Reuse of rejuvenated media during laboratory and pilot scale cultivation of Nannochloropsis sp.

Bulk cultivation of microalgae in large scale production systems is subject to high production costs. Recycling of growth medium contributes to reducing water, nutrient and salt expenditure, and hence to increase both the economic viability and sustainability of microalgae production systems. In this study it was shown that, upon algae harvesting by means of centrifugation, spent broth from a Nannochloropsis sp. production system can be treated by means of microfiltration and reapplied as rejuvenated growth medium without negatively influencing subsequent growth. During recirculation of growth medium, nutrients consumption rates were documented and used to adjust the medium recipe to enable long term medium recirculation. An 80% recycle rate could be maintained for 167 days during a course of ten production runs, translating into a decrease in nutrient, salt and water expenditure of 44%, 74% and 80%, respectively. The potential for long term reuse of medium for monocultures of multiple economically interesting species should be assessed in future research to evaluate the broad applicability of medium re-use in microalgae cultivation.