University of Antwerp
A New Step in the Development of Biorefineries: The Valorization of Aromatic Waste Streams to Microbial Oil
Focus area / active in:
- Bioprocesses & technologies
- Circular economy
- Microbial oil
- Phenolic waste stream
- Rhodococcus opacus PD630
In recent years, lignocellulose biorefineries have gained importance, providing sustainable resources as an alternative to classic fossil-based resources(1). While much attention has been paid to the use of sustainable substrates and green processing technologies, the literature on the valorization of the biorefinery’s aromatic waste stream is still scarce. Considering that this wastewater treatment contributes up to 15 % of the minimal selling price of lignocellulosic ethanol, insights in the simultaneous purification and conversion to valuable compounds are necessary(2).
It has been shown that Rhodococcus opacus PD630 can metabolize individual monocyclic aromatic compounds, typically found in biorefinery wastewaters(3). The present study evaluates R. opacus’s ability to intracellularly accumulate lipids while it consumes the aromatics in the dilute aromatic wastewater obtained from steam explosion pretreatment of poplar wood. First, the composition of the waste stream was elucidated by identifying and quantifying the most common lignocellulose derived compounds. Secondly, the toxicity of the effluent and its individual aromatic compounds was investigated. Lastly, the influence of the dilution of the effluent (v%), nitrogen addition (wv% NH4Cl), and the use of inoculum adaptation was investigated on the detoxification (% aromatic removal) and lipid accumulation (% lipids/CDW).
The effluent contained 2.4 g/L (hemi)cellulose derived sugars (primarily xylose), 0.8 g/L lignin-derived phenolics (e.g. 4-hydroxybenzoic acid), 0.2 g/L furans (i.e. furfural, 5-hydroxymethyl furfural) and 3.5 g/L organic acids (i.e. formic acid, acetic acid). As shown in Figure 1, the lipid content increased with an increasing volume percentage of wastewater, as more substrate is available to the microorganism. None of the other investigated parameters influence the lipid content after 24 hours. R. opacus consumed up to 99.7 % of the aromatic compounds in the wastewater and accumulated up to 61 % cell dry weight of lipids.
Figure 1: Lipid content after 24 hours, on the left with 15 v% wastewater in the inoculum medium for adaptation, on the right without adaptation. The center point (CP) is represented in grey with 7.5 v% wastewater in the inoculum medium.
R.opacus paves the way for biorefinery wastewater valorization, as it converts the aromatic compounds to lipids and intracellularly accumulates them.
1. Bio-based industries consortium. (2017), vol. 2020.
2. A. A. Koutinas, A. Chatzifragkou, N. Kopsahelis, S. Papanikolaou, I. K. Kookos, Design and techno-economic evaluation of microbial oil production as a renewable resource for biodiesel and oleochemical production. Fuel 116, 566-577 (2014).
3. K. Kurosawa, J. Laser, A. J. Sinskey, Tolerance and adaptive evolution of triacylglycerol-producing Rhodococcus opacus to lignocellulose-derived inhibitors. Biotechnology for Biofuels 8, 76 (2015).
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