Economic efficiency of different light wavelengths and intensities using LEDs for the cultivation of green microalga Botryococcus braunii (NIES‐836) for biofuel production

Abstract

Microalgae have been regarded as potential and alternative next‐generation renewable energy sources because of high lipid content in their cell. An efficient light source is pre‐requisite for rapid production of microalgae biomass in photobioreactor in order to produce biofuel, and light emitting diodes (LEDs) have recently been identified as effective and low‐cost energy sources for microalgae cultivation. Green microalga Botryococcus braunii has relatively higher lipid content than other microalgae. In the present study, we investigated the effects of various LEDs with different light wavelengths and illumination intensities on the growth of B. braunii (strain NIES‐836) for the first time. High intensity blue LED was found to be the most effective light source for the growth of the microalga. Monochromatic blue and mixed red‐green‐blue LEDs produced the highest biomass (0.22 and 0.39 mg d wt mL−1, respectively) and relative growth rates (9.20 ± 2.16 and 9.47 ± 2.67 μg d wt mL−1 d−1, respectively) of the microalga. The growth efficiency, in terms of biomass production and energy consumption (mg d wt mL−1 w−1), of the microalga was the highest with blue‐green LED (5.07) followed by red‐green‐blue (4.00) and blue (3.91) LEDs. The highest economic efficiency in terms of power cost and biomass production (mg d wt mL−1 $−1) was obtained with blue‐green LED (182.54) followed by red‐green‐blue (144.74), blue (132.00), and blue‐red (125.83) LEDs indicating that these LEDs would be more cost‐effective than other LEDs for large‐scale cultivation of this microalga. © 2014 American Institute of Chemical Engineers Environ Prog, 34: 269–275, 2015