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

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.