The production of polyhydroxyalkanoate from waste cooking oil and its application in biofuel production

Abstract

This research presents an approach for using waste cooking oil as a substrate for the production of polyhydroxyalkanoate (PHA) by Bacillus thermoamylovorans. In addition, PHA was utilised as a feedstock for a biofuel, namely 3-hydroxyalkanoate methyl ester (3HAME). The largest amount of biomass (4.0 ± 0.1 g/L) and the greatest production of PHA [3.5 ± 0.1 g/L, corresponding to 87.5% of cell dry mass (CDM)] were obtained under optimal conditions, with 4% (w/v) waste cooking oil (WCO) used as a carbon source at 45 °C and 150 rpm for 48 h under batch cultivation. The isolated polymer was identified as poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(3HB-co-3HV)] with 85 mol% of 3-hydroxybutyrate (3HB) and 15 mol% of 3-hydroxyvalerate (3HV) using gas chromatography–mass spectrometry (GC–MS). Notably, the properties of the copolymer were similar to the properties of the commercial P(3HB-co-3HV). Moreover, P(3HB-co-3HV) was used as a feedstock for the biofuel. P(3HB-co-3HV) methyl ester, a biofuel, was obtained under optimal conditions, with methanol and 15% (v/v) H2SO4 under a reaction temperature of 65 °C and time of 60 h. The highest yield of 3HAME that was obtained was 74.4%, with 97% methyl ester content. Almost all of the properties of 3HAME pass ASTM and Thailand’s fuel standards.