Exploitation of Nannochloropsis gaditana biomass for biodiesel and pellet production

A comparison of different inorganic and organic flocculants at doses of 50, 100 and 200 mg/L was performed to achieve the maximum biomass harvesting of Nannochloropsis gaditana microalgae. The best results were reached by aluminium chloride with 90.9 ± 0.2% biomass recovered followed by copper sulphate with 70.8 ± 0.3% at the maximum doses used. If the behaviour is analysed after spending 24 h, all flocculants recovered more than 90% algal biomass. In the oil extraction process, a maximum of 29.25 ± 1.10% extracted oil was achieved by Soxhlet using methanol-chloroform 2:1 as solvent and applying previous disruption by microwave. 20.4% less oil was released when n-hexane was used. Ultrasound extraction assisted by microwave reached peak values of 22.60 ± 1.03%. Methyl esters of saturated fatty acids (C14:0, C16:0 and C18:0) were found as the major constituents, accounting for about 70% of the total content. Direct transesterification with previous incubation accomplished higher biodiesel conversions than without it. Finally, pellet manufacturing from algal wastes obtained after the transesterification reaction was studied. The results indicated that these pellet should be mixed with another type of biomass (e.g., miscanthus or eucalyptus) to be used as fuel in biomass boilers.