Cultivation of microalgae with recovered nutrients after hydrothermal liquefaction

One of the main concerns regarding the development of microalgal biofuels is the tremendous demand of nutrients that they require for growing, which places a question mark with their sustainability. In this paper, cultivation trials of Nannochloropsis gaditana, Phaeodactylum tricornutum, Chlorella vulgaris and Scenedesmus almeriensis are performed by reusing nutrients recovered from the aqueous by-product obtained during biofuel production via hydrothermal liquefaction. This provides a way to recover nutrients while simultaneously treating the wastewater generated during the production of biofuel. Direct recycling of the aqueous phase is compared to the use of an intermediate step (supercritical water gasification) to purify this stream. Also, two growth parameters (pH and percentage of substitution of nutrients from the standard medium) are studied. The results show that the response of microalgae species to the recycling of nutrients is strain-dependent: P. tricornutum and S. almeriensis were not able to grow satisfactorily in recovered aqueous by-products. On the other hand, C. vulgaris and N. gaditana could grow by replacing 75% of the nutrients from the standard medium with nutrients recovered from HTL without reducing the algae growth, compared to the standard medium.