The use of gaseous chlorine as a microbiocide for industrial cooling systems is declining because of safety, environmental and community impact considerations. Various alternatives have been explored, including bleach, bleach with bromide, bromo‐chlorodimethyl hydantoin (BCDMH), non‐oxidizing biocides, ozone, and chlorine dioxide, among others. Chlorine dioxide offers some unique advantages, due to its selectivity, effectiveness over a wide pH range, and speed of kill. Safety and cost issues have restricted its use as a viable replacement. This paper reviews the chemistry of chlorine dioxide and its use in cooling systems. Comparisons are made with chlorine, bromine and ozone. A novel approach to its use in a safe and effective way is described.

Keywords: chlorine dioxide, chlorine, ozone, bromine, oxidizer, biocide, review article

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