NOVELTY - The system comprises a culture tub to culture the microalgae using a discharged water containing carbon dioxide, a carbon dioxide dissolver to dissolve carbon dioxide in the discharged water, and a diffuser for spraying the carbon dioxide supplied from a supply tube. The supply tube is provided in an upper portion of the dissolver, and is installed at a lower part of a sealed dissolver main body. An outlet part discharges the water from the culture tub. The dissolver main body is connected with a discharged water influx unit. The system further comprises a high pressure jet apparatus.    USE - The system is useful for culturing microalgae (claimed).    ADVANTAGE - The system economically cultures the microalgae with less energy consumption and high efficiency, and effectively removes nitrogen and phosphorus contents in the discharged water.    DETAILED DESCRIPTION - The system comprises a culture tub to culture the microalgae using a discharged water containing carbon dioxide, a carbon dioxide dissolver to dissolve carbon dioxide in the discharged water, and a diffuser for spraying the carbon dioxide supplied from a supply tube. The supply tube is provided in an upper portion of the dissolver, and is installed at a lower part of a sealed dissolver main body. An outlet part discharges the water from the culture tub. The dissolver main body is connected with a discharged water influx unit. The system further comprises a high pressure jet apparatus for jetting the discharged water to the dissolver main body through the inlet tube. An electric gate and an efflux pump are installed with a valve of the outlet part. The supply tube is connected to a carbon dioxide source. An aeration basin is equipped in a sewage disposal plant and/or an anaerobic digester. A light is supplied to the culture tub through the sunlight and a LED lamp. The culture tub is a large size culture tub, and has semicircle space or square space. An internal space is formed in the culture tub along same longitudinal direction. The discharged water is directly placed into the culture tub. An INDEPENDENT CLAIM is included for a method for culturing microalgae.