Bioconversion of a Glycerol- and Methanol-Rich Residue from Biodiesel Industry into 1,3-Propanediol: The Role of Magnesium

Abstract

Biodiesel is one of the most important biofuels worldwide. Besides glycerol, the residual aqueous phase of the transesterification reaction (RAPTR) from the biodiesel industry contains a high concentration of methanol. Here, we propose using RAPTR as substrate for Clostridium beijerinckii Br21 to produce 1,3-propanediol (1,3-PDO). 1,3-PDO is a valuable chemical compound widely used in the production of polymers, cosmetics, and pharmaceuticals. To diminish the methanol content, we pretreated RAPTR by low-pressure evaporation, which minimized water evaporation and prevented other contaminants from being concentrated. We optimized the evaporation conditions by using a 22 central composite rotational design to establish optimal temperature and time of 55 °C and 51.3 min, respectively. Pretreated RAPTR diluted at 20% (v v−1) with a nutrient solution allowed the bacterium to grow, but no glycerol was consumed. Supplementing the nutrient solution with 0.4 g L−1 MgCl2, defined in another experimental design, led the bacterium to consume glycerol and to produce 1,3-PDO. In the optimized conditions, pretreated RAPTR supplemented with MgCl2 gave 2.78 ± 0.01 g L−1 1,3-PDO in higher yield (Y1,3-PDO/glycerol) compared to the theoretical one, 0.61 and 0.50 g g−1, respectively. This result is relevant for biodiesel biorefineries, which could implement the innovative and customized strategy proposed herein to obtain 1,3-PDO, a high-value-added product, from a glycerol- and methanol-rich residue.