What Methods are Used to Monitor Nitrate 24/7, Whether in a Plant or in a Laboratory?

Question

I am in the process of writing a water treatment training manual, I have laid out the various treatment processes along with their equipment and instrumentation, starting with the raw water passing through the intake at the crib and ending with the finished water before leaving the distribution system.
 
Depending upon the chemistry of the source water, I have included the nitrate removal process, which uses an ion-exchanging process as one example. From various methods to measure the residual nitrate after the water leaves the nitrate removal process, I am trying to determine which method is used to monitor this residual online 24/7 in the plant and which method is used in the laboratory to verify that the online instruments are reading correctly. The online 24/7 monitoring system is to ensure that the nitrate removal process is working and maintaining the water quality limits per EPA.
 
I am primarily focusing on the wet colorimetric chemistry applications . All the other methods, such as nitrate ISE, and optical (UV) sensors have been taken care of. I have listed below two questions along with possible methods for each question. It is possible that one method is used in both in the plant and in laboratory. Based upon the information that I found from the literature, I am confused as to which category the methods below belongs to.
 
Which of the methods listed below is designed to monitor this residual online 24/7 in the plant?  If it is possible, please include the name of the instrument that works in this category and an operations manual. In the operations manual, I want to look at the method calibration and any information on the maintenance/troubleshooting. The illustration is used strictly for visual purposes.   
 
The cadmium reduction (I have an online nitrate colorimetric analyzer)
Hydrazine reduction (I have an online nitrate colorimetric analyzer)
Enzymatic reduction (This method may used mainly in the laboratory?)
 
 Which of the methods listed below is designed to verify that the online instruments are reading correctly?  If it is possible, please include the name of the instrument that works in this category and an operations manual. In the operations manual, I want to look at the method calibration and any information on the maintenance/troubleshooting. The illustration is used strictly for visual purposes.  
 
The cadmium reduction (I need a laboratory nitrate colorimetric analyzer)
Hydrazine reduction (I need a laboratory nitrate colorimetric analyzer)
Enzymatic reduction (This method may used mainly in the laboratory?) (I need a laboratory nitrate colorimetric analyzer)
 
Once I know which methods go where whether it is in plant or in the laboratory, I can organize these methods in the right place. Thanks.

Mir Sarfaraz Ali Khan · Answer

Try StormCAD

Stefan Platikanov · Answer

Hi Peter, chemometrics methods   such as Partial Least Squares regression applied on UV spectroscopy data   200-400nm is very appropriate to obtain a robust calibration model for NO3 using as refernce data your actual sensor/method.   This model will work accurately when experimental conditions  do not change significantly with time. These conditions include a similar concentration range, stable background of impurities (operational procedures do not change permanently).  Otherwise , frequent recalibration steps would be needed.  Choosing this chemometric approach you will need to create an experimental system based on continuous flow or  fiber optic cables  going to a classical UV desktop instrument and kind of chemometric software (commercial) or R, or Python scripts to calculate. Look at this article for information
  Dahlen et al. Chemosphere 40 (2000) 71-77.
As alternative to this let say laboratory approach,   on the market, also exist UV submergible sensors   measuring NO3  and other parameters  on line, using their global calibration models.
Hope to be useful,
Stefan

Marcus Moore · Answer

Contact your local HACH Rep.

David Sheehan · Answer

A quick search on line brings up a whole list of companies who are selling on-line nitrate sensors.  Never used one, and I am not sure how they work, but, presumably, some of them are reliable, and work in a drinking water context. 
With respect to laboratory testing, as others have noted, there are some pretty decent kits around, for example, the Merck Kit.  If you are thinking about sending the samples to an external accredited laboratory, it might be worth looking at the standard methods for nitrate analysis detailed in the current edition of APHA's Standard Methods for the Examination of Water and Wastewater, and find a laboratory that offers one of the recommended methods.  APHA's text is still the definitive source of recommended standard methods for the water analysis.
Apologies for not being able to be more specific on the details.
Cheers
David Sheehan

AGGASIT DAD · Answer

Merck kit I used since I was studying for measuring NO3, NO2,NH3..We have to concren about the waste of the mothod we use such as cadmium reduction, COD open reflux having Cr waste that is very worst for our environment.  AGGIE

What Methods are Used to Monitor Nitrate 24/7, Whether in a Plant or in a Laboratory?

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