disclosed is an apparatus and method for anaerobic wastewater treatment , which combines membrane distillation and biological treatment to improve treated water quality , performs anaerobic treatment to the wastewater to generate bio - gas and effectively restrain contamination of a membrane surface . the apparatus comprises a bio - reactor , submerged membrane modules , rotary disks and fluidizable media , wherein the bio - reactor is configured to give a space for filtration and biological treatment of wastewater and operated under an anaerobic condition , wherein the modules are provided in the bio - reactor to filter the wastewater , and wherein the rotary disks are provided at both sides of the module to induce turbulence of the wastewater and moving of the fluidizable media , wherein a channel is provided in the modules so that a cooling water flows therein , moisture of the wastewater is evaporated due to a temperature difference of the wastewater and the cooling water , moved to the channel .