Novel Bare Amperometric Sensors

Chemical biocides have been utilized in cooling towers to prevent biological growth for multiple decades. There are many commercially available chemical biocides, including liquid bleach, activated bromine products, and stabilized chlorine and/or bromine products. Stabilized bromine is a popular choice as a biocide due to its enhanced product stability, efficacy in high pH ranges, and its relatively safe means of chemical handling and pumping compared to other biocide products.

Historically, stabilized bromine concentration has been measured using oxidation-reduction potential (ORP) sensors. ORP sensors provide a measurement of the amount of electrochemically active species present in a sample but are unable to distinguish between chemical species. Given that cooling towers require several chemical additives to operate within compliance, an ORP measurement does not yield the most accurate insight into the stabilized bromine concentration in the tower.

A better alternative to ORP sensors for this application is the use of “bare” or “open cell” amperometric sensor technology. Bare amperometric sensors have shown repeated success in measuring and dosing free and combined chlorine products as well as activated bromine products. Due to their solid-state design, bare amperometric sensors provide an easily interpretable signal that directly relates to the concentration of chlorine and bromine species present.

To demonstrate that bare amperometric sensors could accurately measure stabilized bromine products, we installed a sensor in a 200-ton cooling tower at an industrial plant in the suburbs of Chicago. The cooling tower for this case study is timer-fed, meaning a highly concentrated solution of biocide is introduced at the beginning of the tower’s operation cycle and is consumed as the tower runs.

We found that the Kuntze Zirkon® DIS Total bare amperometric sensor is capable of accurately measuring and controlling a stabilized bromine residual in an industrial cooling tower. The cooling tower was previously timer-fed one to two times per day, which did not provide the tower operators with “peace of mind” that microbiological growth was being managed. After the installation of the Krypton® DIS system to measure and control biocide residual, the tower operator reported feeling much more confident in their water treatment program.

The future direction of this study is to decrease the target setpoint of the biocide residual. This will decrease the amount of biocide discharged during tower blowdowns as well as save on chemical costs. The confidence afforded by the direct biocide concentration from the bare amperometric sensor signal is what makes this step possible and logical.