From metabolic modelling to integrated bio-refineries: How to improve the sustainability of biodiesel plants by Co-production of chemicals

Biofuels, such as bioethanol and biodiesel, which are alternatives to conventional fuels, have recently received increasing interest. However, costly raw materials and inefficient utilization techniques of the waste streams of these industries have resulted in being less competitive to petroleum refineries. The aim of this project is to utilize the side products (mainly glycerol) of biodiesel's industry in an integrated and cost effective point of view. Biodiesel is a transport fuel made from vegetable oils or animal fats through a chemical reaction process called transesterification that co-produces glycerol as by-product (10% w/w) which cannot be absorbed by the present glycerol markets. In this study, we introduce a new and efficient bio-process of succinic acid production from glycerol. Initially, an unstructured model is developed for the prediction of relevant batch experiments that we have performed, which considers both substrate and product inhibition. Based on model' kinetics we examine the best conditions on batch experiments in terms of productivity. In addition to that, we perform an optimal control analysis investigating the best feeding profiles for fed-batch processes in order to maximize the productivity of the desired product. In both cases, computational results are validated with our batch fermentation experiments. Moreover, we try to give further insights to this bacterial process through metabolic modelling. We study Actinobacillus succinogenes' metabolic network and underline the dominate pathways and the main branch points that affect the succinate production. We implement flux balance analysis to compute the unknown intracellular fluxes and linear optimisation techniques to maximise further the productivity. Finally an integrated bio-refinery framework involving a cradle to grave analysis is combined with the above experimental and computational findings. Overall simulations and life cycle analysis of the entire process illustrate the "beneficial" uses of glycerol in terms of economics and sustainability.