Ammonia in Wastewater
Ammonia (NH₃) is found in water and soil samples as the NH₄⁺ ion, while in air it exists as NH₃. According to the environmental laws of different states, ammonia (NH₃) analysis and reporting are considered to be only NH₃. Ammonia is dissolved in water and soil as NH₄⁺ but is free in air only. As the case concerns ammonia analysis in wastewater effluent, dissolved ammonium (NH₄⁺) is analyzed and considered as NH₃. Because NH₃, when absorbed in water, will change into NH₄⁺. This approach may also simplify the analysis of ammonia molecules absorbed in water, as ammonia is present as NH₄-N in some analysis procedures and methods. If anyone solves this problem, the calibration method should only use liquid ammonia or ammonium salt for calculating NH₃; only then will you obtain results for ammonia, not ammonium.
Excess ammonia can be stored in the evaporation pond and reused for fertilizer and soil sediments that may absorb it, depending on composition. By doing so, the company can save some amount and also protect the environment. There are multiple methods for the determination of ammonia in wastewater, but it’s up to the laboratory chemist how he calibrates the instrument and analyzes the sample. However, to resolve this issue, chemists should use the methods present in APHA (4500-NH₃.A,B-G,H) for water and wastewater. Furthermore, for the preparation of the standard of ammonia (NH₃) for calibration, use any salt or liquid ammonia solution.
Nesslerization of Ammonia in Wastewater
This method involves the reaction of ammonia with Nessler’s reagent (K₂ (HgI₄)), forming a yellow color. The intensity of the color is proportional to the ammonia concentration. The color can be read on a spectrophotometer at a 425 nm wavelength, where the standard of ammonia is already present in the calibration graph. Color is produced at a higher pH, while the precipitation of calcium carbonate and magnesium carbonate stays dissolved in sodium potassium tartrate. This addition of sodium-potassium tartrate depends on the presence of calcium and magnesium carbonates.
Ion-Selective Electrodes (ISE) for Ammonia in Wastewater
Ammonia-selective electrodes can measure the concentration of ammonia ions directly. This method is relatively quick and precise. This method is also usable at higher pH when free ammonia is present; the electrode senses it. It has too much interference with the wastewater matrix, like organic and inorganic compounds, while the reading of the standard is an inaccurate value.
Colorimetric Methods of Ammonia in Wastewater
Various colorimetric methods use chemical reactions to produce color changes proportional to ammonia concentration. Indophenol blue, Nessler’s reagent and salicylate methods are examples
Titration Methods of Ammonia in Wastewater
Ammonia is titrated with a standard acid solution, and the endpoint is determined by a pH indicator. This method is titrimetric analysis. pH indicators may be phenolphthalein and methyl red, as the procedure is a simple acid-base titration.
Chemiluminescence
This method exploits the chemiluminescent reaction between ammonia and hypochlorite, producing light. The intensity of light emitted is proportional to ammonia concentration.
Amperometric Methods
Ammonia can be detectable electrochemically through amperometric sensors, providing a rapid and sensitive analysis. The choice of method depends on factors like sensitivity, precision, cost, and the specific requirements of the analysis.
Three common colorimetric methods for ammonia analysis in wastewater are the following:
Ammonia in Wastewater by Indophenol Blue Method
This method involves the reaction between ammonia and the indophenol reagent, resulting in a blue color. The intensity of the color is proportional to the concentration of ammonia. Color complexes will read on a spectrophotometer.
Ammonia in Wastewater: Salicylate Method
In this method, ammonia reacts with salicylate to form a colored complex. The color intensity is then measured and correlated with the concentration of ammonia in the standard reading. Colorimetric methods are easy and cheap to use because they show the concentration of ammonia by changing color.
Ammonia in Wastewater by Nessler’s reagent
This method is widely used in analytical laboratories, having excellent accuracy and less interference and fewer errors. Based on my experience, I always recommend this method for analyzing ammonia in wastewater, and any waste from this method is properly incinerated. Because this method is preferable for analysis of ammonia in wastewater, soil, sludge, manure, and fertilizer.