Optimization cultivation of Chlamydomonas reinhardtii in a tubular photobioreactor (2000 Liter) for biomass and green bioenergy (biodiesel) production

Abstract

The biodiesel can be produced from diverse microalgae lipids as alternative and renewable fuel. Thus, the aim of this study was to optimize the Chlamydomonas reinhardtii promising species as biodiesel feedstock for large-scale cultivation in Egypt. To understand some of the triggers required for the metabolic pathway switch to lipid accumulation, the effect of carbon sources and the three elements availability (N, P, S) in C. reinhardtii growth medium was determined. A local microalgae C. reinhardtii was cultured in modified Sueoka medium containing various concentrations of CO2 and bicarbonate (NaHCO3) (in 2-liter flasks) as a carbon source. The optimal source in term biomass, high lipid productivity (10.3 mgL-1d-1) and a higher lipid content (22.76%) were obtained in 6% CO2 culture. Then, the availability of N, P, S (various concentrations of N, P and S) nutrients elements was added to 6% CO2 culture, for produce a highest lipid content and lipid productivity. As expected, under low availability N-1.78 mM; P-0.14mM and S-0.10 mM mediums, C. reinhardtii showed a high accumulation lipid content. Therefore, to improve the economic feasibility of microalgae biofuels production, its concentrations were selected to combine (N+P+S) in order to cultivation of C. reinhardtii in a multi-tubular photobioreactor (400 liter) to produce high lipid contents. Under limited condition, the biomass dry weight, biomass productivity, lipid content and lipid productivity were found to be 3.11 (gL-1), 0.15±0.012 (g-1L-1d-1), 22.76% (w/w %) and 1.9± 0.35 (mg-1L-1d-1), respectively. The extracted lipid was found to have physical and chemical properties similar that plant oils using for biodiesel production. The FAME profiling of prepared biodiesel shows the presence of considerable amount of 36.97% saturated fatty acids (palmitic acid and stearic acid, together) with 27.33% unsaturated (oleic acid and linoleic acid) fatty acids. The FAME had a low iodine value and high CN, which meet with the appropriate of biodiesel standards (EN 14214 and ASTM D6751). Thus, C. reinhardtii appears to be more feasible for high quality biodiesel production.