Abstract: A system and method to treat biomass to make bioproducts such as biofuels and biochemical is disclosed. The systems are configured to treat a liquid component separated from biomass to yield sugars available to form a fermentation product or bio-product. The system and method comprises treatment and separation of process streams (e.g. liquids, solids, etc.) to produce bioproducts such as fuel and biochemical as well as to recover/reuse and utilize content of process streams. Lignin is separated from the bioproduct stream (e.g. a solids component) forming a recovered bioproducts; efficient removal of lignin facilitates productive operation of the system. The system disclosed is configured to recover and recycle acid (e.g. phosphoric acid) used as a concentrated acid in the process to pre-treat biomass (for bioprocessing). The acid used in the process is recycled and recovered in order to establish economically attractive biorefinery to make bio-products from biomass (e.g.