Abstract
In order to select excellent strains with high CO2 fixation capability on a large scale, nine Spirulina species were cultivated in columnar photobioreactors with the addition of 10% CO2. The two species selected (208 and 220) were optimized for pH value, total dissolved inorganic carbon (DIC), and phosphorus content with intermittent CO2 addition in 4 m2 indoor raceway ponds. On the basis of biomass accumulation and CO2 fixation rate in the present study, the optimum pH, DIC, and phosphate concentration were 9.5, 0.1 mol L−1, and 200 mg L−1 for both strains, respectively. Lastly, the two strains selected were semi-continuously cultivated successfully for CO2 mitigation in 605 m2 raceway ponds aerated with food-grade CO2 purified from a coal chemical flue gas on a large scale. The daily average biomass dry weight of the two stains reached up to 18.7 and 13.2 g m−2 d−1, respectively, suggesting the two Spirulina strains can be utilized for mass production.
Highlights
Global warming caused by CO2 emissions due to human activities has become a significant environmental issue
Nine Spirulina species were tested for their CO2 fixation capabilities by evaluating biomass productivity and CO2 fixation rate in 800 mL columnar photobioreactors under laboratory conditions
The tolerance to elevated temperatures of the strains we studied is an important factor for reducing flue gas released from coal chemical plant, which can be directly injected into open raceway ponds for CO2 fixation on a large scale
Summary
Global warming caused by CO2 emissions due to human activities has become a significant environmental issue. Cardias et al (2018) reported that the growth of Spirulina sp. A promising strategy for enhancing CO2 sequestration in an environmentally friendly and sustainable manner was reported using small doses of sugars together with LED illumination during cultivation of Chlorella vulgaris in different sized photobioreactors (PBRs) (Fu et al, 2019). Among the different strategies for mitigating CO2, biological CO2 mitigation through microalgae has recently received considerable attention due to their higher CO2 fixation capability and bioactive substances contained in their biomass (Wang et al, 2008; Yoo et al, 2010; Matsudo et al, 2012; Hancke et al, 2015; Duarte et al, 2017). Several studies have shown that microalgal growth can be improved by CO2 from the atmosphere or flue gases and they have better CO2 fixation abilities (10–50 times greater) than
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