Investigating the production of biodiesel from Dunaliella salina grown in Gaillard medium (f/2) modified with trace elements

This study was conducted to evaluate the effects of trace elements on growth, oils content, fatty acid profiles, and biodiesel properties of Dunaliella salina.

Algae cells were grown in Guillard medium (f/2) with a salinity of 117 g/L and with 19 nutrient treatments containing different concentrations of trace elements (25, 50 and 75% of the initial concentration of Guillard medium), with 3 repetitions. At the end of the experiment, dry weight and some selected growth parameters, lipids content, fatty acids, and biodiesel fuel properties were determined.

Dry weight of algae was significantly influenced by addition levels of trace elements. The maximum algal biomass and fat content were observed in CuSO4 with 75% of standard concentration (1425.1 mg/L and 374 mg/biomass, respectively) and was significantly higher than the control treatment (P < 0.05). Majority of the fatty acid methyl esters were between C14-18 and C22:1n9., The highest cetane number (82.7) and the lowest iodine value (123.5) were found in CoCl2 with 25% of the standard concentration treatment (P < 0.05). Among all treatments, the highest degree of unsaturation was observed in the 25% manganese treatment (P<0.05). The highest and lowest amount of CFPP was observed in cobalt 75% (4.50°C) and cobalt 25% (-2.86°C) treatments, respectively; being significantly higher than the control treatment (P<0.05).

High-quality biodiesel that was obtained from D. salina grown in CoCl2 with 25% of the standard concentration (higher cetane number and lower long-chain unsaturated fatty acids) showed the great potential for biodiesel production due to higher lipids content (197.92 mg/total biomass) than the control treatment (193.44 mg/total biomass) from lower mass quantity. The exposure of D. salina to trace elements deficiency revealed the ability of this algae to grow the same rate as control (in case of zinc, manganese, cobalt, and molybdate treatments 75%) or even higher growth (75% copper; 1425.1 mg/d.w.). The use of modified Guillard medium (f/2) could be beneficial during the cultivation period of D. salina to prevent biomass loss to some degree (e.g.  nitrogen and phosphorus shock), resulting in higher lipids production.