Effect of pH on Bactericidal Efficacy of Chlorine Dioxide against Escherichia coli

Chlorine dioxide (ClO2) is one of the most effective disinfectants against bacteria, spores, viruses, fungi, and protozoa. However, the jury is still out on the role of pH in its bactericidal performance. This research tested the effect of pH 3–11 on the antibacterial properties of chlorine dioxide against Escherichia coli as the main sanitary indicator in dairy production. The experiment involved solutions with various levels of bacterial contamination with a viable cell count of 105 CFU/cm3. The pH of the medium and the concentration of chlorine dioxide exerted a complex effect on E. coli. The 99.99% disinfection performance occurred at lower pH values. The minimal concentration of chlorine dioxide in this research was 1.7 mg/dm3 (0.05%). It was efficient against E. coli only at pH 3 while 2.5 mg/dm3 (0.075%) was efficient at pH 3–5. A concentration of 3.3 mg/dm3 (0.1%) provided complete inactivation of E. coli in solutions with pH ≤ 8. Chlorine dioxide at a concentration of 6.6 mg/dm3 (0.2%) killed the test culture at pH 3–10. The effective concentration across the total pH range was 8.3 mg/dm3 (0.25%).