ISE sensor vs. Wet chemistry: Analyser for ammonia and ammonium

Which is best for your application? Benjamin Barker, application engineer at Xylem, explains more.

Water resource recovery facilities are faced with several challenges when selecting online instrumentation. Choosing the correct application sensor location, mounting options, and understanding maintenance requirements are crucial for successful online water quality monitoring and process control.  

Here, we will discuss online ammonium measurements, the technologies available, and recommendations on when to use each type.

ISE sensor vs. Wet chemistry analyser
Online ammonium measurement technology can be divided into two types – ion-selective electrode sensor (ISE), and wet chemistry analyser. Although both have their place in wastewater monitoring, they are two very different technologies.

ISE sensors utilise two electrodes that create an electrochemical signal (mV). One electrode contains a selective membrane for only ammonium ions, and the other outputs a stable reference signal. The difference between the potentials, or millivolts, coming from each electrode creates a differential mV signal that increases or decreases based on the amount of ammonium in the water. The electrodes’ mV signal is continuously converted into an ammonium concentration using the Nernst equation and reference samples for calibration. To maintain the sensor’s accuracy, the differential signal must be routinely calibrated to the concentration of ammonium via reference samples.

Ammonium ISE sensors are popular in wastewater for the benefits they can bring to the treatment process at an affordable price. With continuous ammonium measurements, automatic control of aeration can be immediate and proportional to the incoming ammonium load. This strategy allows facilities to be as efficient as possible with aeration, lowering energy costs with a minimal investment in an ISE sensor and controller. These sensors can be immersed directly in the process from a railing, which makes installation and maintenance convenient. ISE sensors requires some maintenance with occasional manual cleaning, calibration via reference sample, and electrode replacement.  

The full article is published on the latest edition of Water & Wastewater Asia Jul/Aug 2021 issue. To continue reading the article, click here.