Enhanced 1,3-propanediol production by a newly isolated Citrobacter freundii strain cultivated on biodiesel-derived waste glycerol through sterile and non-sterile bioprocesses

The production of 1,3-propanediol (PD) by a newly isolated Citrobacter freundii strain [FMCC-B 294 (VK-19)] was investigated. Different grades of biodiesel-derived glycerol were employed. Slightly lower PD biosynthesis was observed in batch experiments only when crude glycerol from waste-cooking oil trans-esterification was utilized and only at elevated initial substrate concentrations employed. Batch bioreactor cultures revealed the capability of the strain to tolerate elevated amounts of substrate (glycerol up to 170 g/L) and produce quantities of PD in such high substrate concentrations. Nevertheless, maximum PD quantities (45.9 g/L) were achieved at lower initial glycerol concentrations (∼100 g/L) employed, suggesting some inhibition exerted due to the increased initial substrate concentrations. In order to improve PD production, a fed-batch fermentation was carried out and 68.1 g/L of PD were produced (the highest PD quantity achieved by C. freundii strains so far) with yield per glycerol consumed ∼0.40 g/g and volumetric productivity 0.79 g/L/h. Aiming to perform a more economical and eco-friendlier procedure, batch and fed-batch fermentations under completely non-sterile conditions were carried out. During non-sterilized fed-batch process, 176 g/L of raw glycerol were converted to 66.3 g/L of PD, suggesting the potentiality of the non-sterile fermentation by C. freundii FMCC-B 294.

► Significant 1,3-propanediol production by a natural Citrobacter freundii on raw glycerol, the highest one reported by Citrobacter strains so far.
► Growth and 1,3-propanediol production observed at very high initial glycerol concentration media.
► Slightly decreased 1,3-propanediol production when glycerol deriving from thermally treated oil was used.
► Enhanced 1,3-propanediol production by C. freundii under completely unsterilized conditions.