Itziar A. Escanciano

In this work, Actinobacillus succinogenes strain DSM 22.257 has been employed for the bioconversion of CO2 into succinic acid, utilizing xylose as the carbon source in a stirred tank bioreactor (STBR). As CO2 is a co-substrate in succinic acid production, special attention has been paid to the transport and consumption of CO2, and to the metabolic influence on the bioprocess, analyzing biomass growth, xylose consumption and succinic acid generation under different conditions of CO2 transport. The influences of agitation and gas flow have been examined by varying the stirring speed from 100 to 700 rpm and supplying CO₂ at a rate of 0.1 L·min⁻¹. The gas-liquid transport rate of CO2 has been studied, and the volumetric mass transfer coefficient has been determined by using a classical dynamic method. An empirical equation for the volumetric coefficient of carbon dioxide transfer has been determined that fit very well the experimental data within the interval of the variables studied. Moreover, uptake rate of CO2 under different conditions has been measured. Under the operating conditions studied, the CO2 uptake rate is slightly higher than the transport rate. Succinic acid concentration of 10.95 ± 0.34 g L-1 with a yield and 0.53 ± 0.01 g·g-1 were reached without supply CO2 to culture, only by initial saturation of the broth. The results indicate that, once the culture is saturated, the dissolved CO2 concentration scarcely affects the succinic acid production.

Circular bioeconomy is one of the major socio-economic objectives for the twenty-first century, which includes the use of biomass waste and its transformation through environmentally friendly processes into biorefinery building blocks. Among these compounds, succinic acid (SA) obtained by fermentation stands out. This work demonstrates the feasibility of using beer bagasse and spent brewer’s yeast as carbon and nitrogen sources for the bioproduction of SA with Actinobacillus succinogenes. The use of a progressive enzymatic treatment liberated simple monosaccharides and peptides that were used by the microorganism, in a subsequent fermentation. Compared to the use of commercial xylose and yeast extract, the used of beer wastes obtained better yields (0.77 g g⁻¹) and selectivity (76%), though with a slightly lower productivity (0.15 g L⁻¹ h⁻¹). Finally, an unstructured non-segregated kinetic model was successfully fitted, facilitating the future performance of bioreactor design, techno-economic analysis, scaling of the process, or design of a control system.

Succinic acid (SA) is one of the most prominent C4 biomass-based platform chemicals that can be biologically obtained. This article verifies, for the first time, the possibility of producing succinic acid with fed-batch or repeated batch operations with Actinobacillus succinogenes in a resting state, that is, in the absence of a nitrogen source. In this work it is possible to optimise separately the stages of cell growth and production in the fed-batch or repeated batch modes, minimising the costs associated with the nitrogen source and facilitating the subsequent purification of SA. These experiments were carried out with xylose, the most abundant monosaccharide in hemicelluloses, with the results subsequently being compared to those obtained in equivalent operations carried out with cells in a state of growth. First, a cost-effective synthetic growth medium was proposed and successfully employed for SA production. Biocatalysts’ reutilisation showed that the bioprocess can be carried out successfully in repeated batch and fed-batch modes. The best mode for growing cells is repeated batch, achieving a maximum productivity of 0.77 g‧L⁻¹‧h⁻¹, a selectivity of 53% and a yield of 51% with respect to xylose consumed. In contrast, the fed-batch mode was found to be the most convenient mode with resting cell biocatalyst, reaching a maximum productivity of 0.83 g‧L⁻¹‧h⁻¹, a selectivity of 0.78 g‧g⁻¹ and a yield of 68% with respect to the xylose consumed. In addition, by-product formation is significantly reduced when employing resting cells. An unstructured non-segregated kinetic model was developed for both biocatalysts, capable of simulating cell growth, xylose consumption, SA production and by-product generation, with successful estimation of kinetic parameters supported by statistical criteria.

Biodiesel is nowadays added in 5–10% v/v to diesel, and its production involves the parallel creation of a vast glycerol amount as a by-product. Despite its many applications, there is a surplus of glycerol (Gly) that has boosted the search for new applications of this compound, now transformed into an industrial synthesis intermediate or platform chemical. Its transcarbonation is a type of reaction that occurs under mild conditions, using weak or moderate basic catalysts, and allows the parallel production of glycols of industrial interest with high selectivity, such as ethylene glycol. In this research, we have studied the activity of a Tunisian clay rich in inorganic carbonates that give it a weak basic character. The raw clay (RC) has been fully characterized by XRD, FTIR, SEM-EDS and nitrogen porosimetry. Subsequently, it has been employed as a catalyst to react glycerol (G) with ethylene carbonate (EC) to obtain glycerol carbonate (GC) and ethylene glycol (EG). The main operating variables and their effects on glycerol conversion and initial reaction rate were analyzed: catalyst concentration (2–6% w/w glycerol), reagent molar ratio (EC:G 1.5:1 to 3:1), and temperature (80–110 °C). Then, an appropriate kinetic model was selected from the results obtained under various reaction conditions, including the total deactivation of order 1 of the catalyst. The kinetic constant activation energy in this reaction using Tunisian smectite was found to be around 183.3 kJ·mol⁻¹. In the second phase of the investigation, we explored the reuse of smectite using the kinetic model to appreciate the effect of cycle-to-cycle deactivation. It can be seen that the kinetic constant of the main reaction generally decreases with the number of cycles at low temperature and goes through a maximum at high operating temperature, while the deactivation constant increases with the number of catalytic cycles. The catalyst shows more stability, in general, at higher temperatures.

Succinic acid (SA) is one of the main identified biomass-derived chemical building blocks. In this work we approach the study of its production by Actinobacillus succinogenes DSM 22257 from glucose, focusing on the development and application of a simple kinetic model capable of representing the evolution of the process over time for a great diversity of process variables key to the production of this platform bio-based chemical: initial biomass concentration, yeast extract concentration, agitation speed, and carbon dioxide flow rate. All these variables were studied experimentally, determining the values of key fermentation parameters: titer (23.8–39.7 g·L⁻¹), yield (0.59–0.72 g_SA·g_glu⁻¹), productivity (0.48–0.96 g_SA·L⁻¹·h⁻¹), and selectivity (0.61–0.69 g_SA·g_glu⁻¹). Even with this wide diversity of operational conditions, a non-structured and non-segregated kinetic model was suitable for fitting to experimental data with high accuracy, considering the values of the goodness-of-fit statistical parameters. This model is based on the logistic equation for biomass growth and on potential kinetic equations to describe the evolution of SA and the sum of by-products as production events that are not associated with biomass growth. The application of the kinetic model to diverse operational conditions sheds light on their effect on SA production. It seems that nitrogen stress is a good condition for SA titer and selectivity, there is an optimal inoculum mass for this purpose, and hydrodynamic stress starts at 300 r.p.m. in the experimental set-up employed. Due to its practical importance, and to validate the developed kinetic model, a fed-batch fermentation was also carried out, verifying the goodness of the model proposed via the process simulation (stage or cycle 1) and application to further cycles of the fed-batch operation. The results showed that biomass inactivation started at cycle 3 after a grace period in cycle 2.

Succinic acid has attracted much interest as a key platform chemical that can be obtained in high titers from biomass through sustainable fermentation processes, thus boosting the bioeconomy as a critical production strategy for the future. After several years of development of the production of succinic acid, many studies on lab or pilot scale production have been reported. The relevant experimental data reveal underlying physical and chemical dynamic phenomena. To take advantage of this vast, but disperse, kinetic information, a number of mathematical kinetic models of the unstructured non-segregated type have been proposed in the first place. These relatively simple models feature critical aspects of interest for the design, control, optimization and operation of this key bioprocess. This review includes a detailed description of the phenomena involved in the bioprocesses and how they reflect on the most important and recent models based on macroscopic and metabolic chemical kinetics, and in some cases even coupling mass transport.