Short CommunicationCO2 fixation and production of biodiesel by Chlorella vulgaris NIOCCV under mixotrophic cultivation
Graphical abstract
Introduction
Mitigation for the accelerated release of greenhouse gases, in particular CO2, is a major global concern (Duarte et al., 2017, Prabakar et al., 2018). A cleaner source of fuel with efficient CO2 capture and storage technologies can potentially reduce CO2 release (Prabakar et al., 2018). Microalgae have been established as a renewable feedstock for clean fuel or other energy conversion processes coupled with absorption of atmospheric CO2. Most microalgal species investigated showed tolerance to CO2 concentrations in the range of 5%-10% (v/v) (Zhou et al., 2017). Zhou et al. (2017) in their review highlighted a concern around the limited availability of microalgal strains tolerating higher CO2 concentrations. Furthermore, the need for microalgal nutrients supplementation (Tan et al., 2018) and freshwater for cultivation (Zhou et al., 2017) challenges the economic sustainability of microalgal-based energy production. Thus, the synergy of CO2 sequestration, wastewater utilization, and biofuel production may improve the efficiency of microalgae-based CO2 capture and energy production (Prabakar et al., 2018).
Untreated wastewater from the seafood processing industry has high loads of organic nutrients inclusive of total organic carbon (TOC), nitrogen (ammoniacal, nitrite, and nitrate), and phosphorus. The untreated discharge from seafood processing industries can create local eutrophic conditions, rendering the coastal ecosystem highly vulnerable.
In this context, the objective of this study was to evaluate the CO2 utilization efficiency of a euryhaline Chlorella vulgaris NIOCCV cultivated mixotrophically in seafood processing industry wastewater with the continuous supply of different CO2 concentrations. The effects of CO2 supply on biomass characteristics such as lipid, fatty acid composition, and higher calorific value were also studied.
Section snippets
Algal species and its cultivation in photobioreactor (PBR) in the presence of CO2
Chlorella vulgaris NIOCCV maintained as an axenic culture in the author’s laboratory at CSIR-National Institute of Oceanography, Goa, India was employed in this study. Before cultivation with CO2, the microalga was acclimatized to the aquaculture wastewater used. The characteristics of the wastewater are summarized in Table S1. The biomass productivity was optimized for wastewater enrichment (15% v/v), salinity (0.5–3.5%), light conditions (100 μmol m−2 s−1), and time period (4 days)
CO2 utilization efficiency of C. vulgaris NIOCCV
Determination of CO2 utilization efficiency () is essential for defining a microalgal strain suitable for CO2 capture, storage, and mitigation. In this study, microalgal tolerance towards moderate to very high concentrations of CO2 in continuous supply was investigated. The CO2 concentrations injected for the cultivation medium of C. vulgaris NIOCCV in this study were similar to the concentrations released (12%–20%) from fossil fuel burning (Saravanan et al., 2018). A significant change in
Conclusion
The tolerance of C. vulgaris NIOCCV to the continuous supply of higher CO2 concentrations represents the most striking feature of this strain. The results of this study advocated for an effective, economically favorable and environmentally sustainable strategy of cultivation of C. vulgaris NIOCCV in seafood processing industry wastewater without use of additional nutrients. The integrated approach of wastewater treatment and quality biodiesel production may support a significant reduction in
Conflict of interest
All the authors mutually agree and state that there is no conflict of interest.
Acknowledgments
The financial support received from the Council for Scientific and Industrial Research, New Delhi, India under the project PSC 0206 and from CSIR-National Institute of Oceanography under project OLP 1707 is gratefully acknowledged. VG would like to acknowledge the financial support received from the INSPIRE Faculty Award (GAP 3022), Department of Science and Technology, New Delhi, India. Authors acknowledge Prof. Juliat C. Coates, School of Biological Sciences, University of Birmingham, UK, for
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Both the authors contributed equally.