Diego López Barreiro

Effective lipid extraction from algae cultures using switchable solvents

a Centro Interdipartimentale di Ricerca Industriale (CIRI), University of Bologna, via S. Alberto 163, Ravenna, Italy. Fax: 0039-0544-937411; Tel: 0039-0544-937353; E-mail: chiara.samori3@unibo.it b Department of Biosystems Engineering, University of Ghent, Ghent, Belgium c Thermo-Chemical Conversion of Biomass Group, Faculty of Science and Technology, University of Twente, Enschede, The Netherlands d Department of Chemistry “Ciamician”, University of Bologna, via F. Selmi 2, 40126 Bologna Italy.

Influence of strain-specific parameters on hydrothermal liquefaction of microalgae.

Algae are an interesting feedstock for producing biofuel via hydrothermal liquefaction (HTL), due to their high water content. In this study, algae slurries (5-7 wt% daf) from different species were liquefied at 250 and 375 °C in batch autoclaves during 5 min. The aim was to analyze the influence of strain-specific parameters (cell structure, biochemical composition and growth environment) on the HTL process. Results show big variations in the biocrude oil yield within species at 250 °C (from 17.6 to 44.8 wt%). At 375 °C, these differences become less significant (from 45.6 to 58.1 wt%). An appropriate characterization of feedstock appeared to be critical to interpret the results. If a high conversion of microalgae-to-biocrude is pursued, near critical conditions are required, with Scenedesmus almeriensis (freshwater) and Nannochloropsis gaditana (marine) leading to the biocrude oils with lower nitrogen content from each growth environment.

Assessing microalgae biorefinery routes for the production of biofuels via hydrothermal liquefaction

The interest in third generation biofuels from microalgae has been rising during the past years. Meanwhile, it seems not economically feasible to grow algae just for biofuels. Co-products with a higher value should be produced by extracting a particular algae fraction to improve the economics of an algae biorefinery. The present study aims at analyzing the influence of two main microalgae components (lipids and proteins) on the composition and quantity of biocrude oil obtained via hydrothermal liquefaction of two strains (Nannochloropsis gaditana and Scenedesmus almeriensis). The algae were liquefied as raw biomass, after extracting lipids and after extracting proteins in microautoclave experiments at different temperatures (300-375°C) for 5 and 15min. The results indicate that extracting the proteins from the microalgae prior to HTL may be interesting to improve the economics of the process while at the same time reducing the nitrogen content of the biocrude oil.

Sub- and supercritical water oxidation of anaerobic fermentation sludge for carbon and nitrogen recovery in a regenerative life support system

Sub- and supercritical water oxidation was applied to recover carbon as CO2, while maintaining nitrogen as NH4+ or NO3-, from sludge obtained from an anaerobic fermenter running on a model waste composed of plant residues and human fecal matter. The objective was to fully convert carbon in the organic waste to CO2 while maintaining nutrients (specifically N) in the liquid effluent. In regenerative life support systems, CO2 and nutrients could then be further used in plant production; thus creating a closed carbon and nutrient cycle. The effect of the operational parameters in water oxidation on carbon recovery (C-to-CO2) and nitrogen conversion (to NH4+, NO3-) was investigated. A batch micro-autoclave reactor was used, at pressures ranging between 110 and 300 bar and at temperatures of 300-500 °C using hydrogen peroxide as oxidizer. Residence times of 1, 5 and 10 min were tested. Oxidation efficiency increased as temperature increased, with marginal improvements beyond the critical temperature of water. Prolonging the residence time improved only slightly the carbon oxidation efficiency. Adequate oxygen supply, i.e., exceeding the stoichiometrically required amount, resulted in high carbon conversion efficiencies (>85%) and an odorless, clear liquid effluent. However, the corresponding oxidizer use efficiency was low, up to 50.2% of the supplied oxygen was recovered as O2 in the effluent gas and did not take part in the oxidation. Volatile fatty acids (VFAs) were found as the major soluble organic compounds remaining in the effluent liquid. Nitrogen recovery was high at 1 min residence time (>94.5%) and decreased for longer residence times (down to 36.4% at 10 min). Nitrogen in the liquid effluent was mostly in the form of ammonium.