JPS6260957B

PURPOSE:To enhance production efficiency of gaseous methane by moving the treating liquid level in a lower tank vertically at every production and removal of the gas thereby allowing the floating scum on the liquid surface to contact with the treating liquid. CONSTITUTION:The inside of a fermentation tank 1 is partitioned to an upper tank 3 and a lower tank 4 by a partition plate 2, and this lower tank 4 is partitioned by partition walls 6a, 6b provided with flow transfer ports 5a, 5b, whereby subchambers 7a-7c are formed. The top end of a pipe 8 for feeding fermentation materials is disposed above the tank 1, and the bottom face is located to face the chamber 7a. The top end of a flow transfer pipe 10 is disposed above the tank 1, and the flow transfer port 10a is located to face the chamber 7c. The flow transfer port 10b projecting to the lower part of the upper tank 3 is formed in the mid-part of said chamber and a pipe 11 for removal of gas is located so that its bottom end at the partition plate 2 faces the upper part of the chamber 7c. Then, at every production and removal of the gas, the level of the treating liquid 13 in the tank 4 moves vertically, and on account of the agitating effect thereof, the contact between floating scum and the liquid 13 is accelerated. Particulrly when the entire gas in the tank 4 is removed, the scum is completely sunk in the liquid by the plate 2.