A portable peritoneal dialysis system for a patient includes an inlet port for providing inflow to the patient's peritoneal cavity, an outlet port for providing outflow from the patient's peritoneal cavity, and a volume of dialysate for flow into and out of the patient's peritoneal cavity, thereby removing from the dialysate uremic waste metabolites that have diffused into the dialysate. The portable peritoneal dialysis system also includes a closed liquid flow loop, including a pump, for flowing the dialysate into and out of the patient's peritoneal cavity, and an organic- and phosphate-removing stage, including at least one replaceable cartridge in the closed liquid flow loop, the cartridge containing material for removing organic compounds and phosphate from dialysate removed from the patient's peritoneal cavity. The portable peritoneal dialysis system further includes a urea- and ammonia-removing stage, including at least one replaceable cartridge in the closed liquid flow loop, the cartridge containing material for removing urea and ammonia from dialysate removed from the patient's peritoneal cavity, the material being packed around semi-permeable hollow fibers with interior fiber walls that reject cations, thereby retaining cations in the dialysate.
