The gasification of microalgae in supercritical water was investigated in this work. The product gas contained mainly H-2, CO2, CH4, and C2H6. Operation at high temperatures and lower biomass concentrations resulted in the highest carbon gasification efficiency and the lowest total organic carbon levels in the residual water. Due to its content of inorganic nutrients, the residual water was applied as cultivation medium for microalgae. However, algal growth in the untreated residual water was inhibited by the existence of potentially toxic substances evolved from gasification. Upon treatment by activated carbon filtration and ultraviolet light degradation, these substances were eliminated and cultivation in the residual water was possible. The major fraction of inorganic residues from gasification was recovered by means of water purging, increasing the potential of nutrient recycling for cultivation.