Non-sterile process for biohydrogen and 1,3-propanediol production from raw glycerol

•Raw glycerol tolerance and contamination risk at hypersalinity were evaluated.•Effect of raw glycerol was similar on a halophile and a non-halophile.•Hypersaline process conditions decrease efficiently the risk for contaminations.•Non-sterile conditions are applicable for halophilic fermentation processes.•Halophilic H2 and 1,3-PD production were combined in a non-sterile 2-stage process.

Raw glycerol is a tempting substrate for fermentations, but contains impurities that can be inhibitory for organisms. In this study, raw glycerol tolerance and contamination risk of pure bacterial culture at hypersaline process conditions were evaluated. The inhibitory effect of raw glycerol was similar on a halophilic (Halanaerobium saccharolyticum) and a non-halophilic (Clostridium butyricum) bacterium implying the inhibition originating from methanol or other impurities rather than salt. The hypersaline process conditions decreased efficiently contaminations and no growth of contaminants was observed at and above 125 g/l NaCl. Halophilic H2 and 1,3-PD production from raw glycerol were studied separately as 1-stage processes and jointly as 2-stage process in non-sterile conditions. Non-sterile conditions were successfully applied and the highest production yields obtained were 3.0 mol H2/mol glycerol and 0.66 mol 1,3-PD/mol glycerol (1-stage processes), whereas the highest cumulative production was 74 mmol H2/l culture and 31 mmol 1,3-PD/l culture (2-stage process).