The use of a hydrated phosphonium ionic liquid, [P(CH₂OH)₄]Cl, for the extraction of microalgæ lipids for biodiesel production, was evaluated using two microalgæ species, Chlorella vulgaris and Nannochloropsis oculata. The ionic liquid extraction was compared to the conventional Soxhlet, and Bligh & Dyer, methods, giving the highest extraction efficiency in the case of C. vulgaris, at 8.1%. The extraction from N. oculata achieved the highest lipid yield for Bligh & Dyer (17.3%), while the ionic liquid extracted 12.8%. Nevertheless, the ionic liquid extraction showed high affinity to neutral/saponifiable lipids, resulting in the highest fatty acid methyl esters (FAMEs)-biodiesel yield (4.5%) for C. vulgaris. For N. oculata, the FAMEs yield of the ionic liquid and Bligh & Dyer extraction methods were similar (>8%), and much higher than for Soxhlet (<5%). The ionic liquid extraction proved especially suitable for lipid extraction from wet biomass, giving even higher extraction yields than from dry biomass, 14.9% and 12.8%, respectively (N. oculata). Remarkably, the overall yield of FAMEs was almost unchanged, 8.1% and 8.0%, for dry and wet biomass. The ionic liquid extraction process was also studied at ambient temperature, varying the extraction time, giving 75% of lipid and 93% of FAMEs recovery after thirty minutes, as compared to the extraction at 100 °C for one day. The recyclability study demonstrated that the ionic liquid was unchanged after treatment, and was successfully reused. The ionic liquid used is best described as [P(CH₂OH)₄]Cl·2H₂O, where the water is not free, but strongly bound to the ions.

Biodiesel expansion is currently limited due to high raw\ud material costs for its produc\ud tion. The potential of using\ud sludge from municipal wastewater treatment plants as an\ud alternative lipid feedstock for biodiesel production was\ud investigated. Experiments were conducted to evaluate the suit\ud ability of four different types of wastewater sludges for\ud biodiesel production. Lipids were extracted from primary, secondary, blended and stabilized sludge in a Soxhlet\ud extractor, using hexane as a solvent. Finally, the lipids were converted by acid catalysis transesterification into their\ud corresponding fatty acid methyl esters (FAMEs) - biodiesel\ud . Results indicated that among four sludge tested, primary\ud sludge achieved the greatest lipids and biodiesel yields. Th\ud e amount of extracted lipids\ud for primary sludge was 25.3%\ud compared to 21.9%, 10.1% and 9.1% (dry wt) for blended, stabilized and secondary sludge, respectively. The FAMEs\ud yields obtained in this study were 13.9%, 10.9%, 2.9% and 1% (dry wt) for primary, blended, secondary and\ud stabilized sludge, respectively. The estimation of annual biodiesel production based on the sludge generated in\ud WWTP of Reus was evaluated, showing that primary sludge consists of 87% of the total biodiesel among the\ud wastewater sludges. Gas chromatography analysis of th\ud e FAMEs revealed a similar fatty acids composition for all\ud sludge tested with a predominance of palmitic acid, stearic acid, oleic acid and linoleic acid.\ud Comparison of sludge\ud fatty acid profile with common biodiesel feedstocks showed their suitability for the production of biodiesel.Peer ReviewedPostprint (published version