Bio-oil production by hydrothermal liquefaction of Rhodococcus opacus biomass utilizing refinery wastewater: Biomass valorization and process optimization

In this research, a pure culture of Rhodococcus opacus strain PD630 was used to treat wastewater generated from a refinery and the lipid rich bacterial biomass obtained was converted to bio-oil. A very high removal (70 +/- 5%) of organics present in the wastewater was achieved at pH 7 within 96 h along with lipid accumulation of 50 +/- 4% w/w by the bacteria. The lipid containing biomass procured by using the wastewater as the sole substrate was converted into bio-oil by hydrothermal liquefaction (HTL) technique. Different operational parameters viz. temperature, time and biomass/water ratio were optimized employing Response Surface Methodology (RSM) to achieve maximum biooil yield. The optimum conditions for maximum bio-oil yield (25.53%) were found to be 215 degrees C, 125 min and 0.25 biomass/water ratio; the bio-oil had a high heating value (HHV) of 20.73MJ/Kg, and it also contained a very low amount of water soluble products in it. GC-MS analysis of the obtained bio-oil product revealed the presence of a variety of compounds, mainly aldehydes, ketones and fatty acids, whereas the water soluble product contained mainly alcohols and phenolic compounds. Further analysis of the aqueous phase obtained as a byproduct concluded its potential for reuse owing to the presence of nutritional compounds. FTIR spectra of bio-oil revealed the presence of C-H bonds due to alkanes as the predominant functional group present in the product. FAME analysis results and other properties of the transesterified bio-oil matched well with the ASTM standard thus indicating its potential for bio-fuel application. This experimental study thus demonstrated that the lipid rich R. opacus biomass grown on cheaply available refinery wastewater is highly suited for potential bio-oil production. (C) 2020 Elsevier B.V. All rights reserved.