Dairy waste management: Optimizing biogas slurry dilution for microalgae Euglena sp. cultivation

This research critically explores the application of biogas slurry (bioslurry) as a culture medium for Euglena sp. to assess its viability in microalgae cultivation.A series of bioslurry dilutions (0%, 10%, 20%, and 30%) were evaluated for their influence on growth rate, biomass production, and lipid content of Euglena sp.The experiment was conducted in a 5 L laboratory scale photobioreactor with 3 controlled repetitions for 16 days.The 10% bioslurry dilution exhibited favorable nutrient ratios, with C/N and P/N values of 2.73 ± 0.17 and 0.58 ± 0.03, respectively, while the 20% dilution showed increased C/N and reduced P/N ratios of 5.30 ± 0.51 and 0.37 ± 0.07.Among the tested conditions, the 10% dilution achieved the highest growth performance, with a peak cell density of 26 × 10⁴ ± 6.75 cells/mL, though it remained lower than the control (0% bioslurry) at 169 × 10⁴ ± 5.14 cells/mL.Conversely, the 20% and 30% dilutions significantly hindered growth, with peak densities of 20 × 10⁴ ± 2.08 cells/mL and 24 × 10⁴ ± 7.02 cells/mL, respectively (p>0.05).The highest lipid content was observed in the control medium (0% bioslurry) at 22.67 ± 2.52 mg/L, followed by 10%, 20%, and 30% dilutions with lipid concentrations of 8.00 ± 1.00 mg/L, 7.33 ± 1.53 mg/L, and 7.67 ± 1.15 mg/L, respectively.These results underscore the potential of a 10% bioslurry dilution as a practical strategy for enhancing Euglena sp.cultivation, offering a sustainable pathway to valorize biogas production residues within a circular agricultural economy framework.