Ammonium in Wastewater

Reflectometric determination after reaction with Nessler’s reagent or by using the indophenol blue method.

Introduction

Nitrogen in the form of ammonium is an important nutrient to test in wastewater. If there is excessive ammonium left in treated water, it can lead to environmental problems including eutrophication— excessive growth of algae and plants—upsetting marine ecosystems.¹ Thus, monitoring ammonium in wastewater is a key step. In this application note, ammonium is determined in wastewater using the Reflectroquant^® system and test strips.

Experimental Method

The test kit catalog numbers apply for the following methods:

• 1.16899 and 1.16892: Ammonium ions react with a chlorinating agent to form monochloramine. This in turn reacts with a phenol compound to form a blue indophenol derivative that is determined reflectometrically.
• 1.16977: Ammonium ions react with Nessler’s reagent to form a yellow-brown compound that is determined reflectometrically.

Reagents and Instruments

Test Kits

• Ammonium Test Method: reflectometric with test strips and reagents 20 – 180 mg/l NH₄⁺ Reflectoquant^® (1.16977) or
  
• Ammonium Test Method: reflectometric with test strips and reagents 5.0 - 20.0 mg/l NH₄⁺ Reflectoquant^® (1.16899) or
• Ammonium Test Method: reflectometric with test strips and reagents 0.2 - 7.0 mg/l NH₄⁺ Reflectoquant^® (1.16892)

Optional semi-quantitative determination

• Ammonium Test Method: colorimetric with test strips and reagent 10 - 30 - 60 - 100 - 200 - 400 mg/l NH₄⁺ MQuant^®

Instruments

• Reflectometer RQflex^® 20 Reflectoquant^® (1.17246)

Note: This application note pertains to RQflex^® 20 and all discontinued instruments (RQflex^® 10, RQflex^® plus)

Sample preparation

The sample can be analyzed in its original form.

Analysis

Reflectoquant^® Ammonium Test, Cat. No. 1.16892, measuring range 0.2 - 7.0 mg/l.

Rinse the test vessel several times with the sample solution and fill to the 5-ml mark. Add 10 drops of reagent NH₄-1 and swirl. Add 1 level blue microspoon of reagent NH₄-2 and swirl again. Press the reflectometer START button and simultaneously place the test strip in the sample (20 - 30 °C) for 8 min, ensuring that both reaction zones are immersed. Allow excess liquid to run off via the long edge of the strip on to an absorbent paper towel. Measure the strip in the reflectometer. The value [mg/l] will be stored automatically. (Please refer to the RQflex^® operating instructions and the instruction for use of the Reflectoquant^® Ammonium Test.

Reflectoquant^® Ammonium Test, Cat. No. 1.16899, measuring range 5.0 - 20.0 mg/l.

Rinse the test vessel several times with the sample solution and fill to the 5-ml mark. Add 10 drops of reagent NH₄-1 and swirl. Add 1 level blue microspoon of reagent NH₄-2 and swirl again. Press the reflectometer START button and simultaneously place the test strip in the sample (20 - 30 °C) for 4 min, ensuring that both reaction zones are immersed. Allow excess liquid to run off via the long edge of the strip on to an absorbent paper towel. Measure the strip in the reflectometer. The value [mg/l] will be stored automatically. (Please refer to the RQflex^® operating instructions and the instruction for use of the Reflectoquant^® Ammonium Test.)

Reflectoquant^® Ammonium Test, Cat. No. 1.16977, measuring range 20 - 180 mg/l.

Rinse the test vessel several times with the pretreated sample solution and fill to the 5-ml mark. Add 10 drops of reagent NH₄-1 and swirl. Press START button and simultaneously immerse both reaction zones of the test strip in the sample solution (15 - 25 °C) for approx. 2 seconds. Allow excess liquid to run off via the long edge of the strip on to an absorbent paper towel. Wait 15 seconds and then measure the strip in the reflectometer. The value [mg/l] will be stored automatically. (Please refer to the RQflex^® operating instructions and the instruction for use of the Reflectoquant^® Ammonium Test.)

Note: If a semi-quantitative determination is sufficient there is the possibility to use MQuant^® test strips, Cat. No. 1.10024; color scale graduation 10 – 30 – 60 – 100 – 200 – 400 mg/l NH₄⁺

Procedure

• Samples containing more than 400 mg/l NH₄⁺ must be diluted with distilled water.
•  Rinse the test vessel several times with the pretreated sample.
• Fill the test vessel with 5 ml of the sample (15 – 25°C) to the 5 ml mark. Add 10 drops of reagent NH₄-1 and swirl.
• Immerse the reaction zone of the test strip in the measurement sample for 3 sec.
• Allow excess liquid to run off via the long edge of the strip onto an absorbent paper towel and after 10 sec determine with which color field on the label the color of the reaction zone coincides most exactly.
• Read off the corresponding result in mg/l NH₄⁺ or NH₄-N.

Results

Comparison with photometric and official DIN method

Sample	Reflectoquant® [mg/l]	Photometry [mg/l]	DIN method (mg/l)
1	33.0	35.0	37.0
2	15.0	13.0	20.0
3	44.0	51.0	49.0
4	29.0	27.0	26.0
5	52.0	43.0	52.0
6	19.0	19.0	12.0
7	36.0	40.0	38.0
8	28.0	28.0	28.0
9	30.0	24.0	25.0
10	16.0	11.0	12.0
11	8.7	8.6	8.6
12	10.0	8.7	8.4
13	16.0	20.0	16.0
14	3.2	3.0	2.9
15	3.0	2.9	2.7
16	7.6	5.5	5.4
17	28.8	26.1	-
18	35.6	38.3	-

References

1. Camargo JA, Alonso Á. 2006. Ecological and toxicological effects of inorganic nitrogen pollution in aquatic ecosystems: A global assessment. Environment International. 32(6):831-849. https://doi.org/10.1016/j.envint.2006.05.002