NOVELTY - Producing (M1) methane by two-phase anaerobic digestion of solid organic material (I), comprises incubating first mixture (X1) comprising (I) and aqueous liquid under anaerobic conditions in a hydrolysis digester (HD), transferring a portion of aqueous liquid of X1 to methane phase digester to form second mixture (X2), incubating X2 for generating methane, and transferring portion of X2 to a (HD).    USE - The method is useful for producing methane by two-phase anaerobic digestion of solid organic material such as sewage sludge, forestry waste, food waste agricultural waste, municipal waste or their combinations. Preferably, methane is produced from agricultural waste comprising rice straw (claimed).    ADVANTAGE - The APS-digester has innovative design features that allow it to handle the solid organic substrates effectively. The hydrolysis reactor is operated in a batch or semi-batch mode to ease the handling of solid materials, and the biogasification reactor operated continuously to maintain active bacterial culture in the system and to produce biogas at a relatively constant level. The device used in the system is of simple design and is economical to construct and operate. The method is highly efficient in converting biomass to desired methane product gas.    DETAILED DESCRIPTION - Producing (M1) methane by two-phase anaerobic digestion of solid organic material (I), involves incubating first mixture (X1) comprising (I) and aqueous liquid under anaerobic conditions in a hydrolysis digester (HD), transferring a portion of aqueous liquid of X1 to methane phase digester to form second mixture (X2), incubating X2 for generating methane, and transferring portion of X2 to a (HD).    (M1) comprises:    (a) incubating for a first period of incubation, a first mixture comprising the solid organic material and an aqueous liquid, under anaerobic conditions, in a first hydrolysis digester having an upper portion and a lower portion and containing a hydrolysis unit in it;    (b) after the first period of incubation, transferring a portion of the aqueous liquid of the first mixture residing in the lower portion of the hydrolysis reactor to a methane phase digester to form a second mixture, the methane phase digester having an upper portion, a lower portion and a methanogenesis;    (c) incubating the second mixture for second incubation period during which methane is generated; and    (d) transferring a portion of the second mixture residing in the upper portion of the methane phase digester to the first hydrolysis phase digester for a third incubation period.    An INDEPENDENT CLAIM is also included for an anaerobic phased solids digester (APS-digester) system (II) for methane production, comprising first hydrolysis reactor containing a perforated support unit separating the reactor into an upper portion and a lower portion, the upper portion having a hydrolysis reactor liquid inlet and the lower portion having a hydrolysis reactor liquid outlet; a biogasification reactor having a biogasification reactor gas outlet, an agitating unit, an upper portion and a lower portion, the upper portion having a biogasification reactor liquid outlet and the lower portion having a biogasification liquid inlet; a first conduit connecting the hydrolysis reactor outlet to the biogasification inlet; and a second conduit connecting the biogasification reactor outlet with the hydrolysis reactor inlet.    DESCRIPTION OF DRAWING(S) - The figure shows the anaerobic solids digester system (APS-digester).