Production of polyhydroxybutyrate from waste cooking oil using magnetically recoverable microbial-based nanocomposites as reusable inocula

Polyhydroxybutyrate (PHB) is produced during bacterial metabolism and can be used for the production of biodegradable plastics. The utilization of wastes as carbon sources and inoculum reuse are potential strategies to reduce production costs. In this study, a method for PHB production from waste cooking oil using a reusable inoculum was developed. Two microbial-based nanocomposites (fabricated bead and bacterial nanocomposites) were used as reusable inocula, and 6% waste cooking oil was used as a carbon source. The addition of 0.1% iron oxide (Fe3O4) increased PHB production and oil removal efficiency. Supplementation with 0.1% pumice enhanced the compressive strength and Young’s modulus of the fabricated bead nanocomposite containing a photosynthetic bacterium, alginate, Fe3O4, and pumice. The bead nanocomposite was reused for nine cycles with single harvesting of PHB. To improve the recycling time, free cells released from the bead nanocomposite were immobilized to generate a bacterial nanocomposite containing bacteria and Fe3O4. Bacterial nanocomposites showed the highest oil removal rates (38%–51%) and PHB contents in multiple harvests (19%–30%). The bacterial nanocomposite was recycled in 11 batches without deterioration and simplified using magnetic harvesting, which eliminated the incubation time and medium required for inoculum preparation. These results suggest that bead nanocomposites can be used to treat cooking oil until they disintegrate and release free cells that are immobilized with Fe3O4 to generate bacterial nanocomposites for unlimited recycling. This study introduces technology for PHB production from waste cooking oil.