Production of energy-dense biomass of microalgae Botryococcus braunii and Chlorella in a photobioreactor

Abstract

We have optimized the cultivation parameters for the microalgae Botryococcus braunii and Chlorella in a photobioreactor: duration of the cultivation cycle, aeration conditions, degree of enrichment of feed air with carbon dioxide, photoperiod and light/dark cycles. We have established that the greatest increase in biomass is observed when using the drain/replenish method, withdrawing 90% of the culture fluid in a 4-day cultivation cycle for Chlorella and a 7-day cycle for Botryococcus braunii, gradually increasing the carbon dioxide content in the feed air (from 0% in the first 24 hours to 2% toward the end of the cultivation cycle), 12 hours total for the light/dark cycle and a photoperiod of 9 hours.Microalgal biomass is one of the most promising feedstocks for production of alternative motor fuels, and many experts believe it represents the future of the alternative power industry. With commercial cultivation, microalgae can accumulate up to 40% (and some species, up to 70%) lipids within their cells, which together with their fast growth rate favorably distinguishes them from higher plants [1].European countries have followed a strategy for transition to the use of alternative fuels involving addition of biofuels to conventional petroleum fuels, gradually increasing the proportion of the biofuel in the blend [2]. In such an approach, biofuels can be used without significant modification of the design of internal combustion engines, ensuring a smooth transition to alternative types of fuel.Among the many species of microalgae studied from the standpoint of obtaining energy-dense lipids, the most promising is the species Botryococcus braunii [3]. This species of microalgae produces up to 40% (relative to the dry weight of the biomass) of a specific oil consisting mainly of isoprenoids in the triterpene series. The structural formulas of some of them are given below [4][5][6].