Flat panel airlift photobioreactor for cultivation of vegetative cells of microalga Haematococcus pluvialis

Abstract

A comparison between the cultivation of Haematococcus pluvialis NEIS-144 in airlift systems with different configurations was carried out. The 3L cylindrical airlift photobioreactor clearly outperformed the other two. However, the upscale of 3L to 17L cylindrical airlift photobioreactor with similar design resulted in a drastically drop in the growth performance where the specific growth rate and the productivity decreased from 0.45 d[superscript -1] and 87x10[superscript 4] cell mL[superscript -1] d[superscript -1] in the 3L to 0.38 d[superscript -1] and 62x10[superscript 4] cell mL[superscript -1] d[superscript -1] in the 17L. The flat panel airlift photobioreactor (FP-ALPBR) was proposed as alternative cultivation system where the upscale was simplified just by increasing the length of the reactor. Without a thorough investigation on the optimal design and operating conditions, the airlift was capable of giving reasonable growth character. The performance of the system was still quite satisfactorily where the attainable maximum cell density of 41 x10[superscript 4] cell mL[superscript -1] and specific growth of 0.52 d[superscript -1] were achieved. The optimal conditions for the cultivation of H. pluvialis in the FP-ALPBR were obtained with the modified F1 medium where: pH = 7, light illuminated at 20 µmol photon m[superscript -1] s[superscript -1] (with normal fluorescence lamps), and aeration with superficial velocity of 0.4 cm s[superscript -1], A[subscript d]/A[subscript r] = 0.4. The semi-continuous culture was successfully implemented where the harvest could be periodically performed. For the 3L system, cell density increased up to the level obtained in the previous cycle within 7 days period, and for these two 17L systems, each cycle required only about 3-4 days. The productivity of semi-continuous culture in 3L, 17L cylindrical ALPBR and 17L FP-ALPBR were 9x10[superscript 7], 7x10[superscript 7] and 7.7x10[superscript 7] cell L[superscript -1] d[superscript -1], respectively. The, thus far, largest scale, 90L, FP-ALPBR could be achieved the maximum cell density of 40x10[superscript 4] cell mL[superscript -1] and the specific growth rate of 0.39 d[superscript -1] which was found to be most attractive as it required relatively low operating cost at approx. 5.26x102 THB for the cultivation of such alga.