Design analysis for an ultrafilter adsorber artificial kidney

Abstract

An adsorber-ultrafilter system can serve as an alternative to the conventional artificial-kidney dialysis system. To this end, the characteristics of the parametric design analysis of the absorber-ultrafilter artificial kidney and its interaction with a uraemic patient is provided. The activated-carbon adsorber is modelled as a 2-phase homogeneous system, accounting for fluid-particle and intraparticle mass-transfer resistances and the axial dispersion of solute in the interstitial fluid phase of the adsorber bed. It is assumed that the ultrafilter is highly permeable to uraemic substances, and that the ultrafiltration rate is 15–25% of the inlet blood flow rate. The detailed design analysis of the ultrafilter has been provided in an earlier paper. The uraemic patient is modelled, for solute transfer, as comprising three major compartments. The results indicate that a single activated-carbon adsorber unit, with a hold-up volume of 50 ml, is adequate for the removal of uric acid and creatinine in a 6 to 8 h treatment period. However, the poor adsorption capacity of activated carbon for urea, necessitates that the adsorber unit be switched to a freshly activated unit in a very short period of time (11 min in this example). Hence, the need for the development of a better adsorbent for urea is emphasised. A parametric design analysis of the adsorber is also presented, so as to provide the basis for arriving at an optimum size of the adsorber unit.