Electrochemical Impedance Spectroscopy as a tool for materials selection: Water for haemodialysis

Abstract

The water used in haemodialysis must meet very stringent purity criteria to avoid infections. Mineral salts are removed through inverse osmosis and/or ion exchange membranes down to produce very low conductivity values (<1 μ S cm −1 typically), and organic contaminants are removed through adsorption by activated carbon filters. The insidious development of biofilms at stagnant areas such as pipe joints and wall roughness requires periodic disinfection of pumps and piping circuitry. Because disinfectants are highly oxidant chemicals, they tend to induce localised corrosion in the metallic parts of the system, which in turn creates new potential sites for biofilm development. Thus, the optimal combination of disinfectant and material that is acceptable, limiting biofilm development, must be determined. The following two stainless steels were studied: medical grade austenitic AISI 316L, commonly used, and a duplex austenitic–ferritic SAF 2205, which is a possible replacement material. The following two disinfectants were also employed: sodium hypochlorite and peracetic acid. Both disinfectants were used at dosages in the range typically used in the medical industry. The results show that the SAF 2205 and peracetic acid are the best combination of material and disinfectant because they produce the fastest repassivation kinetics and the smoothest surfaces during the disinfection treatment of all combinations studied. The results are interpreted in terms of morphology and kinetics of development of the passive film.