TECHNOLOGY FOCUS - BIOTECHNOLOGY - Preferred Process: In producing lipids from biomass, the polysaccharide is selected from cellulose, hemicellulose, or its mixtures. The biomass including at least one polysaccharide is a lignocellulosic biomass. It is subjected to a preliminary grinding process before being subjected to the hydrolysis. The first aqueous phase comprises an amount of glucose higher than or equal to 100 g/L, preferably higher than or equal to 200 g/L, up to the solubility limit of the glucose in the first aqueous phase; from 0 g/L to 200 g/L, preferably from 10 g/L to 100 g/L, of xylose; from 0 g/L to 20 g/L, preferably from 5 g/L to 10 g/L, of arabinose; from 0 g/L to 20 g/L, preferably from 2 g/L to 10 g/L, of mannose; from 0 g/L to 10 g/L, preferably from 2 g/L to 8 g/L, of galactose; from 0 g/L to 8 g/L, preferably from 0 g/L to 5 g/L, of acetic acid; from 0 g/L to 0.7 g/L, preferably from 0 g/L to 0.5 g/L, of furfural; and from 0 g/L to 2.5 g/L, preferably from 0 g/L to 2 g/L, of 5-hydroxymethylfurfural. The retentate is an aqueous solution comprising an amount of sugars higher than or equal to 40 g/L, preferably ranging from 45 g/L to 60 g/L. In the first fermentation device, the fermentation is carried out at a temperature ranging from 20 degrees C to 40 degrees C, for a time ranging from 10 hours to 36 hours, at a pH ranging from 4.5 to 7. In the second fermentation device, the fermentation is carried out at a temperature ranging from 20 degrees C to 40 degrees C, for a time ranging from 2 days to 10 days, at a pH ranging from 4.5 to 7. The oleaginous microorganism is selected from yeasts such as: Rhodotorula glutinis, Rhodotorula gracilis, Rhodotorula graminis, Lypomices starkeyi, Lypomices lipofer, Trigonopsis variabilis, Candida kefyr, Candida curvata, Candida lipolytica, Torulopsis sp., Pichia stipitis, Trichosporon cacaoliposimilis, Rhodosporidium sp., and Cryptococcus curvatus. Fermentation in the second fermentation device is carried out in one or more steps in batch (feed-batch fermentation), semi-continuous or continuous mode. Reverse osmosis is carried out in the presence of at least one polymeric membrane selected from polymeric membranes generally used for desalination (usually known as sea water membranes or brakish water membranes) such as: membranes comprising polyamides, polyimides, polysulfones, and polyethersulfones. The polymeric membrane has a maximum operating temperature ranging from 15 degrees C to 90 degrees C, a maximum operating pressure ranging from 5 bar to 80 bar, a nominal molecular weight cut-off (MWCO) ranging from 30 daltons to 200 daltons, a maximum operating pH ranging from 1 to 13. Reverse osmosis is carried out at a temperature ranging from 5 degrees C to 90 degrees C. It is carried out by applying a pressure in the feeding side (retentate side) ranging from 5 bar to 80 bar. It is carried out by operating at a specific flow-rate (kg of permeate per square meter of surface of the reverse osmosis membrane per hour) ranging from 5 kg/(m2 x hour) to 80 kg/(m2 x hour). Before being subjected to reverse osmosis, the second aqueous phase is subjected to microfiltration or ultrafiltration. The process comprises adding corn steep liquor or corn steep solid to the second fermentation device in an amount ranging from 2 g/L to 20 g/L. EXAMPLE - No suitable example given.