Glycerol utilisation for the production of chemicals: Conversion to succinic acid, a combined experimental and computational study

Abstract

An effective method for the valorisation of the main by-product of biodiesel production, i.e. glycerol is investigated in this work. It involves the biological conversion of glycerol to succinic acid, a top added-value material, which can be used as a building block for the production of various commodity and specialty chemicals. Our aim is to give new insights into this bioprocess, which has so far received little attention and is open for further investigation, through a combination of experimental and computational studies. The microorganism employed here was Actinobacillus succinogenes in batch bioreactors where glycerol was used as the sole carbon source. The highest obtained product yield, final succinate concentration and productivity were found to be equal to 1.23 g-succinate/g-glycerol, 29.3 g-succinate/L and 0.27 g-succinate/L/h, respectively. Furthermore, an unstructured model of the batch experiments was developed by considering both substrate and product inhibition. Kinetic parameters of the model were estimated by minimising the difference between experimental and predicted values. The corresponding optimisation problem was solved by using a combination of stochastic and deterministic methodologies, with the goal to probabilistically compute global minima and the resulting parameter values. The model developed can be utilised to successfully predict the concentration profiles of the five most important state variables (biomass, glycerol, succinic acid, formic acid, and acetic acid) with different initial glycerol concentrations. Scaled-up experiments in larger-scale bioreactors were used for further validation purposes. Our model can be further used to compute optimal operating/parametric conditions, which maximise yield, productivity and/or the final succinic acid concentration.