WTW IQ Sensor Net NitraVis Sensor

UV Spectral Sensors for Nitrate and Nitrite in Wastewater Management

The WTW NitraVis 700 series spectral sensors are advanced spectrophotometers designed for continuous in-situ measurement of nitrate (NO₃), nitrite (NO₂), and total suspended solids (TSS) in water. These sensors are integral to the IQ Sensor Net system, providing precise, reagentless UV-VIS spectral analysis across 256 wavelengths between 200 and 720 nm to get the most accurate measurements with precise compensation for interefences such as turbidity.

They feature robust construction, ultrasonic cleaning technology, and integration capabilities, making them ideal for monitoring and optimizing wastewater treatment processes in influent, aeration, and effluent applications. The models cater to specific measurement needs, ensuring high accuracy and minimal maintenance for reliable long-term operation

Product Features

UV-VIS Spectral Analysis: Scans 256 wavelengths per measurement from 200 to 720 nm for high-accuracy readings.
Reagentless Operation: Eliminates the need for chemical reagents, reducing environmental impact and operational costs.
UltraClean Technology: Ultrasonic cleaning system prevents biofouling, minimizing maintenance requirements.
Robust Construction with IP68 Waterproof Rating: Made from corrosion-resistant materials such as titanium (Grade 2) and PEEK, with a sapphire glass window, ensuring durability in harsh environments.
Wide Measurement Ranges:
- Nitrate (NO₃-N) - All Models
- Total Nitrate (NO₃) - All Models
- Nitrite (NO₂) - 701/705 NI Models only
- Total Suspended Solids (TSS) - 701/705 TS Models only
High Precision: ±3% of the measured value or ±0.5 mg/L.
Factory-Calibrated: Ensures reliable performance and accuracy.
Integration with IQ SensorNet: Seamlessly integrates with the IQ Sensor Net system and controllers for advanced process monitoring and control.
Environmental Compatibility: Meets CE and FCC Class A standards for electromagnetic compatibility and is built for use in a wide range of pH (4 to 12) and temperature (0 to 45 °C) conditions.
Maintenance-Free Design: Features built-in UltraClean ultrasonic cleaning and air holes for added cleaning in high fouling applications, reducing the need for routine maintenance.
Warranty: Comes with a 2-year warranty for defects in quality

The innovative spectral measuring technique of the WTW IQ Sensor Net NitraVis® sensors allows the determination of nitrate and nitrite directly in the process. Based on the measurement of the entire spectrum, cross sensitivities of individual parameters among each other and interference such as turbidty are eliminated effectively. This ensures highly precise and reliable measuring results!

Easy handling:

Based on the optical method, time-consuming steps such as sampling and sample preparation are eliminated. This also eliminates waiting for response time, which allows for a nearly continuous measuring process. This makes measured values available quickly and without complications.

Minimal operating costs:

Spare parts such as wiper profiles and seals are not necessary thanks to the maintenance-free ultrasonic cleaning. The use of a chemical-free measuring method further reduces operating costs to a minimum.

NitraVis 701 (IQ, TS, NI) Variants:

The 701 series is optimized for lower concentration ranges and specific applications such as influent and aeration tanks, making them suitable for initial treatment stages compared to the 705 series.

NitraVis® 701 IQ Optical nitrate probe:
- SKU: 481044
- Nitrate (NO₃-N), Total Nitrate (NO₃),
NitraVis® 701 IQ TS Double sensor Optical nitrate/TSS probe:
- SKU: 481045
- Nitrate (NO₃-N), Total Nitrate (NO₃), TSS
NitraVis® 701 IQ NI Double sensor Optical nitrate/nitrite probe:
- SKU: 481054
- Nitrate (NO₃-N), Nitrite (NO₂)

NitraVis 705 (IQ, TS, NI) Variants:

The 705 series is optimized for higher concentration ranges and is better suited for effluent applications, making them ideal for later stages of wastewater treatment where higher levels of contaminants are expected.

NitraVis® 705 IQ - Optical nitrate probe
- SKU: 481046
- Nitrate (NO₃-N), Total Nitrate (NO₃)
NitraVis® 705 IQ TS - Optical nitrate/TSS probe
- SKU: 481047
- Nitrate (NO₃-N), Total Nitrate (NO₃), Total Suspended Solids (TSS)
NitraVis® 705 IQ NI - Optical nitrate/nitrite probe
- SKU: 481055
- Nitrate (NO₃), Nitrite (NO₂)

Specifications

Specifications	NitraVis® 701 IQ NI	NitraVis® 705 IQ NI	NitraVis® 701 IQ TS	NitraVis® 705 IQ TS	NitraVis® 701 IQ	NitraVis® 705 IQ
Order No.	481056	481057	481045	481047	481044	481046
Measuring method	Spectral Measurement in the UV Range (200 – 390 nm)	Spectral Measurement in the UV Range (200 – 390 nm)	Spectral Measurement in the UV-VIS Range (200 – 720 nm)	Spectral Measurement in the UV-VIS Range (200 – 720 nm)	Spectral Measurement in the UV-VIS Range (200 – 720 nm)	Spectral Measurement in the UV-VIS Range (200 – 720 nm)
Measuring gap (optical layer thickness)	1 mm	5 mm	1 mm	5 mm	1 mm	5 mm
Application (optimized for)	Municipal wastewater:	Municipal wastewater:	Municipal wastewater:	Municipal wastewater:	Municipal wastewater:	Municipal wastewater:
Measuring range and Resolution, Inlet & Aeration: NO3	0.0 ... 300.0 mg/l 0.1 mg/l	-	0.0 ... 300.0 mg/l 0.1 mg/l		0.0 ... 300.0 mg/l 0.1 mg/l
Measuring range and Resolution, Inlet & Aeration: NO3-N	0.00 ... 60.00 mg/l 0.01 mg/l	-	0.00 ... 60.00 mg/l 0.01 mg/l		0.00 ... 60.00 mg/l 0.01 mg/l
Measuring range and Resolution, Inlet & Aeration: NO2	0.0 ... 120.0 mg/l 0.1 mg/l	-
Measuring range and Resolution, Inlet & Aeration: NO2-N	0.00 ... 30.00 mg/l 0.01 mg/l	-
Measuring range and Resolution, Effluent: NO3	0.0 ... 750.0 mg/l 0.1 mg/l	0.0 ... 250.0 mg/l 0.1 mg/l	0.0 ... 750.0 mg/l 0.1 mg/l	0.0 ... 250.0 mg/l 0.1 mg/l	0.0 ... 750.0 mg/l 0.1 mg/l	0.0 ... 250.0 mg/l 0.1 mg/l
Measuring range and Resolution, Effluent: NO3-N	0.0 ... 150.0 mg/l 0.1 mg/l	0.00 ... 50.00 mg/l 0.01 mg/l	0.0 ... 150.0 mg/l 0.1 mg/l	0.00 ... 50.00 mg/l 0.01 mg/l	0.0 ... 150.0 mg/l 0.1 mg/l	0.00 ... 50.00 mg/l 0.01 mg/l
Measuring range and Resolution, Effluent: NO2	0.0 ... 300.0 mg/l 0.1 mg/l	0.0 ... 100.0 mg/l 0.1 mg/l
Measuring range and Resolution, Effluent: NO2-N	0.00 ... 75.00 mg/l 0.01 mg/l	0.00 ... 25.00 mg/l 0.01 mg/l
Inlet TSS			0.00 ... 15.00 g/l 0.01 g/l
Aeration TSS			0.00 ... 20.00 g/l 0.01 g/l
Effluent TSS			0.00 ... 20.00 g/l 0.01 g/l	0.0 ... 900.0 mg/l 0.1 mg/l
Flow rate	≤ 3 m/s	≤ 3 m/s	≤ 3 m/s	≤ 3 m/s	≤ 3 m/s	≤ 3 m/s
Pressure Resistance	Maximum 1 bar (incl. sensor connection cable)	Maximum 1 bar (incl. sensor connection cable)	Maximum 1 bar (incl. sensor connection cable)	Maximum 1 bar (incl. sensor connection cable)	Maximum 1 bar (incl. sensor connection cable)	Maximum 1 bar (incl. sensor connection cable)
Electrical connections	2-wire shield cable with quick fastener to sensor	2-wire shield cable with quick fastener to sensor	2-wire shield cable with quick fastener to sensor	2-wire shield cable with quick fastener to sensor	2-wire shield cable with quick fastener to sensor	2-wire shield cable with quick fastener to sensor
Electromagnetic Compatibility	EN 61326, Class B, FCC Class A Intended for indispensable operation	EN 61326, Class B, FCC Class A Intended for indispensable operation	EN 61326, Class B, FCC Class A Intended for indispensable operation	EN 61326, Class B, FCC Class A Intended for indispensable operation	EN 61326, Class B, FCC Class A Intended for indispensable operation	EN 61326, Class B, FCC Class A Intended for indispensable operation
Certifications	CE	CE	CE	CE	CE	CE
Mechanical	Housing: Titan Grade 2, PEEK Window: Sapphire glass Protection class: IP 68	Housing: Titan Grade 2, PEEK Window: Sapphire glass Protection class: IP 68	Housing: Titan Grade 2, PEEK Window: Sapphire glass Protection class: IP 68	Housing: Titan Grade 2, PEEK Window: Sapphire glass Protection class: IP 68	Housing: Titan Grade 2, PEEK Window: Sapphire glass Protection class: IP 68	Housing: Titan Grade 2, PEEK Window: Sapphire glass Protection class: IP 68
Weight (without cable)	Approx. 8.82 lb (4 kg)	Approx. 8.82 lb (4 kg)	Approx. 8.82 lb (4 kg)	Approx. 8.82 lb (4 kg)	Approx. 8.82 lb (4 kg)	Approx. 8.82 lb (4 kg)
Warranty	2 years for defects in quality	2 years for defects in quality	2 years for defects in quality	2 years for defects in quality	2 years for defects in quality	2 years for defects in quality

FAQ

What do I want to measure and why?

When selecting a UV or UV Vis sensor, you first and foremost need to know what and why. What parameters do you want to measure? What is the application? How will the sensor be used? Depending on the application, it may even be beneficial to monitor multiple parameters on a single sensor.

Nitrogen

The nitrogen parameters, nitrate and nitrite, are commonly measured in biological nutrient removal (BNR) applications. Nitrate can provide several opportunities for process optimization, such as ensuring efficient completion of nitrification, monitoring nitrate removal, controlling carbon dosing in anoxic zones, and ensuring effluent compliance with nitrogen limits. Nitrite is less often measured as it is the intermediate stage of the nitrification process. Monitoring nitrite may be beneficial if a wastewater facility has an issue with nitrite accumulation or is utilizing a shortcut denitrification process.

There are many possible applications for UV and UV Vis sensors and some instances where multiple parameters on a single sensor can be beneficial to the operator. As an example, total suspended solids (TSS) is a common measurement within aeration basins which indicate the concentration of microorganisms present (MLSS – mixed liquor suspended solids). Monitoring several parameters with a single sensor can provide additional value by acquiring more useful data from a single sensor.

The NitraVis 700 Series can measure nitrate, nitrite, and TSS.

NitraVis 701/705 IQ measures Nitrate (NO₃-N) and total Nitrate (NO₃).
NitraVis 701/705 IQ NI measures Nitrate (NO₃-N) and Nitrite (NO₂).
NitraVis 701/705 IQ TS measures Nitrate (NO₃-N) and TSS.

What’s the difference between single-wavelength and spectral sensors?

Some manufacturers only have single-wavelength sensors where others like WTW have single-wavelength and spectral sensors which offer more parameters and higher accuracy. Previously, we have been discussing the spectral sensors in which 256 wavelengths of UV and visible light are scanned per measurement to get a concentration of your desired parameter. These sensors measure absorbance at each wavelength to produce a ‘spectral footprint’. Each ‘spectral footprint’ is then calculated into a mg/L concentration based on algorithms programmed in the sensor (Smith, 2019). This spectral measurement provides better precision and accuracy then single wavelength sensors because absorption by a molecule occurs over a band of wavelengths, rather than just one. The additional wavelengths provide several benefits including more absorption data for each parameter, a range of wavelengths for turbidity correction, and can even help detect different forms of organic molecules.

The 256 wavelengths scanned by UV Vis spectral sensors span across both UV and visible wavelengths from 200 to 720nm. The 256 wavelengths scanned by UV spectral sensors span between 200 and 390nm. This allows UV sensors to be able to measure and differentiate between nitrate and nitrate. Nitrate and nitrite typically absorb at the shorter UV wavelengths (<250nm), while the organic molecules absorb most strongly at UV wavelengths between 250-350nm. Absorbance across 380 to 720 nm is from turbidity which is measured and corrected for with each measurement (Smith, 2019).

However, there are two single-wavelength sensors that use the absorbance of one wavelength to determine the concentration of a particular parameter. The UVT-254 sensor (or SAC-254) measures the transmission or absorbance (%) of light at the 254nm wavelength. Ultraviolet light at 254nm is absorbed by organic molecules, making this sensor useful for trending organics concentration within drinking water and wastewater. With the UVT-254 sensor, a correlated value of COD, BOD, and TOC can be reported with an accurate calibration and a second wavelength (550nm) is measured for turbidity correction. The NOx sensor measures the sum of nitrate (NO3 - N) and nitrite (NO2 - N) using a single wavelength which can be sufficient for monitoring nitrogen in some biological nutrient removal applications.

Although single-wavelength sensors can provide useful data and trending, they are limited in accuracy and repeatability compared to the spectral sensors. With the single-wavelength measurement and turbidity correction, these sensors may not detect some forms of organic molecules, can not differentiate between nitrate/nitrite, and do not compensate for turbidity as accurately.

The single-wavelength and spectral sensors both provide benefits, so which is best for your application? The single-wavelength sensors can provide trending for organics or NOx at a moderate price, and there are even applications which specifically utilize single-wavelengths sensors, such as UVT-254 for UV disinfection. However, the spectral sensors are calibrated to specific applications (influent, secondary treatment, effluent) and because they scan 256 wavelengths, they provide higher accuracy, higher repeatability, and better correction for turbidity than single wavelength sensors.

What is the path length and why is it important?

Path length, or distance between the light source and detector, is important to the spectrophotometric measurement. Path length (aka gap width) is a factor in the calculation of absorbance according to the Lambert-Beer law and is affected greatly by the turbidity of the sample water. For that reason, UV Vis sensors usually have fixed path lengths and provide different gaps for specific applications. The IQ Sensor Net UV Vis sensors have 2 choices for path length: 1 mm and 5 mm. The 1 mm gap is for monitoring untreated wastewater and secondary treatment due to the high turbidity that is typical of these applications. The 5 mm gap is for monitoring treated effluent, wastewater with low turbidity, and can sometimes be adapted to some surface water or drinking water applications. Other manufacturers can have gap lengths of 10-50 mm gap lengths depending on the type of application. When choosing a WTW UV Vis sensor, choose the 701 style sensor for a 1mm path length (untreated wastewater or activated sludge) or the 705 style sensor for the 5 mm path length (low turbidity treated effluent).

How will I mount my UV Vis sensor?

UV Vis sensors are typically larger and heavier than other online sensors and special consideration must be taken when deciding between mounting options. Same as with all online sensors, location and sensor mounting should be chosen based on safety and accessibility. Sensors will need to be easily reached for occasional maintenance, so it is important to have plenty of space to work with the sensor. Mount the sensor in locations that meet the required safety standards for hand railings and walkways. Along the same lines, the mount for UV Vis sensors should be easy to use and allow for easy maneuverability of the sensor. Finally, since the sensors can be heavier, a mount that is robust and able to handle the weight is very important, especially for wastewater facilities with ragging issues.

The most common way to mount UV Vis sensors in wastewater is with immersion mounting. Immersion mounting provides direct measurement of the process water by submerging the sensor directly into a basin or stream. There are two options for immersion mounting WTW UV Vis sensors: a rigid mount or swing/chain mount. Rigid mounts involve fixing the UV Vis sensor to a metal pole and then mounting to either a railing or wall. This type of mount is best when a more robust solution is needed, for example, if the water is turbulent or has ragging. For typical immersion mounting applications, a swing and chain mount can provide several benefits. This type of mount provides better ease of use, as the sensor is suspended at the end of a chain and is simply raised or lowered into the basin with the chain. The swing arm extends the sensor out across the basin, but can be easily accessed by swinging the sensor closer to the railing to remove the sensor for maintenance.

For clean water applications such as treated wastewater effluent, water reuse, or drinking water, a flow-thru cell may be the best option. Immersion mounting may not be possible in these applications due to lack of suitable location or NSF requirements. With a flow-thru cell, the UV Vis sensor is wall mounted and the cell creates a chamber for water to flow across the optical window. Flow is continuously brought to the sensor for measurement and then drained. Whether you are using a WTW UV Vis sensor for clean water or dirty water, choosing the best mounting option for the application will ensure the sensor operates correctly and keeps the required maintenance to a minimum.

Maintenance Requirements

Although UV Vis sensors are light on maintenance and do not require reagents, they still require occasional attention for optimal operation. The WTW UV Vis sensors have the huge benefit of requiring the least amount of maintenance compared to other online sensors. These sensors have built-in UltraCleanTM technology, a unique and automatic ultrasonic cleaning system. This system not only helps keep the measuring windows cleaner for longer, but the system is also entirely internal to the sensor, so there are no seals or wipers to replace.

Maintaining a clean UV Vis sensor is vital to sensor performance. For this reason, UV Vis sensors often have automatic cleaning systems, which are effective in reducing the overall time required to maintain the sensor. WTW offers two types of automatic cleaning systems: UltraClean which is built-in to all sensors and secondary air blast cleaning systems. The UltraClean ultrasonic cleaning system subtly vibrates the optical windows of the sensor, dislodging any solids building up. This technology has proven to be very successful in wastewater applications with high solids and is also utilized on WTW’s ViSolid (TSS) and VisoTurb (turbidity) sensors. The other option for automatic cleaning of WTW UV Vis sensors is an air blast system.

This system uses an air compressor to periodically force pressurized air over the optical windows, removing any solids that could disrupt the measurement. The WTW air blast system links directly to the sensor and is programmable within the controller to clean at a desired interval. Both automatic cleaning systems are capable of keeping sensors reading accurately for several weeks within wastewater applications.

Automatic cleaning systems are great for reducing overall maintenance time, but occasional manual cleanings are still required for optimal performance. Removing the UV Vis sensor from the process every two weeks for a manual cleaning goes a long way in reducing potential measurement issues. Manual cleaning is a quick 1 minute procedure that involves flushing out the measuring gap with clean water, applying a cleaning solution, polishing the lens with a soft cloth, and rinsing thoroughly. Furthermore, keeping a routine maintenance schedule ensures a clean sensor.

Another aspect of maintenance is calibration and verification. Calibration for WTW UV Vis sensors is performed using lab reference samples, which are used to adjust the slope correlating the sensor’s raw signal to the concentration value. As previously mentioned, the spectral sensors are factory calibrated to specific applications, but they can be calibrated to adapt the sensor’s measurements to the process water. The single-wavelength sensors can also be calibrated for their main parameters, but the correlated values (BOD, TSS, TOC etc.) must be calibrated to be accurate to lab measurements. Calibration is performed as needed, such as when a sensor is first installed, moved to a new location, or the sensor is inaccurate to reference samples. WTW UV Vis sensors have a dual channel measuring system, in which an identical reference channel monitors and corrects for aging in the lamp or detector, preventing any potential calibration drift in the sensor. This makes routine calibrations unnecessary, however routine verification of the sensor measurement using a lab reference is recommended to ensure the accuracy of the sensor.

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IQ Sensor Net System WTW IQ Sensor Net NitraVis® 700 Series Sensor