High oil content microalgae are a source for biofuel production. They can be
produced in open ponds or closed photobioreactors. To efficiently grow such
microalgae, illumination for photosynthesis, CO2 consumption, and the pH and
nutrient content of the growth medium must be monitored and precisely
controlled. In a closed photobioreactor, illumination is the most critical
parameter because it is the most expensive factor of algae production and
must be operated 24 h per day. In this research, Chlorella kessleri (UTEX
398) microalgae were grown in photobioreactors. All parameters were
identical, except the source and intensity of the illumination. The light sources
included red light-emitting diodes (LED), blue LED, and fluorescent lights.
Growth of the microalgae was observed for seven days and the effects of the
three illumination sources on cell count, cell weight, and cell size were
determined. In the first experiment, in which the current of all three light
sources was the same, red LED produced the highest number of cells with the
highest weight while blue LED light produced the largest cells. In the second
experiment, in which the light intensity was the same for all three light
sources, the highest weight was again achieved with the red LED. Thus, we
suggest that most advantageous production system may be to use a red light
initially to produce the desired cell concentration, then switch to a blue light to
increase cell size.