Comparison of heterotrophic and mixotrophic Chlorella pyrenoidosa cultivation for the growth and lipid accumulation through acetic acid as a carbon source

In order to overcome the bottleneck of the high cost of microalgae biodiesel production, biomass and lipid accumulation of microalga Chlorella pyrenoidosa feeding on the low-cost carbon source, acetic acid (AcA), were investigated. The results showed that C. pyrenoidosa had the ability of mixotrophy and heterotrophy, which could tolerate 50 g/L of AcA in the heterotrophy with the biomass concentration of 137.89 ± 2.03 mg/L. Under heterotrophic condition, the biomass productivity at logarithmic stage was positively correlated with the AcA dosage, and the maximum biomass productivity of 187.26 ± 3.61 mg/L/d was obtained at 10 g/L of AcA. Four AcA concentrations (6, 10, 20 and 30 g/L) were set to evaluate the effects of AcA on the growth and lipid accumulation of C. pyrenoidosa under heterotrophic and mixotrophic conditions. Heterotrophic mode at 10 g/L of AcA was demonstrated to be the most potential condition with the maximum biomass productivity of 134.91 ± 5.74 mg/L/d and the highest lipid productivity of 42.04 ± 0.21 mg/L/d, and the lipid production (44.03 ± 2.84 mg/L) was 15-fold higher than the control of BG-11 medium. In addition, C. pyrenoidosa achieved the highest nutrient removal efficiency (30.0% and 85.9% for total nitrogen and phosphorus, respectively) and the highest AcA assimilation efficiency (74.1%). This study highlighted a promising win-win method of AcA recycling and microalgae-based biodiesel production.