NOVELTY - Integrated system comprises: a pretreatment apparatus (18) for converting raw plant materials into sugars; a fermentor (19) including yeast for fermenting the sugars to produce a beer comprising ethanol; a distillation apparatus (20) for separating the beer into the ethanol and a whole stillage; a separator for separating the whole stillage into a thin stillage and wet distillers grains, where the thin stillage comprises non-fermentable solids and organic acids; and a biogas apparatus (200) for processing a first portion of the thin stillage to produce biogas and a biogas effluent.    USE - The integrated system is useful for producing ethanol and biogas from raw plant materials (claimed) e.g. sugars or sugar derived from starches or converted cellulosic material.    ADVANTAGE - The integrated system: provides increased ethanol production; eliminates the separate addition of ammonia; eliminates or reduces the need to dispose of waste water and other byproducts, where the by product must be disposed for free or at net cost; reduces the fresh water usage; eliminates or reduces use of waste streams; and eliminates syrup load-out.    DETAILED DESCRIPTION - Integrated system comprises: a pretreatment apparatus (18) for converting raw plant materials into sugars, where the pretreatment apparatus is supplied with fresh water and backset; a fermentor (19) including yeast for fermenting the sugars to produce a beer comprising ethanol; a distillation apparatus (20) for separating the beer into the ethanol and a whole stillage; a separator for separating the whole stillage into a thin stillage and wet distillers grains, where the thin stillage comprises non-fermentable solids and organic acids; and a biogas apparatus (200) for processing a first portion of the thin stillage to produce biogas and a biogas effluent, where the biogas apparatus converts a percentage of the non-fermentable solids and organic acids in the thin stillage into biogas and reduces the concentration of the non-fermentable solids and organic acids in the biogas effluent and the backset comprises the biogas effluent recycled from the biogas apparatus to the pretreatment apparatus. An INDEPENDENT CLAIM is also included for a biogas apparatus for processing at least one of thin stillage and syrup produced by an ethanol production system, for producing biogas and for returning biogas effluent to the ethanol production system as backset, where the thin stillage comprises non-fermentable solids and organic acids and the thin stillage and syrup are provided to the biogas apparatus in any ratio, comprising at least one anaerobic digester including microorganisms for converting non-fermentable solids and organic acids in the thin stillage into biogas, thus producing a biogas effluent having a reduced concentration of non-fermentable solids and organic acids, where at least some of the microorganisms are adapted for an ammonia environment and pH control of the digester is accomplished by adding ammonia to the thin stillage and nitrogen from the ammonia is recycled to the ethanol plant in the biogas effluent backset for use as a yeast nutrient.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic illustration of ethanol production system including a biogas apparatus for converting at least a portion of the thin stillage into biogas and a biogas effluent, where a portion of the backset is cleaned up and the syrup load-out is eliminated.    Ethanol production apparatus (10)    Pretreatment apparatus (18)    Fermentor (19)    Distillation apparatus (20)    Biogas apparatus (200)