Evaluation of the Feasibility of Using CO₂ from Molasses-Based Ethanol Fermentation as a Carbon Source for Arthrospira platensis Cultivation in a Closed Tubular Photobioreactor
Tran Trung Kien
Institute of Life Sciences, Vietnam Academy of Science and Technology, Ho Chi Minh City, Vietnam.
Nguyen Hoang Dung
Institute of Life Sciences, Vietnam Academy of Science and Technology, Ho Chi Minh City, Vietnam.
Do Dang Giap
Institute of Life Sciences, Vietnam Academy of Science and Technology, Ho Chi Minh City, Vietnam.
Tran Quang Vinh
Institute of Life Sciences, Vietnam Academy of Science and Technology, Ho Chi Minh City, Vietnam.
Le Quynh Loan
Institute of Life Sciences, Vietnam Academy of Science and Technology, Ho Chi Minh City, Vietnam.
Tran Thi My Ngoc
Institute of Life Sciences, Vietnam Academy of Science and Technology, Ho Chi Minh City, Vietnam.
Vu Thi Tuyet Nhung
Institute of Life Sciences, Vietnam Academy of Science and Technology, Ho Chi Minh City, Vietnam.
Nguyen Thi Thuy
Institute of Life Sciences, Vietnam Academy of Science and Technology, Ho Chi Minh City, Vietnam.
Nguyen Thi Linh Phuong
Binh Tho Junior High School, Ho Chi Minh City, Vietnam.
Phan Van Dan *
Institute of Life Sciences, Vietnam Academy of Science and Technology, Ho Chi Minh City, Vietnam.
*Author to whom correspondence should be addressed.
Abstract
Background: Carbon dioxide generated during ethanol fermentation is a biogenic carbon source that may support cyanobacterial cultivation, although its direct use in closed photobioreactors may be constrained by gas-liquid mass transfer, pH variation and reduced bicarbonate buffering.
Aims: This study evaluated the feasibility of using off-gas from molasses-based ethanol fermentation as a supplemental carbon source for Arthrospira platensis cultivation in a closed tubular photobioreactor.
Study Design: A. platensis was cultivated under three carbon-supply conditions: standard Zarrouk medium containing NaHCO₃ with ambient-air aeration; bicarbonate-free modified Zarrouk medium with ambient-air aeration; and bicarbonate-free modified Zarrouk medium supplied with fermentation off-gas.
Place and Duration of Study: The experiment was conducted at the Institute of Life Sciences, Vietnam Academy of Science and Technology, Ho Chi Minh City, Vietnam, between March and September 2025.
Methodology: Biomass concentration, medium pH, biochemical composition, inlet and outlet CO₂ levels and an apparent CO₂ retention indicator were evaluated.
Results: The fermentation off-gas treatment reached a maximum biomass concentration of 0.79 ± 0.03 g/L, which was higher than that in the bicarbonate-free treatment with ambient air (0.66 ± 0.06 g/L) but markedly lower than that in standard Zarrouk medium containing NaHCO₃ (3.49 ± 0.02 g/L). The fermentation off-gas treatment produced biomass containing 52.43 ± 0.03% crude protein, 11.65 ± 0.05% carbohydrate, 6.14 ± 0.05% lipid, 7.12 ± 0.08 mg/g chlorophyll, 65.62 ± 0.11 mg/g phycocyanin and 1.29 ± 0.05 mg/g carotenoid. The apparent CO₂ retention indicator was approximately 1.8%, suggesting limited CO₂ retention under the current configuration.
Conclusion: Fermentation-derived CO₂ can support A. platensis growth, but it did not replace bicarbonate completely under the tested operating conditions.
Keywords: Arthrospira platensis, fermentation-derived CO₂, ethanol fermentation, molasses, closed tubular photobioreactor, bicarbonate, biomass