Extraction of polyhydroxyalkanoate from activated sludge using supercritical carbon dioxide process and biopolymer...

Polyhydroxyalkanoates (PHA) are biodegradable polymers and have the potential to substitute with fossil-fuel based polymers since they have similar properties. Many studies on the production of PHA have been conducted, but the extraction/purification processes have received less attention. Mostly, solvent extraction has been studied, and the effect of different solvent types on the separation processes have been investigated. A better extraction method for PHA makes it a feasible alternative to fossil-fuel based polymers. In this study, a new protocol for the extraction of PHA from activated sludge by supercritical carbon dioxide disruption (sCO₂) and biopolymer recovery from disrupted cells were proposed. Extraction experiments were carried out with sCO₂ at different pressures, temperatures, times, biomass amounts, and modifier volumes. The operation yield was expressed based on the polyhydroxybutyrate (PHB) release efficiency. The biomass for the extraction experiments was obtained from a PHA production reactor where activated sludge was fed with anaerobically pretreated yeast industry wastewater. 80 % PHB releasing efficiency was achieved by disturbing 2 g of biomass at a density of 57 g/L (biomass/volume) with sCO₂ at 200 bar pressure for 15 min at 40 °C. The PHB purity and molecular weight (M_v) of biopolymers were 80 % and 0.27•10⁶ respectively. The use of methanol as a modifier during the sCO₂ disruption increased the M_v to 0.37•10⁶. Characterization studies by Fourier transform infrared spectroscopy (FTIR) and thermal degradation analysis (TGA) demonstrated that the biopolymer recovered with this extraction protocol was comparable to commercial PHB. As a clear advantage over the other extraction protocols; operationally fast and simple extraction procedure was achieved.