Towards a water-wise world Annual report 2014

PWN and KWR research 

Tracing disinfection by-products through nitrogen labelling

20 August 2014BTO

Advanced oxidation (with UV radiation and possibly hydrogen peroxide) is used at various drinking water production sites. During the treatment of raw water with advanced oxidation, undesirable by-products can be formed, some of which show mutagenetic activity. These by-products are then removed in subsequent steps in the drinking water production process. Now, thanks to the application of nitrogen labelling, more is known about the nature of these by-products and the conditions under which they are formed. This helps PWN, and other water companies that want to use advanced oxidation, to monitor the safety of the drinking water in all steps of the production process.

One good way of removing organic micropollution from water is through UV radiation, whether or not in combination with hydrogen peroxide. Known as advanced oxidation, this technology is used in several of PWN’s drinking water production installations. Previous research showed that during this disinfection step by-products can be formed, some of which might be mutagenetic. In order to remove these undesirable by-products, the water companies, after having treated the water with UV radiation, filter it using activated carbon, which absorbs the by-products.

The researchers discuss the detection of nitrogenous disinfection by-products using mass spectrometry.

The researchers discuss the detection of nitrogenous disinfection by-products using mass spectrometry.

Labelling with nitrogen

We still do not know a lot about the nature of the substances that can form during advanced oxidation. What is clear is that the presence of natural organic material and nitrate in the water, when combined with UV radiation, contributes to the formation of these disinfection by-products. This is why KWR and PWN have together developed a new method to trace these by-products. First, “artificial” water is made, containing natural organic material and nitrate that is labelled with nitrogen isotopes. The researchers then treat this water using advanced oxidation, whereby disinfection by-products are formed that are also labelled with nitrogen isotopes. The nitrogen isotopes are again encountered in 84 different by-products, which therefore must have been formed during the advanced oxidation. By comparing this treated artificial water with water released right after the advanced oxidation step in the production process, the researchers establish that 22 of the 84 by-products from the artificial water are also formed during the drinking water production process and, therefore, justify closer research.

Mutagenicity

Over the course of 2014, KWR has optimised the test which allows mutagenicity to be demonstrated. This so-called “Ames fluctuation” test now produces clearer results and fits in better with the laboratory quality systems. Research using the Ames test into disinfection by-products demonstrates that the degree of mutagenicity is connected to the quantities of the 22 disinfection by-products that are formed. This new knowledge makes it possible for KWR and the water companies to discover how the undesirable by-products are formed and which of them are mutagenetic. The ultimate goal is to prevent the formation of these compounds as much as possible.

© 2017 KWR Watercycle Research Institute

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