Aeration modulates fatty acid profile in microalgae-yeast consortium when using VFA-rich digestate as low-cost carbon source

Anaerobic fermentation (AF) of organic wastes generates liquid digestate streams rich in volatile fatty acids (VFAs), which are challenging to manage but also represent valuable feedstocks for integrated carbon recovery in circular economy schemes. In this context, the waste-derived VFAs transformation by microbial co-cultures offers a promising route to generate high-value products. Among these, microbial oils (MOs) are considered attractive sources of fatty acids (FAs) for oleochemical applications. However, conventional MOs production relies on sugar-based feedstocks, limiting economic viability, whereas waste-derived VFAs can provide a more cost-effective carbon source when available as residual streams. Therefore, this study evaluates the influence of aeration period (0, 6, and 12 h d −1 ) on the performance and macromolecular composition of a microalgae-yeast consortium cultivated in photobioreactors fed with a real VFAs-rich digestate from AF, with a particular focus on lipid and protein production. System performance was assessed through microbial growth, VFAs consumption, lipid and protein accumulation, and FAs and amino acids (AAs) profiles. The non-aerated system showed the highest lipid content (42.5 ± 2.3% w/w ) and yield (0.17 g g −1 VFAs consumed). In contrast, 12 h d −1 aeration enhanced VFAs consumption and biomass growth and increased protein content to 40.4 ± 1.3% w/w corresponding to a protein yield of 0.22 g g −1 VFAs consumed. Aeration also influenced FAs profile, particularly the distribution of C18:1 isomers, with a decrease in C18:1 trans and an increase in C18:1 cis under 12 h d −1 aeration. By contrast, AAs profile was not affected. These results highlight the potential of this system for valorizing VFAs and underscore aeration as a key operational parameter to tailor lipid or protein production, depending on target applications.