Chlorine Dioxide Dosing

Why does it so often go wrong in the building services sector?

From our experience over the years, chlorine dioxide has gained as many friends as it has enemies.

Let’s ask ourselves why?

Well, in our opinion not least, it is a combination of issues ranging from the blatantly obvious to the hidden, even misunderstood aspects of practices developed and adopted over the years within the industry.

“The obvious”

where safety goes wrong right from the onset with installation and remedial maintenance poorly practiced, operator error through lack of training causing accidental spillages, over and under dosing of chemical reagents leading to poor biocidal efficacy, corrosion and unnecessary DBPs, to name a few.

“The hidden”

issues where poor ClO2 generator design fails to protect correct reaction chemistry and hence biocidal efficacy due to inadequate metering accuracy, poor calibration and tampering with reagent pump settings, vulnerability in operation due to poor quality materials failing prior to PPM visits, chemical reagent drums running empty and unnoticed, maintenance companies offering service contracts for equipment they have little expertise dealing with day to day and so the generator slowly falls into disrepair and performs poorly often without the knowledge of the operator.

“The misunderstood”

aspects, for example: –

  • The use of Redox in downstream monitoring was adopted many years ago to try to limit risk of over and under dosing in combination with pulsed water meters – but Redox as we know could go high due to high acid dosing ratio, interference through fluctuations in background free-chlorine residuals and water balance, unable to detect quantitative ClO2 residuals for minimum and maximum thresholds to be controlled, maintaining, cleaning and replacing Redox electrodes frequently needed.
  • Amperometric/Potentiostatic residual ClO2 measurement implemented for downstream monitoring, adopted to help improve on the limitations of earlier Redox control systems but this then misses the point that these analysers were often installed to protect over and under dosing events due to poor equipment design rather than just biocidal compliance. Poor installation and/or maintenance of the analyser simply causes yet another major vulnerability to hazardous over and under ClO2 dosing events occurring.
  • Industry specifications based on old practices and outdated designs, unclear industry guidance and real lack of understanding on what compliance means in so far as correct equipment installation scheme and that WRAS only covers the components or product in contact with potable water and has absolutely nothing to do with suggesting the installation is WRAS approved. The entire installation has to be in accordance with local water supplier byelaws and the drinking water supply to remain wholesome at all times within the building.

Prevention is better than Cure!

Protect the operator, secure the chemical reaction efficacy, build a robust product that is both simple to install, maintain and operate.

Sounds easy but why is this not happening enough in practice then?


Technology plays a great part as we know in the advancement of improving and influencing most things we see and do every day in life. The same is no different in this case.

Take for instance the chloriDOS® iOX®, a completely unique and Patented chlorine dioxide generation technology:

  • Offers inherently safe operation of chemical transfer and chlorine dioxide reaction under vacuum.
  • Secures chemical reaction efficacy through precise volumetric measurement of the chemical blending and chlorine dioxide dilution process, all of which is calibrated for the life of the unit.
  • Very few working parts to replace and constructed out of high quality PVDF/PTFE/FPM materials exposed to aggressive chemicals.
  • Allows simple installation design restoring confidence and enabling dependency on the robust concept of a pulsed water meter delivering the correct ClO2 dose every time.
  • Use a potentiostatic ClO2 analyser where necessary downstream to assist with monitoring/trending and not control, except for threshold limits/alerts.
  • There is absolutely no reason for chlorine dioxide to be regarded as unsafe and should produce the excellent results expected.
  • However, the industry needs the right companies, technicians, products and technologies to make it happen.
  • Otherwise, nothing is going to change anytime soon regardless of having great technology available.

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