1,3-Propanediol production from crude glycerol by Clostridium butyricum dsp1 in repeated batch

Abstract

Background: The production of biofuels from renewable energy sources is one of the most important issues in industrial biotechnology today. The process is known to generate various by-products, for example crude glycerol, which is obtained in the making of biodiesel from rapeseed oil. Crude glycerol may be utilized in many ways, including microbial conversion to 1,3-propanediol (1,3-PD), a raw material for the synthesis of polyesters and polyurethanes.

Results: The paper presents results of a study on the synthesis of 1,3-propanediol from crude glycerol by a repeated batch method with the use of Clostridium butyricum DSP1. After the substrate concentration inside the bioreactor fell below 15 g/L, 30% of the culture broth was removed from the bioreactor and replaced with an equal volume of fresh sterile nutrient medium with the same composition as that used for the start-up of batch bioreactor cultivation. Three cycles of fermentation medium replacement were carried out. The final concentration of 1,3-PD was 62 g/L and the maximum productivity, obtained during the second cycle, reached 1.68 g/L/h. Additionally, experiments conducted in parallel to the above involved using the entire quantity of the culture broth removed from the bioreactor to inoculate successive portions of fermentation media containing crude glycerol at concentrations of 80 g/L and 100 g/L. Under those conditions, the maximum 1,3-PD concentrations were 43.2 g/L and 54.2 g/L, obtained from 80 g/L and 100 g/L crude glycerol, respectively. The parameter that increased significantly in comparison to what was observed during standard batch fermentations was productivity, resulting in a 1,3-PD productivity of 1.73 g/L/h, which may indicate the adaptation capabilities of C. butyricum DSP 1.

Conclusions: The experiments proved that by using a portion of metabolically active biomass as inoculum for another fermentation formula it is possible to eliminate the stage of inoculum growth and thereby reduce the length of the whole operation. Additionally, that strategy avoids the phase of microbial adaptation to a different source of carbon such as crude glycerol, which is more difficult to utilize, thus improving the kinetic parameters of 1,3-PD production.