An update on valorising dark fermentation effluent through microbial lipid synthesis.

The transition to a sustainable bioeconomy requires effective transformation of biomass, including biogenic residues, into high-value products. Dark fermentation effluent is a promising feedstock for microbial lipid production, offering a renewable and cost-effective alternative to conventional carbohydrate substrates. Rich in short-chain carboxylic acids, this effluent provides essential carbon sources for microbial growth and supports circular biorefinery strategies, particularly when produced from locally available biogenic waste streams. This review assesses the potential of microbial lipid production from dark fermentation effluent, focusing on three key microbial groups: oleaginous yeasts, marine protists, and microalgae. Among these, yeasts and protists exhibit significant advantages over microalgae, including faster growth rates, higher lipid yields, and superior adaptability to the complex composition of dark fermentation effluent. To enhance utilization, two-stage operation allow for the independent optimization of biomass production and lipid accumulation, with controlled feeding in dissolved oxygen or pH-auxostat modes. However, challenges remain, especially with respect to solid-liquid separation, sterilization, and the overall integration of two distinctly different biotechnological processes, which require suitable monitoring and control strategies.