Chlorine Analyzers & Water Conservation​

The city started searching for a wet tap chlorine analyzer that was approved by the National Science Foundation (NSF) and American National Standards Institute (ANSI) and didn’t generate a waste side stream. After several months, the city found a company, Halogen Systems, which advertised a chlorine analyzer for seawater use. Although the analyzer wasn’t NSF/ANSI 61-approved, the city worked with the company on trial projects to determine whether the analyzer would meet its needs.

First Trial: Flow-Cell Version. In April 2021, Halogen Systems developed its first prototype, and the city tried the flow-cell version of the company’s MPS sensor at one of its booster stations. The best way to test the new analyzer was to compare with the existing analyzer at the booster station, so the flow-cell version was installed to track chlorine residuals from the same sample tube (Photo 1). Data were collected for several months.
The new sensor was installed without any flow regulator, start-up configuration was simple, and results were accurate within 0.04 mg/L of the existing ana-lyzer. During the next six months of operation, the new sensor didn’t require any calibration and needed only minor maintenance to clean the cells from manganese buildup. After six months of operating with both sensors, the city decided to take the existing sensor offline. The city was confident that monitoring results from the Halogen Systems’ flow-cell analyzer were accurate and reliable. The city continued to check accuracy by collecting grab samples after the old sensor was removed. The city’s experience with other membrane-style amperometric sensors is that they require regular calibration besides other periodic maintenance.
The Halogen MP5 was different, with features such as being flow-independent and self-cleaning. It has been operating since April 2021 and started up with no calibration or flow adjustment. There was a 0.05 mg/L difference in DPD, with no drift.

Second Trial: Wet-Tap, In-Pipe Version. The flow-cell version worked well, but the city was particularly interested in the company’s wet-tap, in-pipe version of the sensor. Once Halogen Systems had received NSF/ANSI 61 and NSF/ANSI 372 certification, the city tested the wet-tap version. Because it was the first wet-tap installation, there were a few setup issues. However, once the bugs were worked out, the sensor was installed at a well location where there was no ongoing monitoring. The wet-tap sensor’s results were compared with grab samples, and its performance was similar to the flow-cell sensor. Shortly after installing the wet-tap sensor, a notification was sent to plant operators that the chlorine residual had dropped. An operator was able to quickly resolve the issue. However, without the wet-tap sensor, the well may have continued to deliver water to the distribution with little chlorine residual. The city realized the importance of continuous monitoring at each well location.