A process engineering approach to improve production of P(3HB) by cupriavidus necator from used cooking oil

Different feeding strategies, namely, exponential feeding and DO-stat mode, were implemented for the production of poly(3-hydroxybutyrate), P(3HB), by Cupriavidus necator DSM 428 with used cooking oil (UCO) as the sole carbon source. With the exponential feeding strategy, a cell dry mass of 21.3 ± 0.9 g L ⁻¹ was obtained, with a polymer content of 84.0 ± 4.5 wt.%, giving an overall volumetric productivity of 4.5 ± 0.2 g L ⁻¹ day ⁻¹ . However, the highest P(3HB) volumetric productivity, 12.6 ± 0.8 g L ⁻¹ day ⁻¹ , was obtained when the DO-stat mode was implemented together with the use of ammonium hydroxide for pH control, which served as an additional nitrogen source and allowed to reach higher cell dry mass (7.8 ± 0.6 g L ⁻¹ ). The P(3HB) obtained in all experiments had a high molecular mass, ranging from 0.6 × 10 ⁵ to 2.6 × 10 ⁵ g mol ⁻¹ , with low polydispersity indexes of 1.2-1.6. Melting and glass transition temperatures were also similar for the polymer produced with both cultivation strategy, 174 ^° C and 3.0-4.0 ^° C, respectively. The polymer exhibited a crystallinity ranging from 52 to 65%. The DO-stat strategy to feed oil containing substrates as the sole carbon sources was reported for the first time in this study, and the preliminary results obtained show that it is a promising strategy to improve P(3HB) production. Nevertheless, the process requires further optimization in order to make it economically viable.