I. Why does pickling wastewater testing often show Ammonia Nitrogen > Total Nitrogen?
Ammonia Nitrogen (Nessler’s Method – N2/N3) reads falsely high.
Pickling wastewater characteristics: High Cl⁻, heavy metals, acidic, potential presence of residual chlorine/organic matter.
Nessler’s reagent (N2/N3): Poor interference resistance; easily affected by color, turbidity, metals, and Cl⁻, leading to artificially high results.
1. Total Nitrogen: UV Method (HJ 636-2012)
Lianhua: Uses UV method reagents; dual-wavelength (220/275 nm) measurement automatically corrects for organic matter interference.
High Cl⁻/organic matter in pickling water: The UV method offers significantly better interference resistance than visible light methods.
2. Ammonia Nitrogen: Nessler’s (N2/N3) vs. Salicylate Reagent
Nessler’s (N2/N3): Susceptible to interference from heavy metals, Cl⁻, and color; often yields falsely high readings in pickling water.
Salicylate (LH-NH3-SAH/SAL): Strong interference resistance, stable color development, and superior tolerance to Cl⁻ and heavy metals; suitable for industrial wastewater.
Actual measurement: For the same pickling water sample, Salicylate results are lower and more accurate than Nessler’s results.
II. Reagent Operation Steps
Ammonia Nitrogen (Salicylate Method)
Reagents: LH-NH3-SAH (0.5–50 mg/L) or SAL (0.02–2.5 mg/L).
Pre-treatment: Flocculation and sedimentation (50 mL sample + 1 mL 10% ZnSO₄ + NaOH to adjust pH ≈ 10.5), then collect the supernatant; filter through a 0.45 μm membrane if necessary.
High Ammonia Nitrogen: Dilute (e.g., 10-fold) before testing.
Total Nitrogen (UV Method)
Reagents: Lianhua UV method reagents; use instrument LH-TN360 or a multi-parameter meter with UV capability.
Digestion: 150°C, 20 min.
Colorimetry: Add dilute hydrochloric acid before colorimetric measurement. III. Summary
The phenomenon where “ammonia nitrogen > total nitrogen” in pickling wastewater stems from an artificially high ammonia nitrogen reading (via the Nessler method) combined with an understated total nitrogen reading (via the non-UV method).
This inversion issue can generally be resolved by using the UV method for total nitrogen and the salicylate reagent for ammonia nitrogen, alongside simple pre-treatment.
Post time: Jul-03-2026
