TECHNOLOGY FOCUS - BIOLOGY - Preferred Enzymes: The cellulases are produced by Aspergillus, Humicola, Trichoderma, Bacillus and/or Thermohifida.    TECHNOLOGY FOCUS - INSTRUMENTATION AND TESTING - Preferred Components: The feedstock supply line, comprises a pre-treated feedstock. The solids-liquid separator is a settling tank, a clarifier zone or a filter (all preferred), a clarifier or a centrifuge.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Process: The aqueous slurry is introduced at the bottom of the hydrolysis reactor with a uniform radial distribution and one or more than one flocculating compound is added to the aqueous slurry, separately from and/or together with the cellulase enzymes. The flocculating compound is added before and/or during the introduction of the aqueous slurry into the hydrolysis reactor. The pre-treated cellulosic feedstock is obtained from wheat straw, oat straw, barley straw, com stover, soybean stover, canola straw, sugar cane bagasse, switch grass, reed canary grass, cord grass, oat hulls, sugar beet pulp or miscanthus. The pre-treated cellulosic feedstock is subjected to pre-treatment at 160-280degreesC, for 3 seconds to 30 minutes at a sulfuric acid concentration from 0-5% prior to enzymatic hydrolysis. The cellulase is added at a dosage of 1-40 FPU/g of cellulose and the flocculating compound is added at a dosage of 0.1-4.0 kg/tonne of solids.Prior to the step of removing, at least a portion of the hydrolysis product is separated from the unhydrolyzed solids by using a clarifier zone at the top of the hydrolysis reactor. In the step of removing, the aqueous stream comprising the hydrolysis product and unhydrolyzed solids is transferred to a solids-liquid separator to separate at least a portion of the hydrolysis product from the unhydrolyzed solids. The hydrolysis product and the unhydrolyzed solids are removed from the clarifier zone at separate locations. In the step of providing aqueous slurry, the pH of the slurry is 4-6, preferably 4.5-5.5, and the temperature is 45-70 (preferably 45-65)degreesC, and the slurry comprises 5-20 wt.% of undissolved solids, and the undissolved solids comprise 25-70 wt.% of cellulose.The cellulase and the flocculating compound are added to the slurry together or separately. A liquid stream comprising sugar is separated from the pre-treated cellulosic feedstock of prior to the step of introducing the aqueous slurry. A washing step is used during separation of the liquid stream from the feedstock, where the wash medium is water, a recycled process stream and/or treated effluent. The average slurry flow velocity is 0.1-12 (preferably 0.1-4) feet/hour.Preferred Components: The hydrolysis product comprises glucose and/or cellobiose. The flocculating compound is a cationic polymer (a polyacrylamide) (preferred), a non-ionic polymer, an anionic polymer, an amphoteric polymer, salts and/or alum. EXAMPLE - Pre-treated wheat straw (having an aqueous slurry of 7.8% undissolved solids, at a temperature of 70degreesC, and a mass flow rate of 553 t/hr) was cooled to 60degreesC in a heat exchanger, against the product stream. The slurry at 60degreesC was then cooled to a final temperature of 50degreesC by cold water at heat exchanger. The slurry was pumped into the hydrolysis make-up tank along with cellulase enzymes (5 FPU/g cellulose) and ammonia (1200 g/tonne of wet slurry), to adjust the pH to 4.5-5. The contents were mixed for 40 minutes and then the combined stream was pumped out of the make-up tank and down a pipe through the middle of the hydrolysis tank. The hydrolysis tank was jacketed with 15 psig steam used to maintain a temperature of 50degreesC. At the bottom of the hydrolysis tank, the slurry was pumped upward and dispersed across the width of the hydrolysis tank. The liquid flowed upward in the hydrolysis tank faster than the solids, which settle to a concentration of 10% throughout the tank. The cellulose was held up in the tank for 188 hours, which was long enough to convert 92% of the cellulose to glucose. The aqueous sugar stream and the unhydrolyzed solids flowed out of the top of the tank and were pumped to the settling tank.    In the settling tank, which had a volume of 1.12 million gallons, the solids settle to the bottom to a concentration of 10% and were pumped out via line to a lignin filter press to recover sugar from the solids by pressing and washing. The sugar from this stream was combined with the sugar stream from the top of the settler, which was then sent for fermentation to ethanol.