Dialysate regeneration via urea photodecomposition with TiO2 nanowires at therapeutic rates

Abstract

Background: The standard weekly treatment for end-stage renal disease patients is three 4-h-long hemodialysis sessions with each session c'onsuming over 120 L of clean dialysate, which prevents the development of portable or continuous ambulatory dialysis treatments. The regeneration of a small (~1 L) amount of dialysate would enable treatments that give conditions close to continuous hemostasis and improve patient quality of life through mobility.

Methods: Small-scale studies have shown that nanowires of TiO₂ are highly efficient at photodecomposing urea into CO₂ and N₂ when using an applied bias and an air permeable cathode. To enable the demonstration of a dialysate regeneration system at therapeutically useful rates, a scalable microwave hydrothermal synthesis of single crystal TiO₂ nanowires grown directly from conductive substrates was developed. These were incorporated into 1810 cm² flow channel arrays. The regenerated dialysate samples were treated with activated carbon (2 min at 0.2 g/mL).

Results: The photodecomposition system achieved the therapeutic target of 14.2 g urea removal in 24 h. TiO₂ electrode had a high urea removal photocurrent efficiency of 91%, with less than 1% of the decomposed urea generating NH₄ ⁺ (1.04 μg/h/cm² ), 3% generating NO₃ ^- and 0.5% generating chlorine species. Activated carbon treatment could reduce total chlorine concentration from 0.15 to <0.02 mg/L. The regenerated dialysate showed significant cytotoxicity which could be removed by treatment with activated carbon. Additionally, a forward osmosis membrane with sufficient urea flux can cut off the mass transfer of the by-products back into the dialysate.

Conclusion: Urea could be removed from spent dialysate at a therapeutic rate using a TiO₂ based photooxidation unit, which can enable portable dialysis systems.

Keywords: TiO2 nanowire; air-breathable electrode; dialysate regeneration; microwave hydrothermal synthesis; urea photodecomposition.