TECHNOLOGY FOCUS - BIOLOGY - Preferred Microorganism: The oleaginous yeast is chosen from Rhodotorula glutinis, R.gracilis, R.graminis, Lipomyces starkeyi, L.lipofer, Trigonopsis variabilis, Candida kefyr, C.curvata, C.lipolytica, Torulopsis sp., and Pichia stipitis.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Components: The alkyl or aryl sulfonic acids are 9-15C alkyl or aryl sulfonic acids. The organic acid is soluble in water and extractable with organic solvent insoluble in water. The alkyl or aryl sulfonic acids are chosen from dodecylsulfonic acid, para toluene sulfonic acid, 1-naphthalenesulfonic acid, 2-naphthalenesulfonic acid, 1,5-naphthalenedisulfonic acid and their mixtures. The halogenated carboxylic acids are chosen from carboxylic acids having not greater than 20C, preferably trifluoroacetic acid, dichloroacetic acid, trichloroacetic acid, perfluorooctanoic acid and their mixtures. The first aqueous phase comprises at least one sugar (5-6C) and organic acid. The organic solvent insoluble in water is chosen from halogenated hydrocarbons (such as methylene chloride, monochlorobenzene, dichlorobenzene or their mixtures), aromatic hydrocarbons (toluene, xylene or their mixtures), and 4-6C aliphatic alcohols (n-butanol, n-pentanol or their mixtures). The second aqueous phase comprises 5-6C sugar. Preferred Composition: The content of organic acid in the aqueous solution is 0.1-5 wt.% with respect to the total weight of the aqueous solution. Preferred Method: The biomass is subjected to preliminary milling or sizing process before acid hydrolysis. The biomass is treated until the obtained particles have a diameter of 0.1-10 mm. The first mixture is subjected to extraction with organic solvent insoluble in water. The method involves recycling the organic acid in the acid hydrolysis. The method involves recycling the organic solvent insoluble in water during extraction. The fermentation is fed-batch fermentation. The aqueous suspension (obtained at the end of the fermentation) is subjected to thickening treatment, where the concentration of the yeast cells is 5-50 wt.% with respect to the total weight (dry weight) of the aqueous suspension. The mixture (oily phase and aqueous phase) obtained at the end of the thermal treatment is cooled to 40-90 degrees C, before being fed to a section of separation/recovery of the oily phase comprising bio-oil and third aqueous phase. The third aqueous phase is recycled to the fermentation. Preferred Condition: The temperature is 100-150 degrees C. The acid hydrolysis is carried out for 20 minutes-6 hours. The fermentation is carried out at 20-40 degrees C. The fermentation is carried out for 3-10 days. The fermentation is carried out at a pH of 4.5-6.5. The thermal treatment is carried out at 80-350 degrees C. The thermal treatment is carried out at a pressure of 0.1-25 MPa. The thermal treatment is carried out for greater than or equal to 1 minute. The thermal treatment is carried out for 0.5-2 hours.    TECHNOLOGY FOCUS - POLYMERS - Preferred Components: The polysaccharide is chosen from cellulose, hemicellulose and their mixtures. The first solid phase comprises lignin and cellulose. The second solid phase comprises lignin. Preferred Composition: The content of the biomass in the reaction mixture is 5-40 wt.% with respect to the total weight of the reaction mixture. EXAMPLE - No suitable example given.