Cultivation of Chlorella protothecoides in polyglutamic acid wastewater for cost-effective biodiesel production

The combination of gamma-polyglutamic acid (gamma-PGA) wastewater treatment and oil-producing microalgae culture could not only achieve the wastewater reuse for gamma-PGA production, but also provided nutrients and a large amount of water for microalgae culture. Thus the effects of wastewater concentration, different nutrients on the biomass yield and lipid content of Chlorella protothecoides were investigated separately. The results showed that 60% gamma-PGA wastewater was very suitable for the cultivation of C. protothecoides. Only 5.86 g/L glucose, 0.73 g/L NaNO3 and 0.2 g/L K2HPO4 needed to be added in the gamma-PGA wastewater. In the optimized wastewater medium, the lipid yield could reach 1.77 +/- 0.03 g/L, which was 195.0% higher than that in the SE medium(0.60 +/- 0.03 g/L). C. protothecoides had high absorption capacity for nitrogen and phosphorus. The nitrogen, phosphorus removal rate of wastewater reached 93.87% and 88.39%, respectively, after 7 days of culture. In addition, the wastewater treated by C. protothecoides could be reused for gamma-PGA fermentation for four times. These investigations laid a foundation for reducing the pollution of gamma-PGA wastewater, explored a late-model for oleaginous microalgae and gamma-PGA cleaner production. (C) 2021 The Authors. Published by Elsevier B.V. on behalf of King Saud University.