Wastewater analysis: Kjeldahl nitrogen (TKN) is defined as the sum of which nitrogenous forms present in the sample?

Introduction / Context:
Kjeldahl nitrogen (often reported as TKN) is a key parameter in sewage and sludge analysis. It is used to estimate the nitrogen that will exert oxygen demand during biological treatment and to size nutrient removal processes.

Given Data / Assumptions:

• Standard digestion and analysis procedures for TKN.
• Oxidized forms (nitrite, nitrate) are considered separately.

Concept / Approach:

TKN includes organic nitrogen and ammonia nitrogen. During Kjeldahl digestion, organic nitrogen converts to ammonium, which is then measured. Nitrite and nitrate are not included in TKN unless reduced to ammonia prior to analysis (modified methods); molecular nitrogen (N2) is not part of TKN.

Step-by-Step Solution:

Verification / Alternative check:

Standard Methods for the Examination of Water and Wastewater defines TKN accordingly, with nitrite and nitrate covered by separate analyses.

Why Other Options Are Wrong:

(a) includes N2 gas, which is not measured by TKN; (b) is vague and includes nitrogen gas; (d) cannot be correct since (a) and (b) are incorrect; (e) refers to oxidized forms not part of TKN.

Common Pitfalls:

Confusing TKN with total nitrogen (TN), which includes nitrate and nitrite; overlooking pre-reduction steps in modified methods.

Final Answer:

Organic nitrogen and ammonia nitrogen