New methods to increase microalgae biomass in anaerobic cattle wastewater and the effects on lipids production

Abstract

In the present study, the microalgae Spirulina platensis DRH 20 was cultivated in 4 photobioreactors with lighting intensity of 330 (±13.2) μmol m−2 s−1, 24 h d−1. No additives were added in PBR 1, while CO2 and phosphoric acid (pH control) were added in PBR 2, phosphoric acid was added in PBR 3, and CO2 was added in PBR 4. Dry biomass reached a maximum of 20.7 g L−1 and productivity reached a maximum of 4.3 g L−1 day−1 in PBR 2. The highest value of CO2 biofixation rate was also found in PBR 2, with 7.758 mg L−1 d−1. The highest μmax and the shortest doubling time were found in PBR 4. Regarding bioremediation, percentages between 76.9% and 79% of COD, 90.9 and 99.3% of NH4+, 85% and 92%. NO3−, were removed. The highest lipid production was recorded in PBR 4 (0.581 g L−1 d−1), which could generate 52.800 gallons of crude oil per year for each hectare cultivated and a biodiesel production yield of 121.7 g kg−1. From the analyses of fatty acids, it was possible to observe that producing biodiesel with the biomass generated in PBR 4 can promote better yields in lipid production and better quality.