PROBLEM TO BE SOLVED: To keep a high org. matter decomposing capacity without need for the heating by an external heat source by composing the purifier of an acid fermentation tank and a methane fermentation tank and connecting the acid fermentation tank to an aerobic reaction tank through a pump connected to a feed pump.
SOLUTION: This purifier is composed of an aerobic reaction tank 100 and a two-phase fermentation tank 101 placed in the aerobic reaction tank 100. A photosynthetic bacteria carrier 102 immobilizing photosynthetic bacteria is disposed at the bottom of the aerobic reaction tank 100, and a blower 103 for sending air into the aerobic reaction tank is attached to the inner wall or outer wall of the aerobic reaction tank 100. The aerobic reaction tank 100 is produced by the use of an insulating material when used in a cold district. The org. matter in sewage is partially decomposed by the photosynthetic bacteria, and the lower fatty acids such as acetic acid are oxidized by the bacteria. As a result, the heating by an external heat source is not needed, and a methane-bacteria purifier maintaining a high org. matter decomposing capacity is obtained.