Field study on attached cultivation of Arthrospira (Spirulina) with carbon dioxide as carbon source.

Microalga is considered as a promising candidate for CO2 bio-sequestration. Biofilm attached cultivation is a newly developed technology with many advantages over conventional aqua-suspended methods. In this research, the field performance of this technology was investigated with a 10 m2 pilot system under greenhouse condition by cultivating Arthrospira (Spirulina) platensis with CO2 as carbon source. The system run continuously for two months without contamination bloom. Averaged biomass productivity was 38.3 g m-2 d-1 with protein content over 60% and overall CO2 usage efficiency of 75.1%. Construction cost for the pilot system was over US$200 per m2 which was much higher than that of open pond. However, there was a great reduction space in future large-scale application if the most expensive materials were substituted with cheaper ones. These results indicated the attached cultivation was a promising technology for industrialized application of microalga in CCUS (carbon capture, utilization and storage).

Developing a CO2 bicarbonation absorber for promoting microalgal growth rates with an improved photosynthesis pathway.

In order to solve the problems of the short residence time and low utilization efficiency of carbon dioxide (CO2) gas added directly to a raceway pond, a CO2 bicarbonation absorber (CBA) was proposed to efficiently convert CO2 gas and sodium carbonate (Na2CO3) solution to sodium bicarbonate (NaHCO3), which was dissolved easily in the culture medium and left to promote the microalgal growth rate. The CO2 gas reacted with the Na2CO3 solution (initial concentration = 200 mM L-1 and volume ratio in CBA = 60%) for 90 min at 0.3 MPa to give the optimized molar proportion (92%) of NaHCO3 product in total inorganic carbon and increase the microalgal growth rate by 5.0 times. Quantitative label-free protein analysis showed that the expression levels of the photosystem II (PSII) reaction centre protein (PsbH) and PSII cytochrome (PsbV2) in the photosynthesis pathway increased by 4.8 and 3.4 times, respectively, while that of the RuBisCO enzyme (rbcL) in the carbon fixation pathway increased by 3.5 times in Arthrospira platensis cells cultivated with the NaHCO3 product in the CBA at 0.3 MPa.

Promoting helix pitch and trichome length to improve biomass harvesting efficiency and carbon dioxide fixation rate by Spirulina sp. in 660 m2 raceway ponds under purified carbon dioxide from a coal chemical flue gas.

The helix pitch and trichome length of Spirulina sp. were promoted to improve the biomass harvesting efficiency and CO2 fixation rate in 660 m2 raceway ponds aerated with food-grade CO2 purified from a coal chemical flue gas. The CO2 fixation rate was improved with increased trichome length of the Spirulina sp. in a raceway pond with double paddlewheels, baffles, and CO2 aerators (DBA raceway pond). The trichome length has increased by 33.3 µm, and CO2 fixation rate has increased by 42.3% and peaked to 51.3 g/m2/d in a DBA raceway pond. Biomass harvesting efficiency was increased with increased helix pitch. When the day-average greenhouse temperature was 33 °C and day-average sunlight intensity was 72,100 lu×, the helix pitch of Spirulina sp. was increased to 56.2 µm. Hence the biomass harvesting efficiency was maximized to 75.6% and biomass actual yield was increased to 35.9 kg in a DBA raceway pond.