Algae-Based Carbon Capture System: Modelling Photosynthesis for Carbon Dioxide Reduction

Aaron Sarkar

Age 17 | St. John’s, Newfoundland and Labrador

Canada-Wide Science Fair 2019 Finalist

Climate change is an existential threat to the earth and is primarily caused by the release of CO2 into the atmosphere due to the burning of fossil fuels (USEPA, 2017). Although renewable and nuclear energies are developing rapidly, by 2040, more than three-fourths of the world’s energy usage will still come from fossil fuels (IEA, 2019; USEIA, 2018). Therefore, capturing CO2 before it is released into atmosphere is one potential climate change mitigation solution. Microalgae can efficiently capture dissolved CO2 in aquatic systems, and scientists are experimenting with this method to reduce CO2 emissions (Sayre, 2010; Adamczyk, Lasek, & Skawińska, 2016; Singh, & Singh, 2014). However, limited efforts have been put forth to make this initiative commercially successful. Therefore, it is imperative to develop a microalgae-based system for use by industry sectors for the sustainable operation of capturing CO2.

Introduction

The current project is the extension of an experiment conducted in 2018 in which an Algae-Based Carbon Capture System (ABaCCaS) was built, and the change of pH of microalgae (Nannochloropsis oculata) was used as an indicator to measure the utilization of dissolved CO2 by photosynthesis and to study the impacts of temperature, sunlight and ultraviolet (UV) light on pH change rates. The study showed that light and temperature are essential inputs for maximizing the CO2 capture capacity of ABaCCaS. The project was presented at 2018 CWSF (Ottawa) and published in the inaugural issue of CWSF’s journal (Sarkar, 2018). However, the project has raised several research questions with regard to the efficiency of ABaCCaS, such as CO2 capture capacity in various light conditions and dissolved CO2 levels and their relevance in industry (fossil fuel-based power plants). Therefore, more advanced-level experiments are warranted to answer these research questions.

OBJECTIVES

The specific objectives of this project are: a) to determine the photosynthetic efficiency of Nannochloropsis at various levels of dissolved CO2 and light intensity (in lumens), b) to identify time-specific trends of CO2 absorption or O2 production through the photosynthesis of Nannochloropsis, and c) to develop a simple model to identify optimum inputs (light and CO2) and times for the maximum absorption of CO2 for best practices in industry.

PROCEDURES

Creation of ABaCCaS – This system has three interconnected (with pipes) components (Fig 1 and 2).

Figure 1. Major components of ABaCCaS (CPU, CHC and ACs)

Figure 1. Major components of ABaCCaS (CPU, CHC and ACs)

Figure 2. CHC with various parts (syringes, air pump, tubes, etc.)

Figure 2. CHC with various parts (syringes, air pump, tubes, etc.)

  1. CO2 production unit (CPU): A 2-liter soda bottle filled with 5% vinegar (CH 3 COOH). Baking soda (NaHCO 3 ) was weighed at the biology laboratory at Memorial University, and I made a total 45 wraps of varying weights (g) of NaHCO 3 (0.1, 0.4, 0.8, 1.2, 1.6, 2.0, 2.4, 2.8 and 3.2) (5 wraps for each weight category).
  2. CO 2 holding chamber (CHC): An airtight plastic box fitted with 48 syringes (10 ml) and an air pump.
  3. Algae chamber (AC): The AC consisted of four serially interconnected 1-liter soda bottles containing Nannochloropsis. Live Nannochloropsis was collected from the Ocean Sciences Center (Memorial University). Each bottle contained 1 litre of algae. Each experiment began by adding baking soda to the bottle of vinegar and sucking out the produced CO 2 by creating negative pressure by pulling the plungers of the syringes. Then, the air pump was run for the infusion of CO 2 in AC for 4 hours in a dark environment (to stop any photosynthesis). After the CO 2 infusion, the individual bottles (AC) were exposed to four light conditions (using bulbs of 800 lumens (L) UV, 800 L and 1500 L and a dark bottle by wrapping it with aluminum foil). A Dissolved O2 probe with LabQuest 2 (Vernier®) was used to measure the dissolved O2 in four bottles every 10 minutes (Figure 3). The testing continued until the dissolved O 2 level of the bottle exposed to 800 L reached the saturation level. The experiment steps are displayed in Figure 4. Prior to commencing the actual experiment, a test run and two series of quality control and quality assurance (QC/QA) measures were carried out. The test run checked for any leaks or malfunctions in the system. Dead Nannochloropsis (by exposing a sub-sample of microalgae to 90°C in oven for 15 minutes) was used in QC/QA-1 to identify if there were any additional factors affecting the levels of dissolved O 2 . To confirm the association between exposure to light and photosynthesis of Nannochloropsis, QC/QA-2 was conducted. For the actual experiment, each day, 3 wraps (1 for each experiment) were used to produce CO2 (starting from 0.1 gm and gradual rising thereafter until reaching 3.2 gm). For each experiment, an air pump was run for 4 hours. Then, each bottle was exposed to four light conditions, and every 10 minutes the dissolved O2 in each bottle was measured. Temperature was controlled and maintained at 14–16°C. For analysis of the data, the following steps were taken: 1) 800 L and 1500 L were found to be the ideal light intensities for the best O 2 production rate because the O 2 levels reached saturation level (indicating the complete utilization of CO 2 ). On the other hand, the dark and UV bottles never reached the desired saturation levels. 2) Dissolved O2 levels of 800 L and 1500 L for all wraps were taken for calculation of the O 2 production rate (mg of O 2 produced every 10 min). 3) The O 2 absorption rate (mg of CO 2 absorbed in every 10 min) was calculated from the figure of each O2 production rate using the photosynthesis equation (6 CO 2 +6 H 2 O → C 6 H 12 O 6
  4. 6 O 2 ). For each category of weight (of wrap) and light condition, the average, standard deviation (SD), and standard error (SE) of 5 values (mg of CO2 absorbed in every 10 min) were calculated. A Chi-square test was done and a p-value <0.05 data-preserve-html-node="true" data-preserve-html-node="true" was considered significant. 4) The ‘actual CO 2 production’ for each wrap was measured using the equation (NaHCO 3
  5. CH 3 COOH→CH 3 COONa+H 2 O+- CO 2 ). 5) Exploring industry model simulations (the Holyrood thermal power plant of Newfoundland burns an average of 12,000 kg of bunker oil each day) (J. Whelan, Plant Engineer, Holyrood, personal communication, September, 14, 2018).
Figure 3. Accessories of ABaCCaS (bulbs, cardboard cylinders, dissolved oxygen probe and lab quest, glasses and syringes.

Figure 3. Accessories of ABaCCaS (bulbs, cardboard cylinders, dissolved oxygen probe and lab quest, glasses and syringes.

Figure 4. Steps 1-3 of the experiment.

Figure 4. Steps 1-3 of the experiment.

RESULTS

Nannochloropsis exposed to 1500 L had faster CO2 utilization than that exposed to 800 L. Irrespective of CO2 production, almost 100% of dissolved CO2 was captured by Nannochloropsis within 20 minutes of exposure to 1500 L, and for 800 L, 100% capture took a much longer time, and the results were statistically significant (p<0.05) data-preserve-html-node="true" (figures 5-13, page 5). Considering the proportion of CO2 absorbed from actual CO2 production, for the optimum utilization of photosynthetic capacity for each bottle (1 litre) of Nannochloropsis, 3–5 mg (av. 4 mg) of dissolved CO2 is the desired option. For the complete capture of CO2 by photosynthesis under the 1500 L light needs a total of 4 hours + 20 minutes. Thus, 4 daily cycles of CO2 infusion can be done (assuming inter-cycle time for the resting of algae and maintenance of the system), and thereby, 1 litre of Nannochloropsis can absorb 16 mg (4 x 4) of CO2 per day. The industrial-scale (Holyrood power plant) model showed the requirement of 230,000 cubic-meters of Nannochloropsis for complete absorption of the CO2 produced each day.

Figures 5-13. Carbon dioxide capture in every 10 minutes by 1 litre of Nannochloropsis in two light conditions (800L and 1500L).

Figures 5-13. Carbon dioxide capture in every 10 minutes by 1 litre of Nannochloropsis in two light conditions (800L and 1500L).

CONCLUSION

Nannochloropsis has great potential for capturing dissolved CO2. In high-intensity light conditions (1500 L), 1 Litre of Nannochloropsis can absorb 16 mg of dissolved CO2. Due to this efficiency, the ABaCCaS can capture CO2 produced by fossil fuel-based industries (such as thermal power plants).

ACKNOWLEDGEMENTS

I would like to gratefully thank Ms. Natasha Janes & Mr. Jamie Parsons (HHM School, St. John’s, NL) for their instrumental support and continuous encouragement. I am grateful to Mr. Danny Boyce (Ocean Sciences Centre, MUN) & Ms. Rebecca White (Badger Bay Mussel Farms) for supplying Nannochloropsis, Prof. Tom Chapman (Biology, MUN), Prof. Francesca Kerton & Ms. Nathalie Vanasse, (Chemistry, MUN) for providing laboratory support, and Dr. Arifur Rahman (Medicine, MUN) for statistical analysis.

REFERENCES

Adamczyk, M., Lasek, J., Skawińska, A. (2016). CO2 Biofixation and Growth Kinetics of Chlorella vulgaris and Nannochloropsis gaditana. Appl Biochem Biotechnol. 179(7):1248-61. International Energy Agency. (2019). Energy snapshot. IEA. Retrieved from https://www.iea.org/newsroom/energysnapshots/global-carbon-dioxide-emissions-1980-2016.html

Sarkar, A. (2018). Algae-Based Carbon Capture System: A Sustainable Solution for CO2 Emissions. Canadian Science Fair Journal, 1:15-18. Sayre, R. (2010). Microalgae: The potential for carbon capture. BioScience. 60(9):722-27.

Singh, S.P., Singh, P. (2014). Effect of CO2 concentration on algal growth: A review. Renewable and Sustainable Energy Reviews. 38:172-179. U.S. Energy Information Administration. (2018).

International Energy Outlook 2018. USEIA. Retrieved from https://www.eia.gov/outlooks/ieo/

United States Environmental Protection Agency. (2017). Global Greenhouse Gas Emissions Data. USEPA. Retrieved from https://www.epa.gov/ ghgemissions/global-greenhouse-gas-emissions-data

BIBLIOGRAPHY

Kroumova, A.D., Módenes, A.N., Trigueros, D.E.G., Espinoza-Quiñones, F.R., Borba, C.E., Scheufele, F.B., Hinterholz, C.L. (2016). A systems approach for CO2 fixation from flue gas by microalgae—Theory review. Process Biochemistry. 51(11):1817-1832.

Yahya, L., Chik, M.N., Pang, M.A.M.A. (2013). Biological carbon fixation: A study of Isochrysis sp. g rowth under actual coal-fired power plant’s flue gas. IOP Conference Series: Earth and Environmental Science.16 012116. [doi:10.1088/1755-1315/16/1/012116]

Aaron Sarkar

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Aaron Sarkar is a grade 12 student at Holy Heart of Mary High School (St. John’s). Aaron is very passionate about science, especially in new and innovative discoveries. In free times he enjoys going to gym, play basketball, and playing flute, reading books. His future plan for the project is to advance his research in the field of algae-based carbon capture system.