Ammonia nitrogen (NH₃-N) is a core conventional parameter in Wastewater Monitoring. Routine detection of water quality indicators after wastewater treatment covers chemical oxygen demand (COD), total phosphorus (TP), total nitrogen (TN), and ammonia nitrogen. This paper systematically summarizes the monitoring and analytical methods of NH₃-N, an important conventional indicator in water environment detection.

1.Sources of Ammonia Nitrogen in Electroplating Wastewater

This study takes electroplating wastewater as the research object. The ammonia nitrogen in electroplating wastewater mainly comes from ammonia-containing and aniline-based corrosion inhibitors in pickling solutions, leveling agents and brighteners used in post-plating rinsing processes, as well as ammonium salt components contained in plating baths and stripping solutions. The ammonia nitrogen concentration detected in water samples refers to inorganic nitrogen existing in the form of ammonium ions (NH₄⁺) and free ammonia (NH₃). A small part of ammonia nitrogen in electroplating wastewater is derived from organic amines. In the dissolved air flotation (DAF) process, such substances can form larger flocs with coagulants and be removed from water bodies, which has little impact on the accuracy of subsequent ammonia nitrogen monitoring data.

2.Impact of Coagulants on NH₃-N Monitoring Accuracy

Polyacrylamide (PAM) is a commonly used coagulant for flocculation treatment in dissolved air flotation processes. However, PAM will release inorganic ammonium salts during the flocculation reaction, which leads to abnormal changes in ammonia nitrogen concentration data, specifically the phenomenon that the detected value of ammonia nitrogen after water treatment is higher than that before treatment. To eliminate the interference caused by coagulants and ensure the precision of NH₃-N detection results, polyaluminum chloride (PAC) can be used instead of PAM for coagulation treatment in practical detection work.

3.Analytical Methods for NH₃-N

A variety of mature analytical methods can be applied for the determination of water ammonia nitrogen, and the appropriate method can be selected according to on-site operating conditions and detection requirements. The NH3N-8000 Online Ammonia Nitrogen Monitoring Instrument adopts potassium persulfate oxidation combined with UV-visible spectrophotometry, which can realize automatic and unattended long-term water quality monitoring. The specific detection process is as follows:

· Sample Pretreatment: The collected water samples are pre-treated to remove interfering impurities, and then transferred to the digestion reaction chamber for subsequent treatment.

· Digestion Reaction:Potassium dichromate is added into the reaction chamber, and the sample is fully reacted under controlled temperature (120–150°C) and pressure (0.1–0.15 MPa) conditions with the assistance of mercury and silver salt catalysts.

· Colorimetric Detection: The ammonia nitrogen concentration is calculated through solution color comparison. Meanwhile, manual colorimetric verification can be carried out by adding salicylate reagent or Nessler’s reagent into the cuvette containing water samples.

Both automatic instrument detection and manual colorimetric detection follow the same quantitative principle: the color change degree of the solution has a linear correlation with the ammonia nitrogen content in the water sample, and the ammonia nitrogen concentration can be determined by measuring the solution absorbance value.

· Key Points for Improving Monitoring Accuracy

Electroplating wastewater has a complex water matrix, and various interfering substances in the water may cause deviations in monitoring results. To improve the reliability and stability of detection data, staff need to first clarify the basic water quality characteristics of wastewater (such as pH value and organic pollutant content) before detection. In addition, it is necessary to strictly follow standardized sampling and testing specifications, including collecting representative water samples, conducting timely sample preservation treatment (acidification to keep pH below 2), and finishing sample detection within the specified time, so as to effectively guarantee the accuracy of ammonia nitrogen monitoring results.