PURPOSE: To uniformly disperse sludge at the time of charging of the sludge and to accelerate the digestion thereof by providing a baffle plate in the lower part of a charging pipe and bringing the charged sludge into collision against this plate.

CONSTITUTION: The sludge collides against the baffle plate 6 provided below the charging pipe 2 when the sludge is charged through the pipe. The sludge is then dispersed uniformly in the four directions of the baffle plate 6 by the impact force of the collision, by which the sludge is successively dispersed into the stirring liquid in the digester tank 1. The charged sludge is forcibly separated and dispersed by the baffle plate 6 in such a manner and, therefore, the sludge lumps are not formed even if there is a temp. difference between the sludge temp. and the liquid temp. in the digester tank 1. The direct short circuiting of the undigested sludge to a sludge withdrawing pipe 4 does not, therefore, arise and since the charged sludge is completely digested, about 35% VTS is attained.