TECHNOLOGY FOCUS - POLYMERS - Preferred Method: In (M1), the aqueous mixture is obtained from hydrolysis of a polysaccharide based plant derived material; and the flocculating agent is present in an amount of 0.002 - 1 wt.%, based on the weight of solid matter. The solid matter are subjected to at least one wash cycle comprising washing the solid matter and then repeating stages (a) and (b).Preferred Components: The flocculating agent is water-soluble or water swellable natural, semi-natural and synthetic polymer; or charged microparticulate material (preferably water soluble or water-swellable polymer and a charged microparticulate material). The polymer is polyacrylate salt, polyacrylamide, copolymer of acrylamide with (meth)acrylic acid or its salt, copolymer derived from acrylamide and dialkylaminoalky(meth)acrylate acid salt or quaternary ammonium salt, polymer derived from diallyldimethyl ammonium chloride, polyamine or polyethylene imine. The charged microparticulate material is swellable clay, anionic, cationic or amphoteric microparticulate silica based material and organic cross-linked polymeric microparticle.    TECHNOLOGY FOCUS - BIOLOGY - Preferred Components: The plant derived material is herbaceous biomass, softwood biomass, hardwood biomass, sewage sludge, paper mill sludge and the biomass fraction of municipal solid waste. EXAMPLE - Softwood chips (100 parts) were added to 77 % sulfuric acid (170 parts) and the temperature was maintained below 80 degrees centigrade and the resulting gelatinous mixture was thoroughly mixed. The gelatinous mixture was diluted with water to an acid concentration of 25 %. The reaction mixture was heated to 100 degrees centigrade for 60 minutes. After hydrolysis, the obtained slurry was fed to separation equipment for pressing. Prior to pressing, a copolymer of acrylamide (69 wt.%) and cationic monomer (dimethylaminoethylacrylate quaternized with methyl chloride) (31 wt.%), IV approximately 12 dl/g flocculant, at solids (0.2 %), and a particulate suspension (sodium bentonite, at 5 % solids) were added into the feed stream with agitation at a dose of 0.2 kg polymer (as supplied) per tonne of solids and 0.5 kg bentonite (as supplied) per tonne solids. The acid sugar solution was separated by pressing from the remaining solids, releasing 35 % acid and 17 % sugar. After pressing, the resultant cake containing the solid matter was washed with approx. an equal amount of water. Prior to re-pressing the flocculant solution and sodium bentonite were added into the feed stream with agitation at a dose of 0.2 kg per ton of solids of polymer and 0.5 kg per ton solids of bentonite. 16 % acid and 9 % sugar was released by pressing. The recovered biomass cake was then subjected to a repeat process of acid treatment (hydrolysis) above to release further sugar. The resulting cake contains more lignin compared to the content of the first cycle.