From waste to energy: Microalgae production in wastewater and glycerol

• Highest biomass and lipid productivities where achieved at mixotrophic cultivation.
• Lipids from mixotrophic biomass were more suitable for biodiesel production.
• Nutrient removal achieved below the most strict threshold limits.
• Positive energy production scenarios can be designed coupling distinct processes.

The present work aimed to evaluate the auto/mixotrophic growth of microalgae using domestic wastewater (WW) amended with glycerol aiming biofuels production. The best results were obtained with the highest glycerol supplementation (50 mM). In such condition, Chlorella vulgaris and Botryococcus terribilis showed a biomass productivity of 118 and 282 mg l−1 d−1, which produced about 18 and 35 mg l−1 d−1 of lipids, respectively. Thus, if scaled-up (200 m3 d−1 of WW, 240 working days y−1) biomass and lipid yields may be about 5.6 tons y−1 and 894.2 kg y−1 or 13.5 tons y−1 and 1.6 tons y−1 for C. vulgaris and B. terribilis, respectively. The mixotrophic production of lipids can generate high quality biodiesel according to estimations using their fatty acids profiles. The whole process can be advantageously combined with the production of other biofuels (e.g. methane and bio-ethanol) in a biorefinery scenario. This combination of algal biomass production with waste treatment (WW amended with glycerol) can have a significant impact in the water treatment sector and local markets.