Development of hybrid thermochemical-biological technologies for the obtainment of sustainable chemicals

Hybrid thermochemical-biological (HTB) technology has emerged as a promising strategy for developing circular and low-carbon routes for chemical production through the valorisation of biomass-derived C1-rich streams (syngas). However, the direct fermentation of syngas remains challenging. For this purpose, syngas produced from integrated pyrolysis-gasification was continuously fermented in a char-based biofilm sparger reactor (CBSR) using mixed microbial cultures (MMC) under mesophilic conditions. Process performance was investigated across six sequential experimental phases at different dilution rates to evaluate fermentability of real syngas and process compatibility with the CBSR system. Steam-CO2 gasification-derived syngas enabled stable fermentation and achieved a maximum volatile fatty acids (VFA) concentration of 28.8 g COD L-1 with volumetric productivity of 4.85 g COD L-1 d-1. This study establishes the CBSR as a viable platform for the biological upgrading of real syngas. Moreover, the potential of the hybrid thermochemical and biological approaches was further evaluated by Co-fermenting the pyrolysis-derived water soluble (WS) fraction and gasification-derived syngas within CBSR system. This strategy enabled the simultaneous utilization and conversion of liquid and gaseous streams into volatile fatty acids without causing significant toxicity to the MMC. To facilitate integrated processes such as carbon capture and fixation (CCF), the CBSR system was scaled up by optimizing the design of the sparging device. The scaled-up CBSR with open-top sparger configuration showed outstanding results, achieving 95 g COD L-1 at continuous mode and 165 g COD L-1 at semi-batch mode. Later, CBSR was integrated with two different carbon capture units to validate the continuous carbon capture and biological fixation. The results demonstrate the feasibility of both carbon capture approaches including, alkaline scrubbing and resin-based capturing, especially the resin-based capturing is the most promising approach. To recover the VFAs, resin-based separation was investigated using simulated concentrations of fermentation broth, confirming its suitability for downstream processing