Haemodialysis water production by double reverse osmosis

A filtration unit composed of two reverse osmosis membranes in series was evaluated for haemodialysis water production. For this purpose, hard and soft water were formulated based on European drinking water directives. The study showed that the double reverse osmosis process is efficient to produce haemodialysis water with the quality defined by the pharmacopeia requirements from synthetic soft water and hard water. In both cases, nitrate and sodium ions diffuse through the membrane limiting the water treatment. This phenomenon is correlated to the electrostatic interactions, the Donnan effect and the ion diffusivity, which govern the membrane selectivity.

Research Highlights
► Donnan effect and dielectric exclusion controlled the selectivity of the membranes.
► Nitrate transfer through the reverse osmosis membrane is higher than chloride transfer.
► Reverse osmosis membrane present lower selectivities with soft water than hard water.
► Double reverse osmosis is an efficient technique to reduce pre-treatment of water for production of haemodialysis water.