Abstract
Hybrid bio-thermochemical based technologies have the potential to ensure greater feedstock flexibility for the production of bioenergy and bioproducts. This study focused on the bioconversion of syngas produced from low grade technical lignin to C2-/C4-carboxylic acids by Butyribacterium methylotrophicum. The effects of pH, medium supplementation and the use of crude syngas were analyzed. At pH 6.0, B. methylotrophicum consumed CO, CO2 and H2 simultaneously up to 87 mol% of carbon fixation, and the supplementation of the medium with acetate increased the production of butyrate by 6.3 times. In long-term bioreactor experiments, B. methylotrophicum produced 38.3 and 51.1 mM acetic acid and 0.7 and 2.0 mM butyric acid from synthetic and lignin syngas, respectively. Carbon fixation reached 83 and 88 mol%, respectively. The lignin syngas conversion rate decreased from 13.3 to 0.9 NmL/h throughout the assay. The appearance of a grayish pellet and cell aggregates after approximately 220 h was indicative of tar deposition. Nevertheless, the stressed cells remained metabolically active and maintained acetate and butyrate production from lignin syngas. The challenge that impurities represent in the bioconversion of crude syngas has a direct impact on syngas cleaning requirements and operation costs, supporting the pursuit for more robust and versatile acetogens.
Highlights
Concerns regarding the depletion of finite feedstock resources have shifted industrial sectors to the use of renewable biomass and the adoption of circular business models
Acetic and butyric acids were quantified by High-Performance Liquid Chromatography (HPLC) with a Biorad Aminex HPX-87H column (Bio-Rad Laboratories, CA, USA) at 35 ◦C, in a LaChrom L-7490 (Merck, Darmstadt, Germany) chromatographer equipped with a differential refractive index detector
Gas samples were analyzed through gas chromatography (GC) in an Agilent/HP 6890 gas chromatograph equipped with a gas sampling valve, two filling columns (Molecular Sieve 5A and Porapak Q) and two detectors (Thermal Conductivity Detector and Flame Ionization Detector) mounted in series
Summary
Concerns regarding the depletion of finite feedstock resources have shifted industrial sectors to the use of renewable biomass and the adoption of circular business models. In 2020, the bio-based industry in Europe was represented by 2362 facilities, from which 788 integrated the production of bioproducts and energy, including biofuels and other types of energy from biomass [1]. Biomass plants tend to be efficient at its conversion, there are still waste streams generated from this process. Low-grade technical lignin from lignocellulosic biomass is one of such examples. Its polymeric composition and high stability make it impervious to enzymatic hydrolysis and other biological decomposition processes [2]. Due to its recalcitrant properties and high heating value, lignin has become a preferred feedstock for thermochemical plants, for gasification [3]
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