Light for Algae and B. braunii Growth.

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Light is an important physical element in the growth of Algae and Botryococcus braunii. Different research work conducted have an average light intensity of 60 W/M², with a light period of 12 hours per day but this may vary from one specie to another by some degree ( Jian,2005). Different strains of B.braunii have been found in different countries such as China Japan and UK with more focus being on physical requirement of B. braunii (China strain 1) which is found in China. The determination of light intensity for the B. braunii strain involved use of two ranges of light intensity; low and high light intensity and examining the effect of the light intensities on their growth under 23 °C and 12 hour light and another 12 hour dark period using four different light intensities; 8, 12, 20 and 30 W/m2with three replicates at each level of light intensity. Another second experiment involved the exposure of the algae to 30, 60, 100, 150, 200 and 300 W/m2 with three replicates and then assessing the samples after a period of two weeks. The results from these experiments showed a great variation as most of the algae cells under 30 W/m2 light intensity died and the cultivation colour also turned brown under 8 and 12 W/m2. The results also showed that under 30 W/m2, the algal generation time (G) was shortest at about (3.85 ± 0.12 days), but the proliferous rate for the algal (K) was greatest at (0.078 ± 0.002). The experiment for higher light intensity range showed that the 30 and 60 W/m2 treatments were more suitable to algal culture than high light intensities. Under high light intensities of over 150 W/m2 the algae were bound by filamentous bacteria in some flasks. Algae exposed to 300 W/m2 light intensity died.

From these experiments, the most important finding was that algae cultured under lower illumination, could reduce hydrocarbon production by these algae (Chirac et al.1985). The China 1 strain was found to be able to survive in light intensities of between 30 and 100 W/m2 for good growth. Other research work have also shown that light intensities in the range of between 15 and 180 W/m2 is capable of stimulating an adequate growth with a doubling time of between 5 and 2.5 days for 15 and 180 W/m2 light intensities respectively (Vladislay et al. (1994). Light intensity of less than 30 W/m2 inhibits algae growth. Light intensity also affects the lipid content of the algae which decreases when the light intensity is above 100 W/m2 due to low biomass and availability of fewer hydrocarbon droplets. Different studies have therefore shown that the optimal light intensity for the China 1 strain is between 30 and 60 W/m2 (Lagreau et al. 1980)

References.

Chirac,C., Casadevall,E., Largeau, C. & Metzger,P. (1985). Bacterial influence upon growth and hydrocarbon production of the green alga Botrococcus braunii. Journal of Phycology,21, 380-387.

Jian, Q. (2005). Bio -Hydrocarbons from Algae: Impacts of temperature, light and salinity on algae growth. Rural Industries Research and Development Corporation, Australia.

Largeau, C., Casadevall, E., Dif, D. & Berkaloff, C. (1980). Renewable hydrocarbon production from the agla Botryococcus braunii, p. 653-658, Publisher:London.

Vladislay,C., Jaromír, L. (1994). The effect of high irradiances on growth, biosynthetic activities and the ultrastructure of the green alga Botryococcus braunii strain Droop 1950/807-1. Journal of Archiv fur hydrobiology, 115-131.