Abstract: A method and a system for regenerating a body fluid, such as a peritoneal dialysis fluid. The body fluid is removed into an extracorporeal circuit comprising an electrofilter for removing charged ions from the body fluid, a nanofilter for removing large molecules, such as Dextran 40, and a reverse osmosis filter for concentrating the body fluid, for producing a synthetic urine to be discarded. The removed ions and large molecules are returned to the patient together with pure water from the reverse osmosis filter through an ultrafilter.

Abstract: A system comprising a blood circuit including a membrane arranged in a blood filter (7) in which blood is in contact with a first side of said membrane; and a dialysis circuit in which a dialysis fluid is in contact with the other side of the membrane for exchange of substances and ions through the membrane as well as water. The dialysis fluid is circulated from a dialysis compartment and through a RO filter (9). The permeate fluid, i.e. water is returned to the dialysis compartment. The retentate fluid from the RO filter (9) passes through a separation filter (13). The retentate fluid is returned to the dialysis compartment and the permeate fluid is removed from the dialysis circuit as a waste fluid to a receptacle (19). The retentate fluid is concentrated in the RO filter in a ration of at least 3:1.