Light-emitting diode lighting parametric study of internally illuminated photobioreactor for good growth of nannochloropsis species cultivation

Abstract

Microalgae such as Nannochloropsis sp. are single-cell organism, well known as a photosynthetic microorganism and have been identified as one of the most potential renewable feedstock for the third generation biofuels. Light quality and quantity are essential for a good growth of microalgae cultivation. In this research, lighting parametric study using light-emitting diode (LED) was conducted to analyse the effect of different light spectrum onto the growth of Nannochloropsis sp. cultivation. In addition, the effect of light intensity with different optical path length on different working volume culture was also evaluated. In order to validate a good growth of cultivation, culture growth curve was analysed and maximum cell density was recorded. The study was performed in three stages of experimental photobioreactor (PBR) setup which is lab-scale, mock-up and scale-up PBR. In the lab-scale experiment (0.5 working volume), LED with red spectrum (wavelength 660 ) and blue spectrum (wavelength 457 ) were compared to the white fluorescent light with same incident light intensity (100 at short optical path length (20 to 55 ). It was found that LED with combination of red and blue spectrum generated higher maximum cell density by 19% compared to the white fluorescent light, which recorded at 11.2 106 . In the mock-up PBR experiment (20 working volume), light intensity of red and blue LED module with narrow beam angle (55 ) was evaluated within 15 to 120 of optical path length by using variation of current supply (200 to 500 ). As the result, the maximum cell density recorded is 7.1 106 at 355 of light intensity. Additionally, the relationship between light intensity and culture cell density was also established at this stage. Next, the cultivation was performed continuously in the scale-up PBR with bigger working volume (30, 65 and 100 ) at 100 optical path length. It was found that light saturated condition happened at cell density around 7.5 106 to 8.0 106 when the light intensity is at 350 . The maximum cell density can be increased further to 9.3 106 by applying higher light intensity (450 ). As a conclusion, LED with red spectrum promoted the growth in the exponential growth phase, while blue spectrum had a significant role during the linear growth phase especially in the higher cell density culture. Application of high intensity LED light with narrow beam angle was feasible to be used in internally illuminated PBR with longer optical path length. On top of these findings, a vertically stackable LED luminaire design concept was proposed to provide flexibility and to increase efficiency for mass cultivation operation using internally illuminated PBR.