Maximizing biomass productivity and cell density of Chlorella vulgaris by using light-emitting diode-based photobioreactor

Green microalgae have recently drawn attention as promising organisms for biofuel production; however, the question is whether they can grow sufficient biomass relative to limiting input factors to be economically feasible. We have explored this question by determining how much biomass the green microalga Chlorella vulgaris can produce in photobioreactors based on highly efficient light-emitting diodes (LEDs). First, growth results were improved under the less expensive light of 660 nm LEDs, developing them in the laboratory to meet the performance levels of the traditional but more expensive 680 nm LEDs by adaptive laboratory evolution (ALE). We then optimized several other key parameters, including input superficial gas velocity, CO2 concentration, light distribution, and growth media in reference to nutrient stoichiometry. Biomass density thereby rose to approximately 20 g dry-cell-weight (gDCW) per liter (L). Since the light supply was recognized as a limiting factor, illumination was augmented by optimization at systematic level, providing for a biomass productivity of up to 2.11 gDCW/L/day, with a light yield of 0.81 gDCW/Einstein. These figures, which represent the best results ever reported, point to new dimensions in the photoautotrophic performance of microalgal cultures. (C) 2012 Elsevier B.V. All rights reserved.