Screening of bacterial strains capable of converting biodiesel‐derived raw glycerol into 1,3‐propanediol, 2,3‐butanediol and ethanol

The ability of bacterial strains to assimilate glycerol derived from biodiesel facilities to produce metabolic compounds of importance for the food, textile and chemical industry, such as 1,3‐propanediol (PD), 2,3‐butanediol (BD) and ethanol (EtOH), was assessed. The screening of 84 bacterial strains was performed using glycerol as carbon source. After initial trials, 12 strains were identified capable of consuming raw glycerol under anaerobic conditions, whereas 5 strains consumed glycerol under aerobiosis. A plethora of metabolic compounds was synthesized; in anaerobic batch‐bioreactor cultures PD in quantities up to 11.3 g/L was produced by Clostridium butyricum NRRL B‐23495, while the respective value was 10.1 g/L for a newly isolated Citrobacter freundii. Adaptation of Cl. butyricum at higher initial glycerol concentration resulted in a PD_max concentration of ～32 g/L. BD was produced by a new Enterobacter aerogenes isolate in shake‐flask experiments, under fully aerobic conditions, with a maximum concentration of ～22 g/L which was achieved at an initial glycerol quantity of 55 g/L. A new Klebsiella oxytoca isolate converted waste glycerol into mixtures of PD, BD and EtOH at various ratios. Finally, another new C. freundii isolate converted waste glycerol into EtOH in anaerobic batch‐bioreactor cultures with constant pH, achieving a final EtOH concentration of 14.5 g/L, a conversion yield of 0.45 g/g and a volumetric productivity of ～0.7 g/L/h. As a conclusion, the current study confirmed the utilization of biodiesel‐derived raw glycerol as an appropriate substrate for the production of PD, BD and EtOH by several newly isolated bacterial strains under different experimental conditions.