Exploring the compatibility between hydrothermal depolymerization of alkaline lignin from sugarcane bagasse and metabolization of the aromatics by bacteria.

Although hydrothermal treatments for biomass fractionation have been vastly studied, their effect on the depolymerization of isolated lignins in terms of yield, composition, and compatibility of the produced lignin bio-oils with bioconversion is still poorly investigated. In this study, we evaluated the hydrothermal depolymerization of an ß-O-4'-rich lignin extracted from sugarcane bagasse by alkaline fractionation, investigating the influence of temperature (200-350 °C), time (30-90 min), and solid-liquid ratio (1:10-1:50 m.v-1) on yield of bio-oils (up to 31 wt%) rich in monomers (light bio-oils). Principal Components Analysis showed that the defunctionalization of the aromatic monomers was more pronounced in the most severe reaction conditions and that the abundance of more hydrophobic monomers increased in more diluted reactions. While the high-molecular-weight (heavy) bio-oil generated at 350 °C, 90 min, and 1:50 m.v-1 failed to support bacterial growth, the corresponding light bio-oil rich in aromatic monomers promoted the growth of bacteria from 9 distinct species. The isolates Pseudomonas sp. LIM05 and Burkholderia sp. LIM09 showed the best growth performance and tolerance to lignin-derived aromatics, being the most promising for the future development of biological upgrading strategies tailored for this lignin stream.

Batch and fed-batch simultaneous saccharification and fermentation of primary sludge from pulp and paper mills.

Primary sludge from a Portuguese pulp and paper mill, containing 60% of carbohydrates, and unbleached pulp (as reference material), with 93% of carbohydrates, were used to produce ethanol by simultaneous saccharification and fermentation (SSF). SSF was performed in batch or fed-batch conditions without the need of a pretreatment. Cellic® CTec2 was the cellulolytic enzymatic complex used and Saccharomyces cerevisiae (baker's yeast or ATCC 26602 strain) or the thermotolerant yeast Kluyveromyces marxianus NCYC 1426 were employed. Primary sludge was successfully converted to ethanol and the best results in SSF efficiency were obtained with S. cerevisiae. An ethanol concentration of 22.7 g L-1 was produced using a content of 50 g L-1 of carbohydrates from primary sludge, in batch conditions, with a global conversion yield of 81% and a production rate of 0.94 g L-1 h-1. Fed-batch operation enabled higher solids content (total carbohydrate concentration of 200 g L-1, equivalent to a consistency of 33%) and a reduction of three-quarters of cellulolytic enzyme load, leading to an ethanol concentration of 40.7 g L-1, although with lower yield and productivity. Xylitol with a concentration up to 7 g L-1 was also identified as by-product in the primary sludge bioconversion process.