Production of Polyhydroxyalkanoates (PHAs) from Waste Frying Oil by Bacillus subtilis

Abstract

Polyhydroxyalkanoates (PHAs) are biodegradable biopolymers synthesized by bacteria as secondary metabolites under nutrient-limited conditions with excess carbon. However, PHA production is often constrained by the high cost of carbon substrates. The utilization of waste materials, such as waste frying oil, offers a cost-effective alternative. In this study, PHA was produced by Bacillus subtilis using waste frying oil as the carbon source. Cultivation was carried out in modified Mineral Salt Medium (MSM) supplemented with 2% waste frying oil and 0.1% yeast extract at 30°C and 150 rpm for 72 h. PHA was extracted using chloroform and precipitated with cold methanol. Sudan Black staining confirmed intracellular PHA accumulation. Fourier Transform Infrared Spectroscopy (FTIR) analysis identified characteristic PHA functional groups, including O–H, C–H, C=O, CH₃, C–O–C, and C–O. X-ray Diffraction (XRD) revealed a predominantly amorphous structure with low crystallinity and an average crystallite size of 42.87 nm. Scanning Electron Microscopy (SEM) showed a fibrous surface morphology. Thermal characterization by Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA) indicated a melting temperature of 163.54°C and a degradation temperature of 311°C. These results demonstrate the potential of waste frying oil as an economical carbon source for PHA production by B. subtilis.