Fast and precise chlorine detection protects Veolia’s RO membranes one year after commissioning

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Rapid and accurate chlorine detection is critical to protecting reverse osmosis RO systems from long-term damage. While reagent-based chlorine measurement methods can be costly to operate and impractical to manage on a continuous basis, traditional amperometric chlorine electrodes often fail to respond quickly enough when precise detection is essential.

In a detailed performance study carried out in collaboration with Bürkert, Veolia Water Technologies Ireland has demonstrated how its RO system can be protected from even trace levels of chlorine. One year on from commissioning, the installation is also achieving and maintaining zero chlorine conditions downstream of granular activated carbon filtration using Bürkert’s Online Water Analysis System.

Greg Wainhouse, Bürkert’s Regional Business Development Manager for Industrial Water, North Europe, explains the importance of rapid chlorine detection in modern water treatment systems.

burkert online water analysis — Bürkert’s Online Water Analysis offers precision monitoring of several parameters including chlorine, ORP, pH and temperature.

Why chlorine monitoring matters in RO systems

A reverse osmosis system removes dissolved impurities and contaminants from water by forcing it through a semipermeable membrane. RO technology is widely used to produce purified and ultra-purified water across multiple sectors, including pharmaceutical manufacturing, food and drink production and healthcare applications in hospital environments.

RO membranes contain microscopic pores that allow water molecules to pass while rejecting dissolved salts, organic compounds and chemical contaminants depending on their size charge and chemical properties. However, chlorine exposure presents a significant risk. Chlorine is commonly present when feed water is supplied from mains sources or disinfected boreholes and RO membranes have a limited tolerance to chlorine contact.

Typically RO membranes are rated at around 1,000 parts per million of cumulative chlorine exposure over time measured in ppm hours. Exceeding this threshold causes membrane degradation and a reduction in filtration performance. For this reason precise continuous chlorine monitoring upstream of the RO membrane is essential to safeguard system integrity and operational reliability.

post gac detection — Graph shows that if ORP was the control, it would result in some Cl2 penetrating through to the RO membranes.

Protecting the RO membrane at Veolia’s training facility

Veolia Water Technologies Ireland supplies purified water solutions to the pharmaceutical and food and beverage industries. At its Customer Experience and Life Science Centre of Excellence engineer training facility near Dublin the site operates a granular activated carbon GAC filtration system installed specifically to remove chlorine ahead of an RO membrane.

The GAC vessels dechlorinate the feed water and protect the RO membranes from chlorine attack. To maintain filtration efficiency the vessels are periodically backwashed to remove accumulated particulates and preserve bed hydraulics. During these operational events continuous chlorine monitoring is required to confirm effective dechlorination and to identify any chlorine breakthrough particularly during backwash and rinse cycles.

Veolia reported that reagent based chlorine measurement techniques do not provide continuous monitoring and require ongoing management of chemicals and consumables. Traditional amperometric probes were also found to be maintenance intensive due to their susceptibility to drift caused by manual sampling and analysis methods.

Achieving accurate and reliable results using these approaches demands frequent testing which drives up costs in both reagents and operator time. Reducing the testing frequency for example, to hourly checks does not provide sufficient resolution to reliably protect RO membranes from short-duration chlorine exposure events.

In contrast, continuous online chlorine monitoring delivers stable real-time readings and enables precise analysis that directly supports effective membrane protection. To assess available technologies and identify a reliable easy-to-manage solution for online chlorine monitoring Veolia commissioned fluid control and measurement specialist Bürkert.

Back wash of the GAC caused some Cl2 breakthrough.

Online water analysis with Bürkert

Bürkert supplied its Type 8906 Online Water Analysis System equipped with an MS02 chlorine sensor and an MS04 oxidation reduction potential ORP sensor. The ORP sensor was included as a secondary verification method to indicate the presence of oxidising substances including chlorine which typically registers at around 650mV.

The trial was designed to compare measurement precision and response times between the two sensor types. While ORP sensors can indicate the presence of oxidising species they are influenced by other elements in the water. Although ORP detects oxidising agents such as chlorine it cannot confirm specific chlorine concentrations which is essential for calculating chlorine contact hours on RO membranes.

Veolia was particularly interested in evaluating the performance of Bürkert’s MS02 chlorine sensor. Conventional amperometric chlorine sensors typically have a T90 response time of around 120 seconds meaning the time taken to reach 90 percent of the measured chlorine concentration. Bürkert’s MS02 chlorine sensor delivers a significantly faster T90 time of under 30 seconds.

This rapid response is achieved through a specially designed single membrane that protects the MEMS sensor. Unlike traditional designs that use a membrane pair surrounding an electrolyte pH buffer the single membrane design reduces resistance for chlorine ions before detection resulting in faster measurement and improved accuracy.

determination of concentration — Two similar ORP peaks but with different concentrations of Cl2, showing that determination of CI2 concentration with ORP is impossible.

Eliminating polarisation issues in low chlorine environments

Most amperometric chlorine electrodes require servicing and recalibration every three to four months. A more serious limitation however is their susceptibility to polarisation when used downstream of GAC filtration. In environments where chlorine is absent for extended periods the electrode surface can accumulate residual ions or film layers causing the sensor to lose equilibrium.

When chlorine is reintroduced, the sensor response may be significantly delayed or fail entirely. This presents a major risk in post GAC applications, where chlorine breakthrough events may be short-lived but still damaging.

Thanks to its integrated electrode block which provides a continuous reference point, the MS02 chlorine sensor does not suffer from polarisation even after long periods without chlorine detection making it particularly well suited to RO pre-treatment monitoring.

determination of concentration 2 — Two similar ORP peaks but with different concentrations of Cl2, showing that determination of CI2 concentration with ORP is impossible.

Results from the performance study

The study began in October 2024 with both sensors installed on the inlet to the GAC system, where higher chlorine levels were expected prior to filtration. The MS02 chlorine sensor demonstrated significantly faster detection, while the ORP sensor failed to detect chlorine presence below 650mV for an initial three-hour period.

This scenario occurred again later in the study when the ORP sensor failed to register chlorine for more than 20 hours, during which chlorine levels fluctuated between 0 and 300mV. While these represented relatively low chlorine concentrations, the cumulative exposure over time could still be sufficient to damage RO membranes.

Downstream of the GAC system, a backwash event caused limited chlorine breakthrough. Veolia was able to divert this water to the drain, preventing any chlorine exposure to the RO membranes. Although the total detection time difference between the two sensors was narrower in this scenario, the results showed that relying solely on ORP measurement would have resulted in chlorine reaching the RO membrane.

If an electrodeionisation EDI system had been in use instead of RO membranes, even trace chlorine concentrations as low as 0.05ppm could have caused damage, highlighting the importance of rapid and precise chlorine detection.

cl2 detection failures — Cl2 detection failures below 650mV by ORP methods due to slow reaction times, denoted by areas within red lines.

Rapid detection and precise analysis in operation

When chlorine is detected by the Type 8906 Online Water Analysis System, real-time alerts can be issued and visual alarms configured to trigger immediate operational responses. The system features a 7-inch touchscreen displaying live process data while historical trends can be reviewed using the integrated data logger.

As a result of the study, Veolia Water Technologies Ireland now has the capability to prevent virtually all chlorine traces from entering its RO systems. This enables the consistent achievement of zero chlorine conditions at the RO inlet while significantly improving membrane protection.

In addition to improved reliability, the solution reduces operational costs and maintenance time compared with traditional reagent-based or manual chlorine measurement methods.

“Bürkert recognised a real operational pain point for Veolia and translated it into a practical, technically sound monitoring solution that protects our RO membrane systems,” said Kieran Lyons, Project Director Ireland, Veolia Water Technologies.

Bürkert Fluid Control Systems
Greg Wainhouse, Regional Business Development Manager for Industrial Water, North Europe
Tel: +44 1285 64 87 20
Email: sales.uk@burkert.com
Web: www.burkert.co.uk

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Burkert Fluid Control Systems

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Bürkert is present in thirtyfive countries around the world. We also work with a large network of distributors and partners, which means we are as close as possible to our customers. This global presence ensures full service and support to all of our customers in every country around the world. Research is the lifeblood of our company.

At Bürkert, we are never satisfied with the status quo and are continually seeking new technologies and solutions for our customers. Every year, our people develop new and highly advanced products and solutions, ranging from integrated process measurement and control units to the most sophisticated systems used in pharmaceutical research. To be a market leader, we are also an R&D leader.

Therefore, our investment in research & development is one of the highest in our industry. In our research centres in Germany and France, 150 people are committed to working for a common future for our company and our customers. We are committed to offering our expertise wherever it is needed, anywhere in the world. This global presence ensures that our advances in fluid control technology are also global.

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