(10c) Effects of pH on Cell Growth, Lipid Production and CO2 Demand of Microalgae Chlorella sorokiniana

Microalgae have emerged as one of the most promising alternative energy feedstocks. Some advantages include the simple cellular structure, short production cycle, high lipid content, and fast growth. However, high production costs due to high CO₂ usage and low lipid productivity have been one of the major challenges impeding the commercial production of algal biofuels, Here, cell growth and lipid contents of Chlorella sorokiniana DOE 1412 were tested at different pH in flask cultivation. Culture pH was manipulated by CO₂ addition. The optimal pH for DOE1412 is 5.8-6.0 when only taking into account the cell growth and lipid production. A flat panel airlift photobioreactor (PBR) was used for scale-up cultivation at five different pH levels (6.5, 7.0, 7.5, 8.0 and 8.5). Data of pH value and the CO₂ addition was collected by a data logger. Biomass productivity increased with decreasing pH. By taking into account not only the cell growth and lipid production but also CO₂ demand, the lowest value of g CO₂/g dry biomass was achieved at pH 8. Also, the fatty acid profiles and biodiesel properties in different culture pH were investigated. Cetane number (CN) of biodiesel in the pH 6.5, 7 and 7.5 treatments satisfied the US standard ASTM D6751; among them, the pH 6.5 treatment met the Europe standard EN 14214. Finally, protein content in algae biomass increased with increasing pH, while C/N ratio in cells decreased.