Recovery of Furfural and Acetic Acid from Wood Hydrolysates in Biotechnological Downstream Processing

Wood hydrolysates contain sugars that can be used as feedstock in fermentation processes. For that purpose, the hydrolysate must be concentrated and inhibitors that harm fermentation must be removed. Herein, the integration of these tasks with the recovery of inhibitors is studied. The wood hydrolysate is represented as a mixture of water, xylose, acetic acid, and furfural. Acetic acid and furfural are two frequently occurring inhibitors and valuable chemicals, and thus, their recovery is studied. Furfural is recovered from the vapors by heteroazeotropic distillation. It is shown that this can be achieved without additional energy. The recovery of acetic acid by distillation is also possible, but not attractive. The new process is simulated by using a thermodynamic model based on experimental data.

Evaluating the Potential of Rhodosporidium toruloides-1588 for High Lipid Production Using Undetoxified Wood Hydrolysate as a Carbon Source

The study aims to explore microbial lipid production using an abundant and low-cost lignocellulosic biomass derived from forestry residues. Sugar-rich undetoxified hydrolysate was prepared using hardwood and softwood sawdust and used for lipid production as a carbon source from an oleaginous yeast, Rhodosporidium toruloides-1588. The maximum biomass obtained was 17.09 and 19.56 g/L in hardwood and softwood hydrolysate, respectively. Sugar consumption in both hydrolysates was >95%, with a maximum lipid accumulation of 36.68% at 104 h and 35.24% at 96 h. Moreover, R. toruloides-1588 exhibited tolerance to several toxic compounds such as phenols, organic acids and furans present in hydrolysates. The lipid characterization showed several monosaturated and polyunsaturated fatty acids, making it a potential feedstock for biofuels and oleochemicals production. This study confirms the credibility of R. toruloides-1588 as a suitable lipid producer using hydrolysates from forestry residues as a substrate. Additionally, lipids obtained from R. toruloides-1588 could be a potential feedstock for advanced biofuel production as well as for food and pharmaceutical applications.

Conversion of Xylose from Birch Hemicellulose Hydrolysate to 2,3-Butanediol with Bacillus vallismortis

Biotechnologically produced 2,3-butanediol (2,3-BDO) is a potential starting material for industrial bulk chemicals, such as butadiene or methyl ethyl ketone, which are currently produced from fossil feedstocks. So far, the highest 2,3-BDO concentrations have been obtained with risk class 2 microorganisms and pure glucose as substrate. However, as glucose stays in competition to food and feed industries, a lot of effort has been done in the last years finding efficient alternative substrates. Thereby xylose from hydrolysed wood hemicelluloses is a promising substrate for the production of 2,3-BDO. The risk class 1 microorganism Bacillus vallismortis strain was identified as a very promising 2,3-BDO producer. The strain is able to utilize xylose almost in the same manner as glucose. B. vallismortis is less prone to common inhibiting compounds in lignocellulosic extracts/hydrolysates. When using a concentrated hemicellulose fraction from birch wood hydrolysate, which was produced with ultrafiltration and after which the acetate concentration was reduced, a yield of 0.43 g g−1 was achieved and the xylose consumption and the 2,3-BDO production is basically the same as using pure xylose.

Microalgae Cultivation for the Biotransformation of Birch Wood Hydrolysate and Dairy Effluent

In order to investigate environmentally sustainable sources of organic carbon and nutrients, four Nordic green microalgal strains, Chlorella sorokiniana, Chlorella saccharophila, Chlorella vulgaris, and Coelastrella sp., were grown on a wood (Silver birch, Betula pendula) hydrolysate and dairy effluent mixture. The biomass and lipid production were analysed under mixotrophic, as well as two-stage mixotrophic/heterotrophic regimes. Of all of the species, Coelastrella sp. produced the most total lipids per dry weight (~40%) in the mixture of birch hydrolysate and dairy effluent without requiring nutrient (nitrogen, phosphorus, and potassium—NPK) supplementation. Overall, in the absence of NPK, the two-stage mixotrophic/heterotrophic cultivation enhanced the lipid concentration, but reduced the amount of biomass. Culturing microalgae in integrated waste streams under mixotrophic growth regimes is a promising approach for sustainable biofuel production, especially in regions with large seasonal variation in daylight, like northern Sweden. To the best of our knowledge, this is the first report of using a mixture of wood hydrolysate and dairy effluent for the growth and lipid production of microalgae in the literature.