Giannis Penloglou

Microbial production of polyhydroxybutyrate with tailor-made properties: an integrated modelling approach and experimental validation.

The microbial production of polyhydroxybutyrate (PHB) is a complex process in which the final quantity and quality of the PHB depend on a large number of process operating variables. Consequently, the design and optimal dynamic operation of a microbial process for the efficient production of PHB with tailor-made molecular properties is an extremely interesting problem. The present study investigates how key process operating variables (i.e., nutritional and aeration conditions) affect the biomass production rate and the PHB accumulation in the cells and its associated molecular weight distribution. A combined metabolic/polymerization/macroscopic modelling approach, relating the process performance and product quality with the process variables, was developed and validated using an extensive series of experiments and measurements. The model predicts the dynamic evolution of the biomass growth, the polymer accumulation, the consumption of carbon and nitrogen sources and the average molecular weights of the PHB in a bioreactor, under batch and fed-batch operating conditions. The proposed integrated model was used for the model-based optimization of the production of PHB with tailor-made molecular properties in Azohydromonas lata bacteria. The process optimization led to a high intracellular PHB accumulation (up to 95% g of PHB per g of DCW) and the production of different grades (i.e., different molecular weight distributions) of PHB.

A combined metabolic/polymerization kinetic model on the microbial production of poly(3-hydroxybutyrate)

In the present work, an integrated dynamic metabolic/polymerization kinetic model is developed for the prediction of the intracellular accumulation profile and the molecular weight distribution of poly(3-hydroxybutyrate) (P(3HB) or PHB) produced in microbial cultures. The model integrates two different length/time scales by combining a polymerization kinetic model with a metabolic one. The bridging point between the two models is the concentration of the monomer unit (i.e. 3-hydroxybutyryl-CoA) produced during the central aerobic carbon metabolism. The predictive capabilities of the proposed model are assessed by the comparison of the calculated biopolymer concentration and number average molecular weight with available experimental data obtained from batch and fed-batch cultures of Alcaligenes eutrophus and Alcaligenes latus. The accuracy of the proposed model was found to be satisfactory, setting this model a valuable tool for the design of the process operating profile for the production of different polymer grades with desired molecular properties.

Model-based Dynamic Optimisation of Microbial Processes for the High-Yield Production of Biopolymers with Tailor-made Molecular Properties

Abstract The dynamic optimal control of microbial processes for the economically efficient production of biopolymers with tailor-made molecular properties is a complicated problem. In the present work an integrated metabolic/polymerization/macroscopic model for the production of polyhydroxybutyrate (PHB) in A. latus bacteria was developed. The model relates the process performance and product quality with operating variables of interest and predicts the dynamic evolution of the biomass growth, the polymer accumulation, the consumption of carbon and nitrogen sources and the average molecular weight of the final biopolymer. The process optimization led to a high intracellular PHB accumulation (up to 95% g of PHB per g of DCW) of different biopolymer grades with a maximum molecular weight equal to 8.08×10 5 g/mol.

Development of a Macroscopic Model for the Production of Bioethanol with High Yield and Productivity via the Fermentation of Phalaris aquatica L. Hydrolysate

This study deals with the development of a structured macroscopic model for the dynamic simulation of the bioethanol production through the fermentation of sugars derived from the hydrolysis of lignocellulosic biomass of the perennial herbaceous species Phalaris aquatica L. In the proposed model, the growth of Saccharomyces cerevisiae cultures consuming hydrolysate sugars as carbon source in parallel with the intracellular bioethanol production and excretion are quantitatively described accounting for substrate and product inhibition phenomena. A number of different feeding policies were designed and investigated on a model-base and verified experimentally in a real fermentation process. Substantial improvement on the real process performance was attained, resulting in a final ethanol concentration equal to 59.1 g/L corresponding to 2.19 g/(Lh) overall ethanol productivity.