Low-structured kinetic model of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) production from waste animal fats via fed-batch cultivations.

Polyhydroxyalkanoates are fully biodegradable biopolymers and represent a sustainable alternative to conventional, fossil-derived plastics. To improve their economic feasibility, this study investigates the microbial production of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) from low-quality waste animal fats using the recombinant strain Cupriavidus necator Re2058/pCB113. A series of high-cell-density fed-batch fermentations were conducted under varying feeding strategies for carbon (waste animal fat) and nitrogen (urea). Based on the experimental data, a low-structured dynamic kinetic model was developed incorporating both extracellular and selected intracellular processes relevant to polyhydroxyalkanoate synthesis via ß-oxidation. Sensitivity analysis of the 31 model parameters revealed 13 as sensitive to process variations, which were re-identified for improved adaptability. The model was validated against independent cultivation data, demonstrating accurate predictions of biomass, polymer concentration, and 3-hydroxyhexanoate content. This model supports process optimization and the design of feeding strategies, contributing to reduced experimental effort and enhanced scalability the of polyhydroxyalkanoates production from waste-derived substrates.