NOVELTY - Producing (P1) a digested biomass stream involves: (a) providing biomass containing celluloses, hemicelluloses and lignin; (b) producing pretreated stream by contacting biomass with a solution containing alpha -hydroxysulfonic acid at less than 150 degrees C; (c) providing solution stream and pretreated biomass stream by separating portion of solution from residual biomass; (d) providing digested biomass stream and chemical liquor stream by contacting pretreated biomass stream with cooking liquor; and (e) removing portion of lignin and hemicellulosic material in digested biomass stream.    USE - For producing a digested biomass stream; for producing alcohol (claimed) used as chemicals and biofuels; and for the production of alcohols from cellulosic biomass.    ADVANTAGE - The concentrated acid processes have been somewhat more successful, producing higher yields of sugar. However, these processes typically involve the use of about 60% to 90% sulfuric acid to affect hydrolysis, leading to high cost due to the cost of handling concentrated sulfuric acid and it subsequent recovery. The process produces sugars and alcohols in high yields from biomass containing cellulosic fibers. The process has significant benefits over other acidic pretreatments where the toxic components such as furfural and acetic acid are essentially eliminated for the fermentation system. Also, bulk removal of lignin allows improved mass transfer of enzymes to cellulose for conversion to fermentable sugars and lower equipment and energy requirements due to smaller volumes going forward. The process allows for higher recovery of carbohydrates and thereby increased yields; and allows additional flexibility to treat a hemicelluloses rich stream to be converted to a fuel or chemical via different processing route more amenable to the chemical composition of this stream. For example, the five-carbon sugars present in the hemicelluloses rich stream can easily be converted to furanic fuels via dehydration in high yields without fermentation that requires long residence times and hence high capital investments. The pre-digestion of the hemicellulose reduce the load on the recovery boiler in the pulp mill, thereby increases capacity of feed and hence more fuel is produced.    DETAILED DESCRIPTION - Producing (P1) a digested biomass stream involves: (a) providing a biomass containing celluloses, hemicelluloses and lignin; (b) producing a pretreated stream by contacting the biomass with a solution containing at least one alpha -hydroxysulfonic acid at a temperature of less than 150 degrees C, where the pretreated stream comprises a solution comprising at least a portion of hemicelluloses and a residual biomass comprising celluloses and lignin; (c) providing a solution stream and a pretreated biomass stream by separating at least a portion of the solution from the residual biomass; (d) providing a digested biomass stream and a chemical liquor stream by contacting the pretreated biomass stream with a cooking liquor comprising (i) 0.5-20 wt.%, based on the cooking liquor, (ii) at least one alkali selected from sodium hydroxide, sodium carbonate, sodium sulfide, potassium hydroxide, potassium carbonate, and ammonium hydroxide, (iii) water, at a biomass to cooking liquor ratio of 2-6, at a temperature of 60-230 degrees C, where the digested biomass stream comprises digested biomass containing cellulosic material, hemicellulosic material, and at least a portion of lignin, and the chemical liquor stream comprises at least a portion of lignin and at least one sodium compound, potassium compound, or ammonium compound; and (e) removing at least a portion of lignin and hemicellulosic material in the digested biomass stream and producing lignin-removed digested biomass stream by washing the digested biomass stream with a water stream. An INDEPENDENT CLAIM is included for producing (P2) alcohol involving: performing the steps (a)-(e) of the process (P1); (f) produce a hydrolyzate containing 4-30 wt.% fermentable sugar by hydrolyzing the lignin-removed biomass stream with an enzyme solution comprising cellulases and optionally xylanases at a pH of 3-7 at a temperature of 30-90 degrees C; (g) producing an alcohol stream containing at least one 2-18C alcohol by fermenting the hydrolyzate in the presence of a microorganism at a temperature of 25-55 degrees C at a pH of 4-6; and (h) recovering at least one of the alcohol from the alcohol stream.