NOVELTY - A square optional internal circulation anaerobic treatment device comprises a first reaction region (6), a lower three-phase separator (7), a second reaction region and an upper three-phase separator (9), which are sequentially connected from top to bottom. A water distribution device (5) is arranged at a bottom part of the first reaction region, and communicated with a water inlet pipe (1). A water outlet device is arranged at a top part of the upper three-phase separator. A water-gas separation pot is arranged on the upper three-phase separator.    USE - Square optional internal circulation anaerobic treatment device.    ADVANTAGE - The device is simple in internal structure, excellent in structure stability, less in hydraulic loss, and small in lift.    DETAILED DESCRIPTION - A square optional internal circulation anaerobic treatment device comprises a first reaction region (6), a lower three-phase separator (7), a second reaction region and an upper three-phase separator (9), which are sequentially connected from top to bottom. A water distribution device (5) is arranged at a bottom part of the first reaction region, and communicated with a water inlet pipe (1). A water outlet device is arranged at a top part of the upper three-phase separator. A water-gas separation pot is arranged on the upper three-phase separator. An exhaust pipe is arranged at the top part of the water-gas separation pot. The bottom part of the water-gas separation pot is communicated with a dredge pipe at the bottom part of the first reaction region. An upper part of the water-gas separation pot is communicated with the lower three-phase separator by an ascending pipe. A biogas pipe communicated with the upper three-phase separator is arranged on the water-gas separation pot above the ascending pipe.    DESCRIPTION OF DRAWING(S) - The drawing is a schematic view of square optional internal circulation anaerobic treatment device.    Water inlet pipe (1)    Water distribution device (5)    First reaction region (6)    Lower three-phase separator (7)    Second reaction area (8)    Upper three-phase separator (9)