During the production of fatty acids from plant oils, e.g. for the production of biopolymers or in the biodiesel and soap production, glycerol accumulates as a side product. Using this residual material with Clostridium diolis for the production of 1,3-propanediole is not efficient, due to inhibitory effects of impurities. Fatty acids have been identified as inhibiting substances. After removal of the residual fatty acids by pretreatment with adsorbents, it has been possible to use this glycerol with high conversion efficiency towards 1,3-propanediole.