NOVELTY - Co-production of biomass fiber for downstream processing and conversion and inorganic mineral fertilizer from source biomass is carried out by reducing average particle size of source biomass; mixing size reduced source biomass and a fluid to extract inorganic minerals from biomass to form a mixture; separating solid biomass fiber from the mixture to produce a liquid extract phase and a solid phase comprising biomass fiber; drying solid phase to obtain biomass fiber for downstream processing and conversion; and concentrating liquid extract phase to co-obtain inorganic mineral fertilizer.    USE - Method of co-production of biomass fiber for downstream processing and conversion and inorganic mineral fertilizer from source biomass (claimed).    ADVANTAGE - The method is capable of extracting inorganic nutrients from biomass and of co-producing a significantly improved biomass fiber and liquid inorganic fertilizer in a continuous and compact reactor that requires less than 40 minutes biomass residence time in the reactor. It has high extraction efficiency using only water as extraction solvent at room-temperature, thus reducing energy consumption. The method can remove greater than or equal to 95% of chlorine, greater than or equal to 90% of potassium, greater than or equal to 80% of phosphorus, greater than or equal to 70% of magnesium and sodium, and greater than or equal to 40% of nitrogen in the biomass. Further, the method allows for more than 80% of water used in the extraction process to be recycled within the process, thus reducing the demand for make-up water.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic diagram of a system for co-production of biomass fiber for downstream processing and conversion and inorganic mineral fertilizer from source biomass.    Screener (1)    Size reduction apparatus (2)    Feed hoppers (4A, 4B, 4C)    Nutrient extraction vessels (5A, 5B, 5C)    Primary liquid-solid separator (7)    Reverse osmosis system (12)