Semi-continuous cultivation for enhanced protein production using indigenous green microalgae and synthetic municipal wastewater

<jats:title>Abstract</jats:title><jats:p>Cultivation of microalgae has gained significant interest as an alternative protein source, potentially becoming a target commodity recovered from microalgae-based wastewater treatment. This study examined a semi-continuous cultivation strategy to optimize protein accumulation of the indigenous freshwater chlorophytes, <jats:italic>Lobochlamys segnis</jats:italic> and <jats:italic>Klebsormidium flaccidum,</jats:italic> and simultaneously remove nutrients from wastewater efficiently. A strain-specific regime was made based on a fixed biomass concentration at the start of 24-h cultivation cycle, i.e., a constant initial cell density, which regulated harvesting and fresh medium supply volume according to the dilution rate. Six cultivation cycles were conducted in lab-scale 1L reactors with a synthetic municipal wastewater. <jats:italic>Lobochlamys segnis</jats:italic> and <jats:italic>K. flaccidum</jats:italic> grew exponentially in all cycles. The biomass productivity was 573 and 580 mg L<jats:sup>–1</jats:sup> day<jats:sup>–1</jats:sup>, in which the total protein consisted of 62 and 45% of dry cell weight (dw), respectively. When a culture medium deficient in nitrogen and phosphorus was used, protein level was significantly reduced. <jats:italic>L. segnis</jats:italic> consumed all NH<jats:sub>4</jats:sub><jats:sup>+</jats:sup> and PO<jats:sub>4</jats:sub><jats:sup>3–</jats:sup> supplied by the medium replacement, giving the removal rate of 9.2 and 5.2 mg L<jats:sup>–1</jats:sup> day<jats:sup>–1</jats:sup>. Whereas <jats:italic>K. flaccidum</jats:italic> removed 13.8 mg L<jats:sup>–1</jats:sup> day<jats:sup>–1</jats:sup> NH<jats:sub>4</jats:sub><jats:sup>+</jats:sup> without completing PO<jats:sub>4</jats:sub><jats:sup>3–</jats:sup> removal. The amino acid profile of both strains was characterized by glutamic acids content (4–5% dw). We concluded that the designed cultivation regime would support a constant biomass production with stable and high protein content, along with an efficient removal of nutrient from the wastewater.</jats:p>