Nitrite in Wastewater

Reflectometric determination after reaction with Griess reagent.

Introduction

In order to remove ammonia, wastewater is often subjected to nitrification, the two-step bacteria-mediated oxidation to nitrite, then nitrate, followed by denitrification to nitrogen gas. Monitoring nitrite in wastewater is therefore an important aspect of treatment because an excess of nitrogen compounds can lead to environmental issues including eutrophication—excessive growth of algae and plants—upsetting marine ecosystems.¹ As a result, determining wastewater nitrite is important for environmental reasons. Here we describe the reflectometric analysis of nitrite after a reaction with Griess reagent using the Reflectoquant^® Nitrite Test Kit.

Experimental Method

In the presence of an acidic buffer nitrite ions react with an aromatic amine to form a diazonium salt, which in turn reacts with N-(1- naphthyl)-ethylene-diamine to form a red-violet azo dye that is determined reflectometrically.

Reagents, Instruments and Materials

Test Kits

• Reflectoquant^® Nitrite Test with test strips 0.5 - 25.0 mg/l NO₂ (1.16973)

Instruments

• Reflectometer RQflex^® 20 (1.17246)*

*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.

Instrumental Analysis

• Press the reflectometer START key and simultaneously dip the test strip into the sample (15 - 30 °C) for ca. 2 seconds, 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.
• 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 package insert of the Reflectoquant^® Nitrite Test.)

Results

Table 1. Comparison with photometric method

Sample	Reflectoquant® [mg/l]	Photometry [mg/l]
1	3.0	2.8
2	3.4	3.2
3	2.9	2.9
4	< 0.5	0.2
5	0.6	0.5
6	1.5	2.0
7	2.4	2.2
8	2.1	2.4
9	1.7	1.5
10	0.9	0.8
11	0.8	0.8
12	2.7	2.6
13	2.8	2.6
14	1.5	1.5
15	2.1	2.2

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