Outdoor cultivation of Chlorella vulgaris FSP-E in vertical tubular-type photobioreactors for microalgal protein production

Aquafeeds rely heavily on fishmeal as the major protein source. However, the recent increase in the price of fishmeal and sharp decrease in fish resources have resulted in a major threat to the aquaculture industry. Therefore, cost-effective and sustainable fishmeal alternatives should be found. While microalgae are considered a promising alternative to fishmeal, the cultivation scale should be enlarged and its protein production cost should be much lower. In this study, Chlorella vulgaris FSP-E was grown in 50-liter outdoor photobioreactors (PBRs) to produce microalgal proteins. Using the optimum urea concentration (18.6 mM), inoculum size (0.2 g/L) and aeration rate (0.05 vvm), the maximum biomass productivity (268.1 mg/L/d) and protein productivity (155.4 mg/L/d) were obtained. Semi-batch operation with a 50% medium replacement ratio attained a high protein content and productivity of 52.2% and 125.2 mg/L/d, respectively. The resulting microalgal protein contained 60.3% indispensable amino acids, thus possessing a high commercial value.