Free chlorine remains the most widely used disinfectant in drinking water practice worldwide. However, it has only moderate to marginal effectiveness as a disinfectant of such important pathogenic organisms as Cryptosporidium parvum, Mycobacterium avium, and Giardia lamblia. Recent findings by our group suggest that inactivation of chlorine-recalcitrant microorganisms may be markedly enhanced by utilizing sunlight to photolyze free chlorine to the highly-reactive hydroxyl radical (HO�) during conventional chlorination. For example, our results indicate that a >3-fold increase in inactivation rate of chlorine-recalcitrant B. subtilis spores can be achieved at pH 8 and 25� C in solutions dosed with 3-7 mg/L as Cl2, following exposure to simulated sunlight for as little as 12 minutes. No enhancement of inactivation rates was observed in the presence of 50-mM t-BuOH (HO� scavenger), and no inactivation was observed under simulated sunlight alone, highlighting the key role of photochemically-generated HO�.

Photochemical activation of free chlorine to hydroxyl radical for enhanced inactivation of chlorine-resistant waterborne pathogens

244th National Meeting (2012)

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