Validation of Chlorine Efficacy to Disinfect Process Wash Water Simulating Industrial Conditions

Introduction: Disinfected water is necessary to avoid cross-contamination during washing in the fresh-cut industry. Chlorination is the most used method but excessive doses, particularly hyperchlorination, have several potential negative effects. Alternative disinfection methods have been tested but although they can be just as effective as chlorine, they are always more expensive. The main goal for the fresh-cut industry should be the management of the optimal use of chlorine, based on its antimicrobial efficacy.

Purpose: The purpose of this study was to validate the efficacy of chlorine to inactivate E. coli O157:H7 in process wash water simulating the conditions in the fresh-cut industry.

Methods: A cocktail of E. coli O157:H7 strains was used. To simulate an industrial process, a washing tank containing tap potable water was continuously filled with concentrated process wash water with high organic matter and inoculated with the E. coli cocktail (5 log CFU/ml) at a flow rate within the range 3.6 – 7.5 l/h. A peristaltic pump dosed a ca. 2 mg/l free chlorine solution to the washing tank during the whole duration of the test. Free chlorine concentration was adjusted to ca. 0.5 - 3 mg/l.

Results: Maintenance of a concentration of free chlorine of ca. 0.5 mg/l significantly reduced the accumulation of E. coli O157:H7 in process wash water by 2.5 logs compare to untreated process wash water. However, free chlorine concentrations of ca. 3 mg/l, were enough to completely inactivate E. coli in process wash water.

Significance: Results indicate that chlorine is an effective treatment to inactivate E. coli O157:H7 under industrial conditions using around 3 mg/l free chlorine, with no effect on COD removal and a very low generation of THM. Validation of the chlorine efficacy by using a dynamic system might facilitate the implementation of selected treatments in the fresh-cut industry.