Determination of Adequate pH of Electrolyzed Acidic Water for Disinfection, Under Consideration of Sub-Effective Corrosion Against Metals

Electrolyzed acidic water (EAW) is one of the most commonly used disinfectants. EAW has sufficient bactericidal efficacy; however, it corrodes instruments in clinical settings. The component that significantly contribute to the bactericidal efficacy of EAW is hypochlorous acid (HClO). According to the equilibrium of free residual chlorine (FRC), the ratio of HClO in solution is maximum at approximately pH 5–6. Considering the balance between bactericidal efficacy and corrosion, a higher pH of EAW should provide optimal bactericidal efficacy. In this study, we examined the bactericidal efficacy of EAW at pHs 2.2, 3.5, and 5.0. As a result, EAW at pH 2.2 showed the highest bactericidal efficacy. The reason for the enhanced bactericidality of EAW at pH 2.2 was considered to be the synergistic effect of both FRC and acidity. However, because the corrosive effects of EAW at pHs 2.2, 3.5, and 5.0 were almost the same, it was not confirmed that higher pHs could prevent metal corrosion. This study revealed that the optimum pH of EAW as a disinfectant should be predominantly considered in relation to the bactericidal potential of EAW.