In recent years, instrument manufacturers have responded to customer demands, improving the quality of direct sensor technology and expanding the range of sensors available. However, careful consideration of instrument / sensor suitability for any given application is still required. For continuous ammoniacal-nitrogen measurement, there are two fundamentally different technologies available.
Proam ammonia analyser methodology
The analyser methodology is an "off-line measurement" requiring sample to be pumped, often to a sample preparation system which removes suspended solids and biology, prior to measurement. Additionally, if an existing building is not available, a secondary housing is required to provide frost protection to the instrument and prevent reagents from freezing, during winter.
Ammonium probe methodology
The direct probe technology is simpler. The ammonium ion-selective measurement technique does not need a reagent so can be directly mounted into a chamber to provide "in-line measurement". However, since there is no automatic calibration available, the technology is completely reliant on user-calibrations, against spot sample analysis which must be performed frequently, with precision. Additionally, the ammonium ISE methodology is also affected by the variations in the potassium ion which particularly affects performance, at low ammonium concentrations. The sensor technology is
useful for trend analysis within basins containing high ammonium but it should be used with caution at low concentrations.
Final effluent compliance monitoring
For compliance measurement of final effluent, where strict consents have been imposed by the regulatory authorities, measurement confidence is critically important. Consents have become progressively tighter and there are now many sites with ammoniacal-nitrogen limits set at 3.0mg/L Nor below.
In these instances, the distinct advantage of a suitable analyser technology, is the ability for the instrument to automatically calibrate to validate measurements and correct for sensor drift. The integration of automatic chemical cleaning and sample preparation to remove suspended solids and biology, is also very important.
Sample preparation aids reliable analytical measurement
Considerable effort to develop a simple but effective sample preparation system has enabled PPM to provide a reliable analytical solution especially for waste water monitoring applications. There are also many parallels with river water quality monitoring. Intake protection systems installed at potable water treatment works are faced with the same sample difficulties. The same membrane sample preparation system has been successfully used to remove entrained biology and suspended solids which would otherwise cause fouling and blockage, within the analyser pipework.
Within the Proam ammonia monitor, pinch valves are used to distribute the fluid to a reaction vessel containing an ammonia (gas sensing) ion selective electrode. Elevating the sample pH above pH11 liberates the ammonium ion as ammonia gas which can be measured without interference from other dissolved ions. This technique has thus proved to be very reliable in waste-water monitoring applications where there can be inherent sample variability. A tactile keypad provides a simple user interface for changing settings and checking calibration history etc.
The Proam continuous ammonia monitor provides many benefits
Many operators have witnessed the benefit of installing continuous measurement. The ability to connect instrument-signals to telemetry and alarm unacceptable events, in real time allows notification prior to site failure. The Proam measurement technology has been extensively installed. Numerous UK municipal installations such as Anglian Water, Severn Trent Water and Wessex Water use the Proam ammonia monitor for continuous measurement. Many industrial users have also benefited including applications within landfill, agro-chemical, bio-chemical, precious metal processing, semi-conductor waste and the poultry industry.
Image: Proam at AWS - mounted in a secondary enclosure by PPM
Image: Proam at AWS mounted in a walk-in analyser kiosk by PPM
Added value bespoke builds and service support
Two key services which PPM also provide are bespoke builds and after- sales, service support.
Both of these services have proved to be very popular with our customer base. PPM has a wealth of application knowledge and is well placed to provide a bespoke build to take in to account specific installation requirements. Making the correct installation is critically important to the future reliability of an analytical measurement system.
Additionally, we can provide scheduled routine maintenance and emergency call out cover for our instrumentation in addition to scheduled chemical supply ensuring reliable instrument operation, once installed.
Pollution & Process Monitoring Ltd
Bourne Enterprise Centre
Tel: 01732 882044