Hydrothermal liquefaction of biomass in near-/supercritical water has attracted great attention in recent years. Although this technology seems to be promising for transformation of microalgal biomass, the information on the impact of feedstock and processing variables of continuous hydrothermal liquefaction on the properties of bio-oil provided in previous literature is scarce. Herein, the low-lipid Scenedesmus sp. biomass has been transformed to bio-oils through continuous hydrothermal liquefaction under various process conditions. The influence of temperature and residence time on bio-oil characteristic was discussed based on characterization by IR, GC-MS and gel permeation chromatography. The relative degree of branching of carbon chain of bio-oils components was estimated based on deconvolution of methyl and methylene IR absorption bands. The presumptive pathways of the reactions have been postulated. Finally, it was found that the parameters of bio-oil may be tailored by adjustment of processing variables, however, possible subsequent/parallel effects must be considered while designing the process.

Algal fuel cells: Repeated nutrient recycling is demonstrated by reusing the aqueous phase obtained from the hydrothermal liquefaction (HTL) of microalgae. This is achieved, for the first time, by performing a complete set of four continuous growth–HTL cycles. Results show similar growth rates in each cycle, the potential of nutrient reduction, as well as cell morphology changes. This study demonstrates progress towards the standalone operation of algae biorefineries.