A two-stage culture process using Chlorella vulgaris for urban wastewater nutrient removal and enhanced algal lipid accumulation under photoautotrophic and mixotrophic conditions

Abstract

Microalgae such as Chlorella vulgaris contain sufficient fatty acids to suggest their use as feedstocks for biodiesel production. Their capacity to remove nitrogen, phosphate, and other nutrients from a culture medium makes them a potentially useful element in urban wastewater treatment systems. A two-stage process was used to grow Chlorella vulgaris under mixotrophic and autotrophic conditions in artificial wastewater and urban wastewater media. Growth rate, nutrient removal, and lipids accumulation were quantified. Initially, the media were nitrogen-enriched (90 mg−1; Stage I), and then nitrogen limited (30, 20, and 10 mg l−1; Stage II). Growth was not inhibited under either of the culture conditions, and nitrogen uptake rates were above 90%. Total organic carbon removal was higher (56.2%–86%) under mixotrophic conditions than under photoautotrophic conditions (15.2%–69%). Lipids productivity was 2.7 times higher under mixotrophic conditions and nitrogen limitation than under photoautotrophic conditions and nitrogen limitation. Palmitic acid and linoleic acid accounted for 25.0% of total fatty acids contents, which is an adequate profile for biodiesel production. Culture of C. vulgaris in urban wastewater can improve the efficiency of nitrogen and total organic carbon removal, and water reuse, while simultaneously producing algal biomass with sufficient lipids content and an acceptable fatty acids profile for use as a biodiesel feedstock.