What are nitrate and nitrite?

Nitrate (NO3−) and nitrite (NO2−) are different nitrogen-containing ions. Each contains one nitrogen atom; nitrate contains three oxygen atoms and nitrite contains two. Reporting the whole-ion concentration is different from reporting its nitrogen content.

Nitrate

Nitrates represent a more oxidized state of nitrogen. Autotrophic bacteria convert ammonia to nitrite and then to nitrate under aerobic conditions; lightning converts large amounts of atmospheric nitrogen (N2) directly to nitrate. Bacterial reduction of nitrate can also produce nitrite under anaerobic conditions.

Nitrite

Nitrite nitrogen occurs as an intermediate stage of ammonia/ammonium biodegradation. Autotrophic bacteria convert ammonia to nitrate under aerobic (aerobic) conditions.

Nitrification and denitrification

This process occurs naturally in lakes, rivers and other water and natural environments. These biological processes are often applied in wastewater treatment or biofiltration to remove nitrogen. Nitrification may occur in drinking water distribution systems, which is not required and should be closely monitored.

Nitrification is a two-step aerobic biological oxidation of ammonia to nitrite and finally to nitrate. Denitrification is a microbially facilitated process in which nitrate is reduced anoxically to produce molecular nitrogen as the final step.

Monitor the different nitrogen species at the relevant treatment stages and manage dissolved oxygen and alkalinity for the process. Nitrification and denitrification require different conditions; a nitrate reading alone is not a measurement of ammonia, nitrite or total nitrogen.

nitrate sensor 01 — NO3-201 Digital Nitrate Nitrogen Sensor

nitrite sensor 01 — NO2-201 digital Nitrite Ion Sensor

Why measure nitrate and nitrite?

As components of the nitrogen cycle in the environment, nitrite and nitrate are important sources of nutrients and nitrogen for plants and the complex organisms that consume them. Nitrate ions are composed of oxygen and nitrogen and are naturally present in the soil. Because nitrites are readily oxidized to nitrates, they are not commonly found in surface waters.

When concentrations are adequately monitored and maintained, nitrite and nitrate play an important role in many industrial and municipal water quality monitoring programs:

Nitrites are commonly used as corrosion inhibitors in industrial process water and cooling towers.
The food industry uses nitrite compounds as preservatives.
Many granular commercial fertilizers contain nitrogen in the form of nitrates.

High nitrite and nitrate concentrations can negatively impact water treatment processes and pose health risks:

High levels of nitrate in water may indicate biological waste in the final stages of stabilization or runoff from heavily fertilized fields.
Nitrate-rich wastewater discharged to receiving waters can promote excessive algae growth, thereby reducing water quality.

Nitrite and nitrate concentrations can negatively affect wastewater treatment processes and pose health risks:

Nitrate can cause degradation of systems that maintain biological phosphorus removal by contaminating anaerobic zone conditions.
The presence of nitrite can reduce the effectiveness of chlorine disinfection systems.
Total inorganic nitrogen (TIN) levels in wastewater can lead to degradation of water quality.

Drinking-water limits: specify region and reporting basis

For U.S. public drinking-water systems, the EPA National Primary Drinking Water Regulations list a nitrate MCL of 10 mg/L measured as nitrogen (as N) and a nitrite MCL of 1 mg/L as N. These are not universal limits for every country, water use or discharge permit. Use the applicable current requirement and sampling method for the actual location and purpose.

Do not confuse mg/L NO3− with mg/L NO3−-N, or mg/L NO2− with mg/L NO2−-N. The latter expressions report the nitrogen mass, while the former report the whole ion. Confirm the unit configured in the sensor/controller and on the laboratory report before comparing results or limits.

An ion-selective sensor result also depends on its calibration, sample matrix and interfering ions. A sensor’s operating range is not a drinking-water acceptance limit. Refer to the EPA regulations and their explicit “measured as Nitrogen” labels for the cited U.S. values.

How does nitrite & nitrate sensor work?

Nitrate sensors and nitrite sensors are devices used to measure the concentration of nitrate and nitrite in aqueous solutions, respectively.The principles of the two probes offered by Apure are relatively similar, and are based on the ion-selective electrode (ISE) principle. ISE sensors are sensors based on the potentiometric method of measurement, which operates on the principle of utilizing selective electrodes to measure the response potential of specific ions (e.g., nitrate ions, nitrite ions). is measured by the response potential of the selective electrode to specific ions (e.g. nitrate ions, nitrite ions).