This paper describes a new Aseptrol ClO2 delivery system that is capable of at least two months of unattended operation in small-to-medium-size cooling systems up to 30,000 gallons in capacity. Multiple safety features have been incorporated into the feeder to significantly minimize the risk of exposure to chlorine dioxide. Results from field trials will be reported in which Aseptrol biocide was dosed into cooling systems via this feeder, allowing for the effective control of microbiological (MB) growth, especially biofilm. Trial data showing MB counts, ATP data, Aseptrol biocide feed rates, ClO2 residuals, and corrosion rates will be presented. Additionally, performance data from field trials will be presented that compares efficacy and cooling system operation during treatment with Aseptrol biocide to baseline data collected during treatment with other biocides.