Systems and methods for producing carbohydrate (e.g., sugar) streams (and recycling enzymes) from a pretreated or untreated biomass such as cellulosic feedstock, including, for example, “brown stock” feedstock, or waste or recycled fiber sludge produced in the pulp and paper industry, such as for biochemical (e.g., biofuel) production, are provided. In one example, the system and method can produce high purity C6 (glucose and/or fructose) and/or C5 (xylose) sugar streams, and other carbohydrates and/or fibrous materials, from cellulosic feedstocks, such as brown stock or waste fiber sludge, that can be effectively converted into various biochemical products, such as ethanol.