Microalgae growth on the aqueous phase from Hydrothermal Liquefaction of the same microalgae

Cultivation of Desmodesmus sp. microalgae in the recycled aqueous phase (AP) recovered after Hydrothermal Liquefaction (HTL) of the same microalgae was studied to evaluate the potential of nutrients recycling. AP dilution ratio was systematically varied, using either water or water enriched with standard medium, while keeping the same N concentration (either as total-N or as sum of ammonia and nitrate) as that in the standard medium. More than 90% of the organic compounds in the AP were indentified and quantified and potential growth inhibiting substances (e.g. phenols) were found. However, the combination of growth and analytical results showed that the lack of (macro-/micro-)nutrients, other than N and P, in the AP is the main cause of growth reduction rather than toxicity due to insufficient AP dilution, as pointed in previous investigations. Therefore, these (macro-/micro-)nutrients such as Mg should be supplied upon AP recycling. For this specific cultivation case, algae production costs related to nutrients consumption can be significantly reduced considering that a 50% N-replacement was achieved, while showing nearly identical growth as that in standard culture medium.