A single-step cultivation approach for lipid production by Nannochloropsis using a carboxymethyl cellulose‑bonded anaerobic digestate tablet

ABSTRACT This study developed a carboxymethylcellulose (CMC)‑bonded anaerobic digestate tablet (CADT) that utilizes nutrients derived from anaerobic digestate for microalgae cultivation. The anaerobic digestate was tabletized via crosslinking by 1 w/v% Ca²⁺ with 1 w/v% carboxymethyl cellulose (CMC) chains, enabling gradual nutrient dissolution into algal medium upon the addition of the tablet to the medium. Notably, the maximum NH₄-N dissolved from CADT was 7.8 mg-N g⁻¹, and the resulting concentration in the medium (≤19.5 mg L⁻¹) remained consistently below the toxicity threshold, ensuring safe nutrient availability and supporting sustained growth of Nannochloropsis oceanica . The cell density of Nannnochloropsis oceania in the CADT medium was 1.5–2.0 times higher than that in the f/2 medium. The CADT medium and the control medium produced a comparable amount of lipids, achieving values of 40.9% and 43.9%, respectively, for the total lipid content on dry weight basis. The lipid productivity achieved using the CADT medium was 10.7 mg L -1 d -1 . This approach eliminates the need for medium replacement during cultivation because CADT facilitates a seamless transition from a nutrient-rich medium in the logarithmic growth phase to a nutrient-depleted medium in the stationary phase. Consequently, lipid accumulation was induced without additional cultivation steps. The developed simplified single-step method of algal cultivation provides a promising strategy for biofuel production.