Chemical absorption and CO2 biofixation via the cultivation of Spirulina in semicontinuous mode with nutrient recycle.

The chemical absorption of carbon dioxide (CO2) is a technique used for the mitigation of the greenhouse effect. However, this process consumes high amounts of energy to regenerate the absorbent and to separate the CO2. CO2 removal by microalgae can be obtained via the photosynthesis process. The objective of this study was to investigate the cultivation and the macromolecules production by Spirulina sp. LEB 18 with the addition of monoethanolamine (MEA) and CO2. In the cultivation with MEA, were obtained higher results of specific growth rate, biomass productivity, CO2 biofixation, CO2 use efficiency, and lower generation time. Besides this, the carbohydrate concentration obtained at the end of this assay was approximately 96.0% higher than the control assay. Therefore, Spirulina can be produced using medium recycle and the addition of MEA, thereby promoting the reduction of CO2 emissions and showing potential for areas that require higher concentrations of carbohydrates, such as in bioethanol production.

Effect of the carbon concentration, blend concentration, and renewal rate in the growth kinetic of Chlorella sp.

The microalgae cultivation can be used as alternative sources of food, in agriculture, residual water treatment, and biofuels production. Semicontinuous cultivation is little studied but is more cost-effective than the discontinuous (batch) cultivation. In the semicontinuous cultivation, the microalga is maintained in better concentration of nutrients and the photoinhibition by excessive cell is reduced. Thus, biomass productivity and biocompounds of interest, such as lipid productivity, may be higher than in batch cultivation. The objective of this study was to examine the influence of blend concentration, medium renewal rate, and concentration of sodium bicarbonate on the growth of Chlorella sp. during semicontinuous cultivation. The cultivation was carried out in Raceway type bioreactors of 6 L, for 40 d at 30°C, 41.6 µmol m(-2) s(-1), and a 12 h light/dark photoperiod. Maximum specific growth rate (0.149 d(-1)) and generating biomass (2.89 g L(-1)) were obtained when the blend concentration was 0.80 g L(-1), the medium renewal rate was 40%, and NaHCO3 was 1.60 g L(-1). The average productivity (0.091 g L(-1) d(-1)) was achieved with 0.8 g L(-1) of blend concentration and NaHCO3 concentration of 1.6 g L(-1), independent of the medium renewal rate.