BACKGROUND: Immobilization of laccase may cause more or less mass transfer limitation in practical applications. In order to enhance the reaction rate, there is great interest in developing an effective way to increase the rate of diffusion in reactions catalyzed by immobilized laccase.

To improve biomass and microalgal oil production of Botryococcus braunii, fedbatch culture was investigated in an airlift photobioreactor. The optimal feeding time of the fed-batch culture was after 15 days of cultivation, where 1.82 g/L of the microalgal biomass was obtained in the batch culture. Nitrate nutrient was the restrictive factor for the fed-batch cultivation while phosphate nutrient with high concentration did not affect the microalgal growth. The optimal mole ratio of nitrate to phosphate was 34.7:1, where nitrate concentration reached the initial level and phosphate concentration was one quarter of its initial level. With one feeding, the biomass of B. braunii reached 2.56 g/L after 18 days. Two feedings in 2-day interval enhanced the biomass production up to 2.87 g/L after 19 days of cultivation. The hydrocarbon content in dry biomass of B. braunii kept at high level of 64.3% w/w. Compared with the batch culture, biomass production and hydrocarbon productivity of B. braunii were greatly improved by the strategic fedbatch cultivation.