Chlorine Analysers For Residual Chlorine Monitoring – HaloSense
Free residual chlorine and Total residual chlorine analysers measure the chlorine in water that is ‘residual’ (left over) after disinfection has happened. i.e. if you add chlorine to water it disinfects, and if there is any leftover, it is ‘residual’ and therefore available to disinfect more. This residual chlorine can be measured and used to give confidence that disinfection is complete. Pi has three products for measuring residual chlorine; HaloSense (that uses electrochemical sensors), DPDSense (that uses online DPD technology), and Chloribrid® (that uses a hybrid of both). Free chlorine refers to HOCl and OCl–, and total chlorine refers to free chlorine plus chloramines. Both free and total chlorine are effective disinfectants.
Principle of Operation
Chlorine Analyser
The free and total residual chlorine sensors are three electrode amperometric sensors. Two of the electrodes (the gold working electrode and the silver/halide reference electrode) are behind a membrane that separates the sample from the electrodes and are submerged in an electrolyte. The membrane allows the movement of chlorine from the sample to inside the sensor where a low pH environment converts the vast majority of any OCl– present to HOCl. The HOCl is measured at the working electrode and a current proportional to the concentration of chlorine is produced which is reported back to the analyser.
Key Benefits
Applications
Options
FAQs
Downloads
- Low purchase cost
- Low cost of ownership
- Reduced pH dependency (largely pH independent)
- Stable and reliable
- Bufferless
- Reagentless
Many water companies want to measure free chlorine residuals without the need for chemical buffers traditionally associated with such measurements. Acetate and phosphate buffers are expensive and environmentally unfriendly. Buffer delivery systems are maintenance intensive and have costly consumables, and there are health and safety considerations in the handling of the acids and high disposal costs if the acid treated water is unable to be fed back into the water supply.
Amperometric sensors and most polarographic probes only respond to hypochlorous acid, (HOCl). HOCl dissociates into hypochlorite (OCl–)pH dependently. This is why most chlorine monitors need acid buffers in most applications. The typical pH of water measured on a water treatment works may range from 7 to 9.2. Chemical buffering reduces the pH to between 5 and 6 and ensures that the majority of the residual chlorine is present as HOCl (see graph below).
The HaloSense Free Chlorine Sensor measures all the HOCl and the majority of the OCl– present (blue line on graph). This results in a vastly reduced pH effect and means that most chlorine monitoring applications require no buffer and no pH compensation.
Small water treatment plants, secondary disinfection plants etc. tend to suffer from similar problems wherever they are in the world. The first is lack of communications SCADA infrastructure, the cost of which to install can be prohibitive. The second is the lack of a central DCS control infrastructure, again the installation of which can be cost prohibitive. The third is the remote location. Often these water treatment plants are in remote and difficult to access locations.
For some free chlorine applications with high and variable pH, pH compensation can improve the accuracy of the analyser. For pH compensation to be valid it must be done with the highest quality pH sensors and with chlorine sensors that have a reduced susceptibility to varying pH, such as those used in the HaloSense range."We at Scottish Water have been using the excellent Pi LabSense 3 and portable UV254 instruments in the field for optimizing our Water Treatment processes for some years now. We find them easy to use and invaluable for detecting and resolving issues in a timely, efficient and effective manner. Two great pieces of kit!”
Paul Weir
Scottish Water - UK
"I want to thank you and all at Process Instruments for all the assistance, information and handholding during the year. The help that was so freely given was very much appreciated. Can you please extend my appreciation to all at Pi and let me wish you all a happy, safe and wonderful Christmas and I look forward to working with you again in 2021."
Michael Bailey
Wexford Co. Co. - Ireland
"Excellent level of support and always so much more prompt than a lot of our suppliers."
Phill Tuxford
Detectronic - UK
"The plant can’t produce good quality water without the CoagSense."
Mick Murphy
Wexford Co. Co. - Ireland
"We've used the CRIUS® with chlorine, pH and conductivity sensors for several years and confirm quality, performance and reliability has been wholly satisfactory to date."
David Kerr
Karis Technical Services Ltd. - UK
"We in ECM ECO Monitoring can only recommend Process Instruments products and services to all other potential clients. They have very complex portfolio of products for water quality monitoring in various types of industries, friendly attitude, very quick delivery time and prompt reaction to all our needs and inquires. Our clients especially appreciate the particle counters and sizers allowing identification of drinking water treatment problems. The Streaming Current Monitors are a great tool for optimisation of expensive chemicals.”
Branislav
ECM ECO Monitoring - Slovakia
"Simply the best turbidity available."
John Clark
Chemtrac - Atlanta, GA
"In 2019, we purchased 29 particle counters which were installed in our water plants. So far, their performance has been perfect."
Li Yongjun
Jinan Hongquan Water Company - China
"We have installed hundreds of ozone analyzers from Pi over the years. They are just accurate, reliable and require low maintenance."
Jiao Tumei
Qingdao Guolin Environmental Technology Co., Ltd., - China
"Over the last few years we've purchased chlorine and turbidity analyzers from Chemtrac and with routine calibration the probes measure the chlorine and turbidity without any issue. We are very happy with this product and would highly recommend them."
Daniel "Buck" Owen
Ocoee Utility District - Ocoee TN
"We've been using these analyzers since 2008. They're easy to use and very stable. Calibration and maintenance is quick and simple."
Lloyd Gruginski
Chehalis WTP - Chehalis, WA
"The Pi products provide excellent value for money and represent the best municipal drinking water analyzers available."
John Clark
Chemtrac - Atlanta
“Servicing customers is much more than just solving problems or addressing complaints and Pi does that very competently with technical and quick efforts providing a good experience."
Clovis Tuchapski
Buckman - Latin America
"Pi's technical team has enabled us to be one step ahead of our competitors by adding value to our projects thanks to their fast and excellent support from the moment you first reach out.
Ibrahim Kaplin
Thermomed - Turkey
"Going from ORP control to amperometric chlorine sensor control has undoubtedly improved the pool water immensely!"
Chris Tedeschi
Link Automation - USA
"The Streaming Current Monitor from Pi is the best SCM I have ever used. The analyser responds quickly and has many powerful functions, which helps me save a lot of money."
Ye Yancong
Xiamen Xishan Water Plant - China
“Process Instruments has a broad range of high quality and user-friendly solutions for water-industry problems. The short lead times and great customer support make Pi a reliable partner.”
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SC KATALIN NOHSE CHIMIST IMPORT SRL - Romania
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Izasa Scientific - Spain
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Equip Solutions - Illinois, USA
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Allpronix - South Africa
Louis Wilmot
+44 7944 344511
louis.wilmot@processinstruments.net
Mukhtar Patel
+44 7377 374583
mukhtar.patel@processinstruments.net
