How to perform real-time analysis of nitrate and nitrite in the harshest wastewater conditions

The  Aquamonitrix® was created to operate in the harshest conditions the wastewater sector has to offer. This recently introduced game-changing device offers simultaneous and distinct real-time data of nitrite separate from nitrate and enables low-intervention operation over long deployments, whilst performing with laboratory-quality accuracy on potable water, wastewater, environmental and aquaculture samples.

A blockage-resistant sample-intake line ensures that the Aquamonitrix is making precise readings even in tricky wastewater applications; nitrate and nitrite are measured independently and individually from the same sample. This portable analyser that offers instant data transmission, performs, maintenance-free and is simple to set-up and service and has low operational costs. 

Precise nitrate and nitrite measurement in tough wastewater applications   
Nitrate is ubiquitous in effluent discharged by municipal wastewater treatment plants, intensive poultry and pig farms, aquaculture and a variety of manufacturing sectors. 

Obtaining reliable nitrate and nitrite measurements has traditionally been a difficult task with autonomous analysers until now. They are prone to accuracy drift and then there are the annoying tasks of recalibrating and dealing with biofouling and blockages. Many WWTP managers opt for manual grab sampling followed by lab analysis, which works, but needs a skilful operator, costs extra time and money and takes longer to obtain the vital data.

However, help is at hand; the rugged Aquamonitrix® delivers accurate, real-time results with low intervention and maintenance requirements, even in the harshest conditions.   

The analyser’s analytical technology is based on rapid ion chromatography and UV LED detection. As shown in Figure 1, the integral sample intake system works using a sample loop through which the sample is drawn and fills an internal reservoir. A few microlitres are taken from the reservoir for analysis. The sample is passed through an anion exchange separation column and then into the custom UV LED-based detector, where nitrite and nitrate are selectively detected. All analyte concentrations and system control data are transmitted automatically in real-time to the operator’s preferred choice of proprietary IoT platform, telemetry system and/or SCADA control infrastructure. 

Thanks to the microlitre level volume of sample used, the simple in-built sampling system is ideal for a majority of wastewater applications. You can even use the Aquamonitrix for activated sludge if you include a simple, low-cost filter system for a few hundred Euros or Pounds – a significant saving when you consider that conventional UV-based analysers may need a further investment of £15,000 for additional wastewater sampling systems.  

Accurate real-time measurement of nitrite independent of nitrate 
There are some automated, real-time devices for monitoring nitrate and total nitrogen or the sum of nitrate and nitrite. The reason Aquamonitrix is such as stand-out instrument is because it offers precise and real-time analysis of nitrate and nitrite not just simultaneously from the same sample, but taken separately (see Fig.2) 

Accurate measurement of nitrite or its ratio to nitrate is an important parameter for optimising many water and wastewater processes. 

One example of such a process is biological nitrogen removal (BNR). Short-cut BNR processes that reduce aeration energy requirements try to either partially or totally avoid nitrate formation opting to convert nitrite directly to nitrogen gas. In this scenario, the capability to monitor nitrate and nitrite precisely in real-time will improve process understanding and dynamics considerably. 

Drinking water providers who experience the occasional excess of nitrate also benefit from real-time and individual readings of nitrate and nitrite, instead just measuring the sum total. Aquamonitrix® can be installed on intake and outlet lines in drinking water treatment facilities, with configurable alarms that can alert personnel in real-time of excess nitrate and/or nitrite. 

Real-time measurement of nitrite separate from nitrate is also vital in finding, controlling and evading nitrification problems in potable water treated by chloramine disinfection on route through the distribution network to the consumers’ taps. 

In aquaculture applications, biological filters convert built-up ammonia in recirculating systems to nitrite and then nitrate, therefore real-time monitoring for the build-up of the nitrite intermediate is critical considering its high level of toxicity to fish. 

Intervention-free high-frequency environmental monitoring 
Nitrate is getting more and more attention as an environmental contaminant. Wales is now designated as a ‘Nitrate Vulnerable Zone. In the area around southern England’s Solent there was a halt in housing construction in 2020 while deals needed to be struck over nitrate trading and mitigation. These high-profile cases have highlighted the need for groundwater monitoring, environmental assessments and nitrate trading schemes which in turn require frequent, accurate and reliable nitrate monitoring. 

Aquamonitrix® was tested in a series of three-month surface water monitoring applications. The analyser was up and running within an hour of arriving at the location and sending precise data in real-time through IoT to the users’ PCs. The sampling line can be deployed directly in a river, reservoir or lake; the sampling troughs needed for conventional UV detection are no longer required. 

Figure 3 shows how the readings were in close corroboration with results taken from grab samples and then analysed for nitrate in an accredited lab. 

During the 13-weeks in which the analysers were deployed, the only site visits needed were to replenish the reagent cartridge and empty the stored waste sample. Thie easy task took less than five minutes and, with samples taken on an hourly basis, was only needed to be carried out roughly once every four weeks. This period could easily be lengthened by using bigger reagent and waste cartridges. 

To conclude: the Aquamonitrix® proved itself to truly be a plug, play and forget system that provides laboratory quality precision in real-time.