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

• Published in: Journal of applied phycology 2024-06, Vol.36 (3), p.1105-1116
• Main Authors: Umetani, Ikumi, Sposób, Michał, Tiron, Olga
• Format: Article
• Language: English
• Subjects: Algae; Amino acids; Aquatic microorganisms; Biomass; Biomedical and Life Sciences; Cell culture; Cell density; Cultivation; Culture media; Dilution; Dry cells; Ecology; Freshwater; Freshwater & Marine Ecology; Inland water environment; Life Sciences; Microalgae; Municipal wastewater; Nutrient content; Nutrient removal; Nutrients; Phosphorus; Phytoplankton; Plant Physiology; Plant Sciences; Proteins; Wastewater treatment
• ISSN: 0921-8971; 1573-5176
• DOI: 10.1007/s10811-023-03179-6

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, Lobochlamys segnis and Klebsormidium flaccidum, 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. Lobochlamys segnis and K. flaccidum grew exponentially in all cycles. The biomass productivity was 573 and 580 mg L –1 day –1 , 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. L. segnis consumed all NH 4 + and PO 4 3– supplied by the medium replacement, giving the removal rate of 9.2 and 5.2 mg L –1 day –1 . Whereas K. flaccidum removed 13.8 mg L –1 day –1 NH 4 + without completing PO 4 3– 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.