Abstract
Algae research has gained significant attention due to its potential in carbon capture and biofuel production. Understanding the role of CO2 in algae growth is critical to optimize these processes. This study investigates the impact of CO2 on the growth of Chlorella sorokiniana under various experimental conditions. All experiments were conducted at a temperature of 35°C, a light intensity of 234 µmol m-2 s-1, and a 12-hour light window. For the main set of experiments, CO2 flow percentage was changed from 5% to only air flow to see the effect on growth rate. The results showed that excess CO2 doesn’t significantly affect growth, however when it is no longer in excess as concentration drops the growth rate decreases. A one-parameter model was applied to the data, providing values that accurately represent the data. In another experiment, the effects of CO2 flow being on always was compared with CO2 flow only being on during the light phase. The results supported the hypothesis that CO2 flow at night has a negligible impact on growth. In the final experiment, the flowrate of air was lowered while CO2 flow remained the same across both runs. This would be so that one run would have a total flow of 2 LPM and the other a total flow of 1 LMP. This is because although air flow is needed for oxygen content, excess can strip the CO2 from the reactor reducing efficiency. The results confirmed this as the 1 LPM experiment had a lower pH, meaning that there was more dissolved CO2 in solution.
Table of
Contents
Abstract
5
1
Introduction
6
2 Literature Review
7
2.1 Algae Growth
7
2.2 Temperature and
Light Intensity Growth
8
2.3 Nutrient Based
Models
14
2.4 Review
Conclusion
18
3 Methodology _ 19
3.1 Piping and
Instrumental Diagram (PID)
19
3.2 Experimental
Parameters
20
3.3 Reactor Setup and
Takedown
20
3.4 Media
21
3.5 Desktop PC 22
3.6 Manual OD
23
3.7 General
Maintenance
24
3.8 Calibration of
Probes and Sensors 25
3.9 Calibration of pH
Probe
25
3.10 Calibration of DO
Probe
26
3.11 Algae Shaker
27
3.12 Ash Free Dry
Weight
29
4 Results and Discussion 30
4.1 Experimental
Results and Discussion
30
4.1.1 Difference in
Growth Between Constant CO₂ Versus Light-Phase-Only CO₂ 30
4.1.2 Effects of lowering air
flowrate while keeping CO₂ flow the same
33
4.1.3 Effects of different
CO₂ percentages on algae growth
36
4.2 Model Results and
Discussion
44
5 Conclusion
___ 50
6 References _
___ 51
1.
Introduction:
With all the world’s social and
economic issues, global warming is becoming an increasingly important issue
that must be addressed. Global warming is attributed mainly due to greenhouse
gas emissions, the most common of those gases being carbon dioxide (CO2).
Greenhouse gases like CO2 trap heat warming up the planet (1). Many
may assume global warming is only about the environment, however it has been
shown to affect other things such as population health and the economy (2)(3).
These effects of global warming have resulted in a large push to find solutions
that can help combat the problem.
The most well-known and currently
practiced way in combating this issue is switching to non-CO2 emitting
energy sources such as solar, wind, hydro, etc. Currently, only 14%
of the world’s energy comes from renewable sources although it is projected by
2040 that the number will rise to 50% (4). The petrol industry will never fade
away fully as other things such as plastics and medicine are petrol based.
Thus, there needs to be other solutions that can directly combat emissions
coming from petrol such as stack gas.
The University of Arizona, Tucson
Electric Power, Lawrence Livermore NL, Sandia NL, and Southwest Technologies
are working on a collaborative project that involves the usage of algae to
capture CO2. Algae are microorganisms with many different species
found in both fresh and salt water that can convert CO2 into
biomass. When CO2 is
dissolved in water it turns into bicarbonate which is what the algae uses for
energy production (5). The algae can be used for various things ranging from
animal food to its usage in biofuels. This means this form of carbon capture
not only reduces emissions but also provides a source of renewable energy (6).
The project involves the usage of a porous material that absorbs CO2
from stack gas which can then be placed in water where the CO2 will
leach off. With the CO2 dissolved in the water it turns into
bicarbonate where the algae can then convert it into biomass. The UA is
specifically tasked with running growth experiments and fitting them into a
model.
Previous work done at UA explored
the effects of light and temperature on algae growth (7). In this work, we
explore the effect of varying CO2 concentrations on algae growth and
apply a single parameter model to the data. The idea behind the experiments is
that at higher concentrations of CO2 there is higher growth until it
is no longer a limiting reactant where additional CO2 will have
little effect on the growth rate. The research was done using a Bio115 reactor
which allowed air and CO2 to be mixed and injected into the reactor
at different ratios. Algae needs oxygen to survive which is why air is mixed
with CO2 (8). Dissolved oxygen, pH, temperature, and cell
concentration calculated from optical density measurements were recorded during
the experiments. The algae species selected was Chlorella sorokiniana because it has been shown to have high light
use efficiency and the media of choice was Pecos media (9).
A couple separate experiments were
done on top of the main tasks. The first experiment was to see the effect of
having CO2 flow always on versus only having CO2 flow be
on during the light phase. It was hypothesized this would not greatly affect
the data as during the dark phase there is not any light for the algae to
convert the CO2 into biomass. The second experiment was to explore
the effects of lowering air flow while maintaining the same CO2 flow.
The reason behind this is air is needed but the exact amount is unknown. It is
hypothesized excess air will lower the absorption of CO2 in the system.
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