Dual-mode cultivation of the mixed microalgal culture to induce lipid synthesis using anaerobic digestate as an ammonia source

Abstract

Anaerobic Digestate (AD) is a desirable and significant nutrient source for microalgal growth. It can be utilized as a part of the circular economy in the generation of high-value-added products. Dual-mode cultivation with AD as a substrate can be an efficient strategy to enhance the algal biomass and produce high-quality biodiesel. As dilution is required to prevent growth inhibition, in this study, growth optimization was initially carried out to figure out the best dilution ratio of AD, which corresponded to a wide range of 0 to 2,000 mg NH4-N/L concentrations. The Bold’s basal medium with triple nitrate (3NBBM) that supplemented AD at 4 % dilution resulted in the highest biomass (2290 mg·L−1). After maintaining the highest biomass-producing condition, stressors such as sodium chloride (NaCl) and ferric chloride (FeCl3) have also been searched to increase lipid production. The lipid content has increased by 1.8-fold as a result of the stress (at 20 g·L−1 NaCl and 0.1 mg·L−1 FeCl3). At those stress conditions, the saturated fatty acid concentrations were around 33 % of the total fatty acid methyl esters (FAME). In addition, compliance with the biodiesel standards has also been ensured at 0.1 mg·L−1 FeCl3. The combination of AD with nutrients and salt stressors, like NaCl and FeCl3, within the concept of dual-mode cultivation, could be a viable strategy to produce sustainable, high-quality biodiesel with a high proportion of algal biomass and could be integrated into microalgae production facilities.