Cultivation of Nannochloropsis salina using anaerobic digestion effluent as a nutrient source for biofuel production

The biomass and lipid productivities and the nutrient removal capacity of microalgae Nannochloropsis salina grown using anaerobically digested municipal wastewater effluent as a nutrient source were evaluated in this study. Results from bench-scale batch reactors showed that N. salina grew well under 3%, 6%, 12%, and 18% (v/v) anaerobic digestion (AD) effluent loading with the highest growth rate being 0.645 d−1 obtained at 6% AD effluent loading. The growth of N. salina decreased when the effluent loading was increased to 24%. The highest biomass productivity of 92 mg l−1 d−1 was obtained with 6% effluent loading. Three harvesting frequencies (1, 2, and 3 d intervals) and two harvesting ratios (25% and 50%, v/v) were tested in semi-continuous bench-scale reactors with 6% effluent loading. The highest lipid productivity of 38.7 mg l−1 d−1 was achieved with a 2-d harvesting interval and 50% harvesting ratio, where nitrogen and phosphorus were removed at rates of 35.3 mg l−1 d−1 and 3.8 mg l−1 d−1, respectively. The fatty acid (FA) profile showed that palmitic acid (C16:0), palmitoleic acid (C16:1), and eicosapentaenoic acid (C20:5) were the major components, accounting for 32.1%, 26%, and 15.7% of the total FAs, respectively.