Total Nitrogen (TN) Determination

Total nitrogen is the sum of nitrate nitrogen (NO₃-N), nitrite nitrogen (NO₂-N), ammonia nitrogen (NH₃-N) and organically bound nitrogen. TN differs from TKN (Total Kjeldahl Nitrogen), which is the sum of ammonia-nitrogen and organically bound nitrogen, but does not include nitrate-nitrogen or nitrite-nitrogen. Nitrogen in freshly polluted water is initially present as organic nitrogen and ammonia. In the natural biochemical processes, organic nitrogen is gradually converted into ammonia, which is the form of nitrogen most available be utilized as a nutrient by microorganisms during the treatment process. Under aerobic conditions, the conversion of organic nitrogen into ammonia reaches a peak. Under the appropriate biological conditions, organic nitrogen is first biochemically oxidized into nitrite and then converted into nitrate. When nitrite and ammonia nitrogen are at their lowest concentrations and nitrate is at its highest value, the wastewater is considered to be completely nitrated, and a completely nitrated wastewater will have little or no organic nitrogen. Thus, nitrogen in wastewater exists in four main forms, each of which is usually analyzed as a separate constituent, with TN calculated as the sum of the four forms. TN is often regulated as an effluent parameter for municipal and industrial wastewater treatment plants, and state regulators place strict limits on an individual form of nitrogen, such as ammonia. Waste treatment plants with TN limits typically require nitrification and denitrification treatments to meet the nationally recognized TN limits.

BOC Sciences has established a wet chemical analysis method for measuring total nitrogen in water and soil using alkaline persulfate digestion combined with a Nitrate Reductase assay.

TN Analysis Methods

Since organic nitrogen is a very small component of total nitrogen in fully nitrified wastewater, the standard TN determination method applies the sum of the individual analytical results for ammonia-nitrogen, nitrate-nitrogen and nitrite-nitrogen. Organic nitrogen can be estimated from the nitrite and ammonia concentrations. High nitrite-nitrogen indicates incomplete nitrification or denitrification.

• Our experts obtain samples from intermediate points within the nutrient removal process. This is because the individual values and trends for ammonia nitrogen, nitrate and nitrite at intermediate and effluent sample points are much more indicative about the process status than the TN values.
• In addition, BOC Sciences has introduced a rapid UV-sulfate oxidation method to measure the organic fraction of TN in the raw influent wastewater. Raw wastewater samples (especially prior to screening, grit removal, FOG removal and primary clarification) are difficult to analyze, and the total nitrogen load on the treatment process is the sum of soluble organic nitrogen and ammonia contributed by the incoming wastewater, plus any nitrogen contributed by the return activated sludge plus the nitrogen from any recirculation flow back from the nitrification stages of the treatment process. Sample points are carefully selected to ensure that fat, oil and grease (FOG) content is low enough not to interfere with the sample filtration method selected for the analyzer system. And the initial sampling point for our process load estimation is after RAS and recirculation is added to the primary effluent. We perform denitrification treatment in the initial anaerobic zone, and separate measurements of nitrate and nitrite in the influent and effluent to the denitrification zone are a valuable process control parameter.

Figure 1. Distribution of total nitrogen (TN) together with its different species (μM) in surface waters. (Shreadah, M. A.; et al. 2020)

Nitrogen Management

Measuring total nitrogen, nitrate and nitrite is critical to meeting water safety standards. BOC Sciences' TN measurement analysis service can provide useful recommendations for nitrogen fertilizer applications that producers make on their fields.

• Collect the data
• Provide real-time variable and average fixed rate nitrogen prescriptions
• Recommend nitrogen and yield potential
• Optimize yields and improve nitrogen efficiency

Our TN Determination Process

At BOC Sciences, we have designed a method to measure total nitrogen in water and soil using an alkaline persulfate digestion and nitrate reductase assay. Our well-developed method customizes the measurement of total nitrogen by combining alkaline persulfate digestion with a nitrate reductase assay using enzyme-based green chemistry.

Figure 2. Determination of Total Nitrogen (Ferdinand Hill)

• Firstly, all nitrogen present in the sample is oxidized to nitrate using an alkaline persulfate reaction
• Then, in the presence of NADH, nitrate reductase is used to catalyze the reduction of nitrate to nitrite
• Next, the nitrite is treated with Griess reagents to produce a pink color, and the absorbance of this color is measured by employing a spectrophotometer at 540 nm
• Finally, a comparison with the standard curve of nitrate treated by the reduction and coloration steps can be used to determine the total nitrogen content of the sample measured