Effects of Lignin Gasification Impurities on the Growth and Product Distribution of Butyribacterium methylotrophicum during Syngas Fermentation

This work evaluated the effects of condensable syngas impurities on the cell viability and product distribution of Butyribacterium methylotrophicum in syngas fermentation. The condensates were collected during the gasification of two technical lignins derived from wheat straw (WST) and softwood (SW) at different temperatures and in the presence or absence of catalysts. The cleanest syngas with 169 and 3020 ppmv of H2S and NH3, respectively, was obtained at 800 degrees C using dolomite as catalyst. Pyridines were the prevalent compounds in most condensates and the highest variety of aromatics with cyanide substituents were originated during WST lignin gasification at 800 degrees C without catalyst. In contrast with SW lignin-based condensates, the fermentation media supplemented with WST lignin-derived condensates at 1:100 vol. only supported residual growth of B. methylotrophicum. By decreasing the condensate concentration in the medium, growth inhibition ceased and a trend toward butyrate production over acetate was observed. The highest butyrate-to-acetate ratio of 1.3 was obtained by supplementing the fermentation media at 1:1000 vol. with the condensate derived from the WST lignin, which was gasified at 800 degrees C in the presence of olivine. B. methylotrophicum was able to adapt and resist the impurities of the crude syngas and altered its metabolism to produce additional butyrate.