The present invention relates to an anaerobic reactor (10) for the treatment of industrial and other wastewaters at psychrophilic temperatures, the reactor comprising a mixing chamber (12) in which is located, during use, a granular sludge fluidized bed, the reactor further comprising a biofilm chamber (16) fed from the mixing chamber and housing a biofilm colonized pumice-based carrier material, and a separation chamber (18) in fluid communication with the biofilm chamber and in which treated effluent and biogas produced within the reactor are separated.

Provided is a method for treating wastewater, the method being capable, even during low water temperature periods, of efficiently purifying organic wastewater that experiences large temperature differences in a year. A method for treating organic wastewater uses a device including a predetermined reaction tank containing activated sludge and a culture tank and includes the steps of: culturing, in the culture tank, a microorganism contained in the activated sludge, while maintaining a temperature of a content of the culture tank at a temperature that is at least 5? C. lower than a water temperature of the organic wastewater at a start of culturing of the microorganism and not lower than ?1? C. and not higher than 10? C.; and then introducing the microorganism into the reaction tank.

The present invention relates to an anaerobic reactor for the treatment of industrial and other wastewaters at psychrophilic temperatures, the reactor comprising a mixing chamber in which is located, during use, a granular sludge fluidised bed, the reactor further comprising a biofilm chamber fed from the mixing chamber and housing a biofilm colonised pumice-based carrier material, and a separation chamber in fluid communication with the biofilm chamber and in which treated effluent and biogas produced within the reactor are separated.