Marcelo C. Matsudo

CO2 from alcoholic fermentation for continuous cultivation of Arthrospira (Spirulina) platensis in tubular photobioreactor using urea as nitrogen source

Carbon dioxide released from alcoholic fermentation accounts for 33% of the whole CO2 involved in the use of ethanol as fuel derived from glucose. As Arthrospira platensis can uptake this greenhouse gas, this study evaluates the use of the CO2 released from alcoholic fermentation for the production of Arthrospira platensis. For this purpose, this cyanobacterium was cultivated in continuous process using urea as nitrogen source, either using CO2 from alcoholic fermentation, without any treatment, or using pure CO2 from cylinder. The experiments were carried out at 120 μmol photons m−2 s−1 in tubular photobioreactor at different dilution rates (0.2 ≤ D ≤ 0.8 d−1). Using CO2 from alcoholic fermentation, maximum steady‐state cell concentration (2661 ± 71 mg L−1) was achieved at D = 0.2 d−1, whereas higher dilution rate (0.6 d−1) was needed to maximize cell productivity (839 mg L−1 d−1). This value was 10% lower than the one obtained with pure CO2, and there was no significant difference in the biomass protein content. With D = 0.8 d−1, it was possible to obtain 56% ± 1.5% and 50% ± 1.2% of protein in the dry biomass, using pure CO2 and CO2 from alcoholic fermentation, respectively. These results demonstrate that the use of such cost free CO2 from alcoholic fermentation as carbon source, associated with low cost nitrogen source, may be a promising way to reduce costs of continuous cultivation of photosynthetic microorganisms, contributing at the same time to mitigate the greenhouse effect.

Photosynthetic efficiency and rate of CO2 assimilation by Arthrospira (Spirulina) platensis continuously cultivated in a tubular photobioreactor

Similar to other photosynthetic microorganisms, the cyanobacterium Arthrospira platensis can be used to produce pigments, single cell proteins, fatty acids (which can be used for bioenergy), food and feed supplements, and biofixation of CO(2) . Cultivation in a specifically designed tubular photobioreactor is suitable for photosynthetic biomass production, because the cultivation area can be reduced by distributing the microbial cells vertically, thus avoiding loss of ammonia and CO(2) . The aim of this study was to investigate the influence of light intensity and dilution rate on the photosynthetic efficiency and CO(2) assimilation efficiency of A. platensis cultured in a tubular photobioreactor in a continuous process. Urea was used as a nitrogen source and CO(2) as carbon source and for pH control. Steady-state conditions were achieved in most of the runs, indicating that continuous cultivation of this cyanobacterium in a tubular photobioreactor could be an interesting alternative for the large-scale fixation of CO(2) to mitigate the greenhouse effect while producing high protein content biomass.

Simultaneous use of urea and potassium nitrate for Arthrospira (Spirulina) platensis cultivation

Urea has been considered as a promising alternative nitrogen source for the cultivation of Arthrospira platensis if it is possible to avoid ammonia toxicity; however, this procedure can lead to periods of nitrogen shortage. This study shows that the addition of potassium nitrate, which acts as a nitrogen reservoir, to cultivations carried out with urea in a fed‐batch process can increase the maximum cell concentration (Xm) and also cell productivity (PX). Using response surface methodology, the model indicates that the estimated optimum Xm can be achieved with 17.3 mM potassium nitrate and 8.9 mM urea. Under this condition an Xm of 6077 ± 199 mg/L and a PX of 341.5 ± 19.1 mg L–1day–1 were obtained.

Cultivation of Arthrospira (Spirulina) platensis by Fed-Batch Process

This chapter comments on fed-batch cultivation of Arthrospira platensis under different carbon and nitrogen sources, pH, temperature, light intensity, type of photobioreactor and typical parameters of the fed-batch process, such as feeding time, addition protocol and flow rate. Inexpensive nitrogen sources, such as urea, ammonium salts and nitrogen-rich wastewaters can be used for A. platensis cultivation, with results that can be comparable to those with classical nitrate sources. Closed photobioreactors are useful for preventing ammonia loss. The use of organic carbon sources needs to be carried out under aseptic conditions, and it is necessary to evaluate the best supplying conditions when using fed-batch process. The addition of CO2 ensures the control of pH and, at the same time, supply of the carbon source into the culture medium. The fed-batch process can be useful for the production of A. platensis using CO2 from industrial plants, particularly from industrial alcoholic fermentation.