Monday 16 May 2011

Ion selective measurement

In control of nitrification and denitrification with continuous ammonium and nitrate measurement

The new ion-selective measuring system ISEmax CAS40D is part of Endress+Hauser's platform concept for liquid analysis. It speaks the same language as all sensors of their platform: Memosens. The digital protocol guarantees reliable, comprehensive data transmission and an easy-to-use system. So ISEmax CAS40D offers fast and easy control of processes in the area of wastewater treatment and visibly reduces the costs for power used in aeration systems.

ISEmax measures the concentration of ammonium, nitrate, potassium and chloride quickly and continuously in municipal wastewater treatment plants. The robust in-situ measurement allows measuring several parameters simultaneously with one sensor. A distinguishing feature of ISEmax is its short response time. Since ISEmax is immersed directly into the medium, the measuring system responds very quickly to changes in the concentration. The rapid trend display supports the early control and regulation of the processes.

Easy installation and low maintenance
Thanks to the Memosens protocol, ISEmax CAS40D is simply connected to one channel of the Liquiline CM442 transmitter. The other transmitter channel remains free for any additional sensor. ISEmax CAS40D is mounted on the basin rim with a suitable retaining unit and is immersed directly into the process with the electrodes. The unit is easy to use: the measuring system does not use any chemicals, is low-maintenance and does not require external sampling. Furthermore, integrated automatic compressed-air cleaning prevents the membranes from fouling.

Comprehensive application in municipal wastewater treatment plants
ISEmax covers a large measuring range:
• Ammonium - nitrogen: 0.1 - 1000 mg/l NH4-N
• Nitrate-nitrogen: 0.1 - 1000 mg/l NO3-N
• Potassium: 1 – 1000 mg/l K+
• Chloride: 1 – 1000 mg/l Cl-

Typical applications in municipal waste water treatment plants include measuring the concentration of ammonium and nitrate directly during sludge activation, measuring the ammonium (pH-compensated) load in the inlet to sludge activation, and load-dependent aeration control.

Sensor layout
The sensor ISEmax CAS40D consists of ion-selective electrodes, a pH electrode with in-tegrated reference, potential matching, a temperature sensor as well as automatic compressed-air cleaning and a pre-amplifier.

Up to three ion-selective electrodes simultaneously measure ammonium, nitrate and another measured variable, if so required by the customer. They exhibit easily replaceable membrane caps which are selective for the ion to be measured. A membrane kit with easy-to-use replacement caps is also available as an accessory. The membranes are robust and can be used for up to six months. Thanks to the integrated compressed-air cleaning system, they are kept free from fouling and contamination and are thus always operational.

Ion-selective measuring principle
Potentiometric measurement using ion-selective electrodes is similar to pH measurement: as a result of charged ions "migrating", a potential difference occurs between the measuring electrode and the reference electrode. This difference in potential is meas-ured and is proportional to the ion concentration.

The bottom line
ISEmax CAS40D combines robust, ion-selective in-situ measurement with the advan-tages of the Memosens technology such as plug&play, easy handling, storage of sensor- and process-specific data and safe digital data transfer. It offers potential for other parameters and industries.

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