Zellweger eases chlorine problem
15 Jan 2000
Adding chlorine to drinking water is a tricky business. Its bactericidal action makes it necessary, but the amount added is critical - there has to be just enough of the active form of chlorine, HOCl, to do the job, but not so much that there is a residue left once the water reaches the taps.
Zellweger Analytics has developed three instruments to handle this job. The Polymetron monitors, developed for drinking water treatment plants, distribution networks and cooling water providers.
The simplest of the three, the Chloromat 9184 HOCl, uses a flow-through-cell, sensor probe and transmitter to measure active chlorine. Next up, the Chloromat TFC/pH adds a pH electrode, enabling it measure both active and free chlorine. The most advanced, the TFC/Acid unit, includes a facility to add a buffer solution to bring the pH below 6.0, transforming all the free chlorine present into HOCl and allowing it to be measured by an amphoteric sensor. This highly accurate measurement is suitable for controlling chlorination pumps.
The sensor works using an HOCl-sensitive membrane which is impermeable to ClO- and chloramine. The membrane lasts for three to six months, and can be changed in a couple of seconds.
