NOVELTY - A digester apparatus for converting wet carbonaceous biomass materials to biogas comprising gaseous organic fuel, has a programmable computer provided with a database comprising previously acquired data relating biomass-biogas conversion for biomass materials of varying compositions to values for respective first and second pressures and time durations of first and second phases.    USE - Converting wet carbonaceous biomass materials to biogas comprising gaseous organic fuel.    ADVANTAGE - The process improves both the speed of digestion and completeness of conversion, which greatly improves the process economic feasibility. The capital and operating costs are reduced by a decrease in hydraulic retention time, a decrease in system reactor volume, and complete conversion of the feed. The combination of great improvements in speed and conversion completeness enables a much smaller system tankage and much improved capital economics and process feasibility. The invention converts wet organic biomass materials, e.g. sewage sludge, to useful energy by optimizing the process through computer control. It utilizes the programmable computer that controls the cyclic digestion process, monitors the process for conditions leading to reduced performance, and takes corrective action to maintain optimum operation. It improves the second stage hydrolysis and digestion in the influent material fed to the system. It improves gas adsorption and penetration, and optimizes the second reactor hydrolysis rate. It prevents the buildup of inorganic materials and maintains system digestion capacity during active continuous digestion. It enables the generation of distributive heat and power at industries, wastewater treatment plants and farms.    DETAILED DESCRIPTION - A digester apparatus for converting wet carbonaceous biomass materials to biogas comprising gaseous organic fuel comprises:    (i) a digestion unit operating at a controlled temperature and having a concentrator component and a pressure swing component each containing anaerobic bacteria;    (ii) a first conveying mechanism for conveying slurried aqueous biomass from a biomass source to the concentrator component;    (iii) a first removing mechanism for removing the biogas from the concentrator component;    (iv) a second conveying mechanism for conveying concentrated aqueous biomass from the concentrator component to the pressure swing component;    (v) a third conveying mechanism for conveying digested aqueous biomass from the pressure swing component to the concentrator component, thus forming a closed loop between the concentrator and pressure swing components;    (vi) a second removing mechanism for removing waste solids from the pressure swing component; and    (vii) a pressure swing pump for controlling the pressure within the pressure swing component in a cycle comprising a first phase having a first time duration at a sub-atmospheric first pressure and a second phase having a second time duration and a second pressure at/or above atmospheric pressure.    The apparatus includes a programmable computer provided with a database comprising previously acquired data relating biomass-biogas conversion for biomass materials of varying compositions to values for the respective first and second pressures and time durations of the first and second phases. The computer operates to continuously monitor the pressure of biogas in the pressure swing component and to adjust the first and second phases in the cycle of the pressure swing pump to optimize biogas conversion of biomass from the biomass source.    An INDEPENDENT CLAIM is also included for a system for converting wet carbonaceous biomass materials to biogas comprising gaseous organic fuel, comprising a gas storage and cleanup unit (112); a combustion engine-generator set (114); an exhaust gas heat exchanger (116); and the digester apparatus.    DESCRIPTION OF DRAWING(S) - The figure is a schematic illustration of a two-stage system for carrying out a biomass-to-energy-process.    Pumps (20, 32, 34, 54)    Valve (58)    Gas storage and cleanup unit (112)    Combustion engine-generator set (114)    Exhaust gas heat exchanger (116)