Chlorine Residual Analyzers – Take Your Choice

Like buying a cup of coffee “I’ll take it black please”, buying a chlorine residual analyzer used to be simple: “I’ll take amperometric please”. Not the case any more with several technologies, makes and models.  The first chlorine residual analyzers originated in the 1960s and incorporated amperometric technology whereby a chlorinated water sample passes through a cell with two dissimilar metals to produce an small electrical current.  The electrical current is amplified, filtered, scaled and transmitted as a 4-20ma signal.  Amperometric analyzers are still available today, they are well proven and are being used in thousands of water and wastewater treatment facilities.  Today you have a choice of: amperometric,colorimetric or amperometric probe type analyzers.  Based upon my experience, I have listed some +/- of the three technologies that are currently approved by EPA and DEP for direct reporting of both free and total chlorine residuals:

Amperometric: Proven for water & wastewater, not good for high solids at low residuals, occasional issues with metals in solution, mechanical cell cleaning systems can be a problem, large cell (Capital Controls Brand) handles solids well, best technology for wastewater, needs reagents pH Buffer & Potassium Iodide (for total chlorine),
Colorimeteric: Proven for water and good quality (low solids & color) wastewater, dependable DPD analysis, lower capital cost (compared to amperometric), some require nitrogen/dry air purge to prevent condensation, needs reagents pH buffer and DPD liquid, reagents higher cost than amperometric.
Amperometric Probe: Proven for water and some select wastewaters, probe cannot be inserted directly into process (requires controlled flow & pressure at cell), cell membrane can become fouled, add electrolyte to cell annually, no reagents required, high capital cost for cell, transmitters can accept multiple probes.

Water and wastewater facilities are required to control chlorine residuals to meet tight standards set by EPA and DEP.
The right chlorine residual analyzer in conjunction with the right chlorine feed system can help you meet those standards.

What is your experience with chlorine reisdual analyzers?