Valorization of poultry manure extract enriched with sodium acetate in mixotrophic cultivation of Auxenochlorella protothecoides

Poultry manure (PM) is byproduct of intensive agricultural production and can be used as a low-cost microalgae growth substrate due to its nutrient and protein-rich content. Microalgae are capable to grow rapidly and thrive in different substrates, thus serving as a valuable source of biomass. In this study, Auxenochlorella protothecoides was cultivated in PM extract supplemented with sodium acetate in order to simulate a volatile fatty acid (VFA) rich substrate after PM thermophilic acetogenic fermentation. The effect of different VFA concentrations (0-30g/L) in the substrate on biomass growth and biochemical composition under mixotrophic conditions was evaluated. A. protothecoides was capable to acclimatize and multiplied in the PM substrate, ultimately achieving the highest biomass concentration at 20 g/L VFA. Proteins were the most abundant component accounting for 38.1-43.9% w/w in the dry biomass, while carbohydrates and lipids followed, comprising 31.5-36.3% and 10.9-14.1%, respectively. The addition of VFA enhanced the protein, carbohydrate and lipid productivity achieving the maximum values 43.9%, 36.3%, 14.1% respectively at 20 g/L VFA. The results indicate that VFA-enriched PM extract can potentially be used as a sustainable and cost-effective growth medium for microalgal cultivation, while the biochemical composition of algal biomass makes it a promising animal feed supplement.