ESTIMATION OF CARBON CAPTURING POTENTIAL OF SPIROGYRA spp. AND
CORRELATION TO ITS GROWTH RATE.
BY
*EGWIM E.C1 AND USMAN H.O2
1
Department of Biochemistry, Federal University of Technology, Minna, P.M.B 65, Minna,
Nigeria.
2
Department of Biological Sciences, University of Abuja, P.M.B 117, Abuja, Nigeria.
*
Corresponding Author: Email:evanschidi@gmail.com,mobile phone; +2347065809494.
ABSTRACT
If algal biomass is grown in a sustained way, its combustion has no impact on the CO2 balance
in the atmosphere, because the CO2 emitted by the burning of biomass is offset by the CO2 fixed
by photosynthesis and therefore serves as a major inexpensive tool for reducing atmospheric CO2
emissions from fossil fuel usage. Thus, in this research work, the % carbon capturing potential of
Spirogyra spp. was estimated and correlated with its growth rate which was estimated using the
spectroscopic method of analysis at a wavelength of 620nm for a period of ten days. The growth
rate was seen to be constantly increasing and was at its peak on day nine with a higher
concentration as compared to its initial concentration on day one and declined afterwards while
the % Carbon Capturing Potential increased constantly with its maximum % Carbon Capturing
Potential as 45.51 ± 0.02 % on day six and declined afterwards till day ten with the minimum %
Carbon Capturing Potential as 15.59 ± 0.01 % .The growth rate is very much sustainable and is
seen to strongly correlate with the Carbon Capturing Potential positively.
Keywords: Spirogyra spp., Carbon Capturing Potential, Algae biomass.
INTRODUCTION
Algae are a large and diverse group of simple, typically autotrophic organisms, ranging from
unicellular to multicellular forms. They are photosynthetic like plants and simple because they
lack the many distinct organs found in land plants. They include Cyanobacteria, Ulva spp.,
Spirogyra spp., Oedogonium spp. e.t.c
Spirogyra spp. is a filamentous green alga that inhabits streams, lakes ponds and various
waterways e.t.c. Adapted to live even under harsh conditions, Spirogyra can store large internal
reserves of nutrients that can sustain maximum growth rates for several weeks (O’Neal,1988).
Algal blooms, though considered by some to be a nuisance and a sign of environmental
degradation, often play an important ecological role in supplying substrate and resources for
epiphytic and browsing organisms (Lorenz ,1991). Algae biomass is proved to be an effective
raw material for many useful products such as fuel oil, fertilizers, protein and other substances
because it does not compete with conventional and agricultural crops and the growth of algae can
well be achieved in any wastewater and reject streams (Govindarajan et. al.,2010).There are five
reasonably well defined phases of algal growth in batch cultures (Fogg and Thake, 1987). Lag,
exponential, declining growth rate, stationary, death phases.
A lag phase may occur if the innoculum is transferred from one set of growth conditions to
another. The condition of the innoculum has a strong bearing on the duration of the lag phase
(Spencer, 1954). An innoculum taken from a healthy exponentially growing culture is unlikely to
have any lag phase when transferred to fresh medium under similar growth conditions of light,
temperature and salinity. The exponential phase determines the measure of the increase in
biomass over time. The duration of exponential phase in cultures depends upon the size of the
innoculum, the growth rate and the capacity of the medium and culturing conditions to support
algal growth. Declining growth normally occurs in cultures when either a specific requirement
for cell division is limiting or something else is inhibiting reproduction. In this phase of growth,
biomass is often very high and exhaustion of a nutrient salt, limiting carbon dioxide or light
limitation become the primary causes of declining growth.
When biomass is increasing
exponentially a constant supply of air or air plus CO2 will only be in balance with growth at one
point during exponential phase. Cultures enter stationary phase when net growth is zero, and
within a matter of hours cells may undergo dramatic biochemical changes. The nature of the
changes depends upon the growth limiting factor. Nitrogen limitation may result in the reduction
in protein content and relative or absolute changes in lipid and carbohydrate content. Light
limitation will result in increasing pigment content of most species and shifts in fatty acid
composition. When vegetative cell metabolism can no longer be maintained the death phase of a
culture is generally very rapid, hence the term “culture crash” is often used. The steepness of the
decline is often more marked than that represented in the accompanying growth figure. Cultures
of some species will lose their pigmentation and appear washed out or cloudy, whereas cells of
other species may lyse but the culture colour will be maintained.
During photosynthesis, algae and other photosynthetic organisms capture carbon dioxide and
sunlight and convert it into oxygen and biomass. Up to 99% of the carbon dioxide in solution can
be converted in large-scale open-pond systems (Weissman and Tillett, 1992). so they naturally
balance most of the CO2 released from combustion.Thereby,offsetting a major contributing
factor to global warming (Colares,2006).This ability is referred to as Carbon Capturing
Potential (CCP).
CO2 is recognized as the most important of the atmospheric pollutants that contributes to the
‘‘greenhouse effect’’ (Coyle, 2007; Bayless et. al., 2007; Milmo, 2008).Most of the
anthropogenic emissions of carbon dioxide result from the combustion of fossil fuels for energy
production. It is the increased demand for energy, particularly in the developing world, which
underlies the projected increase in CO2 emissions. Meeting this demand without huge increases
in CO2 emissions requires more than merely increasing the efficiency of energy production. The
costs
of
removing
CO2
from
a
conventional
coal-fired
power
plant with flue gas desulphurization were estimated to be in the range of $35–$264 per ton of
CO2 ( Sheehan et. al., 2008; U.S Department for Energy, 2006 ), which is very much expensive.
The earth’s photosynthetic capacity is large. It is estimated that algae fix greater than 65 Giga
tonnes of carbon per year. Algae in nature fix carbon equal to the output of about sixty five
thousand, 500 MW generating plants (Hall et. al., 1991; Macedo, 1999).
Among biomass, algae (macro and microalgae) usually have a higher photosynthetic efficiency
than other biomass and have been found to be one of the best sources of biodiesel and the highest
yielding feedstock for biodiesel (Shay,1993) and also have the ability to photosynthetically
convert the CO2 into compounds of high commercial value or mineralized carbon for
sequestration. The advantages of this process include the following (U.S Department for Energy,
2006):

Since high purity CO2 gas is not required for algae culture. It is possible that flue gas
containing 2–5% CO2 can be fed directly to the photobioreactor. This will simplify CO2
separation from flue gas significantly.

Some combustion products such as NOx or SOx can be effectively used as nutrients for
microalgae. This could simplify flue gas scrubbing for the combustion system.

Algae culturing is very easy and yields high value commercial products such as
renewable diesel, hydrogen, alkanes, alcohols e.t.c. that could offset the capital and the
operation costs of the process or mineralized carbon for stable sequestration. By selecting
appropriate algae species, either one or both can be produced.

The proposed process is a renewable cycle with minimal negative impacts on
environment.
The objectives of this research are to culture and measure the algal growth rates in a
photobioreactor spectrophotometrically, show that capturing of CO2 by photosynthesis in a
photobioreactor can be carried out in a sustainable manner, and correlate the increase and
decrease in algal growth to a corresponding increase or decrease in % Carbon capturing potential
respectively.
MATERIAL AND METHODS:
Materials:
Equipments: Buckner flask, retort stand, beakers, burette, conical flask, rubber sieves,
spectrophotometer and cuvettes.
Reagents: 2% Hydrochloric acid (HCl) and Calcium carbonate (CaCO3).
Sample collection:
Spirogyra spp. was harvested from the dams found at Maizube Farms, Minna, Niger state,
Northern Nigeria by filtration.
Methodology:
Estimation of Carbon Capturing Potential (CCP):
The Carbon Capturing Potential (CCP) of the sample was estimated by passing CO2 produced
by reacting 11.2g of Calcium carbonate (CaCO3) with 25mls of 2% Hydrochloric acid (HCl) in a
sealed Buckner flask into the algae samples. Then, calculating the difference between the CO2
fed into the sample and the amount recovered after passing through the sample.
First, two closed inverted burettes clamped by two different retort stands, were immersed in two
different vessels containing water and the volume of water in both burettes were measured (V1).
The CO2 produced initially was then released and allowed to pass through to the first closed
inverted burette immersed in a vessel containing water via a hoose.The new volume of water in
the burette (V2 ) was then measured as a result of a decline in volume of water because of the
pressure of CO2 gas upon passage through the burette. The difference between V1 and V2 gave
the initial amount of CO2 passed through the system P1(CO2).the burette was opened and the
measured CO2 allowed to pass through to a closed vessel containing the algae sample.CO2
was allowed to remain in this vessel for 3hours to become saturated. Then, the gas is released
from this vessel and allowed to pass through to the second burette immersed in water with
known volume (V1) via a hose. The new volume of water in the burette (V2) was then measured
as a result of the decline in volume of water to derive the amount of CO2 derived after capture
by Spirogyra spp. P2(CO2).The Carbon Capture Potential (CCP) was calculated as thus:
P1 (CO2) – P2 (CO2) then expressed in terms of percentage. This procedure carried out in
triplicates daily for ten days at room temperature and the source of light provided was from the
florescent lights in the laboratory.
Fig.1: Experimental set-up for the estimation of growth rate and Carbon Capturing
Potential of Spirogyra spp.
Measurement of Growth Rate of Spirogyra Spp.
The growth rate of this Spirogyra spp.sample was determined spectophotometrically at 620 nm
every two days for ten days by taking 2mls of the sample and taking the reading of absorbance,
transmittance and concentration using a spectrophotometer and this was compared with the
growth rate of a control which was the same Spirogyra spp. that was sealed in a vessel without
any supply of CO2.
RESULTS:
Sample Algae
Days
1
%T
92
Absorbance
0.04
Control Algae
Conc. %T
1
92
Absorbance
Conc.
% Capture
0.04
1
28.29 ± 0.02
2
3
33.74 ± 0.04
89
0.05
4
88
0.05
3
4
5
39.28 ± 0.03
83
0.06
6
85
0.05
5
6
7
41.58 ± 0.02
45.51 ± 0.02
80
0.08
7
87
0.03
2
8
9
36.73 ± 0.04
43.50 ± 0.03
20.36 ± 0.02
79
0.10
10
10
87
0.04
4
19.52 ± 0.02
15.59 ± 0.01
Tab. 1: % carbon capturing potential of Spirogyra spp. in relation to its growth rate and
the control Spirogyra spp. sample.
DISCUSSION:
Table 1. shows the % Carbon Capturing Potential of Spirogyra spp. in relation to its growth rate
and the control Spirogyra spp. sample. It is seen that the growth rate of the Spirogyra spp.
constantly increased from day one up till the end of the experiment. It reached its peak on day
seven with a transmittance, absorbance and concentration of 80, 0.08 and 7 respectively and
continued growing slowly. This is because there was no lag phase as the sample was transferred
from its natural habitat in the original culture it was already growing to the lab and hence
continued growing in the exponential phase. An innoculum taken from a healthy exponentially
growing culture is unlikely to have any lag phase when transferred to fresh medium under
similar growth conditions of light, temperature and salinity. A lag phase may also occur if the
innoculum is transferred from one set of growth conditions to another (Fogg and Thake,1987).
For healthy cells of a robust species, small innoculums equal to 0.5 % of the volume of the new
culture will normally generate new healthy cultures. If the species is delicate or the culture less
healthy then a larger innoculum of ~ 10% may be needed to support a new culture (O’Neal and
Lembe,1988).
It was also observed that the Spirogyra spp. sample thrived better than the control Spirogyra spp.
sample lacking CO2 supply, which also constantly increased in growth rate and reached its peak
on day five with a transmittance, absorbance and concentration of 85,0.05 and 5 respectively and
then a decline in growth rate was observed after wards. This was because CO2 limitation at high
cell densities causes any further biomass increase to be linear rather than exponential with
respect to time and is proportional to the input of CO2 (Rice and Flora,1985).These results from
the growth rate are similar to the results obtained by Govindarajan et.al (2010) in ‘The Kinetic
Study of Algae Biomass Grown In Natural Medium Using Spectroscopic Analysis’ and are also
similar to those of (Doshi,2006) in the ’Measurement of Algal Growth Rate Between Harvests in
An Artificially Lit Photobioreactor under Flue Gas Conditions’ which 17 g ± 2.4 g of algae was
initially loaded and a net 30 g of algae was obtained at the end of the test, suggesting that the
algae doubled over the course of the experiment.
Then % Carbon Capturing Potential increased constantly from day one 28.29 ± 0.02 % to day six
45.51 ± 0.02 % which was the highest % Carbon Capturing Potential estimated and is strongly
correlated positively with the increasing growth rate. This could be as a result of CO2 being a
requirement for photosynthesis for the manufacture of food for growth and also because when
biomass is increasing exponentially a constant supply of air or air plus CO2 will only be in
balance with growth at one point during exponential phase which happens to be at this point.
The % carbon capturing potential began to decrease afterwards even though there was still an
increase in growth rate. This probably might have been due to saturation of the sample with CO2
and hence less demand for the CO2.
In conclusion, the culturing of Spirogyra spp., estimation of algal growth rate in a
photobioreactor and % Carbon Capturing Potential of Spirogyra spp. in a sustained way has been
completed successfully and is found to be strongly correlated. The % Carbon Capturing Potential
of Spirogyra spp. is said to be characterized by a high volume of CO2 captured at relatively low
cost and could be a major tool for reducing atmospheric CO2 emissions from fossil fuel usage if
biomass is grown in a sustained way.
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