| Summary: | (1) Background: Recycling of water and non-converted nutrients is considered to be a necessity for an economically viable production of microalgal biomass as a renewable feedstock. However, medium recycling might also have a negative impact on algal growth and productivity due to the accumulation of growth-inhibiting substances. (2) Methods: Consecutive batch processes with repeated water recycling after harvesting of algal biomass were performed with the saline microalga <i>Microchloropsis salina</i> in open thin-layer cascade photobioreactors operated at a physically simulated Mediterranean summer climate. The impact of water recycling on culture performance was studied and the composition of the recycled water was analyzed. (3) Results: Water recycling had no adverse effect on microalgal growth and biomass productivity (14.9−21.3 g m<sup>−2</sup> d<sup>−1</sup>) if all necessary nutrients were regularly replenished and KNO<sub>3</sub> was replaced by urea as the nitrogen source to prevent the accumulation of K<sup>+</sup> ions. Dissolved organic carbon accumulated in recycled water, probably promoting mixotrophic growth. (4) Conclusion: This study shows that repeated recycling of water is feasible even in high-density cultivation processes with <i>M. salina</i> of more than 30 g L<sup>−1</sup> cell dry weight, increasing culture performance while reducing nutrient consumption and circumventing wastewater production.
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