Feasibility of osmotic dilution for recycling spent dialysate: Process performance, scaling, and economic evaluation

Hemodialysis is one of the therapies for patients with kidney failure. Hemodialysis requires large amounts of pure water, and is one of the most water-hungry medical procedures, and thus represents a clear opportunity where improvements should be made concerning the consumption and wastage of water. In this paper, we explored the potential of forward osmosis (FO) membrane for recycling the spent dialysate using the dialysis concentrate as the draw solution. Partially diluted dialysis concentrate could be further diluted with pure water to form dialysate for further dialysis process. Using commercial cellulose triacetate (CTA) FO membranes, the water recovery of approximately 64% was achieved and the final volume of the partially diluted dialysis concentrate was about four times the initial volume. Flux decline of the FO process was observed, mainly due to concentration of synthetic spent dialysate and dilution of dialysis concentrate, while membrane scaling had little impact on the flux decline. The urea rejection was found to be relatively low owing to the small size and electroneutral nature of the urea molecule. Obvious membrane scaling was observed after three FO cycles. The energy dispersive spectroscopy analysis of the scaling layer indicated that the scalants were phosphates and carbonates. The scaling was removed via osmotic backwash and almost completely recovery of FO flux was obtained. Economic analysis showed that the centralized treatment of spent dialysate in a dialysis center using the proposed osmotic dilution process could greatly save water resources and cost. Improving the urea rejection of FO membrane was identified as an important research focus for future research on the potential application of FO technology for recycling the spent dialysate in hemodialysis.