Optimization of the Growth and Performance of Several Cynobacteria Species in a Pilot Scale Raceway Pond for CO2 Bio-Sequestration

Due to the limited availability of fresh water and the high cost of land for plant culture, microalgae cultivation has attracted significant attention in recent years and has been shown to be the best option for CO2 bio-sequestration. Bio-sequestration of CO2 through algae bioreactors has been hailed as one of the most promising and ecologically benign methods available. This research study was taken up to alleviate certain limitations associated with the technology such as low CO2 sequestration efficiency and low biomass yields. In this study three distinct cyanobacterial strains, Chlorella sp., Synechococcus sp., and Spirulina sp., were tested in 10 litre raceway ponds for their capacity for CO2 bioconversion and high biomass production under various CO2 concentrations at different EC. The highest growth rate of all tested cyanobacterial strains was observed during the first 4 days of cultivation under CO2 5% to 10%. Additionally, all these cyanobacterial strains were explored for their bioremediation capabilities. The results showed that the Chlorella sp., Synechococcus sp., and Spirulina sp. were able to remove COD of the wastewater by 56%, 48% and 77% respectively and the BOD removal efficiency was 48%, 30% and 52% respectively. The primary results indicated that the Spirulina sp. was to be the best cynobacteria studied in terms of biomass production, CO2 bioconversion, and bioremediation capacities. Therefore, the Spirulina sp. was further scaled up in 1500 litre raceway pond for CO2 bio-sequestration and biomass production. The biomass collected was utilised to extract biomolecules such as protein, carbohydrate and lipids.

Growth and Biochemical Composition Characteristics of Arthrospira platensis Induced by Simultaneous Nitrogen Deficiency and Seawater-Supplemented Medium in an Outdoor Raceway Pond in Winter

Arthrospira platensis, a well-known cyanobacterium, is widely applied not only in human and animal nutrition but also in cosmetics for its high amounts of active products. The biochemical composition plays a key role in the application performance of the Arthrospira biomass. The present study aimed to evaluate the growth and biochemical composition characteristics of A. platensis, cultured with a nitrogen-free and seawater-supplemented medium in an outdoor raceway pond in winter. The results showed that the biomass yield could achieve 222.42 g m−2, and the carbohydrate content increased by 247% at the end of the culture period (26 d), compared with that of the starter culture. The daily and annual areal productivities were 3.96 g m−2 d−1 and 14.44 ton ha−1 yr−1 for biomass and 2.88 g m−2 d−1 and 10.53 ton ha−1 yr−1 for carbohydrates, respectively. On the contrary, a profound reduction was observed in protein, lipid, and pigment contents. Glucose, the main monosaccharide in the A. platensis biomass, increased from 77.81% to 93.75% of total monosaccharides. Based on these results, large-scale production of carbohydrate-rich A. platensis biomass was achieved via a low-cost culture, involving simultaneous nitrogen deficiency and supplementary seawater in winter.