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This work is to explore the potential of producing biodiesel and valuable co-products from the biomass of Schizochytrium mangrovei PQ6 which was isolated from Phu Quoc Island, Kien Giang province, Vietnam. This microalga contains high lipid content (up to 70% of dry cell weight) and high level of total fatty acids, which is ideal for making biodiesel. The production of fatty acid methyl esters (FAME) from this marine microalga resulted in a yield of 88% based on algal oil and 44% based on algal biomass. The process of separating the obtained FAME into a first fraction enriched with saturated FAME (SFAME) and a second fraction enriched with unsaturated FAME (UFAME) was then investigated to exploit the valuable co-products. The obtained results shown that the mass fraction of SFAME and UFAME were 70% and 30%, respectively. The UFAME fraction contains a high content of DHA (accounting for 69.000% of TFAs). The test results of the SFAME fraction indicated that specific gravity at 15°C, flash point, water and sediment, kinematic viscosity at 40°C, sulfated ash, sulfur, copper strip corrosion at 50°C, cetane number, carbon residue, iodine number, workmanship meet Vietnam Biodiesel B100 Standard. Moreover, the utilization of waste glycerol from biodiesel process as carbon source for the cultivation of the microalgae S. mangrovei PQ6 and Spirulina platensis was also investigated.

Today microalgae represent a viable alternative source of squalene for commercial application. The species Schizochytrium mangrovei, a heterotrophic microalga, has been widely studied and provides a high amount of squalene, polyunsaturated fatty acids and has good profiles for biodiesel production. Our work was aimed at examining the squalene contents in Vietnam's heterotrophic marine microalga S. mangrovei PQ6 biomass and residues of the biodiesel process from this strain. Thin-layer chromatography and high-performance liquid chromatography (HPLC) methods were successfully applied to the determination of squalene in S. mangrovei PQ6. The squalene content and production of S. mangrovei PQ6 reached 33.00 ± 0.02 and 33.04 ± 0.03 mg g(-1) of dry cell weight; and 0.992 g L(-1) and 1.019 g L(-1) in 30 and 150 L bioreactors, respectively after 96 h of fermentation. In addition, squalene was also detected in spent biomass (approximately 80.10 ± 0.03 mg g(-1) of spent biomass) from the S. mangrovei PQ6 biodiesel production process. The structure of squalene in residues of the biodiesel process was confirmed from its nuclear magnetic resonance spectra. The results obtained from our work suggest that there is tremendous potential in the exploitation of squalene as a value-added by-product besides biodiesel from S. mangrovei PQ6 to reduce biodiesel price.