Simplifying Validation: Fluoride ion monitoring in drinking water applications

Jan. 16, 2006

The constant requirement of adding reagents to the sampling analyzer placed a high burden on the busy maintenance staff, and resulted in reduced plant efficiency. When the problems with the sampling fluoride analyzer could not be addressed, grab sample analysis was used.

The use of constant grab sample during times of problems with the online equipment created an undue burden on the maintenance staff, and defeated the purpose of having an online fluoride monitoring system.

Because multiple measurement points were required, a complex system of piping was installed to deliver sample to the few sampling analyzer available.

Only a few sampling analyzer were installed due to their prohibitively high cost. This caused the two-fold problem of a delay in the measurement due to the piping of the sample to the analyzer and the centralization cause the entire system to go down at once when problems occurred with any of the few analyzers that were installed.

The solution

An inline fluoride ion selective sensor, specially engineered to water and wastewater application was chosen, with a rugged fluoride mono-crystal ion sensing element, and a virtually maintenance solid-state reference system. In order to optimize the stability of the inline fluoride sensor measurement, a low flow sample bypass system was employed.

A menu driven, simple to use, an industrial ion selective transmitter and analyzer that was capable of calibrating, displaying, outputting and controlling in ppm units was selected. A convenient bayonet style twist lock inline installation style was selected for its ease of removal, facilitating the required calibration and cleaning. Various calibration solutions were formulated that were ten fold apart in value and would bracket the target concentration range.

The calibration solutions were designed to closely mimic the expected ionic background of the measured solution. The calibration system simplified the validation of the online fluoride analysis system and reduced the need for grab sample calibration all while replacing the cumbersome sampling fluoride analyzer.

About the Author

Thomas Patko