Effects of seed age, inoculum density, and culture conditions on growth and hydrocarbon accumulation of Botryococcus braunii SAG807-1 with attached culture

Background: Botryococcus braunii is difficult to cultivate and has a limited amount of substantive scale-up and productivity assessments with conventionally suspended cultivation systems, such as open pond or closed photobioreactors. The biomass concentrations of cultivated microalgal biofilms are much higher than those of suspension cultures, and the attached microalgal cells are easily separated from cultivation media. However, studies on the attached cultivation conditions for B. braunii have been rarely performed. Results: Herein, an attached cultivation method for B. braunii SAG 807-1 incubation was introduced. The effects of primary culture conditions on growth and hydrocarbon accumulation were investigated. Seed age influenced the biomass and hydrocarbon accumulation in B. braunii, and the highest values were 5.97 and 2.99 g M-2 day(-1), respectively, when seed age was 14 days. The appropriate range of initial inoculation density was 7.9-10.1 g m(-2). Light intensity was a dominating factor influencing B. braunii's growth in the attached culture, and the light saturation point was 100-150 mu mol m(-2 )s(-1). Periodic illumination in 8:16 light: dark cycle had the highest utilisation of photons at approximately 1.0 g of biomass per mole of photons. The increasing CO(2 )concentration in aerated gas improved the growth rate, but its concentration should be 1%. Conclusions: Attached algal cultivation systems have been widely explored. However, the optimised values for aqueous suspension methods may be unnecessary for the attached system. Optimised seed age, inoculum density, CO(2 )concentration, light intensity and photoperiod can improve the growth and hydrocarbon accumulation of B. braunii SAG807-1 with the attached culture.