
CO₂
removal efficiency (RE, %) was calculated as:
Where
Cᵢ = initial CO₂ concentration (ppm), and Cf = final
CO₂ concentration after 24 h. CO₂ monitoring was done using a digital gas
analyzer.
3.7
Chlorophyll and Lipid Quantification
Chlorophyll
a and b were extracted in 90% acetone and quantified spectrophotometrically.
Total
lipids were extracted using the Bligh and Dyer method. Extracts were dried and
weighed to determine lipid percentage:
3.8
Bio-Oil Extraction and Transesterification
Extracted
lipids were subjected to acid-catalyzed transesterification using methanol and
sulfuric acid. The resulting fatty acid methyl esters (FAMEs) were analyzed
using GC-MS to determine suitability for biodiesel.
3.9
Statistical Analysis
Data were
analyzed descriptively to evaluate trends and relative differences among
microalgal species. One-way ANOVA was applied where appropriate to examine
differences among treatments at p < 0.05. Results are presented in tabular
and graphical formats to facilitate comparison. Statistical analyses were
performed using OriginPro and Microsoft Excel.
All three microalgae Chlorella vulgaris,
Nannochloropsis oculata, and Spirulina
platensis show
overall growth over 20 days (table 1 &
figure. 1), following
typical microalgal phases: lag (days 0–2), exponential (days 2–15), and
early stationary (days 15–20). Chlorella
vulgaris has
the highest growth, reaching 2.90 by day 20. S. platensis shows moderate growth, ending at 2.72. N. oculata has the slowest
growth, reaching
2.18, and enters stationary phase earlier. One-way ANOVA revealed a significant
difference in optical density among the three microalgae species across the
cultivation period (p < 0.05).
Table 1: Daily Optical Density (OD₆₈₀)
Readings of Microalgae Species (0–20 Days)
|
Day |
Chlorella
vulgaris |
Nannochloropsis
oculata |
Spirulina
platensis |
|
0 |
0.16 |
0.12 |
0.20 |
|
1 |
0.17 |
0.15 |
0.24 |
|
2 |
0.21 |
0.20 |
0.28 |
|
3 |
0.35 |
0.31 |
0.37 |
|
4 |
0.54 |
0.33 |
0.39 |
|
5 |
0.73 |
0.39 |
0.47 |
|
6 |
0.75 |
0.49 |
0.59 |
|
7 |
0.78 |
0.57 |
0.61 |
|
8 |
0.84 |
0.68 |
0.69 |
|
9 |
0.91 |
0.87 |
0.89 |
|
10 |
1.12 |
0.89 |
0.97 |
|
11 |
1.28 |
1.10 |
1.22 |
|
12 |
1.42 |
1.21 |
1.24 |
|
13 |
1.57 |
1.33 |
1.38 |
|
14 |
1.71 |
1.45 |
1.49 |
|
15 |
1.86 |
1.62 |
1.67 |
|
16 |
1.92 |
1.74 |
1.85 |
|
17 |
2.01 |
1.90 |
1.96 |
|
18 |
2.58 |
1.98 |
2.03 |
|
19 |
2.71 |
2.11 |
2.52 |
|
20 |
2.90 |
2.18 |
2.72 |
One-way ANOVA was applied
to OD₆₈₀ values using time points as replicates (n = 21). Differences among
species were considered significant at p < 0.05.
Microalgal Growth Performance
All three microalgae species showed
significant growth under CO₂ enrichment (table 2 & fig. 1). C. vulgaris
showed the fastest growth, reaching 2.90 g/L on day 20, S. platensis followed with 2.72 g/L, while N.
oculate reached 2.18 g/L. Biomass increased by 1713%, 1717%, and 1260% for C. vulgaris, N. oculata,
and S. platensis respectively. One-way analysis of variance showed a significant difference in
biomass accumulation among the three microalgae species across the cultivation
period (p < 0.05). Increased
CO₂ concentration improved growth rate, consistent with its role as a primary
carbon source for photosynthesis.
Table
2: Biomass Growth (Dry Weight) of Microalgae Species (g/L)
|
Species |
Day
0 |
Day
5 |
Day
10 |
Day
15 |
Day
20 |
Net
Biomass Increase
(g/L) |
%
Increase |
|
Chlorella
vulgaris |
0.16 |
0.73 |
1.12 |
1.86 |
2.90 |
2.74 |
1,713% |
|
Nannochloropsis
oculate |
0.12 |
0.39 |
0.89 |
1.62 |
2.18 |
2.06 |
1717% |
|
Spirulina
platensis |
0.20 |
0.47 |
0.97 |
1.67 |
2.72 |
2.52 |
1,260% |
Net Biomass Increase” is: Final – initial biomass (g/L). One-way
ANOVA was conducted using biomass values measured at different cultivation days
as replicates (n = 5). Statistical significance was accepted at p < 0.05.
CO₂
Sequestration Efficiency
CO₂
removal varied among species. C. vulgaris has 44–64% removal (table 3), N. oculata: 10–25% removal and S. platensis: 5–22% removal. The highest
sequestration was observed at 10% CO₂, demonstrating that species with fast
growth rates also showed enhanced carbon assimilation. This aligns with
previous research showing C. vulgaris strong carbon-capture ability.
Table
3: Overall CO₂ Removal Efficiency (%) at Different CO₂ Concentrations
|
Species |
CO₂
Level |
Initial
CO₂ (ppm) |
Final
CO₂ (ppm) |
Removal
(%) |
|
C.
vulgaris |
5% |
10,000 |
5,600 |
44.0 |
|
C.
vulgaris |
10% |
20,000 |
7,200 |
64.0 |
|
Nannochloropsis |
5% |
10,000 |
9,000 |
10.0 |
|
Nannochloropsis |
10% |
20,000 |
15,000 |
25.0 |
|
Spirulina |
5% |
10,000 |
9,500 |
5.0 |
|
Spirulina |
10% |
20,000 |
15,600 |
22.0 |
Chlorophyll Content
Chlorophyll a and b levels increased
with CO₂ supplementation (table 4). C. vulgaris exhibited the highest
pigment concentration 18.4 µg/mL chlorophyll a,
followed by N. oculate 15.7 µg/mL at day 20. The Lowest was S. platensis (12.1 µg/mL). Increased pigment synthesis reflects improved
photosynthetic activity.
Table
4: Comparative Chlorophyll Content at Day 20
|
Species |
Chlorophyll
a (µg/mL) |
Chlorophyll
b (µg/mL) |
Total
Chlorophyll (µg/mL) |
Dominant
Pigment |
|
Chlorella
vulgaris |
18.4 |
7.8 |
26.2 |
Chlorophyll
a |
|
15.7 |
5.6 |
20.7 |
Chlorophyll
a |
|
|
Spirulina
platensis |
12.1 |
3.9 |
16.0 |
Chlorophyll
a |
Lipid
Yield and Bio-Oil Potential
The
results (table 5) for the Lipid productivity were as follows: N. oculata:
40.8%, C. vulgaris: 25.9% and S. platensis: 18.8%. N. oculata
produced the highest lipid content, consistent with its well-documented
oleaginous nature. However, C. vulgaris exhibited higher total biomass,
resulting in competitive overall oil yield.
Table
5: Lipid Productivity and Bio-Oil Yield on Day 15
|
Species |
Biomass
(g/L) |
Lipid
Content (%) |
Lipid
Yield (g/L) |
|
C. vulgaris |
2.90 |
25.9% |
0.75 |
|
Nannochloropsis
oculata |
2.18 |
40.8% |
0.89 |
|
Spirulina
platensis |
2.72 |
18.8% |
0.51 |
Bio-Oil
Composition from FAME Profiling
GC-MS analysis showed high levels of
C16:0, C18:1, and C18:2 fatty acids components desirable for high-quality
biodiesel (table 6). N. oculata had the highest proportion of saturated
and monounsaturated fats, offering good oxidative stability. The highest
saturated fatty acid was produced by N. oculata (38.8%), while the
highest monounsaturated was produced from C. vulgaris (38.1%) and the
highest polyunsaturated was produced by S. platensis (22.9%)
Table
6: Biofuel Quality Based on FAME Composition at day 20
|
Fatty
acids (Bio-Oil) |
Characteristics
of the Bio-oil |
C. vulgaris |
N.
oculata |
S.
platensis |
|
Saturated
(C16:0 + C18:0) |
Oxidative
Stability |
29.2% |
38.8% |
23.4% |
|
Saturated
(C1:4+C1:0) |
Moderate
stability |
20.4% |
35.2% |
40.7% |
|
Saturated
(C2:6) |
Low
viscosity |
30.6% |
12.9% |
7.5% |
|
Monounsaturated
(C18:1) |
cetane
number |
38.1% |
27.9% |
24.7% |
|
Polyunsaturated
(C18:2 + C20:5) |
cold
flow |
20.1% |
19.8% |
22.9% |
|
Others |
Variable |
13.5% |
6.4% |
21.7% |
Performance
of the Microalgae Species
Findings
show that microalgae possess strong potential for CO₂ mitigation and renewable
fuel production (table 7). C. vulgaris and N. oculata performed
significantly better than S. platensis in both biomass accumulation and
CO₂ sequestration. Although N. oculata had the highest lipid percentage,
C. vulgaris superior biomass yield enabled comparable total lipid
output. Elevated CO₂ supply enhanced growth, photosynthetic activity, and lipid
accumulation, a trend consistent with previous studies reporting improved
microalgal productivity under carbon enrichment.
Table 7: Overall
Performance Ranking of Microalgae Species
|
Parameter |
C. vulgaris |
N.
oculata |
S.
platensis |
Best
Species |
|
Biomass
Yield |
+++ |
++ |
+ |
Chlorella |
|
Lipid
% |
++ |
+++ |
+ |
Nannochloropsis |
|
Total
Lipid Yield |
++ |
+++ |
+ |
Nannochloropsis |
|
CO₂
Sequestration |
+++ |
++ |
+ |
Chlorella |
|
Pigment
Content |
+++ |
++ |
+ |
Chlorella |
|
Biodiesel
Quality |
++ |
+++ |
+ |
Nannochloropsis |
Keys; +++ = high, ++ = moderate, + = low
Figure 1. Growth curves of Chlorella vulgaris,
N. oculata, and Spirulina platensis cultivated
under controlled conditions over a 20-day period.
Discussion
The findings of this study show clear species-specific
differences in growth rate, biomass accumulation, and CO₂ sequestration
efficiency among Chlorella vulgaris, Nannochloropsis oculata, and
Spirulina platensis. Chlorella vulgaris demonstrated the highest
biomass yield and fastest optical density increase throughout the 20-day
cultivation period, consistent with earlier reports that Chlorella
species possess high photosynthetic efficiency and adaptability to CO₂-rich
conditions (Sydney et al., 2010; Wang et al., 2008). The substantial biomass
increase observed in Chlorella reflects its superior ability to
assimilate carbon and convert it into cellular components, reinforcing its
suitability for large-scale CO₂ mitigation processes.
The CO₂ removal efficiency results further support the
strong carbon-fixation potential of Chlorella vulgaris. Its removal
capacity (44–64%) exceeded that of both Nannochloropsis and Spirulina,
aligning with previous studies that identified Chlorella as one of the
most effective CO₂-sequestering microalgae due to its robust
carbon-concentrating mechanisms and tolerance to elevated CO₂ levels (Kumar et al., 2010). In contrast, the relatively lower
removal efficiency recorded in Nannochloropsis oculata may be linked to
its slower growth rate and moderate pigment concentration compared with Chlorella.
Chlorophyll results also highlight distinct physiological
capabilities among the species studied. Chlorella vulgaris recorded the
highest chlorophyll a and total chlorophyll values, which correlates with its
superior growth and carbon assimilation rates. High pigment concentrations
enhance light absorption and increase the efficiency of photosynthesis, which
ultimately contributes to biomass productivity (Ritchie, 2006). Spirulina
platensis had the lowest chlorophyll concentration, which is consistent
with the fact that cyanobacteria possess different pigment systems dominated by
phycobiliproteins rather than chlorophyll b, thereby influencing their
light-harvesting efficiency (Becker, 2013).
Lipid productivity and bio-oil yield demonstrated that Nannochloropsis
oculata is the most oleaginous species among the three, with lipid content
exceeding 40%. This supports a well-established body of evidence describing Nannochloropsis
as a high-lipid marine microalga capable of accumulating significant amounts of
triacylglycerols, particularly under nutrient-stressed or CO₂-enriched
conditions (Rodolfi et al., 2009; Hu et al., 2008). Although Chlorella
produced slightly lower lipid percentage, its higher biomass allowed it to
generate a competitive total lipid yield, demonstrating that both growth rate
and biochemical composition must be considered when selecting species for
biodiesel production.
Fatty acid methyl ester (FAME) profiles revealed the
dominance of palmitic acid (C16:0), oleic acid (C18:1), and linoleic acid
(C18:2), which are desirable biodiesel constituents that enhance oxidative
stability, ignition quality, and cold-flow performance (Knothe, 2008). The
relatively high saturated and monounsaturated fatty acids in Nannochloropsis
indicate its potential to produce biodiesel with excellent stability, while Chlorella
offers a balanced FAME profile suitable for meeting international biodiesel
standards. Spirulina, although lower in overall lipid content, exhibited
notable polyunsaturated fatty acid levels, suggesting its potential use for
nutraceutical rather than purely fuel-based applications.
Conclusion and Recommendation
Further Study
This research still
has limitations, so it is necessary to carry out further research related to
the topic comparative
evaluation of growth dynamics, co₂ sequestration, and bio-oil production in
three microalgae species under controlled conditions in order to improve
this research and add insight to readers.
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