Importance of lignin removal in enhancing biomass hydrolysis in hot-compressed water.

Beech wood was pretreated by ethanol/water mixture or sodium chlorite/acetic acid mixture to prepare two representative samples rich in cellulose/lignin and cellulose/hemicellulose, respectively. These samples were then hydrolysed in hot-compressed water (HCW) using a semi-continuous reactor under optimal conditions where the secondary reactions in the liquid products were minimised. The glucose recovery in the primary liquid products from hydrolysis in HCW is enhanced to ∼80% for the cellulose/hemicellulose rich sample from ∼56% for the raw sample, while that for the cellulose/lignin rich sample only increases slightly to ∼64%. Despite its highest crystallinity index, the cellulose/hemicellulose rich sample achieves the highest glucose recovery at the shortest reaction time during hydrolysis in comparison with the raw and cellulose/lignin rich samples, clearly demonstrating the importance of lignin removal in enhancing hydrolysis reaction rate and sugar recovery during biomass hydrolysis in HCW.

Diauxic growth of Clostridium acetobutylicum ATCC 824 when grown on mixtures of glucose and cellobiose.

Clostridium acetobutylicum, a promising organism for biomass transformation, has the capacity to utilize a wide variety of carbon sources. During pre-treatments of (ligno) cellulose through thermic and/or enzymatic processes, complex mixtures of oligo saccharides with beta 1,4-glycosidic bonds can be produced. In this paper, the capability of C. acetobutylicum to ferment glucose and cellobiose, alone and in mixtures was studied. Kinetic studies indicated that a diauxic growth occurs when both glucose and cellobiose are present in the medium. In mixtures, D-glucose is the preferred substrate even if cells were pre grown with cellobiose as the substrate. After the complete consumption of glucose, the growth kinetics exhibits an adaptation time, of few hours, before to be able to use cellobiose. Because of this diauxic phenomenon, the nature of the carbon source deriving from a cellulose hydrolysis pre-treatment could strongly influence the kinetic performances of a fermentation process with C. acetobutylicum.