NOVELTY - The digester (1) made of material selected from the group comprising polypropylene fiber reinforced plastic (PPFRP), high density polyethylene (HDPE) or reinforced cement concrete (RCC), has lower and upper reaction chambers (11,12) and a circular feed tank (3) connected to the lower chamber. A feed preparation system (2) is connected to the tank. An automatic control valve (7) is attached to the upper and lower chambers. A circular discharge tank (10) has a discharge valve and a lid at the bottom of the said valve, to collect the digested slurry.    USE - Self-mixing anaerobic digester for use in low technology rural areas and sophisticated industrial areas for treating solid organic waste such as municipal waste, industrial waste, agricultural waste and domestic waste.    ADVANTAGE - The digester is simple and inexpensive, and can efficiently treat organic waste of higher solids contents at a shorter residence time. The solid loading rate is increased from 2.5 to 6.7 kgTS/m3 day. The volatile solids (VS) destruction rate is increased from 40-50%. The digester handles a wide range of waste volumes, from small volumes such as small communities, coastal communities, small industries, seafood process, etc., to high volumes such as large industries and municipal wastes. The digester enables intermittent mixing of digester slurry, by using the biogas pressure. Avoids scum formation. Increases the biogas production and methane content in biogas. Eliminates short-circuit of feed in the digester. The energy-efficiency is increased, as gravity feeding instead of pumping and neither internal moving parts nor heating coils are required. The choking and clogging are eliminated completely.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is also included for anaerobic digestion method.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of the self-mixing anaerobic digester.    Self-mixing anaerobic digester (1)    Feed preparation system (2)    Circular feed tank (3)    Inlet pipe (4)    Automatic control valve (7)    Circular discharge tank (10)    Lower chamber (11)    Upper chamber (12)