Integrated biorefinery approach for bioconversion of fish manure to volatile fatty acids and its valorization by Schizochytrium sp for docosahexaenoic acid, squalene, and carotenoids production

To meet environmental sustainable goals, an integrated approach was used to generate volatile fatty acids (VFAs) from fish manure through acidogenic fermentation and their valorization by Schizochytrium limacinum SR21 for value-added biomass production. Acidogenic fermentations were conducted at different pH values (5.0-9.0) and total solid (TS) contents (5 %, 8 %, and 12 %). The highest VFA yield from thermally pretreated fish manure was obtained at pH 9.0 and TS 12 %. In batch culture, 84.0 % of the acidogenic fermentation VFAs were utilized by Schizochytrium limacinum SR21. The highest significant biomass, total fatty acids (TFA), and docosahexaenoic acid (DHA) production were 19, 10.1, and 3.0 g/L, respectively, at C/N ratio of 90 in batch culture with yeast extract as a nitrogen source. Analysis of the effects of three nitrogen feeding strategies with simulated VFA in pH-auxostat fed-batch culture shows that DHA concentration of 15.3 g/L and TFA yield of 53.56 g/L were achieved with low nitrogen (10 g/L) feeding. Squalene and carotenoid contents were 85 mg/g and 0.43 mg/g of dry biomass in fed-batch culture. These findings shows that the production of bio-based volatile fatty acids (VFA) is a cost-effective eco-friendly waste management method and provides high-value-added biomass for biofuel and aquaculture feed production.