Provided are a system and a method of treating wastewater. The system includes a wastewater chamber, positive and negative electrode chambers, acid and basic solution chambers and a buffer chamber. The wastewater chamber receives wastewater containing a first ion. The positive and the negative electrode chambers are respectively on opposite sides of the wastewater chamber. The acid chamber is between the wastewater chamber and the positive electrode chamber. The basic chamber is between the wastewater chamber and the negative electrode chamber. The buffer chamber is between one of the acid and the basic chambers and the wastewater chamber, and receives the buffer solution containing the first ion. The interfaces between the wastewater chamber and the buffer chamber and between the one of the acid and the basic chambers and the buffer chamber are ion exchange membranes having the same electrical properties.