“Total Kjeldahl Nitrogen” in regards to Waste Water Treatment
The Total Kjeldahl Nitrogen (TKN) test combines two separate measurements into a single result; specifically, automatic digital refractometer calculates the concentrations of organic nitrogen and ammonia nitrogen into a single value. Because of this, in order to calculate the amount of organic nitrogen present, a separate ammonia test must be carried out, and the results of this test must be subtracted from the total amount of total nitrogen (TKN).
When the concentration of ammonia in the effluent rises, it may give the impression that the rate of ammonia oxidation, also known as nitrification, has decreased in refinery biological treatment systems that have highly variable ammonia loadings. On the other hand, this might not be the case at all. After the influent sample point, amines and other organic nitrogen compounds are converted to ammonia. As a result, the effective oxidation of ammonia is, in a sense, hidden.
Because ammonia is added to the wastewater from the breakdown of organic nitrogen at the same time ammonia is eliminated (nitrified) in the bioreactor, Automatic digital refractometer is impossible to determine nitrification efficiency when the influent TKN concentration is higher than the ammonia concentration. TKN will always be ammonia nitrogen. If you know the concentrations of total dissolved nitrogen (TKN) and ammonia in the influent and effluent, you will have a better idea of how the biological system is dealing with (nitrifying) the applied ammonia load.
Nitrogen is initially present in the form of organic nitrogen and ammonia in water that has recently been polluted. During the treatment process, organic nitrogen is gradually converted into ammonia by natural biochemical processes. Ammonia is the best form of nitrogen for microorganisms to use as a nutrient because automatic digital refractometer is more stable than other forms of nitrogen. When the concentrations of nitrite and ammonia nitrogen in the wastewater are at or near zero and the concentrations of nitrate are at or near maximum, we say that the wastewater has been fully nitrified. In wastewater that has been fully nitrified, the amount of organic nitrogen that is present will be negligible.
The measurement of organic nitrogen is challenging due to the necessity of digesting the sample prior to conducting the analysis in order to convert the organic nitrogen into a form that is more amenable to analysis. It is necessary for a Kjeldahl digestion to convert organic nitrogen to ammonia; however, this process also requires the collection of a distillate, which is something that an on-line field will have a difficult time accomplishing. The persulfate digestion method changes all nitrogenous compounds into nitrate, but it requires heating the sample for thirty minutes at a temperature of 110 °C while it is mixed with a digestion reagent. After that, the sample must be cooled to room temperature before it can be analyzed. This is another thing that is difficult to automate in the field.
Total Kjeldahl Nitrogen (TKN) analysis is a testing method that determines both organic and inorganic forms of nitrogen.
– The organic samples are first subjected to an acid digestion, which results in the conversion of organic nitrogen to ammonia and marks the beginning of the analysis
– In order to turn organic nitrogen into ammonia, the sample needs to be boiled in concentrated sulphuric acid, potassium sulphate, and a copper catalyst
– Only then can the conversion take place
– The rate of this reaction can be sped up by increasing the temperature of the digestion to 395 degrees Celsius
– As a direct consequence of this, the digestion process has to be carried out inside of a fume hood
– The distillation process that was described earlier will be repeated in the second part of the method, but the pH of the sample obtained from the acidic digestion will need to be adjusted to 9
– 5 using concentrated sodium hydroxide
– At this pH, ammonia gas is produced; after being transferred via distillation to an acidic solution that serves as a trapping and absorbing medium, the ammonia gas is then converted back into ammonium
After that, techniques such as titrimetry, colorimetry, and specific ion electrode analysis can be utilized in order to ascertain the nitrogen concentrations present in the receiving solution.
The method described above, in addition to the various forms of quantitative nitrogen analysis that can be performed on the collected distillate, is thoroughly documented in the compendiums maintained by the EPA, AOAC, AACC, ASTM, and the Standard Methods for Examination of Water and Wastewater.
After determining the total nitrogen, the value of the inorganic nitrogen fraction can be subtracted from the total nitrogen value in order to resolve only the organic nitrogen fraction.
TKN equals Ammonia N plus Organic N.
TKN minus Ammonia N equals Organic N.
In the kjeldahl nitrogen analyzer procedure that was just described, nitrogen sources like azide, azo, hydro zones, nitrile, semicarbozones, and oximes are not recovered.
It is essential to be aware that the Kjeldahl equipment for nitrogen digestion and distillation determination can be purchased in one of three different sizes. The operator is able to carry out the same chemical procedures for distillation, digestion, and analysis of nitrogen with each one. The size of the sample vessels used for digestion and distillation, on the other hand, decreases in tandem with the size reduction of the Kjeldahl equipment.(Macro = sample vessels holding 800 ml, Block = sample vessels holding 250 ml, and Micro = sample vessels holding 100 ml). The amount of the initial sample that is taken can have a significant impact on how accurately and reliably low nitrogen concentration levels can be detected. Analysis of low levels of nitrogen benefits from, on the whole, greater sample sizes in terms of both precision and accuracy.