Productivity and Biodiesel Quality of Fatty Acids Contents from Scenedesmus obliquus in Domestic Wastewater Using Phototrophic and Mixotrophic Cultivation Systems

Abstract

Microalgae remove nutrients from wastewater with the possibility of grow in mixotrophic and heterotrophic cultures. However, the effluent quality can modify the profile of fatty acids and biodiesel quality.Phototrophic and mixotrophic (light / dark; 12/12 h) cultures ofScenedesmus obliquuson domestic wastewater (WW) and Artificial Wastewater (AW) was carried out to evaluate the lipid accumulation and fatty acid methyl esters profile. The microalgae was first cultivated in an enriched medium (90 mg N-NH4 L-1) and subsequently under nitrogen limitation (30, 20 and 10 mg N L-1) using a two-stage process for both culture media.A higher cell density in enriched AW medium was obtained in phototrophic and mixotrophic culture of 19 x 106cell mL-1and 20 x 106cell mL-1, respectively; than for WW (13 x 106cell mL-1and 14 x 106cell mL-1, respectively). The nitrogen limitation (from 90 to 20 mg N L-1) for AW increased the lipid content by 5.0% and 17.28% under phototrophic and mixotrophic conditions, respectively and only 5% for WW in mixotrophic culture.The high Cetane Number (CN) show a positive correlation with high Saturated Fatty Acids (SFA) content and negative correlation with the Degree of Saturation (DU), suggesting a good ignition of fuel. The Cold Filter Plugging Point (CFPP) (-6.02 to -8.45 °C) and Oxidative Stability (OS) (3.53 - 6.6 h) propose toScenedesmus obliquusas a candidate in the production of biodiesel and potential application for an integral urban wastewater treatment system.