NOVELTY - Producing a gas e.g. methane and hydrogen using two-phase anaerobic digestion of solid organic material, involves incubating a first hydrolysis mixture in a first hydrolysis phase vessel for first period of incubation; transferring a portion of the mixture to a buffer tank; transferring a portion of buffer tank mixture to a gasification reactor containing a methanogenic bacterial culture; incubating biogasification mixture during which methane and hydrogen is generated; and transferring a portion of biogasification mixture into first hydrolysis phase vessel for third incubation period.    USE - For producing a gases e.g. methane, hydrogen and carbon dioxide from organic solid waste, such as sewage sludge, forestry waste, food waste, agricultural waste, green waste, municipal waste (claimed); useful as clean fuel for heat and power generation or transportation.    ADVANTAGE - The anaerobic phase solids (APS) digester converts organic waste into hydrogen, methane and carbon dioxide gases which can be utilized as a clean fuel for heat and power generation or transportation. The system is attractive commercially because it allows higher energy conversion efficiencies and less air emissions from engines if hydrogen, methane and carbon dioxide gases are used together as fuel. The system uses a buffer tank which equilibrates physical and chemical properties of the VFA's (i.e., pH, temperature, conductivity, nutrients, biochemical oxygen demand, etc.) collected from different hydrolysis reactors, and which controls the VFA loading rate into the biogasification reactor. This equilibration process provides higher and more stable gas yields because bacteria in the biogasification reactor react more efficiently on equilibrated VFA's. Fourth, the outlet of the hydrolysis reactor is located on the side of the hydrolysis reactor. Maximum use of the hydrolysis reactor volume leads to the highest conversion efficiency of organic substrates, resulting in maximum gas production and lower capital cost. Fifth, hydrogen gas is also produced in the hydrolysis reactor and the buffer tank. The batch degradation processes used in the APS digester system in the hydrolysis tank allows the production of hydrogen gas to be stable with a high rate. When hydrogen is coupled to other gases (i.e. methane), the APS digester system becomes a more efficient system.    DETAILED DESCRIPTION - Producing a gas e.g. methane and hydrogen using two-phase anaerobic digestion of solid organic material, involves incubating a first hydrolysis mixture in a first hydrolysis phase vessel for a first period of incubation, under anaerobic conditions, the first hydrolysis phase vessel contains a hydrolytic bacterial culture for which the solid organic material is a substrate; transferring a portion of the aqueous liquid of the first mixture residing in the first hydrolysis phase vessel to a buffer tank, forming a buffer tank mixture; transferring a portion of the buffer tank mixture to a gasification reactor containing a methanogenic bacterial culture for which the volatile fatty acid is a substrate, forming a biogasification mixture; incubating the biogasification mixture for a second incubation period during which methane and/or hydrogen is generated; and transferring a portion of the biogasification mixture into the first hydrolysis phase vessel for a third incubation period.    An INDEPENDENT CLAIM is included for an anaerobic phased solids (APS) digester system for production of gas from solid organic material, comprising a first hydrolysis phase vessel containing a bacterial culture for which the solid organic material is a substrate, where the hydrolysis vessel comprises a vessel fluid inlet port communicating fluidically with a first conduit, and a vessel fluid outlet port located on a vertical surface of the hydrolysis phase vessel; a buffer tank having a buffer tank outlet port communicating fluidically with a third conduit, and a buffer tank inlet port communicating fluidically with the second conduit; and a biogasification reactor containing a methanogenic bacterial culture and having a reactor fluid inlet port communicating fluidically with the third conduit; and a reactor fluid outlet port communicating fluidically with the first conduit.    DESCRIPTION OF DRAWING(S) - The figure shows a diagram illustrating process of the APS-digester system for wastewater digestion.