Monitoring Ammonical Nitrogen in Water and Wastewater
Monitoring ammonical nitrogen (NH₃‑N) in water and wastewater is essential for evaluating pollution levels, treatment efficiency, and compliance with environmental regulations. Elevated ammonia concentrations can be toxic to aquatic organisms and often indicate contamination from sewage, industrial discharges, or agricultural runoff.
This article presents a clear, laboratory‑based Standard Operating Procedure (SOP) for determining ammonical nitrogen using the distillation and titrimetric method, a widely accepted and reliable analytical technique.
Why Measure Ammonical Nitrogen?
Ammonical nitrogen represents ammonia and ammonium compounds present in water. High levels may:
- Indicate contamination from domestic or industrial wastewater
- Cause toxicity to fish and other aquatic life
- Interfere with drinking water treatment processes
- Signal incomplete biological treatment in wastewater plants
Accurate measurement of ammonical nitrogen is therefore critical for environmental monitoring, regulatory compliance, and treatment process control.
Objective of the Method
The objective of this method is to determine the concentration of ammonical nitrogen (NH₃‑N) in water and wastewater samples using a standardized laboratory procedure that ensures accuracy, reliability, and repeatability of results.
Principle of Analysis
The method is based on the alkaline distillation of ammonia from the sample. The sample is buffered to a pH of approximately 9.5 using a borate buffer, which minimizes the decomposition of cyanates and organic nitrogen compounds.
Under alkaline conditions, ammonia is liberated and distilled into a receiving solution of boric acid. The absorbed ammonia is then determined by titration with standard sulfuric acid using a mixed indicator. The volume of acid consumed is directly proportional to the ammonical nitrogen content of the sample.
Apparatus and Equipment
The following laboratory equipment is required:
- Pipettes
- Conical flasks
- Nitrogen distillation assembly
- Heating mantle
Reagents
All reagents should be of analytical reagent grade.
- Sodium Tetraborate (0.025 M): Dissolve 9.5 g Na₂B₄O₇·10H₂O in 1 L distilled water
- Borate Buffer: Mix 500 mL of 0.025 M sodium tetraborate with 88 mL of 0.1 N NaOH
- Sodium Hydroxide (6 N): Dissolve 240 g NaOH in 1 L distilled water
- Mixed Indicator Solution: Methyl red and methylene blue dissolved in ethanol or propanol
- Indicating Boric Acid Solution: Dissolve 20 g H₃BO₃ and add 10 mL mixed indicator; dilute to 1 L
- Sulfuric Acid (0.1 N and 0.02 N): Prepare and standardize as required
- Sodium Carbonate (0.05 N): Dissolve 2.5 g in 1 L distilled water
Test Method
Distillation Procedure
- Take 250 mL of dechlorinated sample or dilute the sample to 250 mL.
- Adjust the pH to approximately 7.0, if required.
- Add 25 mL borate buffer and adjust the pH to 9.5 using 6 N NaOH.
- Assemble the distillation unit and begin distillation at a rate of 6–10 mL per minute.
- Collect the distillate in a 500 mL conical flask containing 50 mL indicating boric acid solution.
- Perform a reagent blank under identical conditions and apply blank correction.
Titration
Titrate the collected distillate with 0.02 N sulfuric acid until a pale lavender endpoint is observed.
Calculation
Ammonical Nitrogen (mg/L) is calculated using the formula:
Ammonical Nitrogen (mg/L) = ((A − B) × N × 14 × 1000) / Sample Volume (mL)
Where:
- A = Volume of sulfuric acid used for the sample (mL)
- B = Volume of sulfuric acid used for the blank (mL)
- N = Normality of sulfuric acid
- 14 = Atomic weight of nitrogen
Example Calculation
Given:
- A = 12.5 mL
- B = 0.5 mL
- N = 0.02 N
- Sample volume = 250 mL
Step 1: Blank correction 12.5 − 0.5 = 12.0 mL
Step 2: Multiply by normality 12.0 × 0.02 = 0.24
Step 3: Multiply by atomic weight of nitrogen 0.24 × 14 = 3.36
Step 4: Convert to mg/L 3.36 × 1000 / 250 = 13.44 mg/L
Conclusion
The distillation–titrimetric method is a reliable and widely accepted approach for determining ammonical nitrogen in water and wastewater. Strict adherence to this SOP ensures accurate results, supports regulatory compliance, and aids in effective water quality assessment. Consistent monitoring of ammonical nitrogen plays a vital role in protecting aquatic ecosystems and ensuring sustainable water management practices.
