Method of regenerating organic solvent, organic solvent regenerator, and substrate processing system

An organic solvent regenerator, comprising:

• a collection tank storing a mixed liquid of an organic solvent and water, the organic solvent and the water being discharged from a substrate processing apparatus that processes a substrate;
• a circulator including a circulation pipe connected to the collection tank, and a membrane separator disposed in the circulation pipe, the membrane separator including a first path which is inserted into the circulation pipe and through which the mixed liquid passes, a second path, and a separation membrane which partitions the first path and the second path and which allows the water in the mixed liquid to pass from the first path to the second path;
• a separation pipe connected to the second path of the membrane separator;
• a decompression pump that reduces a pressure in the second path through the separation pipe;
• and
• a controller that performs a separation operation of controlling the decompression pump with a control set value based on a target concentration on a solvent concentration of the mixed liquid, and causing the circulator to circulate the mixed liquid.