PBS ammonia analyser
The PBS ammonia monitor started to become the ammonia analyser instrument of choice in a significant number of wastewater treatment works in 1999. Starting with sites in Southern Water, the PBS has been used extensively in Severn Trent and Yorkshire Water territory, and more recently with Anglian Water.
What is it about the PBS that sets it apart from other ammonia monitors?
A wet chemical ammonia analyser allows automatic calibration. The PBS carries out all of its' analysis right there in the sample stream, meaning that there is absolutely no need for a kiosk or pumping system. There are other 'probes' available such as our own 'AmNiSys' ISE ammonia monitor, but these typically need frequent manual calibration to counteract measurement 'drift'. The PBS ammonia analyser uses standard addition self-calibration (typically at midnight) to ensure reliable analysis for long periods of time.
On the other hand, there are other wet-chemical analysers, but they tend to be cabinet style systems that require sample pumps and filtration. Inevitably, the cabinet analysers will also carry other infrastructure costs such as a kiosk, bringing significant installation costs into the equation. The in-situ nature of the PBS cuts out potential interference and cross contamination that could be cause by sample pumping. A cabinet analyser is dependant on the pumping system, which will periodically break down.
The PBS transmitter is IP65 rated and comes with it's own small GRP weatherproof housing and stainless steel stand - it requires only a hard-standing of approximately 600mm x 600mm for installation, and a mains power supply for commissioning.
How can the PBS self-calibrate?
A calibration routine is included in the PBS ammonia analyser programming, this is typically set to once per day at midnight. The parameters can be changed so that calibration can be done more frequently, or at a different time of day as per the clients' requirements. The 'wet-end' carries EDTA reagent and a calibration solution, the standard addition method means that sample water can be used for base measurement. No external interference is required for the unit to complete a calibration autonomously.
In the standard addition method, one part of a standard solution or several parts by equal aliquots are added to the sample. The result is logged after each addition - the graph illustrates the results of the standard addition method. The calibration results are used along with other parameters to produce a slope and offset which is then used for subsequent ammonia analysis measurements.
An essential part of the batch measurement programmed into the PBS is the settling time. Settling is hardly needed for most final effluent applications and can be set to a minimum (30 seconds). For aeration lanes or other applications where solids may be significant, a period of settling tailored to the specific application is set so that measurement takes place only on the supernatant remaining after solids have settled. Additionally, the EDTA used in the measurement cycle provides an element of self-cleaning of the system.