Recycling Minerals in Microalgae Cultivation through a Combined Flash Hydrolysis–Precipitation Process

Abstract

The high demand of nutrients is one of the major limitations to a sustainable large-scale production of microalgae-derived biofuels. This issue is particularly critical for phosphorus, whose natural reserves will soon be depleted. This work aims at testing the possibility of recycling phosphorus from the microalgal biomass in the form of magnesium ammonium phosphate (MAP, or struvite), a stable fertilizer suitable for transportation and long-term storage purposes, obtained through flash hydrolysis (FH) of microalgae followed by precipitation of the extracted minerals. To this goal, microalgae growth experiments were carried out with Scenedesmus sp., in batch and continuous lab-scale photobioreactors, using struvite recovered from the proposed process, thus replacing traditional phosphate fertilizers in the cultivation medium. Results showed that the growth rate and productivity obtained with the recycled minerals as phosphorus source equal those achieved in the standard medium, suggesting that the proposed process could be a viable and a relatively simple way to increase the sustainability of microalgal production at large-scale.