Pilot scale-up production of poly(3-hydroxybutyrate) (PHB) from starch-based wastewater: A halogen-free process optimization for polymer recovery

Abstract

The intracellular nature of microbial polyhydroxyalkanoates (PHAs) requires two main steps in their production: bioconversion and extraction. The most widely used method for recovering poly(3-hydroxybutyrate) (PHB) is solvent extraction. Traditional approaches involve the use of halogenated solvents, whose environmental and health hazards are well known. New alternatives advocate the use of sustainable agents, which can be an effective and economical choice. In this work, the bioconversion process of starch-based water into PHB by Cupriavidus necator DSM 545 was first scaled-up using previously optimized conditions. A statistical model was then developed to optimize the best conditions for polymer extraction using NaOH by response surface methodology with a central composite design. The optimized and validated conditions were: 0.05 M NaOH at 29.6 °C for 1 h, resulting in 87.31 ± 0.33 % polymer yield, 104.13 ± 2.22 % polymer purity and 104.76 ± 2.41 % polymer recovery. These conditions were validated for operation at three different biomass-to-NaOH concentrations: 5.7 g/L, 20 g/L and 79.5 g/L, and scaled-up without sacrificing polymer yield, with high levels of PHB purity and recovery. In addition, this work proposed an approach for the scale-up of a halogen-free process for PHB extraction using NaOH, considering parameters that can be easily integrated into the common ranges used in the industry.