Abstract:
This research studied the effects of white LED color temperature and airlift photobioreactor design on growth and carotenoids production in microalga Chlorococcum humicola. Results of batch cultivation in 1-L stirred-tank photobioreactor found that daylight LED produced higher growth and carotenoids concentration than cool white and warm white LEDs. Then, the design of internal-loop airlift photobioreactor was conducted to obtain the condition that gave efficient liquid circulation. Dimensions of internal-loop airlift photobioreactor that yielded efficient liquid circulation were as followed: outer diameter 9 cm, liquid level height 34 cm, spherical stone diffuser (2 cm) located at 1.5 cm from bottom of photobioreactor and internal draft tube (height 27 cm and inner diameter 4.5 cm) located at the same level to stone diffuser. When performing microalgal cultivation using the described photobioreactor subjected to different downcomer to riser areal ratios (AD/AR) and aeration rates, it was AD/AR of 3.0 and aeration rate of 0.8 vvm (1.6 L/min) that produced the highest biomass and carotenoids concentration, with the average cell dried weight and carotenoids concentration measured at 1,360 ± 16.7 mg/L and 6.45 ± 0.04 mg/L (4.78 ± 0.04 mg/g-dw), respectively. Finally, the results of LED color temperature and photobioreactor design were combined and used for the cultivation in 60-L internal-loop airlift photobioreactor. The batch cultivation under light intensity of 20,000 lux finally gave cell dried weight concentration of 1,240 ± 10.0 mg/L and carotenoids concentration of 4.40 ± 0.04 mg/L (3.52 ± 0.05 mg/g-dw) without significant biomass sedimentation and attachment on photobioreactor wall. Lutein and beta-carotene were also identified at 30% and 8% of total carotenoids.