Production of 1,3-propanediol by Clostridium butyricum growing on biodiesel-derived crude glycerol through a non-sterilized fermentation process.

The aim of the present study was to investigate the production of 1,3-propanediol (PDO) under non-sterile fermentation conditions by employing the strain Clostridium butyricum VPI 1718. A series of batch cultures were performed by utilizing biodiesel-derived crude glycerol feedstocks of different origins as the sole carbon source, in various initial concentrations. The strain presented similarities in terms of PDO production when cultivated on crude glycerol of various origins, with final concentrations ranging between 11.1 and 11.5 g/L. Moreover, PDO fermentation was successfully concluded regardless of the initial crude glycerol concentration imposed (from 20 to 80 g/L), accompanied by sufficient PDO production yields (0.52-0.55 g per gram of glycerol consumed). During fed-batch operation under non-sterile culture conditions, 67.9 g/L of PDO were finally produced, with a yield of 0.55 g/g. Additionally, the sustainability of the bioprocess during a continuous operation was tested; indeed, the system was able to run at steady state for 16 days, during which PDO effluent level was 13.9 g/L. Furthermore, possible existence of a microbial community inside the chemostat was evaluated by operating a polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) analysis, and DGGE results revealed the presence of only one band corresponding to that of C. butyricum VPI 1718. Finally, non-sterile continuous cultures were carried out at different dilution rates (D), with inlet glycerol concentration at 80 g/L. Maximum PDO production was achieved at low D values (0.02 h(-1)) corresponding to 30.1 g/L, while the elaboration of kinetic data from continuous cultures revealed the stability of the bioprocess proposed, with global PDO production yield corresponding to 0.52 g/g.