Analytical Technology's Q45H chlorine monitoring system achieves accurate and reliable free chlorine measurement even in the presence of high levels of un-dissolved iron and manganese salts
The findings of this analysis are of particular interest for the water industry and are detailed in a new, free of charge application note from ATi.
Most commonly, iron and manganese occur in well water and impounded surface water.
Although these compounds do not pose a serious threat to human health, they still need to be removed during the treatment process because they stain everything they come into contact with, while also promoting the growth of certain filamentous organisms.
This can lead to clogging of pipes in distribution systems.
Typically, iron is removed in a so-called first stage process.
Coagulation is followed by filtration, which removes the precipitated iron salts.
Manganese is removed in a second stage.
In general, chlorine is used to oxidise soluble manganous salts into insoluble manganic salts.
The free chlorine level needs to be constantly monitored and controlled during and after the second stage so as to avoid certain problems for chlorine monitors.
The challenge here is that the sample water is laden with un-dissolved manganese salts, which coat and stain the chlorine monitor resulting in increased maintenance being required.
In addition, manganese salts coat the measuring electrodes of typical monitors and cause zero drift and loss of sensitivity.
High levels of solids can also block sample inlets.
Featuring an A10/62 membraned polarographic sensor, ATi's Q45H chlorine monitor overcomes these challenges.
A platinum cathode and silver anode are immersed in KCl electrolyte behind a microporous membrane.
Chlorine species diffuse through the membrane, electrochemical reduction occurs at the cathode and a current proportional to the chlorine concentration is generated.
This current is measured and then converted to a chlorine concentration.
The presence of the membrane eliminates electrode contamination and zero drift is eliminated.
Typical membrane lifetimes are six to nine months and the maintenance requirement is a 15-minute process of membrane exchange followed by a stabilisation period of around 20 to 40 minutes.
The design of the flow cell of ATi's Q45H chlorine monitor ensures that there is a directed flow of sample across the membrane.
This flow acts as a self-cleaning device.
A soft scouring prevents build up of solids.
The flow cell used in the Q45H has large bore sample inlets and does not block.
