STUDIES OF LIPID PRODUCTION FROM MICROALGAE FOR BIODIESEL PRODUCTION IN FLAT PANEL PHOTOBIOREACTOR

Abstract

Global energy demand and its dependence on fossil fuel have prompted the search for alternative fuel. Noteworthy, the photosynthetic microalgae have gained significant interest as one of the most promising alternative feedstock for biolipid production. In addition, the commercial cultivation of microalgae for biolipid production is commonly achieved by photobioreactor systems, nowadays flat panel photobioreactor are extensively used for mass cultivation of different types of microalgae. Microalgae lipid in photobioreactor is affected by several chemical (nitrogen and phosphate) and physical parameters (temperature, irradiance, and pH). In this study various physical and chemical parameters were optimized for higher biomass and lipid productivity for Botryococcus braunii in flat panel photobioreactor. In the key finding, a pH stat process was developed to enhance the biomass and lipid productivity at high CO2 concentrations The algal strain showed the maximum specific growth rate, biomass productivity and CO2 consumption rate at 20% CO2concentration. A novel consolidate real time model was developed to study the nitrate depletion dynamics in flat panel photobioreactor. This study suggests that optimum nitrate concentration of 1.125 g L-1 in the nutrient medium significantly enhance the process productivity of the photobioreactor. Light availability inside the photobioreactor is often measured by the Lambert – Beer law, and Lambert - Beer law assumptions are not valid at high cell density cultural conditions, because light scattering and differential absorption have significant impact on light transfer in photobioreactor. In this study the Lambert – Beer law was modified by applying differential absorbance in flat panel photobioreactor. Maximum biomass concentration, maximum lipid content and lipid productivity rate were 2.52 g L-1, 19.76% and 114.92 mg L-1 d-1 at 261 μmol m−2 s−1 light intensity respectively. Photoheterotrophic cultivation of microalgae significantly enhances growth, biomass and lipid yield than the autotrophic cultural conditions. The lipid productivity of microalgae is highly influenced by carbon and nitrogen sources present in their nutrient medium. Carbon sufficient and under nitrogen-limited cultural conditions induces high neutral lipids accumulation in microalgae. In heterotrophic cultivation condition the maximum values of biomass productivity, specific growth rate and lipid productivity were 1.11 g L-1d-1, 0.073 h-1 and 0.39 g L-1d-1 obtained respectively. Single stage two-phase fed batch cultivation for microalgae biomass is a promising strategy to boost lipid accumulation and productivity. A cultivation system in the two-phase fed batch mode was adapted to maximize lipid productivity of B. braunii in flat panel photobioreactor. Importantly, during two-phase fed batch cultivation for B. braunii the biomass was increased to 7.9 g L-1, and the lipid productivity was increased from 0.536 g L-1 d-1 to 1.32 g L-1 d-1 compared to single stage heterotrophic batch cultivation