Production and characterization of bio-oil and biochar from the pyrolysis of residual bacterial biomass from a polyhydroxyalkanoate production process

• Residual bacterial biomass from polyhydroxyalkanoate production was characterized.
• Residual bacterial biomass was converted to bio-oil and biochar by pyrolysis.
• Pyrolysis at 500 °C gave a bio-oil and biochar yield of 28 and 46%.
• Pyrolysis bio-oil contains aromatics, hydrocarbons, and nitrogen-rich compounds.
• Biochar is disordered amorphous carbon and rich of N.

Polyhydroxyalkanoate (PHA) production generates a significant amount of residual bacterial biomass (RBB) after PHA extraction. The RBB as a zero-value waste contains proteins, carbohydrates, phenolics, and ash, which can be managed and converted to bio-oil and biochar products by pyrolysis. Thermogravimetric analysis (TGA) was used to investigate the thermodegradation kinetics of RBB and pyrolysis–GCMS studies were employed to determine potential chemical products. Pyrolysis was conducted on a laboratory-scale auger reactor at 500 °C. The bio-oil and biochar yield were 28 and 46%, respectively. The pyrolysis bio-oil was characterized by the combination of GCMS, high-pressure liquid chromatography (HPLC), and electrospray ionization mass spectrometry (ESI–MS). The bio-oil was dominated by nitrogen-containing, hydrocarbons, and aromatic compounds. The biochar was studied for its specific surface area and pore size, chemical functionality by Fourier transform infrared (FTIR) and Raman spectroscopies, and butane absorption activity. Biochar was comprised of a large part of polycondensed phenolic and majorly disordered amorphous carbon.