Hydrothermal liquefaction of microalgae for biofuel production: The recycling of nutrients from an aqueous solution after HTL

Abstract

Microalgae are an alternative source for the renewable biofuels production. One of the promising technologies of microalgae fuel production is the hydrothermal liquefaction (HTL) with obtaining bio-oil as the target product. We have carried out a number of experiments on the hydrothermal liquefaction the biomass of blue-green microalgae Arthrospira platensis rsemsu 1/02-P (collection of Renewable Source Energy Laboratory at Lomonosov Moscow State University). For the HTL of arthrospira biomass the reactor of the Institute of High Temperatures RAS have been used. The outputs of bio-oil, gaseous products, solid residue and aqueous solution were 34-46%, 12-18%, 26-30%, 10-24% respectively. The aqueous solution hydrothermal liquefaction is a by-product, it has a limited energy value and needs to be recycled. Aqueous solution contains the nutrients necessary for growing algae but in quantities that are orders of magnitude higher than the standard ones. Studies growth of different algae species in aqueous solution after HTL have shown that in order to prevent the growth inhibitors toxic effect intensive its dilution is necessary. Microalgae strains, which can be cultivated in 500-fold diluted aqueous solution (Galdieria sulphuraria rsemsu G-1, Chlorella vulgaris rsemsu Chv-20/11-Ps), have been experimentally selected. It allows partially recycling the by-product of bio-oil from microalgae.