Which statement best describes Total Kjeldahl Nitrogen (TKN) measurement?

• A. A test that measures the sum of inorganic nitrogen only.
• B. A test that measures nitrate and nitrite nitrogen.
• C. A test that measures ammonia nitrogen alone.
• D. A test that includes use of a Kjeldahl digestion apparatus to measure the sum of organic nitrogen and ammonia nitrogen in a wastewater effluent sample.

Answer: (D)

Total Kjeldahl Nitrogen quantifies nitrogen that exists as organic forms plus ammonium in a sample. The key step is the Kjeldahl digestion, which breaks down organic nitrogen and converts it into ammonium ions. After digestion, the ammonia is released and measured, usually by distillation followed by titration. Because this method targets organic nitrogen and ammonium, nitrate and nitrite forms are not included in the measurement. So the description that this method uses a Kjeldahl digestion to measure the sum of organic nitrogen and ammonia nitrogen in a wastewater sample reflects what TKN actually measures.