Which of the following statements about dialysis is incorrect?

Dialysis is used to provide an artificial replacement for lost kidney function in people with renal failure. Dialysis works on the principles of the diffusion of solutes and ultrafiltration of fluid across a semi-permeable membrane. This replicates the filtering process that takes place in the kidneys. The two main types of dialysis are Haemo-dialysis and Peritoneal dialysis. In haemo-dialysis, wastes and water are removed from the blood outside the body through an external filter called dialyzer that contains a semi-permeable membrane. Blood is drained from a convenient artery and an anti-coagulant like heparin is added to prevent clotting of blood. It is then pumped into a dialyzer containing dialyzing fluid and coiled cellophane membrane. The dialyzing fluid has the same composition as that of plasma except nitrogenous wastes. The porous cellophane membrane allows the passage of molecules along the concentration gradient. As the nitrogenous wastes are absent in the dialyzing fluid, these substances freely move out from the blood (along the concentration gradient). The cleared blood is pumped back to the body through a vein after adding anti-heparin to it. In peritoneal dialysis, wastes and water are removed from the blood inside the body using peritoneal membrane of the abdominal cavity as a natural semi-permeable membrane.