Abstract: In a purification method for purifying contaminated water, the contaminated water contained in a purification tank is filtered by a membrane module disposed in the purification tank. An adsorption agent with powdered activated carbon is added to the purification tank at a raw side of the membrane module. The membrane module is aerated by inflow of air from below. The steps of filtering, adding, and aerating are carried out in parallel and/or sequentially. The purification method is used as a stage of a purification process of a wastewater treatment plant prior to introducing the water purified by the purification method into a river, lake or the ocean.