Abstract
Hydrothermal liquefaction (HTL) processing of lignocellulosic biomass to bio-oil produces aqueous co-product (AP) which contains significant (~40 wt%) carbon from the original feedstock. This study evaluates macro and micronutrient composition of AP from Ca(NO3)2 catalyzed HTL of cardboard (CbAP) to cultivate bacteria. HPLC, GC-MS and ICP-MS analysis of CbAP revealed presence of C1-C3 carboxylic acids, aldehydes, ketones, phenolics, sub-optimal phosphorous and bio-incompatible levels of calcium. Dilutions (5 - 80 vol%) of detoxified CbAP (DTP-CbAP) in potassium phosphate buffer (pH 7.2) were supplemented with 50 mg·mL-1 of yeast extract and inoculated with metabolically versatile Enterobacter species. The cultures were incubated at 25°C under aerobic conditions. A maximum 9.4 fold increase in the dry cell weight was observed in DTP-CbAP-15 vol%. Co-liquefaction of the bacteria with cardboard in 1:1 and 1:3 weight ratios each produced ~33% more total bio-oil. These had higher HHVs of 34.11 and 31.05 MJ·kg-1, respectively compared with bio-oil from cardboard feedstock alone which had HHV of 30.61 MJ·kg-1. The study highlights the challenges in cultivating microbes in AP from HTL of lignocellulosic biomass (LCB) and the possibility to integrate microbial capture and recycle of the AP carbon for enhanced bio-oil production and quality.
Highlights
Hydrothermal liquefaction (HTL) process converts wet biomass under subcritical temperature (280 ̊C - 374 ̊C) and pressure (10 - 25 MPa) to aqueous, solid char and gaseous products wherein process conditions, catalyst and biomass feedstock dictate product composition, distribution and yield [1] [2]
Solid char was washed with acetone to extract higher hydrocarbons termed as heavy bio-oil (HBO) while dichloromethane extraction of the biocrude was performed to yield light bio-oil (LBO) which consisted of low molecular weight (C4-C11) oxygenated hydrocarbons
We further demonstrate that co-liquefaction of microbial biomass with the cardboard feedstock induced a synergistic increase in bio-oil production and quality
Summary
Hydrothermal liquefaction (HTL) process converts wet biomass under subcritical temperature (280 ̊C - 374 ̊C) and pressure (10 - 25 MPa) to aqueous, solid char and gaseous products wherein process conditions, catalyst and biomass feedstock dictate product composition, distribution and yield [1] [2]. A continuous HTL reactor operation will likely face persistent challenge of wastewater disposal Alternatives such as catalytic hydrothermal gasification [9], photoreforming for H2 production [10], anaerobic digestion for methane production [11] have been investigated to recover organic components of the AP. Another route which is microbe mediated capture of AP carbon and nutrients is more appealing because it will simultaneously reduce the organic load of the waste stream and generate microbial feedstock for additional bio-oil [12] [13] [14]. We further demonstrate that co-liquefaction of microbial biomass with the cardboard feedstock induced a synergistic increase in bio-oil production and quality
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