Effect of ozone pre-treatment on polyhydroxyalkanoate production from dark fermentation effluents

Abstract

This study examines the biosynthesis of polyhydroxyalkanoates (PHAs) by a Cupriavidus necator pure culture using permeates obtained from the acidogenic dark fermentation of ozonized and non-ozonized organic wastes. The influence of ozone pre-treatment on permeate composition, and its subsequent impact on PHA production, was systematically assessed by analyzing PHA yield, volatile fatty acid (VFA) uptake, and microbial growth dynamics. From the results obtained, it was observed that ozonation significantly enriched the permeate, increasing dissolved organic carbon by 59.43% and dissolved nitrogen by 47.61%, resulting in a C/N ratio of 6.55—close to the optimal ratio (C/N = 6) for efficient PHA fermentation. Additionally, ozone pre-treatment shifted the VFA profile, increasing butyric acid concentration by 88%, a preferred substrate for C. necator during PHA biosynthesis. The ozone pre-treatment led to a 15% increase in microbial growth and a 60% improvement in PHA production, raising the final accumulation from 0.85 g/L to 1.35 g/L. Kinetic and stoichiometric modeling corroborated the advantageous role of ozonation, demonstrating a marked enhancement in carbon conversion efficiency, with PHA yields reaching 0.91 g PHA/g VFA and a maximum biomass-specific accumulation of 4 g PHA/g biomass, corresponding to an intracellular PHA content of 80%. These results underscore ozone pre-treatment as a powerful strategy for optimizing VFA-to-PHA bioconversion, revealing its capacity to offer a promising route toward more efficient and sustainable biorefinery processes.