Distinguish between dialysis and ultrafiltration

The dialysis is a separation process that depends on the differential transport of solutes of different sizes across a porous barrier separating two liquids when the driving force is a concentration gradient only. It is usually used to separate solutes too large to diffuse through the barrier from those small enough to diffuse freely through it. The ultrafiltration, sometimes called reverse osmosis, is a more complicated process in that the solvent and solutes up to a certain critical size are forced through the barrier by considerably higher pressure on one side of the porous barrier than on the other. Thus, there is always a flow of solvent moving through the barrier in the same direction as the smaller solutes that are able to pass through the membrane. This sets it apart from dialysis where, owing to osmosis, there is usually a certain net movement of solvent in the direction opposite to the movement of solute.

Dialysis is a clinical application that helps patients to clean their blood artificially while the ultrafiltration is a process that occurs naturally during the urine formation in our kidneys. Furthermore, in dialysis, solutes move from high concentration to low concentration along the electrochemical gradient. But in ultrafiltration, the substances travel due to a pressure gradient. Hence, this is another difference between dialysis and ultrafiltration. Moreover, dialysis occurs in a dialyzer or the membrane lining of our abdomen while ultrafiltration takes place between the glomerulus and the Bowman’s capsule of the nephron.

Furthermore, the rate of ultrafiltration depends on the porosity of the membrane and the speed of blood flow (or the pressure created by the blood flow) while the dialysis rate depends on the dialysate flow rate. Thus, this is also a difference between dialysis and ultrafiltration.