Effect of pH on the Efficacy of Sodium Hypochlorite Solution as Cleaning and Bactericidal Agents

Abstract

The efficacy of sodium hypochlorite (NaOCl) solution as a cleaning and bactericidal agent against Pseudomonas fluorescens was studied as a function of pH. Alumina (Al2O3) particles on which P. fluorescens cells were irreversibly adhered were cleaned with NaOCl solutions of pH 5 to 12 containing free available chlorine (AC) of 120 to 1000 mg/L. The efficiency of the removal of P. fluorescens cells from the Al2O3 surfaces increased with increasing pH and the AC concentration. It was found that the efficacy of NaOCl solution as a cleaning agent depended on the concentration of the dissociated hypochlorite ion (ClO-). On the other hand, the bactericidal activity of NaOCl solution of 2.5mg AC/L increased with decreasing pHs from 9.3 to 5.7. The logarithmic relative reductions of viable P. fluorescens were proportional to the product of the AC concentration and time, and the rate of inactivation depended on the concentration of undissociated hypochlorous acid (HOCl). Our results show that the cleaning and bactericidal activities of NaOCl solution are governed by the percentage of HOCl and ClO- existing in the solution.