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Development of new membranes for the purification of hemodialysis water

Keywords: porous media, membranes, zeolite, dialysate, uremic toxin removal, adsorption, filtration
Fig. 1. Structure of Zeolite ZSM-5-3D (Author M. G. De Angelis)

Water is an essential resource to all forms of life, but its scarcity in large part of the world pose severe challenges. Membrane separation processes play a fundamental role in water treatment, starting from water desalination to wastewater purification and reuse. In this context, an analysis of water consumption of hemodialysis has been performed with the aim of reducing the total amount of water utilized and to recycle part of the dialysis wastewater.

Hemodialysis is a life-saving treatment for patients with chronical renal failure, which uses large volumes of water that are increasing with the number of patients being treated.

Hemodialysis is generally performed according to a strict schedule of 3 to 4 treatments per week. Every single treatment requires about 120 L of dialysis fluid which is made by 99% of high grade water. In addition, the production of 120 L of high grade water requires about 400- 500 L of mains water according to the efficiency of the reverse osmosis system used. After the treatment, the spent dialysate is generally sent to municipal sewage lines, even if some alternatives have been investigated and pursued.

Objective of this work is the development of a membrane process to remove uremic toxins from the spent dialysate. The purified water could then be reused to produce new dialysis fluid, for the same patient, in order to reduce substantially the amount of high pure water required for a single dialysis treatment. Different processes are under investigation, namely reverse osmosis, nanofiltration and functionalized adsorptive membranes.

Several zeolites are considered for the removal of urea, creatinine and other uremic toxins. Their adsorptive properties for the target molecules are investigated in detail in batch experiments. The best performing materials are incorporated in nanofiber membranes prepared by electrospinning in collaboration with prof Maria Letizia Focarete of the Ciamician Department.

The choice of the appropriate zeolites, zeolite concentration and their dispersion in the nanofibers are the first steps towards the development of suitable adsorptive membranes.

Several zeolites are under investigation, among those, is Zeolite ZSM-5-3D, shown in Figure 1, that has given promising results.

The membranes will be then characterized in filtration experiments to test their efficiency in the removal of urea and other uremic toxins in mock solutions, before experiments with real spent dialysate. Comparison with commercial membranes will be performed by using reverse osmosis, nanofiltration and membrane adsorbers.

Main publications

C. Boi, C. Castro, G.C. Sarti, Plasminogen purification from serum through affinity membranes, Journal of Membrane Science (2015) 475, 71-79.

M. Galizia, M.G. De Angelis, M. Messori, G.C. Sarti, Mass transport in hybrid PTMSP/Silica membranes, Industrial & Engineering Chemistry Research (2014) 53, 9243-9255.

M.G. De Angelis, G.C. Sarti, Gas sorption and permeation in mixed matrix membranes based on glassy polymers and silica nanoparticles, Current Opinion in Chemical Engineering (2012) 1, 148- 155.

S. Dimartino, C. Boi, G. C. Sarti, Influence of protein adsorption kinetics on breakthrough broadening in membrane affinity chromatography, Journal of Chromatography A, 1218 (2011) 3966-3972.

S. Dimartino, C. Boi, G.C. Sarti, A novel model for the simulation of protein purification through affinity membrane chromatography, Journal of Chromatography A, 1218 (2011) 1677-1690.

C. Boi, S. Bandini, G.C. Sarti, Pollutants removal from wastewaters through membrane distillation, Desalination 183 (1-3), (2005), 383-394.