Ammoniacal-nitrogen is a key water quality parameter. The determinant can be used to efficiently control the treatment processes, to demonstrate compliance to imposed discharge consents, to indicate the presence of untreated sewage at points of abstraction and infer the associated risk from pathogens.
Instrumentation is now extensively installed to monitor ammonia on-line and report data in real-time. The selection of an instrument with a design that minimizes maintenance, reports accurately and functions reliably, is especially important.
Different Methodologies
Principally three methodologies are available for on-line measurements; Ion Selective Ammonia (gas sensing) electrodes, Ion Selective Ammonium electrodes and Colorimetric. All three techniques have been installed for continuous on-line measurement but their application should be carefully considered. Ion Selective Ammonia techniques prevail in applications requiring continuous analysis such as intake protection and final effluent monitoring.
Since the Ion Selective technique is continuous and is unaffected by the suspended solids content of the sample, it is the preferred methodology for waste water measurement. Analyser systems incorporating the ammonia ISE can validate measurements by automatically calibrating against two known standards. Diagnostic alarms may also be generated to prompt maintenance and identify possible faults. Ion selective ammonium sensors vary considerably in the quality of measurement they provide. They are ideal for trending and have the advantage of direct measurement, without the need to introduce a reagent. However ammonium probes mounted directly into the sample basin do not automatically calibrate, so regular site attendance is required to maintain calibration.
Colorimetric analysis is an intermittent test and can be affected by suspended solids within the sample-limiting it's on-line application without the correct sample preparation. Colorimetric techniques are conveniently packaged for portable test kits designed for grab sample analysis but once again attention should be paid to ensuring samples are free from suspended solids.
Our Design
Pollution & Process Monitoring have optimised the Ion Selective Ammonia (ISE) design especially for applications containing suspended solids. The ProAm analyser has an integral peristaltic sample pump (capable of delivery a sample directly from source) which continuously delivers sample through large diameter tubing to a reaction vessel containing the ISE. The sample is then pH adjusted and agitated using an air-sparging system to liberate free ammonia for analysis.
The internal tubing and the ISE is chemically cleaned using an automatic acid wash sequence at a user selectable interval (typically daily). This sequence removes any biological growth and calcification which can otherwise result in blockages. Emphasis has been placed on designing a measurement system which is simple, compact, robust and repeatable. Above all, reliability of operation has been the main objective.
System Validation
System validation is extremely important especially for applications where compliance to an imposed consent must be demonstrated or where trace level (sub-PPM) concentration must be reliably detected.
Automatic calibration, typically on a daily basis using two known standards, can be used to compensate for any drift within the measurement system but also validates the reported measurements. The loss of sample, reagent, cleaning solution and the failure to clean & calibrate are all indicated locally and output to telemetry.
System Reliability
ProAm has been designed to work where other analysers have failed! The sample delivery system has removed the need to pre-filter sample for applications to 200mg/L suspended solids, improving operational reliability. The analyser may be configured at the time of supply, to back purge the sample line with cleaning acid where sample is drawn directly from source.
PPM has also designed a panel filter mounted into a stainless steel cartridge to accommodate pumped samples and removal of suspended solids. Alternatively the filter membrane can be placed directly in the activated sludge and the analyser's integral pump is used to draw filtrate directly from source. This configuration removes the need to install sample pumps in to harsh environments thus minimizing maintenance and improving operational performance.
NH4-N - Our process
The Proam ammonia monitor has been extensively installed for both industrial and municipal monitoring. More...
