Effects of dilution rate and water reuse on biomass and lipid production of Scenedesmus obliquus in a two-stage novel photobioreactor

Continuous culture of fresh water microalgae Scenedesmus obliquus was developed in a two-stage photobioreactor, avoiding the intermediate harvesting step to achieve a half-way point between the progressive and the sudden N-starvation strategies, guaranteeing light limited conditions in the first stage and N-stress conditions in the second stage. This methodology resulted in biomass productivity values at the best dilution rate (0.118 days−1) of 15.25 ± 1.06 g m−2 d−1, slightly higher than that expected according to batch experiment (12.90 ± 0.75 g m−2 d−1). The dilution rate that maximized the lipid content was coincident with that for the maximum biomass productivity, resulting in a intensification of the lipid productivity. Microalgae can be successfully cultured in reused medium clarified by high pH flocculation-sedimentation and neutralized by bubbling the photobioreactors outlet CO2 current through it. Microalgae flocculation with NaOH does not result in a variation of the obtained lipid profile.