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

Abstract

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 (Mv) of biopolymers were 80 % and 0.27•106 respectively. The use of methanol as a modifier during the sCO2 disruption increased the Mv 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.