Abstract
This work discusses the optimization of the biopolymer PHAs production by Ralstonia eutropha, in a bioreactor carried out under fed-batch mode. Although the optimization of fed-batch fermentations involves the manipulation of the substrate feed rate, which generates a singular optimal control problem, the optimal trajectory can be also set by adjusting small segments by non-linear programming. The cybernetic structured mathematical model used here in is described by a system of 12 differential equations; the strategy involves the maximization/minimization of an Objective Function considering the model as a set of implicit constraints and the discretization of the manipulated variables (substrate feed rates). The sequential quadratic program method is used to solve the optimization problem. PHAs productivity is taken as the objective function and its results are compared to those documented in the literature.
Highlights
In 2015, the global production of conventional petroleumbased polymers was 270 million tons
By using the resulting model of Fit 1 and the objective function to maximize the productivity of the PHB homopolymer by manipulating only one control variable—the substrate feed rate F1 (S1 + S2), the PHB productivity resulted in 3.11 g/(L/h), 41.1 glucose in cellular maintenance (g/L) of maximal active biomass (Xr), final volume of 8.98 L and 103.0 g/L of homopolymer P1 (PHB), in 33.1 h
The use of nonlinear programming to find the optimum trajectories of the feeding flow rates for fermentative processes conducted in fed batch allowed optimizing the production process of polyhydroxybutyrate (PHB), resulting in a product productivity of 3.28 g/(L/h)
Summary
In 2015, the global production of conventional petroleumbased polymers was 270 million tons. In European countries, 31% of these materials were disposed of in landfills in 2014 (Campos 2016) Once discarded, these polymers have a very low rate of degradation and can persist in the soil for many decades. These polymers have a very low rate of degradation and can persist in the soil for many decades An alternative to this problem is the replacement of synthetic polymers with biodegradable ones. These polymers are vulnerable to the action of bacteria and fungi and their carbon compounds are degraded into smaller molecules with energy generation. The global bioplastics production capacity is set to increase from around 2.1 million tonnes in 2018 to 2.6 million tonnes in 2023 Innovative biopolymers, such as PLA (polylactic acid) and PHAs (polyhydroxyalkanoates), are driving this growth (European Bioplastics 2018)
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