Abstract
Biofuel productions from microalgae are considered as potential alternative fuel sources of fossil fuels. The ideal candidate species for biodiesel production need both high biomass and lipid production. In this study, the Plackett-Burman design was used to evaluate the relative importance of ten nutritional independent components to biomass and lipid production in Tryblionella hungarica NIOF-DM-017. These components were Ca(NO3)2.4H2O, K2HPO4.3H2O, MgSO4.7H2O, Na2SiO3.9H2O, Na2CO3, FeCl3.6H2O, Na2.EDTA.2H2O, glucose, NaCl and pH, where twelve different runs of media were conducted. The biomass and lipid content of the control Navicula medium were 0.133 gL-1 and 21.4%, after five days of growth. Most of components found to contribute largely for the biomass and lipids production. The medium run 8 exhibit lowest biomass and lipids of 0.032 gL-1 and 11.6%, while runs 11 and 12 recorded the highest biomass (0.274 and 0.268 gL-1, respectively). Slight to significant decreases were recorded in the lipid content in different experimental runs. The ligand nature of EDTA found to inhibit the growth of the diatom in the runs especially of high EDTA concentration (runs 3, 5, 9, and 10). The results of the main effects of the studied components were used to prepare two verification medium to evaluate the accuracy of the applied Plackett-Burman design. Form the maximum biomass verification medium, the biomass production increased by 85.7% and lipids by 42.9%, when compared to the control medium. Meanwhile, the prepared verification medium for maximum lipids resulted in increase in biomass by 30.8% and lipid content with 61.2% after five days of experimental period. The lipid profile of T. hungarica cultured on Navicula medium and the two verification media was mainly composed of fatty acids and hydrocarbons. The fatty acids comprise about 53%, 64%, and 59.4% of the total lipids of the test diatom cultured in control medium, verification medium for high biomass and verification medium for high lipids, respectively. In general, non-considerable changes were recorded in fatty acids profile between control and verification media. The FAMEs of T. hungarica were dominated by methyl palmiteate (C16: 0), methyl palmitoleate (C16: 1) and methyl linoleate myristate (C18: 2), which are suitable for biodiesel production.

Key words: Biomass, Lipids, Plackett-Burman, Tryblionella hungarica