Assessment of the Efficacy of Intermittent Ozone Disinfection |
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Authors: | Chang Hoon Ahn Bruce E Rittmann |
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Affiliation: | 1. College of Engineering , Seoul National University , Seoul, Korea;2. Center for Environmental Biotechnology, Biodesign Institute, Arizona State University , Tempe, Arizona, USA |
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Abstract: | An example of intermittent disinfection occurs in dental-unit water systems (DUWS), which are disinfected only for a specified time per each day. The efficacy of intermittent ozonation was evaluated using a laboratory-scale, membrane-based ozone disinfection system (MBODS), which delivers bubbleless dissolved ozone to the DUWS. A new tool - the weighted Ct value, or Cw, - was applied to interpret heterotrophic plate counts (HPC) data. To achieve the American Dental Association's (ADA's) criterion (<200 CFU/mL), the required ozone dosage was Cw > 0.07 mg–O3/L. However, even the highest ozone dosage (Cw > 0.130 mg/L) allowed biofilm HPC to persist at over 104 CFU/cm2. Although a higher Cw killed planktonic and biofilm bacteria more thoroughly, it also generated more biodegradable dissolved organic carbon (BDOC). Thus, this research illustrates the inherent trade-off of intermittent ozonation: a higher Cw kills more bacteria during the ozonation period, but creates more BDOC that fosters biofilm regrowth when ozonation is off. |
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Keywords: | Ozone Biofilm Regrowth Dental Unit Water Systems Intermittent Disinfection Weighted Ct |
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