Harifara Rabemanolontsoa

Various pretreatments of lignocellulosics.

Biomass pretreatment for depolymerizing lignocellulosics to fermentable sugars has been studied for nearly 200 years. Researches have aimed at high sugar production with minimal degradation to inhibitory compounds. Chemical, physico-chemical and biochemical conversions are the most promising technologies. This article reviews the advances and current trends in the pretreatment of lignocellulosics for a prosperous biorefinery.

Comparative study on chemical composition of various biomass species

In this study, the chemical composition of 32 samples coming from 29 different biomass species including a gymnosperm, 2 dicotyledonous angiosperms, 17 monocotyledonous angiosperms and 9 algae species was successfully determined using an established method applicable to analyze various biomass species. The obtained data allowed a direct comparison of the biomass in their chemical composition. It was, thus, revealed that although the chemical composition differed from one species to another, and even from different parts of the same plants, similar trends were found in the composition of biomass species belonging to the same taxonomic group. Based on those results, it was clarified that the chemical composition of a biomass sample is related to its taxonomy. Therefore, typical chemical composition for each taxonomic group was proposed and the potential of each group for different biorefinery platforms could be defined.

Holocellulose Determination in Biomass

For determination of holocellulose, the residual yield and its chemical composition during delignification by acidified sodium chlorite have been studied for bamboo (Phyllostachys heterocycla) and Sargassum (Sargassum horneri). It was then found that along with the extended number of chlorination, the residue became yellowish, and then whitish. Accordingly, the holocellulose yield was reduced. Thus, in order not to lose any part of the holocellulose, the number of chlorination was found to be minimized so as for the residue to remain yellowish. Subsequently, lignin and ash corrections were made on the yellowish residue to determine the accurate holocellulose content. Such a modified procedure for the holocellulose determination was proposed in this study.

Evaluation of Different Methods to Determine Monosaccharides in Biomass

Sulfuric acid, trifluoroacetic acid (TFA) and acid methanolysis methods for hydrolysis were evaluated and compared using standard monosaccharides and standard oligosaccharides. As a result, sulfuric acid hydrolysis was found to be suitable to determine crystalline cellulosic and amorphous xylanic saccharides. TFA method, however, could not achieve complete hydrolysis of cellooligosaccharides and xylooligosaccharides, while acid methanolysis was considered appropriate to determine monosaccharides in amorphous hemicellulose. Based on these lines of evidence, a combination of sulfuric acid hydrolysis and acid methanolysis methods was concluded to be appropriate to get accurate monosaccharides determination in biomass species, and the application of this combined method to Japanese beech, bamboo and rice husk samples presented reasonable results.

Effects of gas condition on acetic acid fermentation by Clostridium thermocellum and Moorella thermoacetica (C. thermoaceticum)

Fermentation with acetogens can be affected by cultivation gas phase, but to date, there is not enough evidence on that matter for Clostridium thermocellum and Moorella thermoacetica. In this work, the effects of sparged CO2 as well as sparged and non-sparged N2 on these microorganisms were studied using glucose and cellobiose as substrates. It was revealed that sparged CO2 and non-sparged N2 supported growth and acetic acid production by C. thermocellum and M. thermoacetica, while sparged N2 inhibited both of the microorganisms. Notably, part of the sparged CO2 was fermented by the co-culture system and contributed to an overestimation of the products from the actual substrate as well as an erring material balance. The best condition for the co-culture was concluded to be N2 without sparging. These results demonstrate the importance of cultivation conditions for efficient fermentation by anaerobic clostridia species.