Fermentative Production of 1,3-Propanediol from Glycerol in a Membrane Bioreactor with Microfiltration Membranes: A Feasibility Study

In biotechnological processes, value-added products such as 1,3-propanediol (1,3-PD) are obtained in multi-component mixtures consisting of by-products, nutrient medium, bacterial cells and residual substrate. For this reason, separation to obtain the main product with the use of various techniques is economically unprofitable. Contrary, membrane bioreactors (MBRs) ensure several benefits and may play a crucial role in reducing the operating costs. The main objective of this work was to evaluate the feasibility of producing 1,3-PD in an MBR equipped with capillary polypropylene (PP) membranes for the MF (microfiltration) process. This article provides an in-depth examination of: (i) the yield of batch, fed-batch and fermentation in an MBR, (ii) the fouling mechanism during MF of fermentation broths, and (iii) PP membrane stability. It was found that performing the fermentation in an MBR allowed for production of 1,3-PD with the highest maximum yield, in the range of 0.48 g/g (0.58 mol/mol) to 0.59 g/g (0.72 mol/mol). Moreover, it was demonstrated that the significant decline of the MF process was mainly caused by the formation of a cake layer on the membrane surface. Nevertheless, the efficiency of the process was stable and ensured the high quality of the permeate. In addition, membrane cleaning with the use of 1% NaOH solution allowed to remove most of the foulants from the membrane surface. Despite repeated cleaning procedures, the membranes used in this work maintained their performance and efficiency. Hence, it can be concluded that the capillary polypropylene membranes for the MF process can be successfully used in MBR technology intended for the production of 1,3-PD by glycerol fermentation.